Research Collection

Journal Article

Dynamic unit coupling and decoupling at cruising speed Systematic classification, operational potentials, and research agenda

Author(s): Nold, Michael; Corman, Francesco

Publication Date: 2021-06

Permanent Link: https://doi.org/10.3929/ethz-b-000473438

Originally published in: Journal of Rail Transport Planning & Management 18, http://doi.org/10.1016/j.jrtpm.2021.100241

Rights / License: Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International

This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use.

ETH Library Journal of Rail Transport Planning & Management 18 (2021) 100241

Contents lists available at ScienceDirect

Journal of Rail Transport Planning & Management

journal homepage: http://www.elsevier.com/locate/jrtpm

Dynamic train unit coupling and decoupling at cruising speed: Systematic classification, operational potentials, and research agenda

Michael Nold, Francesco Corman *

Institute for Transport Planning and Systems, ETH Zürich, Switzerland

ARTICLE INFO ABSTRACT

Keywords: The possibility to couple train units into consists, which can be vehicles or platoons, has been Virtual coupling proposed to improve, among other, average passenger speed, energy efficiency, and railway Continuous railway system infrastructure capacity utilization. We systematically review and categorize the technologies and Dynamic coupling application of coupling train units into vehicles or platoons, identifying different generations of (Train) Unit coupling in operation train coupling, which are used for railway operations. The requirements, compatibility in terms of Dynamic mechanical coupling Portion working infrastructure and vehicle equipment as well as backward compatibility are analyzed. The po­ tential of a dynamic train unit coupling and decoupling at cruising speed is proposed, and identified as the 4th generation of train coupling. The possibility of current technology to implement a mechanical dynamic coupling and decoupling at cruising speed is reviewed, with functional requirements and steps of such a process. Based on dynamic coupling at cruising speed, various operating concepts are presented, with focus on commuter-networks between polycentric agglomerations. The potential of dynamic coupling and decoupling at cruising speed might reach travel time reductions in the order of 1/3 and no transfers, for a typical test case in Switzerland between Bern and Zurich.

1. Introduction

Public transport networks, and railway in particular, provide mobility to everybody over a large set of origins and destinations interconnected into a network. A key limitation of public transport, and railway in specific, is its practical impossibility to econom­ ically and efficientlyconnect every starting point with every destination. The essence of a public transport system is the concentration of passenger flowsonto specificlines of movement (Nielsen and Lange, 2007). For this reason, railway transport is usually structured and bundled in lines along high quality routes, which are interconnected at stations or hubs. The lines might have different transport goals, for instance people usually have to transfer between a system with a high accessibility in space (and low speed) and a system with higher speed (but low accessibility in space). A network of lines interlinked and connected with each other enables a considerably larger number of connections between larger amount of origins and destinations, increases frequency of operations, and improves overall travel time (Van Nes, 1999). The amount of services running over each line is related to a maximum infrastructure capacity. In general it is well known that transferring between vehicles reduces the attractiveness for the passenger. In contrast, more direct connections increase the attractiveness of the transport system for passengers. The design of public transport networks strives to

* Corresponding author. E-mail address: [email protected] (F. Corman). https://doi.org/10.1016/j.jrtpm.2021.100241 Received 9 June 2020; Received in revised form 12 February 2021; Accepted 19 February 2021 Available online 7 March 2021 2210-9706/© 2021 Published by Elsevier Ltd. M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241 provide high quality transfers, when possible (Nielsen and Lange, 2007). Given that railway frequencies are often lower than for urban public transport, the waiting time related to a transfer is typically larger. The elasticity of passenger demand to transfers has been identifiedempirically as very high. Empirical evidences include the case of Karlsruhe, where an urban railway system with transferless direct connection (-train) increased passenger demand by a factor of 4, and in the long term by a factor 9 (AVG, 2015). The Bayrische Oberlandbahn (south of Munich, Germany), increased passenger numbers by a factor of 3.3 through direct connections with portion working (we call portion working when two or more train units drive coupled together for a portion of a line; at a stop they split and continue independently on other lines) and usage of automatic couplers (Allianz pro Schiene, 2010). Similar portion working is used in a range of conventional and high speed services throughout the world. To improve railway services, more services can run on a section, larger volumes of demand can be transported. This reduces the fixed costs per service, and enables cheaper and more efficient operations. The bottleneck is the infrastructure capacity, i.e. the maximum amount of that can run in a unit of time. Due to the safety and signaling system standard in railway operations, vehicles are running in absolute braking distance (Hansen and Pachl, 2014), which identifiesa blocking time which is reserved for each vehicle running, depending on its speed, length, and signaling system characteristics. The blocking time limits the amount of vehicles that can run in a unit of time. Most railway mainlines are already saturated at bottlenecks, i.e. they cannot run more services per hour, unless technological (e.g., new signaling system, new signaling technology, improved dynamic characteristic) or infrastructure im­ provements (e.g., more tracks) are made. Infrastructure capacity is related to the maximum passenger flow,i.e. amount of vehicles that can be moved per hour, multiplied by the amount of passenger space available within a vehicle (seating or standing). Having longer units travel through the bottleneck obviously improves the amount of passenger space available within each vehicle, at the expense of a slightly longer blocking time. In reality, the maximum allowed length of vehicles can be limited also by the signaling system, the available platform length at stations, length of the sidings, and some other operational and infrastructure factors. Demand of public transport systems is typically heterogeneous in space. In other terms, there are agglomerations, where most people live, which are separated by longer distances. Demand from the agglomeration can be both directed to another place within the agglomeration, typically a city center; or to other places in other agglomerations. Due to the generalized growth of cities, agglom­ erations tend to develop into polycentric structures. This results in non-uniform utilization of vehicle and infrastructure capacity, when public transport services have to connect them. The resulting increases in costs for operators, and ultimately for users effectively obliges that not all possible origin destination can be served by direct services. Interconnection of services into networks enables a more balanced capacity utilization by means of hierarchical services, which are able to more flexiblyadjust to the different levels of demand. On the other hand, interconnection of services increases the inconvenience for passengers in terms of transfer and time lost when such an interconnection is effectively exploited. The key idea of coupling is to flexiblyadapt the vehicle capacity to various spatial requirements, by running longer vehicles, which have a higher passenger capacity per vehicle. By means of coupling, even small amount of demand can fitsmall units running from a large set of origins to a large set of destinations. When coupling takes place at stand still, there is an obvious increase in travel time, as stops and related braking and acceleration consume (relatively) large amount of time. We therefore investigate the concept of dynamic coupling, where coupling and decoupling might take place at non-zero speed (thus saving the extra stop to change composition). We investigate under which conditions this is beneficial, in order to balance various key performance indicators from operators and passenger side. With a goal of a general perspective, we discuss here the overarching terminology used in the paper throughout multiple gener­ ations of coupling. When specificterms are accepted in the literature for a specificapplication, we might refer to those specificterms, as far as no ambiguity is present. We consider coupling in general as the usage of vehicle, infrastructure and communication technology by which wagons, locomotives, trains, Electric multiple units (EMUs) can be combined with each other. We call transport units or simply units, those wagons, locomotives, trains, EMUs (Vuchic, 2007). Each transport unit has the possibility to provide services to people from an origin to a destination, possibly including intermediate transfer points where passengers have to physically disembark the unit. The larger transport vehicles (again trains, EMUs, platoons) resulting from the combination (coupling) are called consists. Passengers might have the possibility of changing units within a consist, or not. Each consist shares infrastructure capacity when moving between any two places. Units within a consist need to share some mechanical or virtual connection relating to their coor­ dinated movement (same acceleration or braking, by means of mechanical devices transmitting forces, or coordinated tractive/braking efforts), as well as a communication enabling safe monitoring and command of operations. The research question which we consider is therefore: what is the operational potential of dynamic coupling of railway units, towards amount of passengers moved in unit of time, their travel time from an origin to a destination, and the amount of transfers they need? Which are the existing research gaps, which need to be studied, to quantitatively evaluate this potential? To answer this question, we fill the following research gaps: We review the state of the art of coupling of railway units, for which we ask: what are the common aspects able to systematize the variety of past, existing, and possible configurations? We evaluate the requirements for dynamic coupling by means of a simplifiedquantitative analysis on a typical case, considering the travel time and generalized travel time, which are estimated on a typical realistic test case; We identify a research agenda, which discusses many still unresolved research gaps for future topics, on operational, policy, economic aspects, which should support the idea of coupling, to bring it to full potential. The paper is organized as follows: Chapter 2 proposes a systematic classificationof coupling. Chapter 3 discusses issues related to cross-compatibility. Chapter 4 proposes a structured process and terminology for the process of dynamic coupling. Chapter 5 reports on a numerical evaluation on a typical test case. Finally, Chapter 6 concludes and proposed a roadmap of research.

2 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241

2. Systematic classification of coupling

There are a lot of operation scenarios, which unit can move over which part, and how units are combined (or separated from each other), on part of their route alone and another part of their route together. Some of those concepts starts in the 19 century as mentioned in Brunello et al. (2009) (Fryer, 1997), some remained futuristic scenarios, some are currently used, some actually dis­ appeared from practice. Some technology can be used for only a part of the trajectory of a vehicle, which therefore changes category over its distance. Some units allow exchange of passengers internally within a consist; some others require passengers to disembark and enter the same consist, or another vehicle, to proceed their journey. To structure this, we defineat firstthe relevant keywords, and then we structure the requirements, to systematically characterize the coupling of train units. We define four types of possible coupling, which is the combination of three types of coupling process (manual, automatic, dy­ namic); and two types of situation of the coupled units (mechanical/virtual). As for the latter:

• We define mechanical as coupling which keeps the units physically together, and this physical contact is able to transmit forces. • We definevirtual a coupling in which the units are not physically in contact, but instead they are kept at a positive limited distance by coordinated speed management.

As for the former.

• We definemanual (static manual in a complete description) when during the coupling process extra personal is needed in the vicinity of the consists/units (for example: to connect the screw coupling, cables, pipes or similar actions). • We defineautomatic (static automatic in a complete description) when during the coupling no extra personal is needed in the vicinity of the consists/units. For example this could be a coupling with the Scharfenberg coupler or other coupling systems which work automatically, and are implemented as multi-function couplers MFCs. • We define dynamic (automatic dynamic in a complete description), when coupling can take place at speeds bigger than 0.

We hinted in the above list to a complete description, where also static is used. We define static a coupling, where the coupling process (but not the decoupling, in general) takes place when one vehicle has speed 0. Manual and automatic, without any further clarification,are static types of coupling. We omit the description static in the rest of the paper, when no confusion is possible. Virtual can only be automatic: there cannot be a mechanical virtual, nor a manual virtual coupling. When decoupling takes place at a non-null speed, it is called manual when personnel is controlling the process to avoid collision; it is called automatic when some sort of automatic distance control is available to avoid collisions. Different technologies have different requirements:

• Consists mechanically made up of units (wagons or trains) with manual couplers need additional railway personal for coupling and/ or decoupling. • Consists mechanically made up of units (EMUs or trains) with automatic couplers need no additional railway personal to realize the coupling/decoupling. • Consists made up of virtually coupled units are not mechanically coupled and driving in a short distance behind each other and need no stop to couple themselves. • Consists made up of mechanically coupled units (EMUs or trains) with special coupling devices (including a Rail Coupling Support Device, more details later) might also perform limited coupling or decoupling dynamically, i.e. at a non-null speed.

Summarizing, we can systematically characterize the various possibilities of technology and operations, enabling four generations of coupling of increased complexity, compared to a baseline (without coupling):

0. (no coupling) trains do not change composition; Units, wagons, vehicles and consists are all the same. 1. Manual mechanical couplers between units, where at least one unit is at standstill for coupling the units together. Additional railway personal is needed in place, for coupling and/or decoupling. 2. Automatic mechanical couplers between units, where one unit is at standstill. No additional railway personal is needed. 3. Virtual coupling of moving units into platoons (vehicles drive separated by less than the absolute braking distance). 4. Dynamic mechanical coupling of moving units (ideally, vehicles at cruising speed).

Moreover, we define a suffix, determining which actions are possible where, as follows:

0. Coupling and decoupling takes place at station/standstill. 1. Decoupling takes place at cruising or operational speed. 2. Coupling and decoupling take place at cruising or operational speed. 3. Passengers can move throughout the consists, once coupled.

In the following these generations will be described as y.z, where y is an index from the former list, and z is an index from the latter list. We moreover use a wildcard.x whenever one of the two indices is not meaningful (e.g. 4.x is the set of all 4.0, 4.1, 4.2. and 4.3, if

3 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241 existing). We discuss those configurations from an operational view, with the aim to provide a systematic overview. Combinations which have not been implemented or do not seem potentially useful are ignored in the list. We are mostly interested in units where coupling can be done at a non-null speed, i.e. while moving. We refer to a cruising speed, when the speed of the units while coupling is acceptable for a revenue-making service, and comparable with the speed that a train not featuring any coupling/decoupling tech­ nology would sustain. The coupling speed can be less than the maximum speed of the vehicles. We refer instead to an operational speed in case the speed usually is less than the cruising speed for operational reasons due to the coupling. Readers interested in technical and construction implementation details can refer to railway engineering handbooks such as Profillidis(2014) , Sachs (1973) or the specific railway regulations of the countries. The baseline of coupling generation (called Unit Coupling in Operation, UCO 0.x) is used to describe the scenario when the train/ vehicles/consists run without a composition change. This is the case of most trains actually in operation right now. Specificexamples are trains which are mechanically composed of several wagons, however, they will not be divided or merged in operation, such as

Table 1 Overview of the generations of the train coupling in train operation.

