sustainability

Article Park and Pool Lots’ Impact on Promoting Shared Mobility and Carpooling on Highways: The Case of Slovenia

Robert Rijavec *, Nima Dadashzadeh * , Marijan Žura and Rok Marsetiˇc

Traffic Technical Institute, Faculty of Civil and Geodetic Engineering, University of Ljubljana, 1000 Ljubljana, Slovenia * Correspondence: [email protected] (R.R.); [email protected] (N.D.); Tel.: +386-1-476-8580 (N.D.)


Received: 13 March 2020; Accepted: 14 April 2020; Published: 15 April 2020


Abstract: Dispersed settlement areas (e.g., Slovenia) result in lower development of fixed public transport lines and thereby car-dependent lifestyles. To avoid congestion inside the cities and on highways in these areas, shared mobility modes e.g., carpooling, is one of the effective solutions, increasing the occupancy of personal vehicles. However, passenger pick-up and drop-off locations still remain an important challenge for carpool users and transport officials. As a collection point for carpooling, we can consider “park and pool (P+P)” lots near highways’ interchanges. This study aims to examine the impacts of P+P lots near interchanges on carpooling behavior of users and on improving sustainable mobility on highways in such dispersed settlement areas. To do so, we employed a field survey, incorporated the P+P lots into the mode choice model, and examined different scenarios using the macroscopic transport model. It is found that factors such as travel cost, public transport service limitations, and improved parking facilities impact highway users’ mode choice. Sixty percent of respondents are willing to leave their car in P+P lots near interchanges. The results also show that P+P lots can increase the number of carpool users. It causes remarkable savings in terms of operating and external costs because of the reduction in total distance and time travelled by personal vehicles as well as parking demand reduction in cities. At the moment, especially in Central Europe, it is easier to invest in a “demand reduction” infrastructure than to increase the capacity of infrastructure. Therefore, P+P lots could be a “win-win” situation for both users and operators.

Keywords: carpooling; park and pool; shared mobility; ridesharing; collection points; transport hubs; mobility hub

1. Introduction and Background

Transport accounts for one quarter of total air pollution and CO2 emissions in Europe [1]. Governments and states globally and in the EU try to reduce traffic congestion and car dependency with policies and regulations, such as giving movement priority to public transport (PT) or reducing space allocated to private cars [2], increasing urban densities, increasing the occupancy (number of people in a vehicle) of vehicles, increasing walkability, supporting cycling, multimodal transport, and shared mobility modes [3]. Shared mobility modes can be divided into two major groups: (i) Sharing a passenger ride (carpooling, vanpooling, etc.), and (ii) sharing a vehicle (carsharing, bike sharing, and scooter sharing) [4]. The range and availability of all kinds of shared mobility modes are rapidly growing and are supposed to become more desirable using information communication technologies (ICTs) and

Sustainability 2020, 12, 3188; doi:10.3390/su12083188 www.mdpi.com/journal/sustainability Sustainability 2020, 12, 3188 2 of 19 new transport technologies like autonomous and connected vehicles [5]. Ridesharing is a specific kind of shared mobility mode in which a couple of people who have a common starting point, destination, or both,Sustainability travel 2 together020, 12, x FOR with PEER a REVIEW car (so-called carpooling) or van (so-called vanpooling). Carpooling2 of 18 is an alternative way to travel that can be implemented without major problems and can provide benefits shared mobility mode in which a couple of people who have a common starting point, destination, for commutersor both, travel and toget society.her with Carpooling a car (so-called is not carpooling) about being or against van (so- thecalled private vanpooling). ownership Carpooling of cars butis is aboutan being alternative against way the to ine travelfficient that use can of be private implemented cars. Carpooling without major is also problems not about and being can provide against PT but isbenefits about for being commuters against and insu society.fficient Carpooling and inefficient is not PT about usage. being “Causal against carpooling” the private ownership is sharing of a ride withcars known but is passengers about being like against friends the orinefficient colleagues, use andof private is used cars for. Carpooling short-distance is also trips not e.g.,about from being home to workagainst or educationPT but is about (school, being university). against insufficient Meanwhile, and “on-demand inefficient PT ride usage. service” “Causal is sharing carpooling” a ride is with an unknownsharing a ride passenger with known on demand passenge viars agreementlike friends onor colleagues web/mobile, and applications, is used for short and- isdistance normally trips used for long-distancee.g., from home trips to work e.g., betweenor education cities. (school, On the university). other hand, Meanwhile, transportation “on-demand network ride companies service” is are providingsharing ride-sourcing a ride with an servicesunknown like passenger vanpooling on demand and ride-hailing via agreement (taxi) on web/mobile services such application as Ubers, and Lyft.and This is kindnormally of service used for aims long to-distance address trips the e.g. limitation, between of cities. using On PT the such other as metro,hand, transportation tram, and bus in particularnetwork in areas companies of low are demand. providing For ride example,-sourcing it can services be a shuttle like vanpooling bus (van) service and ride for-hailing employees (taxi) of a services such as Uber and Lyft. This kind of service aims to address the limitation of using PT such workplace or educational center. The timetable is tailored to the working hours of the participating as metro, tram, and bus in particular in areas of low demand. For example, it can be a shuttle bus companies and is therefore ideal for employees who cannot use PT. (van) service for employees of a workplace or educational center. The timetable is tailored to the workingAcross hours the world of the andparticipating in Europe, companies there areand countriesis therefore/regions ideal for which employees are characterizedwho cannot use by a dispersedPT. settlement, with many stand-alone one-family houses e.g., Slovenia. Such a kind of density of populationAcross results the world in lower and development in Europe, there of fixed are countries/regions public transport which lines. are In addition,characterized the carby is a the numberdispersed one solution settlement, for with travelling many stand to work-alone and one to-family school, houses where e.g. parking, Slovenia is. notSuch the a kind evident of density problem. To avoidof population congestion results inside in thelower cities development and on highways, of fixed public together transport with shared lines. In mobility addition, modes, the car we is shouldthe considernumber shared one solution mobility for infrastructures travelling to work as well. and to school, where parking is not the evident problem. ToThere avoid are congestion two kinds inside of shared the cities mobility and on infrastructures: highways, together (i) Park with and shared ride (Pmobility+R) lots, modes, and (ii) we park andshould pool (P consider+P) lots shared which mobility are described infrastructures below: as well. ParkThere and are ride two (P+ kindsR) lots of areshared generally mobility located infrastructures: out of the i) cityPark ring, and evenride (P+R) better lots, if they and areii) park further and pool (P+P) lots which are described below: away in distance. With this, lots people can leave their car or other vehicle (bicycle, motorcycle), and Park and ride (P+R) lots are generally located out of the city ring, even better if they are further take PT (train, bus) for traveling to the city center [6]. Lots are effective only if there are existing PT away in distance. With this, lots people can leave their car or other vehicle (bicycle, motorcycle), and stopstake nearby, PT (train, or there bus) isfor the traveling possibility to the to city introduce center [6] new. Lots PT are lines effective and stops only nearby.if there are existing PT stopsP+P nearby, lots describe or there parking is the possibility spaces whereto introduce commuters new PT lines and and drivers stops can nearby. meet to form carpools. The differenceP+P lotsbetween describe P parking+R and spaces P+P is where that P commuters+P lots are and built drivers in the can low meet demand to form area carpools. of PT or The where theredifference is no PT networkbetween P+R coverage. and P+P One is that of theP+P potential lots are built places in the to implementlow demand P area+P lots of PT is nearor where interchanges there in theis no dispersed PT network settlement coverage. areas One whereof the potential there are places no fixed to implement public transport P+P lots lines.is near Forinterchanges instance, in there are Pthe+P dispersed lots implemented settlement area nears interchanges:where there are Germanyno fixed public (Parken-und-Mitfahren), transport lines. For instance, the UK, ther thee are USA, Canada.P+P lots the Netherlandsimplemented (Figurenear interchange1a), and News: Germany Zealand (Parken (Figure-und1b).-Mitfahren), the UK, the USA, Canada. the Netherlands (Figure 1a), and New Zealand (Figure 1b),

(a) (b)

FigureFigure 1. P 1.+ PP+P lots, lots, (a ()a carpool) carpool Ede, Ede, GelderlandGelderland (Netherlands), (Netherlands), (b ()b T)akapuna, Takapuna, Auckland Auckland (New (New Zealand) Zealand) (source:(source Google.map.com).: Google.map.com). Sustainability 2020, 12, 3188 3 of 19