Generation Process Used technology Downward Coupling Merge (coupling) Separation (decoupling) compatibility activity Location, activity Location, speed speed

0.x Railway operation No coupling system to – No – – – – without train change the coupling in rail modification during operation train operation is required 1.0 Manually dividing Use of various 0.x Yes Manually Station, Manually by Station, trains at station or mechanical couplers by standstill personnel standstill shunting in the personnel station on through coaches 1.1 Coupling at station, Use of various 1.0 Yes Manually Station, Manually by Anywhere, decoupling at mechanical couplers by standstill personnel, At cruising cruising speed with additional personnel requiring speed with manual distance devices for decoupling some form of control. distance control. 2.0 Automatic coupling/ Automatic coupling 0.x Yes Automatic Station, Automatic Station, decoupling at station device standstill standstill 2.3 Automatic coupling/ Automatic coupling 2.0 Yes Automatic Station, Automatic Station, decoupling at device with additional standstill standstill station, with doors at the front/end passenger transfer at for a gangway with cruising speed passenger transfer between vehicles 3.2 Rail vehicles are not Electronic systems for 0.x only Automatic Anywhere, Automatic Anywhere, coupled virtual coupling and virtually At cruising At cruising mechanically,but supervision of speed speed virtually, running at approach less than absolute braking distance, with automatic distance control. 4.1 Automatic Automatic coupling 2.0 Yes Automatic Station, Automatic Anywhere, decoupling at with railway coupling standstill At cruising cruising speeds support device speed (RCSD), supervision of approach 4.2 Automatic coupling Automatic coupling 4.1 Yes Automatic Anywhere, Automatic Anywhere, and decoupling at with railway coupling 3.2 At cruising or At cruising cruising or support device operational speed operational speeds (RCSD), supervision of speed approach 4.3 Automatic coupling Automatic coupling 4.2 Yes Automatic Anywhere, Automatic Anywhere, and decoupling at with additional 2.3 At cruising or At cruising cruising or railway coupling operational speed operational speeds, support device speed with passenger (RCSD), supervision of transfer at cruising approach, additional speed between doors at the front/end vehicles for a gangway with passenger transfer

4 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241

Fig. 1. Overview of the different technologies, requirements and possibilities. The vehicle speed at coupling, particularly standstill, is considered at the end moment, i.e. conclusion of contact of the coupling systems; The vehicle speed at decoupling is considered at the start moment, i.e. loss of contact of the coupling systems. For coupling and decoupling at cruising speeds, approaching and drive away phases are respectively considered. The cases in which rail cars are, even today, coupled without a brake connection, are considered exceptional and not classified in this scheme. railcars or articulated cars without or with Jacobs , in EMUs consists. Those are most often composed as of several units (wagons); however, they will only divided or merged in a workshop, and not in operations. Table 1 reports a systematic classification, discussed in detail in what follows. Moreover, Fig. 1 reports an overview of possible technologies and devices which enable the various generations of UCO.

2.1. Manual coupling to mechanically change compositions of consists at stops

Train unit coupling in operation (UCO) 1.x refers to the entire set of possibilities, where manual coupling systems are used. In other terms, personnel is required at the coupling device, and one of the units to be coupled remains at 0 speed (static) during the coupling. There are many existing solutions, thereby it is not unusual, that different railway companies have their unique modifications/con­ struction. In the following, the primary focus is for the screw coupling with two side buffers, which is standardized 1886 in Europe as part of the technical unit (Schweizerische Bauzeitung, 1886) and today called as a UIC screw coupling (Janicki and Reinhard, 2008). UCO 1.0 identifiesa manual coupling system, used with through coaches or wagons which are shunted in stations or for dividing trains. The operation with through coaches made it possible realize national and international direct connections. For this purpose, passenger cars occupied by passengers are shunted in train stations and exchanged between different trains (Janicki and Reinhard, 2008). It can also be the case that coaches are coupled to railcars with the UIC screw coupling (NEG, 2016, 2018, 2020). Sometimes complete locomotive trains are also divided (ERI, 2018a; ERI 2018b). A system-related disadvantage of UCO 1.0 is the manual actuation of the coupling and/or the pipes and/or electric train supply and/or the commutation cable/s and or communication devices. Because of that, the use of this technology is declining due to additional operational expenses (Janicki and Reinhard, 2008). For example, SBB (Swiss federal railway) strategy is to increase in the passenger transport the amount of railcars with automatic couplings to 100% until 2040 (Bormann and Kiese, 2020). UCO 1.1 refers to the usage of a manual coupling system and a mechanical supplementary tool to decouple vehicles at cruising speeds. The process of coupling with the same technology is not possible. In United Kingdom, the decoupling of units from consists during the ride was called "Slipping" and used for more than 100 years (Railway Gazette, 1960; Railway Magazine, 1960; Fryer, 1997). For this purpose, passenger cars (called "slip coaches") were decoupled from a main train while running at cruising speeds and braked manually by the train staff, so that the rest of the (main) train did not have to stop at the station (Fryer, 1997). This operation scenario was widespread and used by many railway companies. Moreover, it had a very low accident rate (Railway Gazette, 1936). In Germany, there was a similar operation applied. The "Keller’sche Kupplung" was used, to decouple push locomotives for freight trains at oper­ ational speeds (Lüdecke, 1991). Today in Germany, train compositions are separated at operational speeds during the operation scenario the "uncoupled pushing". Uncoupled pushing is used if the total train weight is too large for the slope and an additional pushing-locomotive is required to complement the unfavorable dynamic characteristics. For this, a main train stops just before the slope and an additional pushing unit (in this case, just a locomotive) approaches from behind. After approaching, the locomotive behind pushes uncoupled (without a pull possibility; only forward traction efforts can be transmitted, but not braking) the main train along the steep route section. At the end of the steep route section, the pushing unit locomotive behind can reduce its speed and thereby separate from the moving main train. This latter keeps moving at operational speed. Such a process is used for freight trains and for passenger trains (Ortloff, 1997; DB NetzAG, 2020). Since at least 1935 in Germany, the separation of trains at operational speeds is regulated for "uncoupled pushing" with the trackside signal term "Ts" (Günther, 1935) and is still valid today (DB Netz AG, 2017). The trackside signal "Ts 1" gives the driver of the pushing unit the information about initiating the unit separation (DB Netz AG, 2017). Before the use of radio equipment, communication

5 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241 between the drivers took place with locomotive whistle signals (Lüdecke, 1991). Today, communication takes place via radio (Ortloff, 1997). There is no communication of brake information via a brake pipe, because the asymmetric coupling between units can transmit pushing efforts but not pulling efforts. For this reasons, the regulatory speed limitation is set to 60 km/h (BMJV, 2012). Instead, "slipping" trains, with a connected brake pipe, to be disconnected at decoupling, were allowed to reach speeds up to 70 mph (≈112 km/h) (Woodhouse, 1936). Up to now "uncoupled pushing" is offered as standard operation scenario at the "Geislinger Steige" (near Stuttgart, Germany) when the heavy trains require so (DB Netz AG, 2020). In Switzerland, uncoupled pushing and train separation at cruising speed is also regulated (BAV, 2015a). A similar form of “uncoupled pushing” is used for brake tests up to the maximum speed. In addition, uncoupled pushing is also used at shunting.

2.2. Automatic coupling to mechanically change compositions of consists at stops

Unit Coupling in Operation UCO 2.x refers the following scenarios, which all use various types of automatic couplings systems (i.e. no mechanical or shunting personnel needed) to enable coupling and decoupling of vehicles, while one of the vehicles is standing still at a station. This technology replaces train coupling 1.x, at many rail companies, including the SBB (Bormann and Kiese, 2020). UCO 2.0 refers to the well-known constructions enabling an automatic coupling, an example of which is the Scharfenberg coupler. These and similar multi-function coupling systems enable to couple and decouple units in an automatic way (Janicki and Reinhard, 2008). The coupling/decoupling process is relatively simple and requires one standing vehicle and a vehicle with a very small speed. This technology enables more flexibleoperating concepts, more direct connections and better capacity utilization. One possible usage is portion working: a train can start from a station C1 and divide with minimal effort when stopping at a station, so that one unit can go to a given line towards a station, and another unit can go to a different line, towards a different end station (possibly including not moving any further, turning around and operating on the way back). The disadvantage of this technology is the inevitable stop, due to the minimum impact forces which can be safely managed. This is especially disadvantageous if there would be in principle no need to stop otherwise, as in this latter case the stop would have only negative effects in time and energy (braking and accelerating). This operating scenario is used, for example, in Switzerland at BLS (von Andrian, 2017), in Germany at BOB (Allianz pro Schiene, 2010) and AVG (AVG, 2016; Bindewald, 2007). UCO 2.3 refers the usage of automatic coupling systems to enable fully automatic coupling/decoupling units at standstill at stations, with the addition of gangway connection at the front and end of the trains. This addition makes it possible to enable a passenger transfer between the coupled units, once they coupled, at operational speed. People can move through the consists, after the coupling took place. This front gangway connections are used today, for example in the Danish DSB-IC3, in the Scottish UK Class 385 (Iwasaki et al., 2017), in the Italian FS ALn 668. Many further vehicles, from several railway companies in several countries use (or used) also front gangway connections. The operational success depends from the technical solution, construction and maintenance efforts. There have been cases of technically poor construction, so that the front gangways have been discontinued due to operational problems, such as malfunctions, or limited stability of operations due to frequent delays (SER, 2006). In a technically good construction, such vehicles with front gangways can be used for a stable rail operation far beyond the planned life expectancy (SER, 2017). UCO 2.1 and UCO 2.2 remain empty, because there is no decoupling with only the use of automatic couplings.

2.3. Virtual coupling to virtually change compositions of consists at cruising speed by communication

The third generation of coupling, UCO 3.x refers to rail vehicles (units) which are coupled virtually. This means, by means of specific electronic communication and guidance system, they run in a coordinated manner, as separate vehicles within a platoon, at a distance which is less than their absolute braking distance. Specifically, only 3.2 looks a meaningful setup, because the used systems also include the functions from 3.0 to 3.1. This is also known as platooning, or virtual coupling. The idea to run rail vehicles in a short distance behind each other is relatively old; this is typically the case for non fail-safe transport vehicles such as private cars, , or buses. The idea of platooning enabled by vehicle to vehicle communication for autonomous road units is receiving increasing attention (Liu, 2017; Liu et al., 2018; Nguyen et al., 2019; Zhang et al., 2019). Specificallyto road-bound public transport, platooning might not be required to increase speed (as average speeds are limited mostly by stopping distance), but for infrastructure capacity increase. For instance (Lutin and Kornhauser, 2014), propose to use platooning on the bus corridor linking New Jersey to the Port Authority Bus Terminal in Manhattan. Depending on the achievable headways, throughput of the lane can be more than doubled. Concerning rail-bound vehicles, this technology is not yet used in practice, but prototypes are available for demonstration (CAF, 2018; Innotrans, 2018) and actively researched in its implication to operations (Flammini et al., 2018; Quaglietta, 2019; Quaglietta et al., 2020). The firstconcrete technical solution to make a platooning possible relates to a patent by the German Aerospace Center, granted in 2009 with the name "Coupling device for rail vehicles" (Grimm and Pelz, 2007). Virtual coupling technologies technically enable that (UCO 3.2):

• Units (Rail vehicles) are coordinated in their dynamics with each other, without a physical connection (Grimm and Pelz, 2007) • The distance between the units (rail vehicles) is controlled by using electronic aids (vehicle-side sensors) (Grimm and Pelz, 2007) • Vehicle dynamic data is exchanged between the units (rail vehicles) (Grimm and Pelz, 2007).

The technological step from the UCO 1.1 above allows to have vehicles running in less than their absolute braking distance not only in specificsituation (i.e. when the following unit is necessarily decelerating) but also in general conditions, and in principle over an entire trip. However, driving rail vehicles in short relative distances has also disadvantages:

6 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241

• A new train control system is required, for the entire line where virtual coupling could be performed. One suitable signaling system could be (a development of) ETCS/ERTMS level 3 or beyond (Mitchell, 2016). • The (typically estimated in a few hundred meters, see Quaglietta, 2019) distance between the units is aerodynamically disad­ vantageous. Compared with a mechanically coupled train, the air resistance is larger for virtually coupled trains (Nold, 2019b) because the front and back resistance/drag has a noticeable influence in the driving (Peters, 1990). • Especially on slopes, either the vehicle distance must be increased, or the tractive force must be limited to be within a range of wheel-rail friction values that can be safely guaranteed. This is necessary because the wheel-rail friction values can suddenly drop at any time. For instance, in the realistic case that the wheel-rail friction coefficientof the front vehicle suddenly drops on a slope, this vehicle would experience a sudden decrease in speed due to the slope resistance, and the rear vehicle would collide with the front vehicle (Nold, 2019b). For this reason, traction force must be limited to be within a safe range of wheel-rail friction coef­ ficient.In practice, this is set at mu = 0.13 (BAV, 2016). Normal wheel-rail friction coefficientare until mu = 0.366 (Nold et al., 2018), which could result in up to 280% more traction force possible. Needing to include this extra safety margin might result disadvantageous for the timetable and the line capacity.