A survey in the USA [7] showed that 1% of private vehicles joining carpooling can save three billion liters of gasoline and 10% can save 28 billion liters annually. Seyedabrishami [8] claimed that about 240 million liters of fuel would be saved annually if 30% of travelers joined carpooling in Tehran. In addition, another study shows that 14% to 18% of vehicle-km would be saved if 28% to 36% of all carpooling requests were fulfilled. Hence, ride-sharing is an effective method of transportation management to reduce the proportion of single-occupant vehicle trips (SOV) and to ease traffic congestion [9]. Jacobson and King [10] identified that carpooling can improve the fuel economy of cars if no additional travel is required to pick up passengers. They conclude that adding one additional passenger for every 100 vehicles would reduce the national annual fuel consumption by 3.03–3.11 million liters per year in the US. But in fact, it is not the fuel economy of cars that defines the total environmental benefit of carpooling, but the reduction in total vehicle kilometers travelled (VKT) results in fuel savings and reduced greenhouse gas (GHG) emissions [11]. Gargiulo et al. [12] examined carpooling’s impacts on travel distance and CO2 reduction in Dublin. Around 12,600 tons of CO2 were eliminated by carpooling on weekdays, which corresponded to approximately 706,428 euros. Amey [13] found that total daily travel distance would be shortened by as much as 9%–27% when 50%–77% of the total commuting population of the faculty and students at the Massachusetts Institute of Technology used carpooling. One of the important questions regarding carpooling is who is interested in carpooling and why. Using a campus travel pattern survey at Ohio State University, Park et al. [14] found that safety, flexibility, and parking cost-savings were the most important factors for people willing to be a passenger; while the convenience and opportunities for socializing through a carpool trip were the most influential factors for people willing to take the role of driver. Olsson et al. [15] also mentioned that psychological factors, namely monetary and time benefits, reducing congestion, and environmental concerns are more important than socio-demographic variables. In a case study in Lisbon, Correia and Viegas [9] concluded that the passengers joining in carpooling were mostly concerned with travel budgets, namely saving fuel costs, toll costs, and workplace parking costs. Huang [16], through conducting a practical trial (survey), found that travel time, travel cost, and safety are three key factors among potential influencing factors. Delhomme and Gheorghiu [17] utilized the binary logit regression to analyze the influence of gender on carpooling choice. Moreover, they developed a multinomial logit regression model to study modal choice between public transit modes, casual carpooling, and driving alone. Huang [16] also examined the impacts of these on each other (particularly the travel time and travel cost) using a binary logit regression analysis. Olaru [18] used discrete choice models to examine the travelers’ attitudes in choosing P+R facilities in Western Australia. Kwon [7] discovered that some high occupancy vehicle (HOV) lanes are under-utilized in California. About 81% of HOV lanes carry below 1400 vehicles per hour per lane during peak hours. Providing HOV lane usage for carpooling vehicles (which can improve their travel time) would attract more drivers and passengers to use this system during peak hours as well as improve its function during off-peak hours [19]. On the other hand, and inside the cities, as Dadashzadeh and Ergun [2] stated, the spatial bus priority methods like dedicated bus lanes provide great benefits to bus movement. Dadashzadeh and Ergun also examined the effects of giving priority to buses on highways, in particular around on-ramp bottleneck areas [20]. Another possible option to improve the travel time and delay of carpoolers is to let them use these bus lanes inside the cities to avoid any conflicts with mixed traffic. This option is also examined as one of our scenarios to explore its effects on the mode choice of road users. Carpool preferential parking permit is another attracting factor which allows carpooling drivers to park in designated carpool parking spaces in the parking lots of workplaces, educational institutions, organizations, etc. These are the effective measures that can be used to develop scenarios. Although carpooling has become more popular these days, passenger pick-up and drop-off locations (matching point) remain an important challenge for drivers, passengers, and transport officials. Selecting a suitable matching location (i.e., P+P lot) along the daily commute of highway users can be a determining factor for how successfully the P+P lot will be utilized. Several factors can Sustainability 2020, 12, 3188 4 of 19 be important. In this study we examine the P+P lots near interchanges’ impacts on carpooling and mode choice behavior of highway users and on improving sustainable mobility. The rest of the article is organized as follows: Section2 proposes a brief background on ridesharing in Slovenia which is followed by survey among Slovene carpoolers and non-carpoolers to understand their attitudes. Section3 describes carpooling modelling and integration with macroscopic transport model. The results of carpooling and P+P lots’ impacts on transport and the environment is discussed in Section4. Lastly, Section5 concludes and discusses the findings of the study and presents a few directions for further research on the subject.

2. Ridesharing in Slovenia (Ljubljana Urban Region) Ljubljana Urban Region (LUR) is located in the center of the country and is today home to around 537,000 inhabitants. It hosts around 43,000 students, 65,000 companies, a large number of tourists, and several events and festivals [21]. One of the largest education institutions in Slovenia, the University of Ljubljana (UL), is located in the city of Ljubljana (LJ). UL has 26 departments (three art academies and 23 faculties), around 38,000 students, and 6100 staff [22]. In the city of Ljubljana, governmental offices, public and private companies, and educational institutes are the three main trip attractors and have an important role in daily traffic inside the city and highways nearby. According to the statistics, around 127,600 people are travelling to LJ from other municipalities every day. Over the last couple of decades, the average occupancy rate for private cars in Slovenia has decreased to approximately 1.35 persons/vehicle, and sometimes even less. Although there are PT services provided by the government and municipalities in the region, PT is still not seen as a sufficiently attractive means of transport. Therefore, the LUR can be considered as a car-dependent region in which the share of cars in transport is around 84.3%, while PT has only a share of 14.6% of total trips [23]. Considering the daily congestion on Slovenian roads, it is necessary to find a solution that would reduce the demand on personal car usage and improve the level of services. Fewer vehicles on the roads would not only mean a reduction in the problems faced by personal cars, but also a decrease in fuel consumption and emissions, and an improvement in road safety. One such solution would be to “fill” the vacant seats within vehicles by encouraging people to travel in pairs or groups when travelling to the same destination point, or for at least a leg of the journey, thereby decreasing traffic volume. For example, it is observed that travelers heading to LJ tend to carpool at interchanges close to settlement areas. The general finding is that the number of parked vehicles at collection points increases with distance from the destination point. We rarely noticed illegally parked vehicles next to interchanges within the ring of LJ. A variety of telecommunication media and services are used to connect the carpoolers. In Slovenia, according to our research, in addition to conventional voice communication over the telephone networks, the most widespread forms of communication occur via the internet or via the use of applications for smart phones. One of the common online platforms for carpooling and vanpooling is www.prevoz.org. Regarding ridesharing facilities, P+R places have been introduced in some parts of the city such as P+R Dolgi Most, Barje, Jezica, and Stozice [24]. Generally, the only transport mode available nearby is a bus. Like other European capitals and cities, ridesharing, in particular carpooling, has become popular in LJ and all over Slovenia. According to a survey carried out by the authors in 2014, about 12,000 users offered carpooling rides through online platforms, of which 75% made offers more than once [25]. We estimated offers where the destination was LJ to be around 1000 per day. Considering the new carpooling data (10/12/2019 to 11/01/2020), it is obvious that there has been a significant increase in the number of carpooling trips offered by drivers (on average around 75%) over the last five years. We have prepared a rough comparison of carpooling trips provided from 10/12/2013 to 11/01/2014 and the same period for 2019 to 2020, divided into trips produced (trip origin) and attracted (trip destination) in Slovenia and also LJ. Having looked at Figure2, it can be seen that LJ (LJ_Produc. and LJ_Attrac.) has a share of around 42% of total trips produced-attracted in Slovenia. Sustainability 2020, 12, 3188 5 of 19 Sustainability 2020, 12, x FOR PEER REVIEW 5 of 18

Sustainability 2020, 12, x FOR PEER REVIEW 5 of 18

FigureFigure 2. 2.Carpooling Carpooling tripstrips comparisoncomparison between 2013 2013–14–14 and and 2019 2019–20.–20. Figure 2. Carpooling trips comparison between 2013–14 and 2019–20. FigureFigure3 demonstrates 3 demonstrates the the average average carpooling carpooling trip trip o ffoffersers from from/to/to LJ. LJ. However, However, carpooling carpooling has has not yetnot been yetFigure paid been su3 demonstratesffi paidcient sufficient attention the average attention despite carpooling its despite merits trip itsof convenience,offers merits from/to of convenience, cost-eLJ. However,fficiency, cost carpooling and-efficiency, sustainability has and in Slovenia.sustainabilitynot yet been in paid Slovenia. sufficient attention despite its merits of convenience, cost-efficiency, and sustainability in Slovenia.

FigureFigure 3. 3.The The average average monthlymonthly carpooling carpooling rides rides offered offered by bycarpoolers carpoolers from/to from Ljubljana/to Ljubljana (LJ) [25] (LJ). [25]. Figure 3. The average monthly carpooling rides offered by carpoolers from/to Ljubljana (LJ) [25]. InIn order order to to increase increase the the proportion proportion of of people people carpooling, carpooling, it would it would be necessary be necessary to make to make In order to increase the proportion of people carpooling, it would be necessary to make infrastructuralinfrastructural changes changes andand effectively effectively promote promote this this mode mode of transport. of transport. One of the One major ofthe issues major that issues infrastructural changes and effectively promote this mode of transport. One of the major issues that thatcarpoolers carpoolers and and transport transport officials offi havecials faced have over faced the overyears theis illegal years parking is illegal in unorganized parking in lots unorganized near carpoolersinterchange ands, resulting transport in officialschaos in haveterms faced of traffic over management the years is andillegal physical parking safety in unorganized (theft of vehicles). lots near lots near interchanges, resulting in chaos in terms of traffic management and physical safety (theft of interchangeHaving lookeds, resulting at the in existing chaos in studies, terms of it traffic can be management found that and P+R physical facilities safety were (theft studied of vehicles). and vehicles). Having looked at the existing studies, it can be found that P+R facilities were studied and Havingimplemented looked well at in the LJ [23,26] existing and studies,around the it world can be [27 found–31] to address that P+R this facilities problem inside were the studied cities. and implementedimplementedHowever, there well well is in noin LJ LJscientific [23 [23,26],26] andand and robust aroundaround study the world regarding [27 [27– –the31]31 ] explorationto to address address this of this the problem problemeffectiveness inside inside of the the the cities. cities. However,However,introduction there there of is P+Pis no no scientificlots scientific near interchange and and robust robusts. studyThus,study this regarding study’s the theobjectives exploration exploration are as of follows: of the the effectiveness e i)ff ectivenessTo explore of ofthe the introductionintroductionthe influencing of of P+ P+PfactorsP lots lots in near near carpooling interchanges. interchange in Slovenis. Thus,Thus,a, and this ii) study’s to model objectives objectives carpooling are are withas as follows: follows:special i)focus (i)To To explore on explore thetheP+P influencing influencing lots near interchange factors factors in in carpoolings .carpooling in in Slovenia, Slovenia, andand (ii)ii) to to model model carpooling carpooling with with special special focus focus on on P+P+PP lots lots near near interchanges. interchanges. Sustainability 2020, 12, 3188 6 of 19

2.1.Sustainability Data Collection 2020, 12, and x FOR Survey PEER REVIEW 6 of 18 2.1.We Data conducted Collection aand survey Survey among road users coming to LJ to examine the influencing factors on carpoolingWe conducted (Appendix aA survey). It is carriedamong road out between users coming two di toff LJerent to examine groups ofthe users, influencing namely factors (i) current on carpoolerscarpooling and (Appendix (ii) non-carpoolers. A). It is carried The out survey between was carriedtwo different out near groups interchanges, of users, namely namely i) Primorska current (e.g.,carpoolers Unec), Gorenjska and ii) non (e.g.,-carpoolers. Kranj), ŠtajerskaThe survey (e.g., was Žalec), carried and out Dolenjskanear interchange (e.g., IvanˇcnaGorica)s, namely Primorska during the(e.g. morning, Unec), peak Gorenjska period. (e.g. In, allKranj), survey Štajerska points, (e.g. it is, Žalec), observed and thatDolenjska some (e.g. people, Ivančna park theirGorica) car during illegally onthe the morning roadside peak to takeperiod. a carpool In all survey vehicle, points, as shown it is observed in Figure that4 somebelow. people Therefore, park their we car asked illegally a few questionson the roadside regarding to the take implementation a carpool vehicle, of P as+P shown lots near in Figure interchanges 4 below. during Therefore, the survey, we asked too. Figurea few 4 depictsquestions the location regarding of the survey implementation points with blackof P+P circles. lots near Tra interchangeffic congestions during levels the on survey, highways too. isFigure shown for4 adepicts Monday the morning location peakof survey hour. points with black circles. Traffic congestion levels on highways is shown for a Monday morning peak hour.

FigureFigure 4. Survey 4. Survey points points (black (black circles), circles), source: source: Adopted Adopted from from Google Google Maps Mapsand and modifiedmodified. [32].

2.2.2.2. Survey Survey among among Carpoolers Carpoolers DespiteDespite the the fact fact that that Slovenia Slovenia isis aa smallsmall countrycountry and it it is is very very difficult difficult to to collect collect data data for for bigger bigger populationspopulation usings using interviews, interviews, our our sample sample size sizewas aroundwas around 9% of 9% the of total the number total number of vehicles of vehicles travelling in peaktravelling hour. in This peak means, hour. in This total, means 247 questionnaires, in total, 247 were questionnaires distributed were via envelopes distributed among via envelopes carpooling usersamong at the carpooling selected users locations. at the They selected were locations. asked to They deliver were questionnaires asked to deliver through questionnaires these two through options: (i)these To the two interviewer options: i) aTo day the after interviewer at the samea day place,after at (ii) the to same send place, them ii to) to our send faculty them viato our the faculty prepaid postvia services. the prepaid post services. TheThe response response rate rate was was around around 50%. 50%. RespondentsRespondents were were unbalanced unbalanced in in terms terms of of gender gender including including 57%57% male, male, and and 43% 43% female female respondents, respondents, withwith anan averageaverage age age of of 35 35 years. years. Respo Respondentsndents were were mainly mainly dailydaily migrants. migrants. The The largest largest number number ofof themthem were travelling 5 5 days days a aweek week (54%), (54%), followed followed by by those those totalingtotaling 4 days4 days a weeka week (24%), (24%) and, and 6 days6 days a weeka week (12%). (12%). Among Among trip trip purposes, purposes, home home to to work work trips trips had a sharehad a of share 80%, of while 80%, homewhile tohome school to school trips weretrips 16%were of16% all of trips. all trips. The majorityThe majority (76%) (76%) most most often often travel withtravel co-workers, with co-workers, to the same to the destination same destination of travel of (76%), travel and (76%) always, and withalways the with same the people same (84%).people (84%). Figure5 shows the most common reasons for carpooling and the occupancy of carpooler vehicles. Figure 5 shows the most common reasons for carpooling and the occupancy of carpooler As seen, the most important factor in choosing carpooling is “travel cost” with a share of 43%, followed vehicles. As seen, the most important factor in choosing carpooling is “travel cost” with a share of 43%, followed by other factors such as “travelling together is more pleasant,” “reduction in environmental pollution,” and a “lack of parking lots at the destination”. Sustainability 2020, 12, 3188 7 of 19 by other factors such as “travelling together is more pleasant,” “reduction in environmental pollution,” and a “lack of parking lots at the destination”. SustainabilitySustainability 2 2020020, ,1 122, ,x x FOR FOR PEER PEER REVIEWREVIEW 7 7of of 18 18

(a) (b)