2.4. Dynamic coupling to mechanically change composition of consists at cruising speed

The fourth generation of Unit coupling (UCO 4.x) refers to units (rail vehicles) which can mechanically couple and decouple at operational speed, automatically by using mechanical and/or electronic systems, beyond the conventional coupling devices. Like the UCO 3.x, this new technology is not yet being used in practice and is under development. The idea of coupling and decoupling rail vehicles while driving is not new. Between 1858 (first official mention; possibly even earlier, unofficially) and 1960, the decoupling of rail vehicles at cruising speed was carried in UK (as discussed above, UCO 1.1) (Railway Gazette, 1960; Railway Railway Magazine, 1960; Fryer, 1997). With the state of the art, which consists of conventional pulling and pushing devices, decoupling is possible while driving (again, UCO 1.1) (Fryer, 1997). Furthermore, when coupling with fully automatic coupling systems to a stationary vehicle, the approaching vehicle can be driven up to an operational speed of up to 20 km/h without causing damage (Janicki and Reinhard, 2008). With increasing speed, the speed tolerances need to decrease, if the collision energy (depending from kinetic energy) is to be kept constant. For instance, the speed difference between two units at 100 km/h must be less than 2 km/h for coupling without extra devices, to have a comparable collision energy as a 20 km/h unit coupling with a standstill unit. The deviation of actual value from a set target speed for good speed controllers is larger than 1–2 km/h (Meyer, 2018). When coupling, this variation must be considered for both units, thus giving a worst case larger than >2–4 km/h. Speed controllers with 1 km/h tolerance have been developed (Nold, 2019a), however in the worst case considering variation for both units leads to just 2 km/h, which would be borderline and probably require additional safety systems. The approach of the two vehicles must also be supervised, probably with a similar technology to 3.x, which allows units to ride within the absolute braking distance from the preceding unit. Moreover, when the units are particularly close, say distance of few meters until contact, some additional device would be required, which can be termed railway coupling support device (RCSD), for instance the patent granted (Nold, 2019b). A railway coupling support device (RCSD) and coordinated communication to handle the movement of trains within their absolute braking distance enable operations at level UCO 4.x:

• Vehicles movements are managed with distance control and vehicle-to-vehicle communication during approaching (Nold, 2019b). • Safe active impact absorption is guaranteed, when two units (rail vehicles) move together into a consist (Nold, 2019b). • The units are stabilized, held, and guided, during the coupling and decoupling process towards/from a consist (Nold, 2019b).

A RCSD could technologically be constructed as spring damper system, which is located on the front and rear of the rail vehicles (Nold, 2019b). Depending on the specificconstruction, it can resemble a buffer or be constructed as rubber diaphragms, resembling an IC3 of the Danish State Railways (DSB). Additional spring damper elements that can be actively influencedmust be integrated in the rubber diaphragms. Furthermore, a RCSD has magnet modules installed on the front, so that the vehicle are connected during, the mechanical coupling. To fixthe units, such magnets allow 100 kN–400 kN of forces, depending on the design (Nold, 2019b). With a RCSD, it is possible to delegate most of the complexity of the dynamic coupling to a device which minimally improves on existing coupling device technology. The most important adjustment required is that the automatic coupling must not initiate emergency braking if the train is disconnected while driving. In the above categories, multiple intermediate steps can be identified, as follows. The first step (UCO 4.1) is the decoupling at cruising speed. This is possible in a short time horizon, because it is similar to the "uncoupled pushing", which is in operation today. The second step (UCO 4.2) includes also coupling at cruising and/or operational speed, i.e. both coupling and decoupling are allowed. A finalstep (UCO 4.3) includes a gangway connection at the front and end, which make a passenger transfer between the coupled units possible. Technically, all those technologies have been shown separately feasible, see the DSB IC3; or the gangway connections like the UK Class 380 or UK Class 385. UCO 4.0 (coupling at standstill with RCSD) is not considered as explicit step, because it is possible with UCO 4.1 vehicle and higher. In fact, a vehicle able to couple while driving, can also couple at standstill, the latter being a specificcase of the former (one vehicle has a speed of zero). This allows for a natural downward compatibility of a 4th generation towards a 2nd generation. UCO has the focus on rail vehicles, however the company Next Future Transportation Inc. has developed a road vehicle with units, which can be coupled. This system is called “Selectively combinable independent driving vehicles” (Gecchelin and Spera, 2018) or “Connectable road vehicle” (Gecchelin and Spera, 2017) or “autonomous pods” (Reuters, 2018). The patent application is currently

7 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241 pending since 2015 (Google Patents, 2020), the design patent is granted (Gecchelin and Spera, 2017), a prototype has been developed and presented in Dubai in the year 2018 (Reuters, 2018). Academically, those ideas have been also investigated (Zhang et al., 2020). Despite such a design has large technical differences compared to the RCSD for railways, and dynamically coupled units, the proposed classification can identify it as a UCO of generation 4.

3. Requirements for infrastructure and vehicles, and downward compatibility for interoperability

We now discuss the requirements that some of the proposed coupling have on vehicles and infrastructure, and possibility of interoperability of different approaches, including downward compatibility. We can distinguish approaches that require some infrastructure specific facility at the moment of coupling, for the entire duration of the coupled ride, at the moment of decoupling, assuming that elsewhere there is a suitable signaling and safety system as usual. UCO 1.x and 2.x do not have special requirement on infrastructure (apart from partially required signalization) as coupling always occurs at standstill, and normally, at stations. Decoupling in UCO 1.1 does not require any special infrastructural device apart from signalization as already discussed. UCO 3.x virtual coupling requires some advanced signaling system for the process of coupling and decoupling, and in addition for the entire duration of the coupling (i.e. as far as the units run in a consist or platoon). UCO 4.x requires specific infrastructure when and where the coupling and decoupling process take place, but no specific signaling system is required compared to current technology, when the units run coupled. Due to those requirements, it might be worthwhile to exploit the flexibility of virtual coupling for relatively short, opportunistic platoons (as proposed in Aoun et al., 2020; and Quaglietta et al., 2020), and instead rely on mechanical coupling (i.e. 1.x, 2.x, 4.x) for very long trajectories, where units should better travel as a single consist. This is graphically reported in Fig. 2. Consider for instance a long distance connection Hamburg - Interlaken/Chur, which should be divided while traveling about 40 km after Basel, near Olten, with the individual units going respectively to Interlaken and Chur. Both units have the same hierarchical role in the transport service, i.e. they are both Inter City Express trains. The interoperability and requirements might be as follows. On the approximately 900-km Hamburg-Olten route (DB Vertrieb GmbH, 2015; Schweers et al., 2012), the consist would have to travel throughout virtually coupled, and the two units travel the last approximately 120 km to Interlaken and approximately 170 km to Chur respectively after decoupling (or dissolution of the platoon). Thus a signaling system able to support virtual coupling might be required for 900 km, even though the potential to decouple is actually needed in a specificpoint. It is still unclear, if the virtual coupling over such a long distance, between two units with same stopping pattern, would reduce the capacity on 900 km line (Hamburg-Olten) compared to a single vehicle, because the distance (several hundred meters) between the units increases the total length of the consist, resulting in an expected increase of blocking time, compared to the same situation in which the two units are mechanically coupled; and thus the consist has the shortest possible length. From a system engineering point of view, it would be better, if the required sophisticated technology for coupling and decoupling could be limited to the specificarea where coupling or decoupling occurs. If the units are mechanically coupled, like in UCO 1.x, 2.x, or 4.x, a single consist (a single vehicle) would run between Hamburg until Olten. Along this long section, the train would correspond to a train with UCO 1.x or 2.x, and have no specificrequirement for infrastructure. In case of 1.1, and 4.1, shortly before Olten the units in the consist would be decoupled, i.e. the second unit would be mechanically decoupled, disconnect mechanically at cruising speeds, and

Fig. 2. Example for an international portion working connection at the connection Hamburg – Interlaken/Chur. (a): Use of the UCO 3.x; (b): Use of the UCO 4.x.

8 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241 then continue separately. In contrast to virtual coupling, this mechanical coupling/decoupling reduces the above described effort (new train control system, vehicle-vehicle-distance) to a short section of the route. The only requirement is the coupling device enabling generation 4.x. Compared to virtual coupling (generation 3.x), dynamic coupling at cruising speed (generation 4.x) has arguably lower investment costs for the new train control system, because it is only required on a short section. Furthermore, generation 4.x is interoperable with existing systems, at all moments when coupling/decoupling are not taking place. When units drive within the absolute braking distance of each other, i.e. in UCO x.1, x.2, an absolute braking distance might need to be enforced at specificinfrastructure locations, for instance switches. This is a key aspect already identifiedfor moving block systems (see Theeg and Vlasenko, 2009) and for virtual coupling (Quaglietta, 2019), and often resulting in the critical headway of the entire system, which cannot be further reduced by coupling or decoupling, be it virtual or mechanical. The requirement stems from the need that a switch is in a safe state at any moment a unit (train) can pass over it, or movement should be forbidden. Some switches have the possibility of a safe merging of two lines regardless of the state of the switch. This is possible with the Abt automatic turnout, but there are currently no widely used devices which allow safe operation in a diverging switch. When such a technological step could be cleared, a larger reduction in the effective headway between consists (or vehicles) would become possible. A later section will discuss the advantage of having switches requiring absolute braking distance separation over them (resulting in different topologies for the network) in order to offer more useful services to passengers. Operations on sections without switches (for instance UCO 1.1 on a straight track) are anyway possible, and if the speed of the following unit can be controlled or guaranteed to be safe, would not pose a safety threat (as also recognized by them being allowed). The requirement for the vehicle is obviously a coupling device, being manual or automatic for 1.x and 2.x respectively. The vehicles require a compatible advanced signaling system for 3.x; similarly the units require a comparable system to manage the approach, in UCO 4.x. Communication can take place between vehicle and track side equipment (as in traditional signaling systems) or partially directly vehicle to vehicle (in a short range), to coordinate dynamic actions in 3.x (throughout) and for the coupling and decoupling process in 4.x. Downwards compatibility, concerns the possibility that a vehicle able to perform a higher UCO (higher number) can still operate with less sophisticated forms of coupling (or no coupling at all). This is discussed in a specificcolumn in Table 1, and more graphically in Figs. 2 and 3. An overview of the requirements and possibilities of the different coupling systems is systematically proposed to this end, together with a structure of the systematic classification.

4. Process for dynamic coupling in different network topologies

4.1. Basic topologies

We here discuss the process by which two units can couple into a consist, and further decouple into individual units, in UCO 4.x. We first categorize three topologies which have different switch layout and thus result in different requirements for the minimum headway. In the simplest case, see Fig. 4, which we call an I-topology, there is in the normal case no switch involved. The two colored lines describe two services running over a railway infrastructure, nodes identify stations (C1 to C5). Trafficgoes from left to right. Each row reports a different case of topology/operation. A train starts at a station C1, travels along a path until node K (possibly a station) and there decouples. After the decoupling, one unit continues the ride towards C5, with no intermediate stops. The other unit either ends or drives to other stops on the same route, say C3 and C4. Still, some different scenarios are given, reported as rows in Fig. 4. The Y-topology is an expansion of the I-topology, with a diverging switch, which allows reaching two separate destinations. Currently, the typical use of the UCO 2.0 is to enable better utilization of capacity through connections in Y-topology. Under this paradigm, a consist starts from city C1, is divided at node K, into a unit going to city C3, and a unit going to city C4 (Fig. 5). Often there might not be enough demand for a stop at node K; nevertheless, with UCO 2.x, a stop at node K is necessary; this extends the travel time and increases energy consumption. To avoid the inevitable stop at node K, the trains from C1 to C3 and from C1 to C4 can also decouple while at station C1, and then travel separately on section C1-K. However, this has the disadvantage that the C1–K route is occupied by two vehicles with negative influenceon the headway and capacity usage. By UCO 4.2, which enables coupling and decoupling while driving, these disadvantages would disappear. UCO 4.2 makes direct connections possible without a compulsory stop at node K and without a double capacity load on the route C1–K.

Fig. 3. Representation of the downward compatibility of the generations.

9 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241

Fig. 4. Services on an I-topology. a) Two separate trains with overlapping service (UCO 0); b) Coupling/decoupling at station with UCO 1.x or 2.x; c) Coupling/decoupling at station at cruising speed with UCO 3.x or 4.x.

Fig. 5. Services on a Y-Topology a) With UCO generation 1x or 2.x b) With UCO generation 3.x or 4.x.

In Switzerland there are some cases with this topology, notably with C1 = Bern, K = Olten, C2 = Zurich and C3 = Basel (SBB, 2019). The bottleneck here is the high-speed-line Mattstetten-Rothrist between Bern and Olten (C1–K), which results in an unfavorable ca­ pacity occupation by running separate trains all the way from C1–C3 and C1–C4. However there is also this application on Swiss meter gauge railways, such as C1 = Interlaken, K = Zweilütschinen, C2 = Lauterbrunnen and C3 = Grindelwald (Jungfraubahnen, 2019). Finally, the H-topology is an expansion of the Y-topology. It is also used to increase the capacity utilization of a railway line. In the following, cities C1 and C2 are connected via node K1. A mainline connects K1 with K2. K2 is also connected with the cities C3 and C4. With this structure, several scenarios are possible. Fig. 6 shows just one example of the connections between nodes K1 and K2, by overlapping or crossing separate lines, or by some coupling solution. It becomes clear that the UCO 4.2 reduces the capacity usage

Fig. 6. Services on an H-topology, with the mentioned boundary conditions. a) Services operated by separate trains. b) With coupling and decoupling at cruising speed and passenger transfers between the vehicles (UCO 4.2).