(a) (b) FigureFigure 5. Reasons 5. Reasons and and occupancy occupancy of of carpooling carpooling (a) (a) Carpooling reasons reasons,, and and (b) (vehicleb) vehicle occupancy occupancy amongFigureamong carpoolers. 5. carpoolers. Reasons and occupancy of carpooling (a) Carpooling reasons, and (b) vehicle occupancy among carpoolers. As noted,As noted, the the average average occupancy occupancy of vehicles of vehicles is around is around1.35 persons/vehicle 1.35 persons in Slovenia/vehicle. Through in Slovenia. Throughthe As field the noted, field survey, the survey, average we found we occupancy found that the that ofaverage vehicles the average occupancy is around occupancy of1.35 the persons/vehicle carpooler of the carpooler vehicles in Slovenia isvehicles around. Through is 2.98 around persons/vehicle. This is a potentially good prospect for an increase in vehicle occupancy at peak hours 2.98the persons field / survey,vehicle. weThis found is a potentially that the average good prospectoccupancy for of an the increase carpooler in vehiclevehicles occupancy is around 2.98 at peak in the event of a change in driving culture and vehicle sharing. hourspersons/vehicle. in the event of This a change is a potentially in driving good culture prospect and for vehicle an increase sharing. in vehicle occupancy at peak hours in the Theevent answers of a change to the in question driving about culture the and reasons vehicle for sharing. choosing a carpool car indicate that most of Thethe people answers were to the dissatisfied question with about the the available reasons PT for services choosing and a carpool connections car indicate (see Figure that 6a). most For of the The answers to the question about the reasons for choosing a carpool car indicate that most of peopletoday were’s lifestyle, dissatisfied where with the thevalue available of time pla PTys services a vital role, and traveling connections by PT (see, especially Figure6 overa). For longer today’s the people were dissatisfied with the available PT services and connections (see Figure 6a). For lifestyle,distances where, is thestill value too long of timecompared plays to a traveling vital role, by traveling car. The disadvantages by PT, especially of PT over in some longer locations distances, today’s lifestyle, where the value of time plays a vital role, traveling by PT, especially over longer is stillare too also long reflected compared in the poor to traveling network diversification by car. The disadvantagesand the insufficient of PTnumber in some of daily locations PT options are also distances, is still too long compared to traveling by car. The disadvantages of PT in some locations offered by the government. reflectedare also in thereflected poor in network the poor diversification network diversification and the insu andffi thecient insufficient number number of daily of PT daily options PT opt offionsered by the government.offered by the government.

(a) (b)

Figure 6. The reasons for choosing a carpool car (a) The reasons to choose carpooling instead of public transport (PT), and (b)( ausers’) expectations of services that should be provided by(b )transport officials near interchanges. FigureFigure 6. The 6. The reasons reasons for for choosing choosing a a carpool carpool car ( a) The The reasons reasons to to choose choose carpooling carpooling instead instead of public of public transporttransportWhen (PT), carpooling (PT and), and (b )( busers users’) users’ were expectations expectations asked about ofof servicesservices satisfaction that that should shouldregarding be be provided provided places bywhere bytransport transport they officialsleave offi theircials nearcarsnear to interchanges. take interchange a carpools. vehicle, only a quarter of those were unhappy with the location. They stated that it could be an organized parking lot. In the next question (see Figure 6b), where respondents WhenwereWhen offered carpooling carpooling the opportuni users users were tywere askedto asked choose about about additional satisfaction satisfaction services regarding regarding at this places location,places where where less they thanthey leave aleave third theirtheir of cars to takecarsrespondents ato carpool take a saidcarpool vehicle, that vehicle,they only did a onlynot quarter miss a quarter additional of those of those were services were unhappy at unhappy the location. with with the Most the location. oflocation. them Theydeclared They stated stated the that that it could be an organized parking lot. In the next question (see Figure 6b), where respondents it couldneed be for an organized organized parking parking lots lot.that Inshould the next remain question free of (seecharge, Figure and6 someb), where expos respondentsed poor public were werelighting. offered the opportunity to choose additional services at this location, less than a third of offered the opportunity to choose additional services at this location, less than a third of respondents respondentsCertainly, said there that isthey a need did tonot arrange miss additional car parks forservices carpooling at the userslocation. to encourage Most of them ridesharing, declared but the said that they did not miss additional services at the location. Most of them declared the need for needit is for doubtful organized whether parking car lots parks that should should be remain charged free for of or charge, not. According and some toexpos the ed survey, poor public most organizedlighting.respondents parking would lots that find should another remain free loc freeation of to charge, park their and somecar if exposed parking was poor introduced. public lighting. The Certainly,purposeCertainly, of therethe there study is a is needis a toneed promote to to arrange arrange such car cara parksmode parks of for for transport, carpooling carpooling so we users believe to to encourage encourage that the introductionridesharing, ridesharing, butof but it is doubtfulitparking is doubtful whether fees is whethernot car a suitable parks car should parkssolution should be for charged parking be charged for lots or intended not. for Accordingor to not. attract According toroad the users survey, to to the leave most survey, thei respondentsr cars most wouldrespondentsduring find another carpooling would free with find location another another to park person. free their loc Onlyation car aif to quarterparking park their of was respondents car introduced. if parking were The was prepared purpose introduced. to of pay the The a study is topurpose promoteparking offee. suchthe The study aaverage mode is to ofamounts promote transport, calculated such so a mode we from believe of the transport, respondents' that the so introductionwe proposals believe that were of the parking €1.40/day introduction fees or € is23 of not a suitableparking/month. solution fee s is fornot parkinga suitable lots solution intended for parking to attract lots roadintended users to toattract leave road their users cars toduring leave thei carpoolingr cars during carpooling with another person. Only a quarter of respondents were prepared to pay a Sustainability 2020, 12, 3188 8 of 19 with another person. Only a quarter of respondents were prepared to pay a parking fee. The average amounts calculated from the respondents’ proposals were €1.40/day or €23 /month.

2.3. Survey among Non-Carpoolers Once the survey among the existing carpooling users was completed, we conducted another Sustainability 2020, 12, x FOR PEER REVIEW 8 of 18 survey among drivers who were not doing carpooling, and most often driving alone. The survey was2.3. carried Survey out among at the Non petrol-Carpoolers and toll stations near to the selected interchanges in the afternoon peak. The questionnaires, together with the envelope and postage stamp, were distributed to identify the Once the survey among the existing carpooling users was completed, we conducted another reasonssurvey why among they drivers do not who carpool were andnot doing what carpooling, the motivation and most would often be driving to opt alone. for this The mode survey of was transport. carriedIn this out survey, at the thepetrol sample and toll size stations was around near to the 15% selected of the interchange total numbers in of the vehicles afternoon travelling peak. The in peak hour.questionnaires, This means a together total of with374 envelopes the envelope with and questionnaires postage stamp, were were distributed distributed among to identify non-carpooling the vehicles.reasons The why response they do not rate carpool was around and what 61%. the motivation Respondents would were be quiteto opt gender-balancedfor this mode of transport. consisting of 49% malesIn this and survey, 51% females. the sample The size average was around age of15% the of respondentsthe total number was of 38.5 vehicles years. travelling The target in peak group of thehour. survey This was means drivers a whototal drove of 374 without envelopes passengers. with questionnaires Of those surveyed,were distributed 82% of among drivers non regularly- travelcarpooling without vehicles. passengers. The respon Most ofse themrate was commute around to61%. work Respondents (87%), but were they quite are daily gender migrants,-balanced as they consisting of 49% males and 51% females. The average age of the respondents was 38.5 years. The travel 5 days a week (78%), followed by those who travel 6 days a week (11%). The majority of those target group of the survey was drivers who drove without passengers. Of those surveyed, 82% of surveyed were locals who reside in the vicinity of the selected interchanges, and most of them were drivers regularly travel without passengers. Most of them commute to work (87%), but they are daily commutingmigrants, toas LJthey daily. travel 5 days a week (78%), followed by those who travel 6 days a week (11%). The majorityIn the preparationof those surveyed of the were survey, locals we who considered reside in the the vicinity possibility of the thatselected people interchange need theirs, and cars for mobilitymost of at them the were destination. commuting In to addition, LJ daily. they probably do not have the opportunity to go to the destinationIn the with preparation another person.of the survey, However, we considered the results the of possibility the survey that showed peopleas need many their as cars 84% for of those surveyedmobility do at not the need destination. their own In addition, car at destination, they probably while do 14% not of have them the stated opportunity they need to go it. to More the than expected,destination around with 56% another of respondents, person. However, also the stated results that of theythe survey have showed an option as many to drive as 84% with of someonethose to thesurveyed same destination, do not need while their 44%own ofcar them at destination, stated they while do 14% not of have them any stated ridesharing they need options. it. More than expected, around 56% of respondents, also stated that they have an option to drive with someone to The respondents were also asked about their views for and against carpooling through a the same destination, while 44% of them stated they do not have any ridesharing options. multiple-choice question as shown in Figure7. The analysis of the answers showed a similar situation The respondents were also asked about their views for and against carpooling through a as inmultiple the case-choice of the question survey as conducted shown in Figure among 7. existingThe analysis carpooling of the answers users. showed The most a similar influential situation factor for doingas in carpooling the case of is the the survey distribution conducted of costs. among In existing addition, carpooling respondents users.believe The most that influential driving factor in company withfor others doing is carpooling more enjoyable is the distribution than driving of alone. costs. In A smalladdition, proportion respondents of the believe answers that weredriving those in who are notcompany interested with others in carpooling is more enjoyable and prefer than to driving drive alone.alone. A small proportion of the answers were those who are not interested in carpooling and prefer to drive alone.

(a) (b)

FigureFigure 7. Views7. Views for for and and against against carpooling (a) (a Result) Result of ofNon Non-carpoolers-carpoolers attitude attitude towards towards carpooling carpooling,, andand (b) (b) Description Description of of possible possible answers.answers.

Obviously,Obviously, the the main main reason reason whywhy people do do not not opt opt for for carpooling carpooling is the is variable the variable working working hours hours causingcausing diffi difficultiesculties in in coordination coordination ofof departures from from home home to towork work or from or from work work to home. to home. Among Among other things, the respondents stated that freedom of movement is restricted by carpooling. Moreover, other things, the respondents stated that freedom of movement is restricted by carpooling. Moreover, some of them were disturbed by the delay of other passengers, which is another important factor for some of them were disturbed by the delay of other passengers, which is another important factor for the successful coordination and implementation of carpooling. Rarely, respondents were concerned theabout successful leaving coordination their car at the and places implementation near interchange of carpooling.s, or if they were Rarely, in carpooling respondents vehicle weres, concernedthey aboutprefer leaving to be driver. their car at the places near interchanges, or if they were in carpooling vehicles, they prefer toThe be driver.finding of a parking lot at the destination or parking fee at the destination were not a big concern for the respondents (73% of respondents do not have a problem with parking at the destination). From this, it can be summarized that parking facilities at the destination will not motivate new users of the carpooling mode, so it will be necessary to look elsewhere for motivation. Sustainability 2020, 12, 3188 9 of 19

The finding of a parking lot at the destination or parking fee at the destination were not a big concern for the respondents (73% of respondents do not have a problem with parking at the destination). From this, it can be summarized that parking facilities at the destination will not motivate new users of the carpooling mode, so it will be necessary to look elsewhere for motivation. One of the possible motivations is P+P parking lots near highway connections, as 59% of respondents are willing to leave their car in such lots. Then, they continue their journey with another person heading to the same or nearby destination. For some, even the setting up of a tidy parking is a prerequisite for making a decision on carpooling. Considering answers to the question about the cost sharing of a possible carpooling, it can be concluded that many respondents are willing to pay for carpooling. Travelers often do not reside close to each other, so they would need a well-organized parking lot at the collection point to continue their journey. To promote carpooling, online platform and infrastructure limitations should be improved by service providers and transport officials. In our case study, these limitations identified:

Carpooling platform should have (i) simplified communication or confirmation of a ride (one-click • booking), (ii) different payment options such as cash, and bank cards, (iii) driver/passenger rating system (e.g., reliability, punctuality, etc.), (iv) pick-up/drop-off points rating system (e.g., location, safety), (v) insurance scheme (part of each payment for a ride could be allocated for passenger insurance). P+P lots should have (i) good lighting (night use of parking lots), (ii) charging stations for electric • vehicles for cases such as electrical carsharing, bike-sharing, scooter-sharing, (iii) dedicated parking spaces for two-wheeled forms of transport (e.g., bicycles) and vulnerable users (disabled and/or elderly people), (iv) telecommunications connection to road management system, (v) traffic variable message signs (shows parking capacity online), and (vi) video surveillance of the area for safety and security reasons.

3. Carpooling and Park and Pool Lots Modelling on Highways A disaggregated four-step transport model has been developed for LUR which contains personal car, PT, cycling, and walking modes [33]. The model was developed using a well-known transport demand modelling software, PTV VISUM [34]. The model contains 482 zones, more than 13,000 nodes and more than 30,000 links. It contains all the data about PT lines, stops, and timetables. The standard four-step transport model generally includes the trip generation, trip distribution, mode choice, and assignment steps. Trip purposes can also be defined as home–work, home–school, home–shopping, home–leisure, home–rest, work–home, school–home, shopping–home, leisure–home, rest–home, work–other, other–work etc. To model the effects of ridesharing on the mode choice and travel behavior of people, the existing calibrated and validated LUR transport model should be upgraded. To this end, two new transport systems (tsys) have been introduced in the VISUM model for LUR as follows: (i) CP1: Carpool using P+P lots, and (ii) CP2: Direct carpool. From driver’s point of view, CP1 referred to as a driver comes to the P+P lots by a private car, and then pick up the passengers (who already left their car at P+P parking lots). While the CP2 refers to a driver collecting passengers from their homes along the journey. Generally, random utility theory and mode choice models (nested, multinomial and mixed logit, and probit) have been used to model the travel behavior of people in different situations [35]. The general formula of utility of mode choice (Ui) is:

Ui = Vi + εi, i = 1, 2, 3, ... , n (1) where Vi indicates the systematic component and εi indicates the random component of the total utility of choosing mode i from n modes. There are also different kinds of logit (logistic probability) models which can be used in modal split step of traditional four-step transport models or EVA model [36], namely multinomial logit, binary Sustainability 2020, 12, 3188 10 of 19 logit, and nested (hierarchical) logit models. In the general form of nested logit model, there are two transport modes, car and PT. PT has also two sub-group modes: Bus and metro. The probability of selection of a specific mode (PT and metro) can be formulated as follows:

eUPT P(PT) = , P(Metro/PT) = P(Metro) P(PT) (2) eUCar + eUPT ×

In this study, the nested logit model has been used to incorporate carpooling into the LUR transport model. After the trip distribution and modal split phases in the EVA model, where origin–destination matrices for all modes were calculated, we add an additional mode choice model for the home–work, and work–home journeys. At this stage, we first divide the trips according to whether they travel alone by their private car (without taking passenger), hereinafter called CAR, or involved ridesharing hereinafter called CP (carpooling). We then divide the trips involving ridesharing into two categories, namely CP1 and CP2. The nested logit model has been used in this study to represent these two transport modes so-called CAR and CP, and the sub-group of CPs namely CP1, and CP2. The viability of given CAR can be calculated by the following formula:

Cost UCAR = 0.016 tt 0.0015 dist (3) − × − × × OCCCAR

The utility function of CP1 user can be calculated by the formula:

Cost UCP1 = 0.016 (tt + lt (OCCCP1 1)) 0.0015 dist + − × ∗ − − × × OCCCP1 (4) 0.032 type + 0.00032 places 2.8 × × − The utility function of CP2 user can be calculated by the formula:

Cost UCP2 = 0.016 tt 0.0015 dist (5) − × − × × OCCCP2 where: tt: Travel time lt: Time lost due to waiting by a passenger/for a passenger: 1.1 min/passenger dist: Distance

OCCCP1: Average occupancy rate of the CP1 car: 3, OCCCP2: Average occupancy rate of the CP2 car: 2, OCCCAR: Average occupancy rate of the car: 1.35, Cost: Travel costs per kilometre travelled: €0.08/km, Places: Number of parking spaces Type: Organization of parking site (1: Un-organized, 2: Marked, 3: Marked and asphalted, 4: 3 and lit, 5: 4 and security measures present)

Total utility of CP1 and CP2 has been calculated using the following equation:

UCP1 UCP2 UCP = ln(e + e ) (6)

The likelihood of using modes CP1 and CP2 has been calculated using the following equations:

eUCP1 p(CP1) = (7) eUCP1 + eUCP2

eUCP2 p(CP2) = (8) eUCP1 + eUCP2 Sustainability 2020, 12, 3188 11 of 19

Lastly, the equilibrium-Lohse [36] method has been used for the assignment step. Then, to evaluate the effects of carpooling and P+P lots near interchanges, a P+P lot has been modelled in one of our observation points at the IvanˇcnaGorica (IG) interchange, along the A2 highway; LJ–Novo Mesto (Slovenia)–Zagreb (Croatia) direction. We conducted traffic counting on three groups of vehicles, namely normal cars, cars with occupancy more than two people, and cars parked illegally on the roadside in the study area. To validate our model using the these modal split formulas, the study area has been simulated with the existing carpooling users and the users parking their car illegally. Then we compared the results of mode choice with the vehicle counting results to ensure that our model represents the actual conditions properly (Scenario V0: Current situation). Once the validity of the model was achieved, the following scenarios were developed and analyzed by the LUR transport model:

Scenario V1 (implementation of P+P lot near IG interchange): We simulated the effectiveness of • introducing the P+P lot in one of the locations where we observed illegal car parking by carpoolers. We estimated that this scenario will increase the number of carpooling users (CP) in general. Scenario V2 (Scenario 1 with the possibility of using bus lanes in LJ): We simulated the effectiveness • of introducing the possibility for vehicles with two or more people in LJ to use the dedicated bus lane. We estimate that this option reduces travel time by one-third. Scenario V3 (Scenario 2 and a congestion pricing for entry into LJ): We simulated the effectiveness of • introducing a congestion pricing policy (entry fee of 5 euro) in LJ. Thereby, we tried to understand the impacts of travel cost on the mode choice of carpooling users.