10 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241 between the nodes K1 and K2 approximately by factor 4, compared to the scenario with separate trains. For example, in Switzerland, an H-topology exits at the constellation C1 = Bern, C2 = Brig, C3 = Zurich and C4 = Basel. The trains are currently traveling from C1 = Brig via C2 = Bern = C2 and from there alternately to C3 = Zurich and C4 = Basel (SBB, 2019). A special case of this H-topology from Fig. 6 can also take place when C1 and C2 are the same station and C3 and C4 are the same station. One train drives without stop between C1/C2 and C3/C4. The other train has intermediate stops from C1/C2 until K1 and from K2 until C1/C2. This special case with stops of different hierarchical level (respectively a main station of a city, and a secondary center) is considered an I-topology and similar to scenario b and c from Fig. 7. The sequence at which the local/ coupling takes place is important, and discussed in a further section. Instead, in case of Y topologies, units can be local in both agglomerations, as the switch can be used as a sorting device allowing a preferred sequence of units in the two agglomerations, without reducing the speed of the other units. This latter is therefore a more hierarchically clean system. In this case of H-topologies, connections from/to all stations in the polycentric agglomerations are possible. This enables direct connections in typical commuter flows, which we name a linked commuter network, as described in Fig. 7. Referring to Fig. 7, many cities (say n = 1.2) have only one long distance train stop Cn, which is called central station, to reduce the amount of stops and associated extra travel time, for the long distance connections (generally called intercity, IC). Sub urban or regional networks have their stops identified as Sn.m, which are usually providing transfer to long-distance networks only via the central stations Cn of the city n (view topology a) of Fig. 7. Because of that, the typical journey of passengers wanting to travel between secondary stops of both agglomerations start from a suburban stop S1.m of the city 1, to central station C1. At the central station a transfer to the long-distance train to another city 2 can be offered, with a variable waiting time, depending on the timetable structure. The travel between the commuter-station Sn.m and the respective central station Cn, and the necessary time for transfer, also including its waiting time, increases the total travel time. Depending on the city topology and travel destination, sometimes is it necessary to drive at firstin the opposite direction to the travel destination (because the central station is in the opposite direction). This case is shown in scenario a of Fig. 7. Scenario b in Fig. 7 proposes direct connection between all polycentric stops, and would present the following advantages to the same passenger as discussed before. For this a commuter train (called regional in what follows, to match the terminology already used) stops at all suburbs of city 1, travels with cruising speed, say 200 km/h on a high speed line, to city 2 and stops there at all suburbs. Technologically this is not a problem because several vehicle manufacturers produce regional train vehicles, suitable for 200 km/h (Bombardier, 2020; Siemens, 2017; Stadler 2019). Concepts for a high-speed commuter service with 225 km/h are state of the art in England since years (Railway Herald, 2009). The main disadvantage of scenario b in Fig. 7 is the large infrastructure capacity utilized by the extra service on the high-speed-line between two cities. Typically, such a link is the bottleneck in terms of capacity. Scenario c in Fig. 7 keeps the advantages of Scenario b, still offering direct connections between all secondary centers, but at smaller capacity utilization on the high speed line. In this scenario a suburban or regional train stops in city 1 at all stops. Instead of ending at the edge of the agglomeration, the regional train accelerates and couples to the IC train at node K1, while keeping the cruising speed. At node K2, the regional train decouples and stops at all secondary stops in the agglomeration. This concept of linked commuter train networks enables direct connections between secondary centers of polycentric agglomerations without major effects on the line ca­ pacity between K1 and K2. From a theoretic point of view, this is a special case of the H topology mentioned above. UCO 4.2 is required for implementation. If a passenger change is to take place while driving, UCO 4.3 is required. The main advantages from Scenario c compared to Scenario b is the reduction of time that units block an infrastructure element, i.e. the infrastructure capacity utilization. Simplifying greatly, the capacity utilization of a unit is made up of an occupation time (time required for the entire length of the vehicle to move) and a headway time (time between two successive units). The longer vehicle

Fig. 7. Simplified schematic representation of the different connection options between two polycentric agglomerations a) Regional train connection in city 1 to the main central station, transfer to IC train to city 2, transfer to a regional train b) Separate additional direct connection, which directly connect all stops of the two centers, including the central stations, albeit at low effective speed (many intermediate stops) c) Linked commuter network which uses dynamic mechanical (de)coupling at cruising speed between regional and IC units, serving respectively the secondary stops and the main stop.

11 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241 would have a longer occupation time of the section compared to a single unit, but a comparable headway. Compared to the two units driving separately, the longer vehicle would have the same occupation time, as it has the same effective length and the same speed; but only requires one headway, instead of two. We see the same trends to have longer trains, to reduce capacity utilization in freight transport. The advantage of coupling freight trains together (which are today up to 750m) to increase the freight train length to 1500 m ¨ is recognized by many operators (VOV, 2009; BMIV, 2015; Müller, 2016). The capacity utilization is improved, by at least 50 Percent, ¨ when doubling the freight train length (VOV, 2009).

4.2. Impact on the passenger flow

We now discuss the polycentric passenger flowof the demand, and its implications on the required services running. We describe the demand focusing on the most relevant relations identifiedin Fig. 7, which are reported in Table 2, and identifiedby a symbol d1 to d6. For those relations, a typical, symmetric Origin Destination Matrix is reported by means of symbolic values in Table 3. Fig. 8 describes the passenger flowover multiple train services, in the two cases of traditional service (transfers), Fig. 8a; and direct connection (additional train or dynamic coupling), Fig. 8b. We use light gray lines to enable the comparison between the two sides Fig. 8a and 8b. Fig. 8a describes the passenger flowof the Scenario a of Fig. 7. We use a suffix.a to identify this. On the left and on the right side the two stations C1 and C2 are identified.The color bars report the 6 demands, and their thickness hints at the amount of people (colored by their respective demand) onboard the trains. We report the IC connection on the top of the Figure, and the bottom reports the amount of people (colored by their respective demand) onboard the regional trains. The regional services collect the passengers for the IC (at City 1: d3+d4; at City 2 d2+d4), throughout the stations in the urban area, and moreover transport further passengers (at City 1: d5; at City 2: d6). The IC train carries 4 passengers groups inside (d1, d2, d3, d4); the total amount of people onboard of the IC, for Fig. 8a directly depends on the demand, and can be described with the following formula:

dIC.a = d1 + d2 + d3 + d4

In the scenario of Fig. 8a, the two flowsof transfer passenger t in the two stations C1 and C2, between the regional trains and the IC

Table 2 Simplified demand structure.

Table 3 Demand matrix of this simplified case.

Fig. 8. Simplified schematic representation of the passanger flow between two polycentric agglomerations a) Passenger flow for Fig. 7a, use a regional train to the main station of C1, transfer to IC train to city 2, transfer to a regional train b) Passenger flowfor Fig. 7b and c, direct connection, realized as additional train or as linked commuter network.

12 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241 train can be described as:

tC1.a = d3 + d4

tC2.a = d2 + d4

Fig. 8b describes the same demand situation but with Scenario b and c of Fig. 7. We use therefore a .bc suffixto identify this. In this case, the passenger flowof demands d2 d3 and d4 can distribute between the IC train and the regional trains which actually cover the entire distance between cities C1 and C2. We describe the ratio of passengers which use the direct connection (i.e. the regional train) by a parameter γ, for each demand. If each γ equals 0, nobody uses the direct connection and the entire passenger flow uses the IC connection. If each γ equals 0, Fig. 8b corresponds to Fig. 8a, because nobody uses the direct connection. If each γ equals 1, the entire polycentric passenger flow uses the direct connection enabled by the regional trains, and not the IC connection. In practice, the value of γ will be between 0 and 1, depending on specifictravel time, value of time and transfers from behavioral models, comfort, availability of dining cars, etc. We want to analyze the situation regardless of the precise value of γ, and assume in general that people will use both possibilities, i.e. one part γ of the polycentric passengers uses the direct connection and another part uses the IC connection. In any case, for any positive γ, the demand inside the IC dIC.bc is reduced compared to dIC.a from scenario in Fig. 8a. In a complementary way, the demand using the direct connection by the regional train dRE.bc is increasing. This can be described with the following formulas, which hold for any positive γ:

dIC.bc = d1 + (1 γ2) · d2 + (1 γ3) · d3 + (1 γ4) · d4 ≤ dIC.a for ​ γ2, γ3, γ4 ∈ [0, 1]

tC1.bc = (1 γ3) · d3 + (1 γ4) · d4 ≤ tC1.a for γ3, γ4 ∈ [0, 1]

tC2.bc = (1 γ2) · d2 + (1 γ4) · d4 ≤ tC2.a for γ2, γ4 ∈ [0, 1]

The formulas described show how in the theoretical special case of the same demand, the additional direct connections reduce the number of passengers in the IC, at the benefitof more uniform usage of the vehicles of the regional services, through the entire distance between the cities. Instead, in scenario a, the demand is very asymmetric, where the maximum is actually found at the main stations. This would allow to use vehicles which are actually smaller, for the IC and the regional services, as their usage is more even. The scenario b and c influencealso the passengers transferring at the stations. By a suitable γ, the main train stations, which have often reached their passenger capacity limit, can be relieved by part of the passenger flowtransferring. In other terms, the passenger demand uses the stations in a different manner. The vehicles are also used in a different manner; for instance, the additional direct connections would require additional vehicles. We ignore in this small illustrative case many behavioral aspects, as well as possible effects of the services, such as elasticity and demand increase. A detailed assessment of the economic influences is very extensive, identified as a further point for the research agenda at the end of this paper.

4.3. Coupling and decoupling process in UCO 4.x

We now discuss in detail the coupling and decoupling process under UCO 4.2, for the H-topology as introduced above. Without loss of generality, we refer to a Swiss test case, targeting the major agglomerations of Bern and Zurich. A detailed calculation of this scenario follows in section 5. One can identify six phases for coupling two units into a consist, while traveling at cruising speed (Nold, 2019b):

1. Approach phase: The units (rail vehicles), which should be coupled, get closer more than their absolute braking distance, and keep getting closer, their approach being supervised by a communication interface, such that only a limited, controlled speed difference is present. When the distance is short enough, distance sensors can coordinate the process, the air filled rubber elements will be fully extended, and a repelling magnetic field from electromagnets is activated (Nold, 2019b). 2. Converge phase: Before the vehicles contact each other, the speed of both rail vehicles is controlled with the distance and/or magnetic sensors. The distance is reduced until both units approach each other, and then drive at the same speed. In addition, the magnetic sensors check whether the other unit also has an opposite polar magnetic field (Nold, 2019b). 3. Fixation phase: When both rail vehicles are in contact, the repelling magnetic fieldin one of the two rail vehicles will be inverted, so that contact between the units is enforced; both units are held together into a consist by the magnets (Nold, 2019b). 4. Longitudinal vibration oscillation compensation phase: After activating the magnetic fixation,possible longitudinal oscillation will be damped. Further the coupling support device is becoming increasingly rigid (Nold, 2019b). 5. Coupling phase: The coupling support device is retracted, to let the automatic coupling fixand couple as standard operation (Nold, 2019b). 6. Final phase: When the automatic couplings are connected, the magnets of the coupling support device are switched off and the coupling support device is retracted and fixed.The mechanical automatic coupling (similar as in 2.x) keeps the units together in the consist (Nold, 2019b).

The decoupling process is similar but inverted, again relying on the coupling support device. There are fivephases (Nold, 2019b).

13 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241

1. Initialization phase: The coupling support devices are extended until the coupling support devices of both vehicles are in contact (Nold, 2019b). 2. Fixation phase: From the point of contact, the electromagnets of both vehicles are activated so that they keep fixedthe train units (Nold, 2019b). 3. Decoupling phase: Coordinated with the extension of the coupling support device, the mechanical automatic coupler is opened (i.e. decoupling occurs similarly to 2.x), and the distance between the rail vehicles is increased (Nold, 2019b). 4. Separation phase: The magnetic fieldof one of the units (rail vehicles) is inverted, so that the magnetic attraction terminates, and instead a magnetic repellant force is present. The magnetic field can dampen possible impacts and smooth the process (Nold, 2019b). 5. Drive away phase: Now the units are two separate rail vehicles, which can increase their distance by different speeds and continue driving alone. Finally, the entire coupling support device is retracted and fixed (Nold, 2019b).

When the units have different hierarchical roles in the transport systems. e.g., an intercity train and a regional train, the sequence in which they are coupled in the consist is important. We show schematically (not to scale) the two possible sequences in a graphical timetable in Fig. 9. Fig. 10 shows a simplified track situation with the trains in the individual time steps. Namely, the two possible sequences are.

• The regional train is coupled behind the IC in the direction of travel • The regional train is coupled before the IC in the direction of travel

Both sequences are shortly analyzed in what follows, from a technical and passenger-service point of view. Regarding safety of operation, and resulting in limitations to headway, the question is whether the units (or the consist) pass the switch facing (i.e. diverging onto two tracks) or trailing (i.e. merging from two tracks into one). Switches as mechanical moving devices might get stuck in intermediate positions, which might results in a safety hazard in general. Because of this, an absolute braking distance is always specified before switches, with additional safety margins including a switch/route setup time and locking time (Hansen and Pachl, 2014). Specifically,if the diverging switch is passed facing, and if the switch is stuck in an intermediate position, the driving direction of the train is undefined. In this case a consist or a unit could divide, with part of it driving along the two directions, resulting in a derailment. If the converging switch is passed trailing and if the switch is stuck in an intermediate position, the driving direction of the train is instead well defined.The switch can be forced into accepting the movement of units towards the only direction possible. With a suitable switch construction, which we call a trailable switch, this forcing can be accepted and the train will not derail, if the passing speed is less than the maximum force which the switch allows when forced. In most cases, such a force corresponds to speed of 40 km/h (Maschek, 2015). If a switch is passed in this way, there is still a risk of collision with another train running from the other direction. The two sequences correspond to different units passing the switches trailing/facing, as shown in Fig. 9. Let us start by sequence 1, i.e. regional train behind IC. From a passenger point of view, it makes sense that the IC leaves as late as possible from the city 1, as far as its speed allows to timely reach its destination. The regional train is waiting at the last station in the agglomeration of city 1 before coupling, on a side track (see Fig. 10a). After the track vacancy detection system has reported that the IC has left the switch, the route and switch can be set for the regional train. Here, having a trailable switch allows reducing this time to a minimum: once the IC train

Fig. 9. Schematic graphical timetable for the two different sequences.a) Sequence 1: IC before the regional train b) Sequence 2: regional train before the IC.

14 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241

Fig. 10. Scheme of the sequence and track assignment, for different sequences, each in three successive steps.a1-a3) IC before regional train when coupling b1-b3) IC before regional train when decoupling. c1-c3) regional train before IC when coupling. d1-d3) regional train before IC when decoupling. has passed, provided no other train is running on the main line, the regional train can immediately depart, pass (or force) the switch, reach the main track and accelerate. The regional train will catch up with the IC train and couple with it. After the coupling, the consist can accelerate until high speed and efficiently use the high-speed line to reach city 2. Shortly before the first station of the agglom­ eration of city 2, the regional train decouples from the IC, while still running at cruising speed, and subsequently reduces its speed (see Fig. 10b). Due to the speed reduction of the regional train, the distance between the trains increases, such that an absolute braking distance is reached, when the regional train has to pass a switch facing. The IC train is not affected from speed reduction due to the switch, and can reach quickly its destination. The opposite sequence is described in Fig. 10c and 10d respectively. The regional train is before the IC; no switch is needed to change the sequence while coupling. After the last stop in the agglomeration of city 1, the regional train runs at reduced speed until the IC reaches it. The regional train accelerates, to match the higher speed of the IC for the coupling process at operational speed. When the IC catches up with the regional train, coupling can occur. After the coupling, the consist can accelerate until high speed and use efficientlythe high-speed line to reach city 2. Shortly before the firststation in the agglomeration of city 2, the IC train decouples from the regional train at cruising speed. The regional train is directed to the siding track. The (now decoupled) IC train has to reduce its speed to increase the distance between the trains, at least reaching absolute braking distance at the switch (see Fig. 10d2). Assuming this can be reached, the switch can be safely locked, a through route can be reserved for the IC train. The regional train can then stop undisturbed while the IC overtakes it, and accelerate again towards its destination. It is clear from the example shown in Figs. 7 and 8 that the regional trains will be used in very different ways, in a scenario with dynamic coupling, compared to a scenario with traditional operation and transfers. On the one hand they need to accelerate and catch up the IC, to couple. On the other hand, they will be traveling longer distances, at higher speed, between the two larger cities. As for the firstpoint, we start by saying that the coupling does not take place at the maximum speed, but in the vicinity of the urban areas, and at intermediate speeds. In any case, modern trains used for regional services have good dynamic performance, and can accelerate sometimes even faster than intercity, as they are designed for frequent stopping. Comparing the power of EMUs of five different manufacturer determines that regionals trains have specific power between 19.7 and 22.7 kW/t (VDE, 2019; Stadler, 2012). Comparing the power of new EMUs from Bombardier IC, Stadler EC and Siemens ICE 3 determines that those long distance trains have a specificpower between 15.7 and 17.6 kW/t (SBB, 2020; Bombardier, 2020b; Starlinger et al., 2016; Siemens, 2015). The maximum speed of modern trains used for regional service is sometimes comparable to that of intercity services, due to standardization. The usage of trains which run on both regional services and long distance services, until speed of 200 km/h is state of the art since several years (Wehinger, 2012). The bogie construction, which is required for enabling such speed, is increasingly similar, due to the pressure for standardization and reduction of design, production, and maintenance costs. This is also achieved as an indirect result of policy measures. For instance, in the new rail track pricing system in Switzerland, vehicle with more advanced have a price reduction (Holzfeind et al., 2015; BAV, 2015b). Several manufacturer develop EMUs for 200 km/h (Bombardier, 2020; Siemens, 2017; Stadler 2019) and those vehicles are based on modular design, also used to for regional train platforms (Stadler, 2016).

15 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241

5. Numerical evaluation of a typical case

The Swiss cities Bern and Zurich will be considered as examples of the use of linked commuter connections. Fig. 11, shows a possible example to connect the two polycentric agglomerations (in Bern the secondary station of Bern Wankdorf is considered; in Zurich the secondary stations of Killwangen-Spreitenbach, Dietikon, Glanzeberg, Schlieren, Altstetten, Hardbrücke are considered. The main stations in Bern and Zurich are identifiedas Bern HB and Zurich HB respectively). We use this example motivated by real life conditions. In 2015 the SBB made an application to have IC trains stopping at both stations Bern Wankdorf and Zürich Altstetten, to catch the existing passenger potential, because a large company has offices on both places, and many employees have to commute between these offices.This application was declined from the Federal Officeof Transport, due to the heavy influenceof the extra stop towards the travel time of the long distance trains (NZZ, 2015; SRF, 2015; Tagesanzeiger, 2015). Because of the potential demand between Bern Wankdorf and Zürich Altstetten, we focus on this connection for the travel time evaluation, in this section. We here remark that the possible trajectory and service of those trains before Bern; or after Zurich does not affect the calculation here reported. Based on Fig. 11, both sequences from the above discussion are examined. A Stadler Flirt will be considered as example vehicle, because this vehicle is available as commuter train until 200 km/h and further sufficientinformation about it is published in journals and by the manufacturer (Legler, 2011; Stadler, 2019). It is a modular vehicle type, considered in a version with a total weight of 206 t, 4500 kW tractive power, 300 kN tractive force, 105.5 m length and over 230 seats (Legler, 2011). We do not discuss here in detail the specificsize that the vehicle should have, because such units can be scaled in a modular way up or down, by the manufacturer (Stadler 2016; Abellio, 2020); it can be coupled (i.e. according to UCO 2.x) towards longer units, as it typically done at peak hours. Moreover Fig. 8 showed that people will use regional and intercity trains in a different manner, thus asking for different amount of seats. Any comparison can be therefore scaled to different length of trains and amount of people, as those do not play a role in the evaluation of the travel time, which is the characteristic of interest. The following sources were also used for the calculations: SBB (2015), Wagli¨ (2010), Schweers et al. (2012) and Bundesamt für Landestopografie (2020). The following assumptions were made regarding the technological needs for coupling, and route setting:

• The coupling at operational speed with the railway coupling support device requires between 29 and 66 s, i.e. the cumulated time from phase 2 to phase 6, according to the partial device specifications available. In the following calculation, the worst case was taken, with 66 s. • The decoupling at cruising speed with the railway coupling support device requires between 16 and 30 s, i.e. the cumulated time from phase 2 to phase 4, according to the partial device specifications available. In the following calculation, the worst case was taken, with 30 s. • The coupling process takes place at speed between 80 and 100 km/h; the decoupling process can take place at higher speeds. • For reasons of comfort, IC drive at 80 km/h until the end of a curve at km 4.5 (which is also the observed case in reality). Tech­ nically, a speed of 100 km/h would be possible at that location. Approximately at km 7 from Bern, the high-speed route begins, with a maximum speed of 200 km/h. • The time duration for setting and locking a switch is maximum 5 s.

Fig. 12 shows the coupling in Bern for sequence 1 (regional train behind IC). Fig. 12a reports the speed space diagram. Fig. 12 b visualizes the graphical timetable and Fig. 12 c shows a zoom of the graphical timetable, regarding specificallythe coupling. Fig. 12 d reports the distance between the regional train and the IC (positive values report the IC in front of the regional). In each plot the regional train is reported as a blue line, the IC train as a red line. Furthermore, the journey of an IC with no coupling (baseline) is shown as a reference as a cyan line. From Fig. 12, one can see how the regional train is waiting at a side track. In case of a trailing switch, the regional train does not need to wait for setting the switch, and can accelerate immediately up to 40 km/h, and further accelerate after the trailing switch is passed (or if the switch is properly set, meanwhile). In the following, the worst case is considered, with no trailing switch, so that the train has to wait until the switch is set, before departing. A time of 5 s is considered to set the switch, increased to 10 s to provide a very conservative worst case. After this time, the regional train can accelerate and catch up the IC train. The trajectories of both units

Fig. 11. Schematic representation of a linked commuter network between Bern and Zurich. The red line represents the IC train and the blue line the regional train.

16 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241

Fig. 12. Coupling process in Bern – sequence 1, regional train behind IC. a) Speed space diagram b) Graphic timetable c) Detail from the graphic timetable d) Train distances. overtaking and approaching again are shown in Fig. 12d). This approaching is phase 1 (approach phase) of the coupling phases described in Chapter 4.2. When the distance between the units is short enough, phase 2 (converge phase) follows. As described above, 66 s are assumed as a conservative estimate for the time from phases 2 to 6. After phase 6, the coupling process is complete, so that the units continue as one consist, and accelerate towards the high speed line. In this calculated example, the IC travel time is increased, compared to the baseline, by 29 s, due to the longer period running at lower speed to enable the coupling. In the example discussed, it is assumed that the coupling does not take place at the maximum speed (200 km/h), but rather at a lower speed of 80 km/h. Fig. 13 shows the complementary sequence, with the IC train running behind the regional train, coupling in Bern (see Fig. 9b). In contrast to the scenario described above, the regional train drives at a reduced speed after its last stop. When the IC approaches, the regional train accelerates, so that the IC can couple behind without further speed reductions. On the sequence calculated here, the IC travel time is increased, comparing to the baseline, by 12 s. Fig. 14 shows the decoupling for sequence 1, regional train behind IC, while approaching Zurich agglomeration. In this case, the IC

Fig. 13. Coupling process in Bern – sequence 2 regional train before IC. a) Speed space diagram b) Graphic timetable c) Detail from the graphic timetable d) Train distances.

17 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241

Fig. 14. Decoupling process in Zürich – sequence 1 regional train behind IC. a) Speed space diagram b) Graphic timetable. has no reduction in its travel speed (similar to trains in "slipping" operation). The regional train decouples at cruising speed, reduces its speed and stops at every station. The IC continues as normal. Fig. 15 shows the decoupling for sequence 2, IC behind regional train. In this case, the IC train faces large influencesin its travel speed, when decoupling. In fact, it is advantageous for the passengers that the IC is ahead of the regional train, as not to suffer from the stopping pattern of this latter. But, due to the sequence considered, this is not the case. Thus, the sequence must be artificiallyflipped, and this requires infrastructure (switch, siding) as well as time extra to safely perform the overtaking. For this overtaking process, a switch must be passed facing. Therefore, the IC has to increase the distance from the regional train, by reducing its speed. The distance between the trains must be large enough, to have the time to set the switch in the worst case, and guarantee absolute braking distance until the switch is properly set and locked. The assumed time to set the switch is conservatively assumed in 30 s, which includes an additional safety factor. It is conceivable to reduce this time somewhat, however, the basic disadvantage remains, that the IC must brake, and reach a large distance with the preceding regional train. After the train IC has overtaken the regional train, both trains can run separately. In this case, the IC loses about 55 s of travel time. The large separation at the facing switch could only be reduced by the

Fig. 15. Decoupling process in Zürich – Sequence 2– IC behind the regional train a) speed space diagram b) Graphic timetable.

18 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241 vehicle directly influencing the switch, similar to an Abt switch (Abt, 1887). This idea was also presented in Brunello et al. (2009). Unfortunately, this technology is not used for mainline railway operations, currently. We present a detailed numerical evaluation of the test case in Table 4. The columns describe the travel time according to possible scenarios, ranging from the current one, to an ideal timetable perfectly synchronized, to two cases of dynamic couplings. We consider both trips from Bern Wankdorf to Altstetten; and the direct IC connection from Bern HB to Zurich HB. The rows describe the values making up the travel time, and distinguish further between pure travel time and generalized travel time. In fact, to enable a clear comparison about the time reduction we use the (pure) travel time, and the generalized travel time to enable a better comparison of trips with and without transfers. This is based on the fact that passengers usually consider transfers as disadvantage and accept usually a little longer pure travel times to avoid transfers. Transfers can be penalized, to replicate this behavioral aspect; by means of the generalized travel time, which is a cost function it is possible to compare different types of trips (Wardman and Hine, 2000; Balcombe et al., 2004). We consider two such formulations for the generalized travel time (GTT), by using penalties and/or weight for the transfer, which is found to depend from the transfer type, trip, region, personal aspects etc. (Wardman and Hine, 2000; Wardman, 2014). According to Wardman (2014), the generalized travel time for railway transport can be estimated as following weighted sum: ∑ GTT = ⏟⏞⏞⏟IVT + (mTT · TTn + mWT · WTn) =PT TT WT n

Where IVT is the in vehicle time, TTn the transfer time at the station n and WTn the waiting time at the interchange station n. The sum of IVT plus TT plus WT makes up the pure travel time, indicated by PT. The coefficientsfor the weighted sum are mTT for the transfer time (TT), where travelers are walking from their origin vehicle to their destination vehicle, evaluated as 1.68; and mWT for the pure waiting time, evaluated as 1.76. According to Garcia-Martinez et al. (2018), the generalized travel time for railway transport can be estimated as the sum of the pure travel time PT, plus a pure transfer travel time penalty (PTP) for each transfer n. The value of this penalty is evaluated being between 15.2 (equal to 15:12 min) and 17.7 min. We use the lower value in our analysis: GTT = PT + n · PTP

We start our analysis from the current timetable of 2020–2021. Today the passenger travels from Bern Wankdorf to Zurich Alt­ stetten in most cases via Bern HB and Zürich HB. The current travel time is 91 min with two transfers, also shown in the second column in Table. The second case considered, in the third column of Table 4, refers to a perfectly synchronized timetable. This is based on the designed minimal transfer time, which is published officiallyby the transport authority. The Federal officeof transport (BAV) and the

Table 4 Summary of the numerical evaluation with the calculated technical timetable-data from Figs. 12, Figure 13, Figs. 14 and 15.