These scenarios have not been produced by the LUR transport model. Scenarios which incorporate carpooling were evaluated by the LUR model. Scenario analysis results are discussed in the next section in terms of their impacts on traffic, economics, and the environment.

4. Results and Discussions

4.1. Traffic Impacts Analysis In this section, the transport network measures will be discussed in two segments: (i) On the ramp of the IvanˇcnaGorica (IG) connection to LJ, and (ii) on highway segment between Novo Mesto and LJ crossing IG interchange. In the current situation (V0), a total of 5205 trips per working day are made on the ramp of the IG connection to LJ. It comprises of 4513 CAR trips (87% of all) in which the driver is alone and 692 CP trips (13% of all) with more than one person. The results of the calculation show that of these 692 trips, 41 were those where passengers entered the P+P lot and changed into a common vehicle (CP1), and 651 were trips where the passengers started the journey either at the driver’s home or were picked up by the driver on the way (CP2). Figure8 shows the transport modal split for the ramp of the IG connection to LJ. For example, in scenario V2, which is thought to be realistic and achievable, the number of journeys by private cars would be reduced by 0.8%, mode CP1 would increase by 15%, and mode CP2 by 4%. On a daily basis, this would mean approximately 1250 fewer vehicle kilometers travelled. If this is expressed in monetary terms, then this represents an annual savings of around 25,000 EUR over the current situation, of which 10% would be savings in external costs [37]. The regulation of the P+P (V1), without any other measures, has little effect on increasing its use (less than one percent). However, the introduction of P+P lots with the possibility of using LJ’s bus lanes leads to an increase in the use of group transport by two percent. Last but not least, considering the results of third scenario, it is found that P+P lots implementation near interchanges in combination with congestion pricing policies inside the cities results in an increase in the use of carpooling by one percent more compared to other scenarios. Figure9 demonstrates the modal split results for scenario V2 at both IG interchange and on a highway segment with a length of 68.8 km. Sustainability 2020, 12, x FOR PEER REVIEW 11 of 18

 Scenario V2 (Scenario 1 with the possibility of using bus lanes in LJ): We simulated the effectiveness of introducing the possibility for vehicles with two or more people in LJ to use the dedicated bus lane. We estimate that this option reduces travel time by one-third.  Scenario V3 (Scenario 2 and a congestion pricing for entry into LJ): We simulated the effectiveness of introducing a congestion pricing policy (entry fee of 5 euro) in LJ. Thereby, we tried to understand the impacts of travel cost on the mode choice of carpooling users. These scenarios have not been produced by the LUR transport model. Scenarios which incorporate carpooling were evaluated by the LUR model. Scenario analysis results are discussed in the next section in terms of their impacts on traffic, economics, and the environment.

4. Results and Discussions

4.1 Traffic Impacts Analysis In this section, the transport network measures will be discussed in two segments: i) On the ramp of the Ivančna Gorica (IG) connection to LJ, and ii) on highway segment between Novo Mesto and LJ crossing IG interchange. In the current situation (V0), a total of 5205 trips per working day are made on the ramp of the IG connection to LJ. It comprises of 4513 CAR trips (87% of all) in which the driver is alone and 692 CP trips (13% of all) with more than one person. The results of the calculation show that of these 692 trips, 41 were those where passengers entered the P+P lot and changed into a common vehicle (CP1), and 651 were trips where the passengers started the journey either at the driver's home or were picked up by the driver on the way (CP2). Figure 8 shows the transport modal split for the ramp of the IG connection to LJ. For example, in scenario V2, which is thought to be realistic and achievable, the number of journeys by private cars would be reduced by 0.8%, mode CP1 would increase by 15%, and mode CP2 by 4%. On a daily basis, this would mean approximately 1250 fewer vehicle kilometers travelled. If this is expressed in Sustainability 2020, 12, 3188 12 of 19 monetary terms, then this represents an annual savings of around 25,000 EUR over the current situation, of which 10% would be savings in external costs [35].

SustainabilityFigure 2020, 1 8.2, xDaily FOR PEER number REVIEW of vehicles among scenarios according to transport modes. 12 of 18

The regulation of the P+P (V1), without any other measures, has little effect on increasing its use (less than one percent). However, the introduction of P+P lots with the possibility of using LJ’s bus lanes leads to an increase in the use of group transport by two percent. Last but not least, considering the results of third scenario, it is found that P+P lots implementation near interchanges in combination with congestion pricing policies inside the cities results in an increase in the use of carpooling by one percent more compared to other scenarios. Figure 9 demonstrates the modal split results for scenario V2 at both IG interchange and on a highway segment with a length of 68.8 km.

FigureFigure 9. The9. The transport transport modalmodal spilt results results of of the the scenario scenario V2. V2.

To haveTo have a broad a broad view view of theof the eff effectivenessectiveness of of thethe introduction of of P+P P+ lotsP lots near near highway highways,s, we need we need to evaluateto evaluate the highwaythe highway segment’s segment’s results results as as well.well. To To do do so, so, Table Table 11 summarizes summarizes traffic tra ffiperformancec performance measures’measures’ results results such such as total as total traffi trafficc volume, volume, total total VKT VKT (vehicle-km), (vehicle-km), total total travel travel timetime (veh-hour),(veh-hour), and total delayand total (hour) delay per (hour) a working per a working day. day. Having looked at the model results, it can be found that scenario V3 is the best scenario for this Table 1. Traffic performance measures comparison among proposed scenarios. segment of IG–LJ highway, with the capability to reduce the total traffic volume by 4567 vehicles, Total total VKT by 3797 veh-km, total travel timeTotal by VKT 75 veh-hour,Total Time and totalTravelled delay by 40Total h. Simultaneously, Scenarios Volume Scenario 2, noted as the more realistic and(veh implementable-km) scenario,(veh-h) has reducedDelay the total (h) traffic volume by 2413 vehicles, total VKT (veh byicle 2256) veh-km, total travel time by 35 veh-hour, and total delay by 16 V0 949,651 881,843 10,007 2687 V1 948,470 880,998 9991 2680 V2 947,238 879,587 9972 2670 V3 945,084 878,046 9932 2646

Having looked at the model results, it can be found that scenario V3 is the best scenario for this segment of IG–LJ highway, with the capability to reduce the total traffic volume by 4567 vehicles, total VKT by 3797 veh-km, total travel time by 75 veh-hour, and total delay by 40 hours. Simultaneously, Scenario 2, noted as the more realistic and implementable scenario, has reduced the total traffic volume by 2413 vehicles, total VKT by 2256 veh-km, total travel time by 35 veh-hour, and total delay by 16 hours. In this study, the P+P lot was modelled for only one intersection on highway (i.e., IG). However, the results presented changes in the whole LUR area and not only for one intersection. Although the differences seem to be not noticeable, e.g., 0.5% reduction in total volume in V3 compared to V0, in such studies is a remarkable change (4567 fewer vehicles).

4.2. Economic and Environmental Impacts Analysis Sustainability 2020, 12, 3188 13 of 19 h. In this study, the P+P lot was modelled for only one intersection on highway (i.e., IG). However, the results presented changes in the whole LUR area and not only for one intersection. Although the differences seem to be not noticeable, e.g., 0.5% reduction in total volume in V3 compared to V0, in such studies is a remarkable change (4567 fewer vehicles).

Table 1. Traffic performance measures comparison among proposed scenarios.

Total Volume Total VKT Total Time Scenarios Total Delay (h) (vehicle) (veh-km) Travelled (veh-h) V0 949,651 881,843 10,007 2687 V1 948,470 880,998 9991 2680 V2 947,238 879,587 9972 2670 V3 945,084 878,046 9932 2646

4.2. Economic and Environmental Impacts Analysis Sustainability 2020, 12, x FOR PEER REVIEW 13 of 18 The calculation of all environmental measures is based on transport volumes. The volumes are adoptedThe calculation from the assignment of all environmental results of the measures model. Thatis based means on thetransport current volumes. traffic volume, The volumes speed, andare adoptedtravel time from per the link assignment and transport results mode of the were model. obtained That viameans links. the current traffic volume, speed, and travelRoad time traperffi linkc air and emissions transport have mode been were determined obtained based via links. on emission factors provided by the Swiss FederalRoad O ffi trafficce for air the emissions Environment have (BAFU) been determined using the macroscopic based on emission simulation factors model provided [34]. According by the Swissto the Federalsoftware Office manual, for the the calculation Environment of the (BAFU) pollutant using emission the macroscopic values is carried simulation out using model the speed[32]. Accordingvalues for carsto the and software heavy vehicles manual, (HGV),the calculation with every of the value pollutant multiplied emission by the values number is carried of vehicles. out usingThis procedurethe speed values is based for on cars emission and heavy factors vehicles issued (HGV), by BAFU with forevery pollutants value multiplied NOx, CO, by HC, the andnumber SO2 , offor vehicles. both cars This and procedure HGVs. To is calculatebased on theemission emissions, factors the issued following by BAFU regression for pollutants polynomial NOx, curve CO, (fifthHC, anddegree) SO2,has for beenboth used:cars and HGVs. To calculate the emissions, the following regression polynomial curve (fifth degree) has been Emissionused: = a + b.v + c.v2 + d.v3 + e.v4 + f .v5 (9) where v is the speed (km/h) of cars= or+ HGVs. + and. the+ coe. fficients+ . namely+ . a, b, c, d, e, and f are determined(9) wseparatelyhere v is considering the speed (km/h) BAFU. of cars or HGVs and the coefficients namely a, b, c, d, e, and f are determinedNoise calculationseparately considering is based on BAFU. the so-called relevant hourly traffic volume M in [car/h]. If the volumesNoise used calculation as a calculation is based basis on the are so available-called relevant as average hourly daily traffic traffic volume volumes M (ADT) in [car/h]. in [car If/24h], the volumesM is determined used as a as calculation mADT by specifyingbasis are available the conversion as average factors. daily To traffic clarify, volumes we have (ADT) just considered in [car/24h], the Mresults is determined for one link as mADT (IG ramp by withspecifying a length the of conversion 220 m) in noisefactors. calculation. To clarify, However, we have just to calculate considered the thepollutant results emissions, for one link the IG–LJ (IG ramp highway with segment a length with of 220 a length meter ofs 34) in km noise has been calculation. considered. However, Figure to10 calculatedepicts the the environmental pollutant emissions, measures the reductions IG–LJ highway in terms ofsegment noise and with air apollution length of compared 34 km hatos current been considered.situation (V0). Figure 10 depicts the environmental measures reductions in terms of noise and air pollution compared to current situation (V0).

(a) (b)

FigureFigure 10. 10. TheThe environmental environmental measures measures reductions reductions in in terms terms of of (a) (a) Noise Noise,, and and (b) (b) pollutant pollutant emissions emissions reductionreduction compared compared to to the the V0. V0.

As seen, Scenario V3 has the best results in terms of reduction in both noise and air pollutant amount compared to V0. This policy is able to reduce the noise level by 0.06 dB, while Scenarios V1 and V2 have a reduction of 0.03 and 0.01 dB, respectively. On the other hand, Scenario V3 is able to reduce the pollutant emissions namely SO2, HC, NOX, and CO by 242, 792, 1557, 5369 g/km, respectively. From the reduction in the total amount of travel time and the total VKT (see Table 1), we are also able to measure the economic and environmental factors that are associated with this form of transport. To do so, first operating cost, namely driving cost, and value of time were calculated using the total VKT by each category (vehicle-kilometers) and total travel time (vehicle-hour). In Slovenia, the driving cost is assumed to be 0.08 €/km as mentioned in Section 3. The average value of time for Slovenians is assumed as about 6.7 €/hour as the average monthly salary is around 1200 €, and monthly working time is around 180 hours. Figure 11 demonstrates the relevant operating cost results.  Driving cost = veh-km/day * 0.080 €/veh-km * 230 working days/year,  Value of time = veh-hour/day * 6.7 €/hour * 230 working days/year. Sustainability 2020, 12, 3188 14 of 19

As seen, Scenario V3 has the best results in terms of reduction in both noise and air pollutant amount compared to V0. This policy is able to reduce the noise level by 0.06 dB, while Scenarios V1 and V2 have a reduction of 0.03 and 0.01 dB, respectively. On the other hand, Scenario V3 is able to reduce theSustainability pollutant 2 emissions020, 12, x FOR namely PEER REVIEW SO2, HC, NOX, and CO by 242, 792, 1557, 5369 g/km, respectively.14 of 18 From the reduction in the total amount of travel time and the total VKT (see Table1), we are also able to measureIn addition the to economic the savings and in environmental operating costs, factors the external that are costs associated of transport with this, namely form ofaccidents, transport. Tonoise do so, and first air operating pollution, cost, climate namely change, driving congestion cost, and (delay) value can of timealso be were calculated. calculated To usingthis end, the the total VKTfollowing by each relationshipscategory (vehicle-kilometers) and relevant unit and costs total assumed travel time using (vehicle-hour). [35]. The results In Slovenia, of calculation the driving for costexternal is assumed costs toare be shown 0.08 € in/km Figure as mentioned 11. in Section3. The average value of time for Slovenians is assumed as aboutAccidents 6.7 € /costhour = veh as the-km/day average * 0.040 monthly €/veh- salarykm * 230 is aroundworking 1200 days/year,€, and monthly working time is around Pollutants 180 h. Figure cost = 11 veh demonstrates-km/day * 0.010 the €/veh relevant-km operating* 230 working cost days/year, results.  Climate change cost = veh-km/day * 0.019 €/veh-km * 230 working days/year, Driving cost = veh-km/day * 0.080 €/veh-km * 230 working days/year, •  Noise cost = veh-km/day * 0.004 €/veh-km * 230 working days/year, Value of time = veh-hour/day * 6.7 €/hour * 230 working days/year. •  Congestion cost (delay) = veh-km/day * 0.009 €/veh-km * 230 working days/year.

(a) (b)

FigureFigure 11. 11.Annual Annual savingssavings (reduction)(reduction) compared to V0 scenario (a) (a) operating cost, cost, and and (b) (b )external external cost cost..

In additionThe total toannual the savings savings in (in operating €) resulting costs, from the the external use of costscarpooling of transport, and P+P namely lot in the accidents, IG area are noise andshown air pollution, in Figure climate 12. change, congestion (delay) can also be calculated. To this end, the following relationships and relevant unit costs assumed using [37]. The results of calculation for external costs are shown in Figure 11.

Accidents cost = veh-km/day * 0.040 €/veh-km * 230 working days/year, • Pollutants cost = veh-km/day * 0.010 €/veh-km * 230 working days/year, • Climate change cost = veh-km/day * 0.019 €/veh-km * 230 working days/year, • Noise cost = veh-km/day * 0.004 €/veh-km * 230 working days/year, • Congestion cost (delay) = veh-km/day * 0.009 €/veh-km * 230 working days/year. • The total annual savings (in €) resulting from the use of carpooling and P+P lot in the IG area are shown in Figure 12. As depicted, the introduction of P+P lots near interchanges in the combination of congestion pricing policy (V3) can reduce the total transport cost (operating + external) by around €210,000 annually. Other scenarios, namely V2 and V1, are also able to reduce the cost by €97,200 and €29,600, respectively. These economic and environmental benefits achieved with the introduction of P+P lots Figure 12. Annual total cost reduction due to the implementation of park and pool (P+P) lot compared to V0. near interchanges to encourage carpooling transport are only in one specific location, the IG interchange. It can beAs much depicted more, the effective introduction if it is extended of P+P lots to allnear interchanges interchange nears in the highways combination in the vicinityof congestion of LUR. pricing policy (V3) can reduce the total transport cost (operating + external) by around €210,000 annually. Other scenarios, namely V2 and V1, are also able to reduce the cost by €97,200 and €29,600, respectively. These economic and environmental benefits achieved with the introduction of P+P lots near interchanges to encourage carpooling transport are only in one specific location, the IG interchange. It can be much more effective if it is extended to all interchanges near highways in the vicinity of LUR.