Connection Bern Wankdorf to Zürich Altstetten Connection Bern HB to Zürich HB

Current Perfectly Dynamic Dynamic Current Dynamic Dynamic timetable synchronized Coupling Coupling timetable Coupling Coupling timetable Sequence 1 Sequence 2 Sequence 1 Sequence 2

Bern Wankdorf to Bern HB 5:00 min 5:00 min – – – – – Bern HB min. transfertime 6:00 min 6:00 min – – – – – Bern HB waiting 8:00 min – – – – – – Bern HB to K1 5:30 min 5:30 min – 5:30 min 5:59 min 5:42 min Bern Wankdorf to K1 – – 3:35 min 4:20 min – – K1 to K2 (incl. entire IC time 40:00 min 40:00 min 40:00 min 40:00 min 40:00 min 40:00 min 40:00 min buffer Bern Zürich) K2 to Zürich Altstetten – – 13:45 min 13:45 min – – K2 to Zürich HB 10:30 min 10:30 min – – 10:30 min 10:30 min 11:25 min Additional 10% buffer for – – 1:23 min 1:23 min – – – operation between K2 and Zürich Altstetten Zürich HB transfer 7:00 min 7:00 min – – – – – Zürich HB waiting 4:00 min – – – – – – Zürich HB to Zürich Altstetten 5:00 min 5:00 min – – – – – Total 91:00 min 79:00 min 58:43 min 59:28 min 56:00 min 56:29 min 57:07 min Transfers 2 2 0 0 0 0 0 Total generalized travel time 121:24 min 109:24 min 58:43 min 59:28 min 56:00 min 56:29 min 57:07 min according Garcia-Martinez (=91 +15:12 (=79+15:12 et al. (2018) (15:12 min +15:12) +15:12) penalty per transfer) Total generalized travel time 109:02 min 88:53 min (= 66 58:43 min 59:28 min 56:00 min 56:29 min 57:07 min according to Wardman (= 66 +13 x +13 x 1.76) (2014)(weighted sum) 1.76 +12 x 1.68)

19 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241

SBB publish the designated minimal transfer time for the stations. This is the minimum time which is assumed required, between arriving with a service and departing with another one. This minimal designed transfer time is for Bern HB 6 min (until 12 min) and for Zürich 7 min (BAV, 2020; King, 2019; Gafafer, 2015). A perfect synchronization does not refer to the current timetable, but assumes that there is a train coming from and leaving to, the secondary centers, exactly at the moment when the intercity leaves/arrives, plus the designated minimal transfer time. The travel time reduces to 79 min. Two cases of dynamic coupling are reported in the next two columns, corresponding to respectively Sequence 1 and Sequence 2. Along the rows, the travel time is associated to the specificparts covered, namely until/from the nodes K1 and K2. The Node K1 is the waypoint directly after the coupling and K2 is the waypoint directly before the decoupling. Because the trains drive as a consist be­ tween these nodes, the travel time between K1 and K2 is always the same, for any column. The difference comes from the way from the departure-station to K1, and from K2 to the destination station. Table 4 shows the travel time values from the technical timetable calculation which are shown in Figs. 12, Figure 13, Figs. 14 and 15. Furthermore, the travel time for the commuter connection between K2 and Zürich Altstetten is calculated with a lower speed than the technically allowed, and operationally used, maximum speed. Further 10% additional timetable buffer is added for the trip be­ tween K2 and Zürich Altstetten. Both buffers have the target to calculate a conservative travel time reduction results. By means of dynamic coupling, the travel time reduces to less than 60 min, and without the need for any transfer. The last three columns focus on the IC service, where the travel time can be compared. The IC train requires, due to the coupling, small travel time extensions. With sequence 2 (IC behind regional train), the travel time increase between Bern and Zürich is in the magnitude of 67 s. With sequence 1 (regional train behind IC), the travel time increase between Bern and Zürich is in the magnitude of 29 s. Sequence 2 is technically much more critical to realize, regarding the switch passed facing, and precise, supervised, braking process towards this switch. Sequence 1 is technically easy to realize, regarding the trailing passed switch and the start after the switch is set. Additional, an IC train should be less influenced in its travel time; therefore, sequence 1 (regional train behind IC) is recommended. The travel time can be reduced by approximately 30 min with the dynamic coupling (UCO 4.2). In other terms, the potential pure travel time reduction for the connection between Bern Wankdorf and Zürich Altstetten, compared to the situation of today, could be conservatively estimated as 34%, in the worst case (sequences 2 with buffer). We then discuss the bottom rows of Table 4, which pertain the generalized travel time, for both formulations proposed. Both consider the transfers as additional penalties, thus increasing greatly the advantage of the dynamic coupling (whose travel time results equivalent to the generalized travel time) against the transfer services. Those latter reach up to 109 and 121 min, i.e. just less than the double than the dynamic coupling. In other terms, by the aspect that (UCO 4.2) can reduce the amount of transfers, there is a potential for very large travel time saving and even larger generalized travel time saving. Table 5 summarizes the time gains in terms of pure travel time and generalized travel time, between the dynamic coupling and the approaches reported in the rows. The columns report the three performance indicators described. In comparison with perfectly synchronized timetable, UCO 4.x can already reach reduction in pure travel time by approx. 25%, for the connection Bern Wankdorf to Zurich Altstetten. For generalized travel time, this goes up to 33 and 51%. We conclude this test case with a couple of remarks. The designed minimal transfer time might not be suitable for older people and people with physical limitations (BAV, 2015c; Gafafer, 2015). Practical recommendations suggest to increase the minimum transfer time by 30–40% (BAV, 2015c). The dynamic coupling solution, without transfers, would gain even further, when such a recom­ mendation is implemented. The magnitude of the travel time losses for the IC trains depends from the speed reduction. If the IC has to reduce its speed only a little bit for coupling/decoupling (for instance from 100 km/h to 80 km/h) the travel time for the IC increases, but not much. This is the case on lines with low speed, which are usually near the cities. If the IC train has to reduce the speed in a large amount for coupling (for instance a speed reduction from 200 km/h to 80 km/h), the IC loses a lot of time due to the coupling. This is the case on lines with higher speed, which are usually away from the cities. However, a linked commuter connection couples the trains usually near the city, which is usually on a section of the route where the IC does not drive that fast anyway.

6. Discussion and research agenda

This paper systematically reviewed different technologies and operating concepts for coupling trains, encompassing overlapping lines, portion working, vehicles being coupled/decoupled and continuing towards/from two destinations, virtual coupling, and what is called dynamic coupling, namely the possibility that units are coupled and decoupled into/from a consist while maintaining a cruising speed. The idea of dynamic coupling is further analyzed and its potential estimated. A systematic description is proposed. linked with state of the art and state of practice. Overall, there is a large potential in terms of generalized travel time, and even pure travel time, by using dynamic coupling. The specificanswers to the research question identifiedis therefore as follows. We remark how benefitsand

Table 5 Reduction from traditional operation, to the worst case of dynamic coupling (UCO 4.2): Scenario 2 with buffer and a travel time of 59:28 min.

Pure travel time Generalized travel time

According to Garcia-Martinez et al. (2018) According to Wardman (2014)

Current timetable 31:32 min ( 34.7%) 61:56 min ( 51.0%) 49:34 min ( 45.5%) Perfectly synchronized timetable 19:32 min ( 24.7%) 49:56 min ( 45.6%) 29:25 min ( 33.1%)

20 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241 disadvantages span different dimensions, i.e. a larger cost results in an improved passenger service, for some passenger demand and infrastructure configuration.We believe tools such as Cost Benefitanalysis should therefore base a conclusion on quantificationof both detailed costs, and detailed benefits that the present paper only aims to identify.

6.1. Systematic classification

We identifiedthe literature and concepts to be rather fragmented, and difficultto put into a single discussion. The worldwide patent database classificationclass B61G (couplings specially adapted for railway vehicles) contains more than 10000 entries (EPO, 2020). There is such a large amount of coupling-devices and technical variations, which can be even confusing; further are these technical variations often not relevant from an operational point of view. We therefore proposed a systematic categorization of coupling operations. We identifiedthat two fields,one describing the type of the coupling, and one describing the speed and location where it takes place, are able to cover all operationally-relevant configura­ tions. We also reflectedon whether there is a need of extra personal for coupling the units or not. Overall, we consciously paid attention to operationally relevant aspects, and deliberately unifiedvarious technical variations. We determined various common aspects, which enable a differentiation for coupling of rail units, which are for example, mechanical or virtual, manual or automatic, et cetera. Based on these common aspects, the variety of the existing coupling solutions could be structured and systematized together from an operational point of view, which is called unit coupling in operation (UCO). That makes it possible to definegenerations, which include the existing railway coupling strategies together with new technologies for dynamic coupling. This also illustrates the dependencies and downward comparability. Moreover there are multiple possible combinations which have not been used so far, and some which do not look particularly promising. This systematic categorization also helps relating pure railway-based developments, such as the virtual coupling, with non-railway based development such as pods joining each other. We believe the systematization proposed can be the common ground for further research, enabling comparison and links between transportation research beyond single modes.

6.2. Key characteristics identified and topologies investigated

By means of studying a test case, with typical characteristics for a commuter flowbetween the peri-urban areas of two large cities, we identify key aspects that at this preliminary level already show their importance. Therefore, this paper has considered only one example-case on only one connection. This connection has already the suitable track infrastructure for UCO 4.x. However there could be also other suitable connection between other cities. But surly there are also several connection, which UCO 4.x not useful and/or needs infrastructure adaptions, which costs money. In each case, there is a need for the UCO 4.x system, which is under development and not existing now. Regarding the early state, the costs of building and installing such a UCO 4.x system are not yet known. However, in general UCO 4.x has advantages in network topologies where no stop is necessary at the train merging/separation, due to avoiding the stop. One of this cases is a linked commuter connection of two cities, which has great potential against current operations. Typically, those latter assume a regional train collects the passengers and transports them to a central station. At the central station the passengers have to transfer to an IC train bound for the next city where the passengers have to transfer again (see also Scenario a Fig. 7). This is easy to realize, however, it has several disadvantages. Polycentric commuters have large travel times and have to transfer at the central station. The central station should provide sufficientspace for those transfers to happen smoothly, which is not always the case in Switzerland. For example, the central station from Bern will be expanded in the next few years, due to the large passenger demand, for a price tag of around CHF 1 billion (ZBB, 2015). An alternative situation would be additional direct connections between the cities (similar to Scenario b of Fig. 7). Due to a polycentric demand between Zürich and Bern, such a connection was studied in the past, and despite the advantages against the current situation, not introduced (SRF, 2015). The technical feasibility of a similar solution is ensured by the increasing technical similarities between regional trains and IC trains. However, the bottleneck for running additional polycentric trains quickly becomes the lack of infrastructure capacity for additional trains. To enable more IC connections, which are urgently needed, investments in the order of magnitude of around CHF 1 billion are currently being made between Zürich and Bern (SBB, 2018). However, polycentric connections with additional IC stops increase the travel time, with negative influences for the passengers (SRF, 2015). In view of the high infrastructure costs and the polycentric demand, the linked commuter connection is a relevant alternative. A train with UCO 4.2 technology would make it possible that a regional train can couple at operational speed behind an IC, drive together to another city, decouple and drive further like a regional train. Such operations have been identifiedwith a large potential reduction in travel time and generalized travel time. This potential comes from the reduction of waiting times at transfers; and from the reduction of extra trip time to go to the transfer station. Depending on the specificassumption for generalized travel time used, the advantage against current operations can go beyond 34% less travel time, and up to 51% less generalized travel time. While the evaluation of the numerical test case has been carried out very precisely, conservatively and with several buffers, results have unavoidably some limitations, and should be interpreted as an order of magnitude; moreover various operational aspects neglected or simplifiedin the treatment might have an impact. For instance, the buffer time is derived from current operations, while it might be further adjusted. As for the technological requirements, due to no existing prototype, system sizes are based on estimates, and when possible conservative estimates are used. The travel time potential comes from reduction of transfer. For existing direct con­ nections, for instance people commuting between Zürich HB and Bern HB, there is no advantage. Summarized, it could be shown that dynamic coupling has a large potential to be a game changer in railway operations, with arguably more potential than virtual coupling. Because dynamic coupling depends on a lot of influences, and choices about many

21 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241 scenarios are still open, there are many points open for further research, summarized in the following research agenda.

6.3. Research agenda

The authors are aware that the current paper is only a preliminary evaluation of only some aspects of a possibly revolutionary idea, which is not new, but has never been used to the potential it promises. Therefore, a series of aspects which go beyond the scope of the current paper, but are identifiedas worthwhile of further study, to better quantify advantages and disadvantages, are discussed in what follows. Passenger potential – travel time. The numerical example for the connection Bern Zürich show estimates an approx. 30 min (approx. 30%) pure travel time reduction in a roughly 100 km commuter connection. This travel time reduction results from the shorter connection and avoiding of transfer. We can therefore expect that the travel time saving will be similar for a longer trip, and not increase proportionally with the length of the trip. In any case, the length of the test case considered matches well the characteristics of the typical commuter flows,which are around 1 h and about 100 km in Switzerland (BFS, 2004; BFS 2016). The extension to multiple flowsof commuters using multiple services exploiting UCO 4.x technology is an interesting aspect. If a regional train couples with UCO 4.2 at operational speed behind an IC train, it can most likely result in very low travel time increase for the IC train. The relation between train travel time increase and passenger travel time decrease depends on the existing/potential passengers flows, which should be quantified properly. Infrastructure capacity saving. Compared to two separate trains, two mechanically coupled trains require only one headway before/after other traffic,because between the two coupled units there is obviously no headway. This saves capacity and increases the capacity utilization. The precise quantificationof the blocking time decrease depends on many factors. A further aspect is that IC trains can not be enlarged further in Switzerland, as they are already as long as the maximum platform length. In other terms, a bottleneck factor for the total transport capacity (passenger/hours) is the usable platform length at stations. Through the coupling after the station and decoupling before the station (which it is described in the test case), passenger trains can be longer than the maximum platform length, and as long as freight trains. A linked commuter connection with dynamic coupling (UCO 4.2) has a clear infrastructure ca­ pacity potential, which can be exploited, to avoid building of new expensive railway lines. Those aspects could be quantifiedbetter for many realistic cases. A further aspect is the saving of station capacity, because the direct connections can reduce the amount of in­ terchanges in the central station (see Fig. 8). Due to this there is a potential, that the operator can avoid further enlargement of the central stations. A precise evaluation could help in designing interchanges, and enables more comfortable transfer at stations, without crowding. The acceleration of two vehicles at similar speed, with limited acceleration and braking characteristic as most trains, might result in specificneed of acceleration/deceleration lanes just outside of the agglomerations, similar to highway acceleration/deceleration lanes. The specification and general requirements in terms of space and speed should be elaborated further. There is therefore a shift in infrastructure capacity, which should be increased in the areas of coupling/decoupling, but which will be used less on the backbone, as effectively fewer vehicles will be running. We here argue that space for extra infrastructure at the boundary of the city centers is more available than in the very city center; and that investing in a localized improvement (at the boundary) will be more efficient than investing in additional infrastructure for the entire length of the intercity corridor. Based on the size and performance requirement for those two cases, only future studies can quantify how the more efficientusage of capacity on high speed backbones will compensate the extra infrastructure required in agglomerations, and result in overall substantial cost reductions. Development of required technology. Currently technologies for safe approach of trains within their absolute braking distance are available, and a device to manage the coupling process is under development. The former is subject of active research under the virtual coupling goal (Grimm and Pelz, 2007; Flammini et al., 2018; CAF, 2018; Innotrans, 2018; Quaglietta, 2019; Quaglietta et al., 2020; DLR, 2020), while for the second, preliminary ideas and a patent exist (Nold, 2019b). The full scale construction and testing of such devices, and modes of operations are an important aspect which would be required in any possible implementation. Influence of timetable and network design. The sequence of units when coupling in the consist is very important, when units have different hierarchical role in the timetable (e.g. regional versus IC trains). The usage of different timetable structures, and different orders, and frequencies between regional and intercity trafficmight influencegreatly the sequence of units, and therefore the performance. Much connections from the secondary nodes to the main node of the agglomeration might turn out to be less needed, and be reduced. The interconnection of services along a public transport network determines, in normal networks, the interconnection points, and the transport speed. The dynamic coupling brings new ideas on both of those aspects; therefore theoretical developments, such as optimization approaches for line planning and timetabling (Schobel,¨ 2017), are needed to work with a flexible line pool of overlapping services. Influence of timetable stability. The coupling process requires synchronization of two services. Having a small delay of one of them might be transmitted to the other one, and the entire consist, as well as result in delayed utilization of the bottleneck resource, on the high speed line. Suitable buffer should be determined, and their influence to the total travel time estimated. This requires the extension of delay propagation also considering coupling activities, to be implemented in theoretical models such as (Goverde, 2007). Quantificationof energy used. Having units effectively promising a shorter travel time for passengers (in the order of 30%) allows to marginally reduce the entire cruising speed of the system, and keep still a large advantage to the current situation. Further the aerodynamic resistances are estimated lower than in the case of virtual coupling (Nold, 2019b). This potential energy gain can be used to reduce total energy consumption at system level, or smooth peaks of energy demand. Quantification of different utilization on infrastructure, vehicles, drivers. Having some units travel less kilometers (specif­ ically, the connections from the secondary center to the main center; and less stops required) will reduce the wear on vehicles and

22 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241 infrastructure with possible system benefits in terms of maintenance. Conversely, the possibility to use units more flexiblyshould in theory enable a higher utilization of the units, similar to what is often proposed for general automated transit. This should be balanced against a higher wear of the units as they would be used more. When the units are operated based on a human driver, each unit which is going to run uncoupled at some time requires a driver. Automated train operations would have an obvious advantage there. For an introduction of UCO 4.x before an introduction of an automatic train operation, there is a need to evaluate this aspect. Quantification of benefits and process for other topologies, or for dynamic transfer of passengers. A more detailed eval­ uation of other topologies, possibly including the passenger exchange during the ride, could be performed, similar to the ideas in Brunello et al. (2009). Polycentric structures might provide the highest potential saving in terms of travel time for passenger, but it is unlikely that every single origin-destination might benefit at the same level from the new concept. A study might want to prioritize those connections where the highest potential is available, and compare its estimated benefits with its costs. Quantificationof passenger benefits. While the travel time of passenger decreases, other typically used indicators, such as the passenger km driven, reduces sharply in the case of dynamic coupling. This might ask the theoretical development of new, suitable patronage indicators, which are able to measure the improvements in the system otherwise untraceable with the current indicators. This might also result in a more widespread utilization of passenger-centric indicators, and further definition/adjustments of gener­ alized travel time formulas. Furthermore, the addition of direct connections might change the mobility pattern in the city. For instance people will take the long distance train in a secondary station, instead of taking public transport to the main station. Statistics of realized demand might not account for this, and the usage of demand models, extended to those scenarios, might be required. Passengers with physical limitations. Each transfer is an obstacle for passengers with physical limitations. UCO 4.x can reduce transfer and offer additional direct connections. This is a positive influence for people with physical limitations, which should be investigated, whether it can fit the requirements set up in policies for an overall aging population. Usability, and passenger guidance. Public transport systems require large acceptance, when introducing new technologies for operations. It can be expected that passengers might be confused at first,with vehicles being coupled and decoupled. When trains are divided, there is a requirement that passengers must be directed to the correct unit, by a passenger information system. The same confusion occurs for portion working, where only part of a vehicle is actually bound for a specificdestination. Currently, platform signs, onboard signs, and onboard announcement by personnel are often used, to familiarize passengers with such a situation. With portion working, the passenger has to enter the correct part of the train on the platform; the wrong part of the train will not perform the service wished by the passenger. This might require to walk along the platform until the right part of the train. For the operator, this has the disadvantage that a complex passenger information system must exist. A dynamic coupling as proposed in the current paper would have the advantage (against portion working) that every unit where a passenger can board has a well-defined destination. In case of linked commuter connection, which is described at Fig. 7c, these problems do not exist, because the trains only couple and decouple after departure, so a passenger boarding can understand clearly the destination of the unit. On the other hand, planned deployment of similar concepts, for instance in Dubai (Reuters, 2018), expect that passengers can appreciate and use such advanced transport techniques. The transfer between units within a consist might be required, which could be eased by large internal space, and by suitable information inside the vehicle. In any case, feedback from real life tests would be required to understand how to best handle passenger comfort and guidance. Reliable estimate of Costs for the required Performance. The implementation of such a project has to do with advanced technology. There are uncertainties in the precise estimate of costs, and the requirements for this. Note that such problems have been found already for well-established technology, and straightforward implementation (Baggen et al., 2010), due to management of mega project; varying, incomplete, or not fully described specifications (Hansen, 2017); usual cost overruns, etc. We postulate that for an advanced technology not yet in operations, those risks should be carefully assessed. Economic efficiency analysis. The analysis showed assumed sufficient railway infrastructure, and vehicles of suitable dynamic performance, in terms of accelerating and maximum speed. We remark that for the chosen test case, both infrastructure and vehicles requirements match well the current state of technique, so no developments of higher performance vehicles is required. Compared to infrastructure investments for reducing the travel time such as tunnels and bridges, we expect a much smaller price tag from implementing the dynamic coupling technology. From an economic perspective, the allocation of costs and benefitsdue to passenger km transported might not be feasible anymore. More advanced forms of variables used to justify subsidies might need to be developed. In case of different economic regulations (for-profit, concession, competitive ) for regional and long distance lines, those eco­ nomic exchanges need to be properly handled. Finally, the process for implementing the railway coupling support device must be coordinated, and rolled out to a sufficientlylarge fleet,before operations could actually start. This might require costs for retrofittingor buying new vehicles, to be borne by the railway undertakings, the authorities, or the infrastructure manager (under the idea that it effectively enables more infrastructure capacity). Impact to spatial planning, pricing, and housing developments. The attractiveness of secondary centers in polycentric ag­ glomerations increases due to the possibilities introduced by a widespread utilization of dynamic coupling. Effectively, the travel time and direct connections would favor further development of polycentric structures, enable new flows of passengers, relieving main stations which are often overcrowded with transferring passengers. The secondary centers have typically cheaper price and value, which can increase due to a better connectivity, for a larger societal economic benefit.The impact to spatial planning are therefore very relevant, and needing some estimation. Policy. The estimated time and transfer saving above are very beneficialfor passengers, but would require findinga new balance between costs and subsidies of regional and long distance trains. This requires agreement from operators (or their obligation from a regulatory point of view), as well as political support to bear the risks of the innovation of such an advanced operation. This can be compared with the troubled implementation of moving block signaling on main lines. In case the regional and long distance services

23 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241 are operated by the same railway undertaking, less need for policy coordination is expected.

References

Abellio, 2020. Fahrzeuge: Stadler Flirt. Abellio GmbH, Berlin. Retrieved on 09.21.2020 at. https://www.abellio.de/de/nordrhein-westfalen/unternehmen-news/ ueber-uns/fahrzeuge/stadler-flirt. Abt, R., 1887. Seilbahn lugano: system Abt. Schweizerische Bauzeitung. https://doi.org/10.5169/seals-14347. Band 9 Nr. 6. Allianz pro Schiene, e.V., 2010. 15 Beispiele erfolgreicher Bahnen im Nahverkehr (Berlin). Aoun, J., Quaglietta, E., Goverde, R.M.P., 2020. Investigating market potentials and operational scenarios of virtual coupling railway signaling. Transport. Res. Rec. 2674 (8), 799–812. https://doi.org/10.1177/0361198120925074I. AVG, 2015. Stadtbahn verbindet Stadt und Region - Eine Idee aus Karlsruhe setzt sich durch. Albtal-Verkehrs-Gesellschaft mbH, Karlsruhe. AVG, 2016. Neuerungen bei Zielbeschilderung von AVG Stadtbahnen. Albtal-Verkehrs-Gesellschaft mbH, Karlsruhe. Published 08.12.2016 retrieved on 10.03.2020 at. https://www.avg.info/unternehmen/presse/pressemitteilungen/meldungen/neuerungen-bei-zielbeschilderung-von-avg-stadtbahnen.html. Baggen, J.H., Vleugel, J.M., Stoop, J.A.A.M., 2010. European experiences with ERTMS implementation: the case of the high-speed railway Amsterdam-Antwerp. WIT Transactions on State of the Art in Science and Engineering 46. https://doi.org/10.2495/978-1-84564–/494914. Balcombe, R., Mackett, R., Paulley, N., Preston, J., Shires, J., Titheridge, H., Wardman, M., White, P., 2004. The Demand for Public Transport: a Practical Guide. TRL report 593. BAV, 2015a. Schweizerische Fahrdienstvorschriften FDV. Bern: Bundesamt für Verkehr. BAV, 2015b. Trassenpreis 2017 - Umsetzungsvorschlag. Bern: Bundesamt für Verkehr. Retrieved on 25.11.2020 at. https://www.newsd.admin.ch/newsd/message/ attachments/40047.pdf. BAV, 2015c. Langere¨ Umsteigezeiten und Haltestellenaufenthaltszeiten – Auswirkungen und Massnahmen. Bern: Bundesamt für Verkehr. SMA. BAV, 2016. Ausführungsbestimmungen zur Eisenbahnverordnung (AB-EBV). Bernoulli: Bundesamt für Verkehr. BAV, 2020. Fahrplanjahr 2020, Linie 550, Bern –Zürich HB. Bern: Bundesamt für Verkehr. Retrieved on 10.12.2020 at. https://www.fahrplanfelder.ch/fileadmin/fap_ pdf_fields/2020/550.pdf. BFS, 2004. Pendlermobilitat¨ in der Schweiz. Bundesamt für Statistik, Bern. BFS, 2016. Pendlermobilitat¨ in der Schweiz. Bern: Bundesamt für StatistikBMIV (2015) Aktionsplan Güterverkehr und Logistik. Bundesministerium für Verkehr und digitale Infrastruktur, Berlin. Bindewald, K., 2007. Die Albtal-Verkehrs-Gesellschaft. Verlag Regionalkultur, Karlsruhe. BMJV, 2012. Eisenbahn Bau und Betriebsordnung. Bundesministeriums der Justiz, Berlin. Bombardier, 2020. AVENTRA Commuter Solutions. Retrieved on 26.04.2020. https://rail.bombardier.com/en/solutions-and-technologies/urban/commuter.html. Bombardier, 2020b. TWINDEXX SwissExpress IC200. Zürich: Bombardier Transportation. Bormann, R., Kiese, A., 2020. Warum setzen die SBB Im Fernverkehr auf Triebzüge? Eisenbahn-Revue. Issue 2, 2020. Brunello, L., Bunker, J., Ferreira, L., 2009. Continuous Railway Systems: an innovative approach to improve high speed rail sustainability. In: Proceedings of the Advanced in Automation for Transport Technologies AATT09 Conference (Athens, Greece). Bundesamt für Landestopografie, 2002. swisstopo. Bern: Bundesamt für Landestopografie. Retrieved on 11.02.2020 at. https://map.geo.admin.ch/. CAF Construcciones y Auxiliar de Ferrocarriles, 2018. Virtual Coupling. Movie. Retrieved on 20.04.2020 at. https://vimeo.com/291454771. DB Netz, A.G., 2017. Signalordnung, Bahnbetrieb International. DB Netz AG, Berlin. DB Netz, A.G., 2020. Ergebnis der Routenanfrage von Stuttgart Hbf nach Ulm Hbf. DB Netz AG, . DLR, 2020. Dynamisches Flügeln. Koln:¨ Deutsches Zentrum für Luft- und Raumfahrt e. V. - Programmdirektion Verkehr. Retrieved on 06.05.2020 at. https:// verkehrsforschung.dlr.de/de/innotrans-2018/dynamisches-fluegeln-1. EPO, 2020. Espacenet-Trefferliste Worldwide Datenbank – B61G Als IPC Klassifikation. München: Europaisches¨ Patentamt. Retrieved an 11.12.2020 at. https:// worldwide.espacenet.com/searchResults?IC=B61G. ERI, 2018a. Aufgabentrager¨ kritisiert Landerbahn¨ nach Fahrplanwechsel. Eisenbahn-Revue International. Issue 2/2018. ERI, 2018b. Wagenmangel bei den Alex-Zügen. Eisenbahn-Revue International. Issue 4/2018. Flammini, F.S., Marrone, R., Nardone, A., Petrillo, S. Santini, Vittorini, V., 2018. Towards Railway Virtual Coupling IEEE International Conference on Electrical Systems for Aircraft, Railway, Ship Propulsion and Road Vehicles & International Transportation ElectrificationConference. ESARS-ITEC), Nottingham, pp. 1–6. Fryer, C., 1997. A History of Slipping and Slip Carriages. Oxford: Oakwood Press, Headington. Gafafer, T., 2015. Umsteigen ohne Hast für Rentener. Luzerner Zeitung. Published on 11.07.2015 at. https://www.luzernerzeitung.ch/schweiz/oev-umsteigen-ohne- hast-fuer-rentner-ld.83942. Garcia-Martinez, Andres, Cascajo, Rocio, Jara-Diaz, Sergio R., Chowdhury, Subeh, Monzon, Andres, 2018. Transport. Res. A Pol. Pract. 114, 52–66. Gecchelin, T., Spera, E., 2017. Connectable road vehicle. Design Patent: USD784853S1. Gecchelin, T., Spera, E., 2018. Selectively Combinable Independent Driving Vehicles. Patent application. US20180022405A1, WO2016161216A1, EP3277561A4, CN107614359A, SG11201708005YA, KR20170133403A. Goverde, R.M.P., 2007. Railway timetable stability analysis using max-plus system theory. Transp. Res. Part B Methodol. 41 (Issue 2) https://doi.org/10.1016/j. trb.2006.02.003, 2007. Grimm, M., Pelz, M., 2007. Kupplungseinrichtung für Schienenfahrzeuge. Deutsches Patent- und Markenamt DE102007050937B4. Gunther (1935) Deutsche Reichsbahn Signalbuch. Munchen: Reichsbahnbetriebsamt. Hansen, I.A., 2017. Review of planning and capacity analysis for stations with multiple platforms - case Stuttgart 21. Journal of Rail Transport Planning & Management 6 (4), 313–330. https://doi.org/10.1016/j.jrtpm.2016.12.002. ISSN 2210-9706. Hansen, I.A., Pachl, J., 2014. Railway Timetabling and Operations: Analysis, Modelling, Optimisation, Simulation, Performance Evaluation. Eurailpress, Hamburg. Holzfeind, J., Nerlich, I., Giger, M., Marsching, S., 2015. Verschleißabhangige¨ Komponente im Trassenpreissystem der Schweiz - ein Anreiz zur Rückbesinnung auf ein Gesamtoptimum. ZEVrail 139, 2015. Innotrans, 2018. Train virtual coupling. Berlin. https://www.innotrans.de/en/Press/Innovations/PDFInnovationsDetail.jsp?newsid=55492. (Accessed 20 April 2020). Iwasaki, M., Furukawa, K., Okamoto, K., Koreishi, K., Kaneyasu, T., Kota, Y., Kawase, K., Radford, A., 2017. Development of class 385 semi-customised/standard commuter rolling stock for global markets. Hitachi Rev. 66. Janicki, J., Reinhard, H., 2008. Schienenfahrzeugtechnik. Bahn Fachverlag, Heidelberg Mainz. Jungfraubahnen, 2019. Fahrplan. Interlaken: Jungfraubahnen. King, J., 2019. Das langste¨ Perron der Schweiz. Berner Zeitung. Published on 29.10.2019 at. https://www.bernerzeitung.ch/region/bern/bahnhof-bern-die-neuen- geleise-werden-in-betrieb-genommen/story/15063016. Legler, T., 2011. Der Flirt für Norwegen. Eisenbahn-Revue. Issue 5/2011. Liu, R., 2017. Automated Transit: Planning, Operation, and Applications. IEEE Press, Piscataway, NJ. Liu, T., Ceder, A., Rau, A., 2018. Scheduled platoons of public transport autonomous modular vehicles, 2018. In: Heart Conference 2018, 2018. https://www.events. tum.de/frontend/index.php?pageid=3316. Lüdecke, S., 1991. Die Baureihe 96 - Malletriese für den Schiebedienst. EK-Verlag, Freiburg. Lutin, J.M., Kornhauser, A.L., 2014. Application of Autonomous Driving Technology to Transit—Functional Capabilities for Safety and Capacity. Transportation Research Board 93rd Annual Meeting. Maschek, U., 2015. Sicherung des Schienenverkehrs, vol. 3. Springer Vieweg, Wiesbaden (Auflage).