5. Conclusions Sustainability 2020, 12, x FOR PEER REVIEW 14 of 18

In addition to the savings in operating costs, the external costs of transport, namely accidents, noise and air pollution, climate change, congestion (delay) can also be calculated. To this end, the following relationships and relevant unit costs assumed using [35]. The results of calculation for external costs are shown in Figure 11.  Accidents cost = veh-km/day * 0.040 €/veh-km * 230 working days/year,  Pollutants cost = veh-km/day * 0.010 €/veh-km * 230 working days/year,  Climate change cost = veh-km/day * 0.019 €/veh-km * 230 working days/year,  Noise cost = veh-km/day * 0.004 €/veh-km * 230 working days/year,  Congestion cost (delay) = veh-km/day * 0.009 €/veh-km * 230 working days/year.

(a) (b)

Figure 11. Annual savings (reduction) compared to V0 scenario (a) operating cost, and (b) external cost.

Sustainability 2020, 12, 3188 15 of 19 The total annual savings (in €) resulting from the use of carpooling and P+P lot in the IG area are shown in Figure 12.

Figure 12. Figure 12. AnnualAnnual total total cost cost reduction reduction due due to the to the implementation implementation of park of park and and pool pool (P+P (P) lot+P) compared lot compared to V0. to V0.

5. ConclusionsAs depicted, the introduction of P+P lots near interchanges in the combination of congestion pricing policy (V3) can reduce the total transport cost (operating + external) by around €210,000 annually.This study Other contributes scenarios, tonamely the debate V2 and regarding V1, are also carpooling able to reduce and the cost implementation by €97,200 and of € P29+,600,P lots nearrespectively. interchanges. These It economic examines and the environmental impacts of Pbenefits+P lots achieved near interchanges with the introduction in terms of P+P transport lots networknear interchange performance,s to economic, encourage and carpooling environmental transport effects. are Moreover,only in one at specifica disaggregated location, level, the IG this researchinterchange sheds. lightIt can on be the much profile more of effective those people if it is who extend areed more to all likely interchange to reduces near their highway car uses afterin the the implementationvicinity of LUR. of P+P lots near interchanges. It is found that: The average occupancy of the carpooling vehicles in Slovenia is around three persons/vehicle, • 5. Conclusions while the average occupancy of non-carpooling vehicles is around 1.35 persons/vehicle. Factors such as travel cost, public transport service limitations, and improved parking facilities • impact highway users’ tendency to reduce car use and use of carpooling. The main reason why people do not opt for carpooling is the variable working hours causing • difficulties in coordination of departures home-to-work or work-to-home. Sixty percent of respondents are willing to leave their car in P+P lots near interchanges. • Parking fees are not a suitable solution for P+P parking lots intended to attract highway users to • leave their cars during carpooling. Only 25% of respondents are willing to pay the parking fee (on average €1.40/day or €23/month). In terms of transport network performance, economic, and environmental effects, thanks to P+P lots, the results show that: Scenario V3 is the best scenario in the highway segment studied (68.8 km) with the capability to • reduce the total traffic volume by 4567 vehicles, total VKT by 3797 veh-km, total travel time by 75 veh-h, and total delay by 40 h. While Scenario 2, noted as a more realistic and implementable scenario, has reduced the total traffic volume by 2413 vehicles, total VKT by 2256 veh-km, total travel time by 35 veh-h, and total delay by 16 h. Scenario V3 is able to reduce the noise level by 0.06 dB, while Scenarios V1 and V2 have a reduction • of 0.03 and 0.01 dB, respectively. On the other hand, Scenario V3 is able to reduce pollutant emissions namely SO2, HC, NOX, and CO by 242, 792, 1557, and 5369 g/km, respectively. Scenario V3 can reduce the total transport cost (operating + external) by around €210,000 • annually. Other scenarios, namely V2 and V1, are also able to reduce the cost by €97,200 and €29,600, respectively. Scenario V2 does not need any political and social consensus, however, Scenario V3 is at the moment politically not acceptable to the Municipality of Ljubljana. Public opinion research on possible improvements of the traffic management in Ljubljana was against congestion charging [38]. Sustainability 2020, 12, 3188 16 of 19

General policy guidance and recommendations for Scenario V2 could be as follows:

Increase the awareness (promotional campaign) of users, in particular private car users, about • shared mobility modes and infrastructure. Improve the education of urban and mobility planners as well as other stakeholders about shared • mobility modes and infrastructure. Prepare national guidelines to support/implement carpooling services and infrastructure, and • improvement of ITS (intelligent transport system and services).

General policy guidance and recommendations for Scenario V3 could be as follows:

Promote and implement other traffic management and spatial planning measures for sustainable • mobility (e.g., space used by private car). Convince local and state authorities (policy stakeholders) to adopt additional objectives to existing • SUMP (sustainable urban mobility plan).

Although implementation of P+P lots is a not-for-profit solution, and not one intended to generate revenue, the provision of its associated systems and services will provide opportunities for the further development of widely dispersed municipalities and regions. To reap the greatest environmental benefits, carpooling promotion policies could be more effective if used in combination with other policies such as the possibility of using HOV lanes and reduced toll payments on highways, and/or dedicated bus lanes, dedicated parking lots, and free entry to congestion pricing zones inside the cities. Last but not least, the research limitations and directions for future studies are:

Slovenia is a small country and field surveys (questionnaires) with a large simple size are a very • difficult and challenging step. Although the sample size of the survey is not large, this article presents some interesting results which can be used as preliminary findings for future studies with a larger sample size. Once P+P lots introduced by the Slovenian government, a before-and-after study at the locations • of potential P+P lots would be needed to have a more reliable assessment of its consequences on modal shifts of highway users. As only explanatory variables like travel time and cost have been used in this study, a “new • hybrid mode choice model” can be developed to examine the effects of explanatory and latent variables simultaneously.

Author Contributions: Conceptualization, R.R., N.D., M.Ž., and R.M.; data curation, R.R., N.D., M.Ž., and R.M.; formal analysis, R.R., N.D., M.Ž., and R.M.; funding acquisition, R.R. and R.M.; investigation, R.R. and R.M.; methodology, R.R., N.D., M.Ž., and R.M.; software, N.D. and M.Ž.; supervision, R.R. and M.Ž.; validation, R.R., N.D., and R.M.; visualization, N.D.; writing—original draft, R.R., N.D., and R.M.; writing—review and editing, R.R., N.D., and M.Ž. All authors have read and agreed to the published version of the manuscript. Funding: This research was partly funded by the RITS-net project of the EU INTERREG IVC program, co-financed by the European Regional Development Fund. Conflicts of Interest: The authors declare no conflict of interest.

Appendix A Detailed information regarding the survey based on participants are given in tables below: Sustainability 2020, 12, 3188 17 of 19

Table A1. Survey details regarding non-carpooling users.

Counted Distributed Sample Response Gender Site Average Age Cars Envelopes Size Rate MF Unec 503 102 20% 45% 46% 54% 38 Žalec 599 97 16% 68% 55% 45% 44 Kranj 130 22 17% 78% 45% 55% 34 IG 1280 153 12% 65% 48% 52% 36 Total 2512 374 15% 61% 49% 51% 38.5 Main Frequencies of Trip Per Week Trip Purpose No Carpooling Origin Site Without 4 5 6 LJ Work School passengers Unec 21% 79% 11% 70% 89% 2% 86% Žalec 32% 69% 9% 88% 81% 1% 83% Kranj 24% 84% 14% 57% 93% 3% 81% IG 35% 82% 12% 82% 88% 2% 79% Total 30% 78% 11% 79% 87% 2% 82%

Table A2. Survey details regarding carpooling users.

Distributed Sample Gender Average Site Counted Cars Response Rate Envelopes Size MF Age Unec 599 42 7% 61% 44% 56% 42 Žalec 637 87 14% 30% 67% 33% 34.5 Kranj 114 12 11% 78% 48% 52% 30 IG 1373 106 8% 59% 55% 45% 35.5 Total 2723 247 9% 50% 57% 43% 35 Main Frequencies of Trip Per Week Trip Purpose Carpooling Origin Site With Same Same 4 5 6 Ljubljana Work School Co-Workers Destination Persons Unec 24% 44% 12% 64% 80% 16% 76% 76% 84% Žalec 32% 54% 9% 88% 92% 6% 71% 71% 83% Kranj 24% 78% 19% 57% 69% 28% 78% 76% 92% IG 35% 62% 13% 82% 72% 22% 77% 79% 83% Total 32% 57% 12% 80% 80% 16% 75% 76% 84%

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