24 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241

Meyer, M., 2018. ETH-vorlesung eisenbahnsystemtechnik I. Zürich. Mitchell, et al., 2016. ERTMS level 4, train convoys or virtual coupling, international technical committee, report on topic 39, IRSE (institution railway signal engineers). IRSE News. Issue 219, February 2016. Müller, W., 2016. Tests mit langen Güterzügen in Deutschland und in der Schweiz. SBB Cargo Blog. Retrieved an 10.12.2020 at. https://blog.sbbcargo.com/20054/ 20054/. NEG, 2016. Kurswagen im Einsatz bei der neg Niebüll GmbH. Niebüll: norddeutsche Eisenbahngesellschaft Niebüll GmbH. Retrieved on 10.01.2020 at. https://www. neg-niebuell.de/PDF/PDF-Fahrzeuge/neg_Kurswagen_Daten.pdf. NEG, 2018. Tradition Trifft Innovation. Niebüll: Norddeutsche Eisenbahngesellschaft Niebüll GmbH, 2016. Retrieved on 19.04.2020 at. https://www.neg-niebuell. de/PDF/PDF_Allgemein/neg_Unternehmensflyer.pdf. NEG, 2020. Norddeutsche Eisenbahngesellschaft - Reservierung Kurswagen. Niebüll: Norddeutsche Eisenbahngesellschaft Niebüll GmbH. Retrieved on 10.01.2020 at. https://www.neg-niebuell.de/index.php/fahrkarten/reservierung-kurswagen. Nguyen, T., Xie, M., Liu, X., Arunachalam, N., Rau, A., Lechner, B., Busch, F., Wong, Y.D., 2019. Platooning of autonomous public transport vehicles: the influenceof ride comfort on travel delay. Sustainability 11, 5237. Nielsen, G., Lange, T., 2007. Network design for public transport success-Theory and examples. Thredbo 10. Nold, M., 2019a. Speed controller for trains with longitudinal oscillations. Railway. Update Issue 1/2019. Nold, M., 2019b. Kupplungsunterstützungsvorrichtung zum An- und Abkuppeln von Schienenfahrzeugen. In: Deutsches Patent- und Markenamt. DE102018009589B3. Nold, M., Jung, M., Klar, O., 2018. Traktionsoptimierungen bei der Gmf 4/4 II. ZEVrail. Issue 11/2018. NZZ, 2015. Keine Intercity-Halte in Wankdorf und Altstetten. Zürich: Neue Zuercher Ztg. Published on 03.12.2015. Ortloff, H.v., 1997. Eisenbahn-Romantik - Mit Volldampf über die Geislinger Steige. Süddeutscher Rundfunk Documentary, Stuttgart. Eisenbahn-Romantik-Episode 229. Patents, Google, 2020. Selectively Combinable Independent Driving Vehicles. Retrieved on 10.12.2020 at. https://patents.google.com/patent/US20180022405A1/ en?oq=US20180022405A1. Peters, J.-L., 1990. Bestimmung des aerodynamischen Widerstandes des ICE/V im Tunnel und auf freier Strecke durch Auslaufversuche. Eisenbahntech. Rundsch. (ETR). Issue 9/1990. Profillidis, V.A., 2014. Railway Management and Engineering. Ashgate, Farnham. Quaglietta, E., 2019. Analysis of Platooning Train Operations under V2V communication-based signalling: fundamental modelling and capacity impacts of Virtual Coupling. Proceedings of the 98th Transportation Research Board Annual Meeting. Washington DC, 13th-17th January. Quaglietta, E., Wang, M., Goverde, R.M.P., 2020. A multi-state train-following model for the analysis of virtual coupling railway operations. Journal of Rail Transport Planning & Management. https://doi.org/10.1016/j.jrtpm.2020.100195. Railway Gazette, 1936. collisions. Railw. Gaz. 64 (21), 987. Railway Gazette, 1960. The last slip coach. Railw. Gaz. 133 (10), 267. Railway Herald, 2009. New timetable brings the launch of the fill High-Speed commuter service. Railway Herald. Issue 206 – 21st December 2009. Railway Magazine, 1960. The last slip coach. Railw. Mag. 106 (714), 675. Reuters, 2018. Dubai Tests Autonomous Pods in Drive for Smart City. Published on 01.03.2018 at. https://www.reuters.com/article/us-emirates-transportation- autonomous-idUSKCN1GD5G6. Sachs, K., 1973. Elektrische Triebfahrzeuge. Huber/Springer, Frauenfeld/Wien. SBB, B.L.S., SOB, 2015. Regelwerk streckentabellen R I-30131. Schweizerische bundesbahnen AG, BLS Netz AG (Schweizerische Südostbahn AG). SBB, 2018. Vierspurausbau olten–aarau: eppenbergtunnel. Olten: SBB AG. SBB, 2019. Liniennetzplan SBB fernverkehr. Schweizerische bundesbahnen AG. Retrieved an 26.02.2020 at. https://www.sbb.ch/content/dam/internet/sbb/de/ fahrplan/fahrplaninformationen/Liniennetzplan-SBB-Fernverkehr.pdf.sbbdownload.pdf. SBB, 2020. Trassenpreisrechner - fahrzeug. Retrieved an 25.11.2020 at. https://www.sbb.ch/de/iframes/preisberechnung.html. Schobel,¨ A., 2017. An eigenmodel for iterative line planning, timetabling and vehicle scheduling in public transportation. Transport. Res. C Emerg. Technol. 74 https://doi.org/10.1016/j.trc.2016.11.018, 2017. Schweers, H., Wall, H., Wessels, M., Würdig, T., 2012. Eisenbahnatlas Schweiz. Aachen, Koln.¨ Schweers + Wall GmbH. Schweizerische Bauzeitung, 1886. Schlussprotokoll der zweiten internationalen Conferenz betreffend die technische Einheit im Eisenbahnwesen. Schweizerische Bauzeitung. https://doi.org/10.5169/seals-13637. SER, 2006. NS Restaurieren ICM-Züge. Schweizer Eisenbahn-Revue. Issue 2/2006. SER, 2017. Danische¨ IC3 sollen zehn Jahre langer¨ fahren. Schweizer Eisenbahn-Revue. Issue 12/2017. Siemens, 2015. Fact Sheet Velaro D - Neuer ICE 3 (Baureihe 407) Retrieved an 26.11.2020 at. https://assets.new.siemens.com/siemens/assets/api/uuid:f87cebe5- 71ab-4224-985d-baa30a934ff0/factsheet-velaro-d-de.pdf. Siemens, 2017. Desiro Verv. München: Siemens AG. SRF, 2015. Keine Intercity-Halte in den Agglomerationen Bern und Zürich. Zürich: schweizer Radio und Fernsehen. Published on 03.12.2015. Stadler, 2012. Elektrischer Doppelstocktriebzug KISS für die Schweizerischen Bundesbahnen (SBB). Stadler Altenrhein AG, Schweiz. Stadler, 2016. Stadler enthüllt zusammen mit den Schweizerischen Bundesbahnen SBB den EC250/Giruno. Schweiz. Bussnang. Retrieved an 09.12.2020 at. https:// www.stadlerrail.com/de/medien/article/stadler-enthuellt-zusammen-mit-den-schweizerischen/36/. Stadler, 2019. Elektrischer triebzug Flirt - norske tog AS. Norwegen. Bussnang: Group. Starlinger, A., Bühl, R., Legler, T., 2016. Das Zulassungskonzept für den EC 250/Giruno Hochgeschwindigkeitszug. Stadler Rail Group. Retrieved on 27.11.2020 at. https://www.schienenfahrzeugtagung.at/download/PDF2016/DiV07_Starlinger.pdf. Tagesanzeiger, 2015. Intercity-Züge halten nicht in Bern-Wankdorf. Zürich: Tamedia Publikationen Deutschschweiz AG. Published on 03.12.2015. Theeg, G., Vlasenko, S., 2009. Railway Signalling & Interlocking: International Compendium. Eurailpress, Hamburg. Van Nes, R., 1999. Design of multimodal transport systems: setting the scene: review of literature and basic concepts. In: TRAIL Studies in Transport Science Series. Delft University Press, Delft. No. S99/3. VDE, 2019. Alternativen zu Dieseltriebzügen im Schienenpersonennahverkehr (Frankfurt). Vertrieb GmbH, D.B., 2015. Ihr Reiseplan – ICE 70 Chur-Hamburg. DB Vertrieb GmbH, Frankfurt. von Andrian, W., 2017. Überfüllte kurzzüge am fasnachtssamstag. Schweizer Eisenbahn-Revue. Issue 4/2017. Vuchic, V.R., 2007. Urban Transit Systems and Technology. Book published by John Wiley & Sons, ISBN 978-0-471-75823-5, p. 624. https://doi.org/10.1002/ 9780470168066. Wagli,¨ H.G., 2010. Bahnprofil Schweiz. AS Verlag & Buchkonzpet AG, Zürich. Wardman, M., 2014. Valuing Convenience in Public Transport. International Transport Forum, Paris. Wardman, M., Hine, J., 2000. Costs of interchange: a review of the literature. In: Working Paper. Institute of Transport Studies. University of Leeds, Leeds, UK. Wehinger, S., 2012. Westbahn - geglückter Start in eine neue Eisenbahnara.¨ Schweizer Eisenbahn-Revue. Issue 4/2012. Woodhouse, E., 1936. Slip Coach Accident at Woodford & Hinton LNER. Ministry of Transport, London.

25 M. Nold and F. Corman Journal of Rail Transport Planning & Management 18 (2021) 100241

ZBB, 2015. Mehr Bahnhof für die Hauptstadt - schritt für Schritt zu einem leistungsfahigeren¨ Bahnhof Bern. Bern: zukunft Bahnhof Bern. Publishers: kanton Bern, Stadt Bern, Schweizerische Bundesbahnen SBB, Regionalverkehr Bern-Solothurn RBS, BLS AG, BERNMOBIL, Bundesamt für Verkehr, PostAuto Schweiz AG, Die Post Schweiz AG, Grosse Schanze AG, Burgergemeinde Bern. Zhang, W., Jenelius, E., Badia, H., 2019. Efficiency of semi-autonomous and fully autonomous bus services in trunk-and-branches networks. J. Adv. Transport. https://doi.org/10.1155/2019/7648735. Zhang, Z., Tafreshian, A., Masoud, N., 2020. Modular transit: using autonomy and modularity to improve performance in public transportation. Transport. Res. E Logist. Transport. Rev. 141, 2020. https://doi.org/10.1016/j.tre.2020.102033.

26