MODERN WHEEL DETECTION AND AXLE COUNTING SYSTEMS FOR URBAN AND MASS TRANSIT

MODERN WHEEL DETECTION AND AXLE COUNTING SYSTEMS FOR URBAN AND MASS TRANSIT SYSTEMS

Operators of urban and mass transit rail transportation systems are faced with many challenges related to an increasing number of passengers and an aging infrastructure. The need to expand current systems, create new ones, or modernize existing systems is a reality that requires important decisions. The focus must be on optimal safety standards, maximum availability/up-time, and low life cycle costs.

Modern wheel detection and axle counting systems offer clear advantages compared to the widely used circuit systems, based on practical experience gained from urban and mass transit projects installed worldwide. Successful installations are dependent upon collaboration between the axle counter manufacturer, operators and integrators. Project-specific adaptations and plans must be drawn up in advance, agreed upon, and implemented with proper training and follow-up made available to the operators by the manufacturer.

New lines and projects are often equipped with modern axle counting systems, either as primary or in the case of CBTC, secondary train detection systems. The benefit of these systems is clear in terms of functionality, up-time, reduced operating costs, and reduced maintenance costs. 1. Requirements for Urban & Mass Transit System

The requirements for this category of transportation systems differs significantly from standard passenger & freight railroad systems.

Examples of these differences include:

 Legal/regulatory considerations  Specific vehicle and rolling stock influences  Rail beds and the surrounding environment.

1.1 Legal/Regulatory Considerations

Since axle counting systems are a relatively new technology in North America, operational rules are not yet covered in the AREMA standards. Therefore, detailed discussions between operators, system integrators and axle counter manufacturers are necessary. These discussions should include the exchange of best practices and accepted international standards. However, AREMA does have well defined environmental standards for the equipment, which will be followed.

One of the international standards is the German Railway Building and Operating Regulations Ordinance (EBO), introduced in Germany for the construction and operation of railroads. It is often used internationally as a benchmark. The basic objective of the EBO is to construct all rail systems and vehicles in a manner that fulfills safety requirements and ensures compatibility, if necessary. The ordinance for the construction and operation of trams (BOStrab) is designed as a standard set of rules for all users.

Figure 1: Axle counting systems are becoming more prevalent in the underground sector 1.2 Vehicle, Rolling Stock Influences

Particularly in the urban and suburban rail transportation sector, wheel and truck geometries, maintenance vehicles, wheel flange dimensions, electromagnetic influences and IGBT vary significantly in different parts of the world.

Wheel sensors have designated sensitivity areas with clearly defined boundaries. As a result, approaching iron masses can be differentiated. There are high and low wheel flanges, narrow and wide running surfaces, and a wide range of wheel diameters. These varying wheel geometries and wheel flanges have a direct influence on reliable wheel detection.

In the case of metros, underground vehicles, urban transport trains and street cars, optimized truck geometries combined with electromagnetic brakes can result in problems with secure and available wheel detection. Since this set of conditions can vary from one project to another, each situation must be thoroughly analyzed, and the correct components selected and configured.

Figure 2: Modern street car systems often rely on axle counters

1.3 Track Beds and Environment

Track beds and the surrounding environment of urban and mass transit transportation systems vary significantly from standard-gauge railways in several areas. These include the construction of the track bed itself, traction, and communications. Differences in various rail profiles must also be considered, such as grooved, bullhead and vignol rails.

In addition to the use of alternating current tractions in urban and mass transit systems, direct current traction is increasingly being used. The voltage of the DC traction systems varies between 600 to 1500 V DC. The direct current can be transmitted via overhead cables, but more frequently it is transmitted via a “third rail” in or alongside the track bed.

The wheels and wheel flanges of street cars run on grooved rails. The grooved rail is surrounded by the superstructure of the railway. The installed wheel detection components must withstand the impact of being driven over and walked on, as well as the effects of flooding, debris and other sources of interference.

Figure 3: Robust, compact enclosure of wheel detection components protects them from the environment and impact

2. Wheel Detection Capabilities

Modern wheel detection systems, comprised of wheel sensors and intelligent evaluation boards, can provide pertinent information in addition to wheel detection. Direction of travel, speed, and wheel diameter are just a few examples of data that can be provided by these systems.

The following four sections provide examples of wheel detection capabilities that are relevant in urban and mass transit applications: 2.1 Securing Grade Crossings

On a global level, there are many variations of grade crossings and how they are controlled. In North America, all crossings must be marked with a , at a minimum. However, many crossings utilize flashing lights, whistles, gates, or a combination. Various automated systems that control these lights, whistles & gates have existed for many years. Modern wheel sensors are used extensively in Europe & many parts of the world to provide this function, and in recent years wheel sensor usage in North America has grown. The wheel sensors essentially switch the crossing on and off, and modern bi-directional wheel sensors are the norm to track trains traveling in either direction. The system is flexible and can be configured with axle counting circuits as well.

Figure 4: Wheel sensors and axle counters can increase safety at grade crossings

2.2 Speed Management

Due to structural circumstances, speed measurement is particularly important for urban and mass transit lines. For certain areas of track, it is important that maximum speeds be adhered to for safety reasons. Wheel sensors are very effective in measuring speed, therefore helping to prevent derailments and other speed related accidents. 2.3 Cancellation of False “Occupied” Signals

A feature of urban & mass transit is high density activity, requiring 24/7 up time. When a train tracking system produces false alarms, the efficiency of the system is compromised. This can have a snowball effect that seriously disrupts schedules and increases passenger inconvenience. Track sections can be reset by the operator, but prior to doing so the determination must be made that the track section is clear. To save time, a special signal can be set allowing the driver to proceed on sight into the “track clear” detection section. This “Proceed on Sight Authority” signal must be reset when a train is traversing the wheel detection sensor located at the beginning of the section, to prevent subsequent trains from entering this now occupied section. When the track section again becomes clear, trains can resume running and the fault signal no longer needs to be cancelled separately. 2.4 Switch Applications

Urban and mass transit systems require additional applications that can be managed via wheel sensors. Examples of these applications include hot box detection systems, flat spot systems, track scales, washing systems, gates, tunnel lighting and passenger information systems. These applications may require the use of track switching functions. Modern wheel detection systems can provide a precise switch-on and switch-off function in real time.

3. Axle Counting Systems

The basic function of axle counting systems is the secure and reliable recording and counting of axles to determine track clear/occupied status. Modern, modular and scalable axle counting systems can also be used for a range of operational requirements. 3.1 Train Detection for Railroad Traffic

Axle counting systems are utilized in urban & mass transit systems for train detection, and subsequently the management of rail traffic. Based on the clear/occupied information received, the signaling system uses track signals to maintain a safe distance between trains.

In contrast to standard gauge railroads, the track section sizes in this sector are much shorter. It would not be uncommon to find track sections that are merely 1/8 mile (200 m) in length. The reason for this is the rapid frequency with which trains move into and out of a given section, in some instances every 2 minutes or less.

Figure 5: Modern axle counting system, Frauscher Advanced Counter FAdC

3.2 Switch Point Protection

Switch-blocking circuits for monitoring a set of points are widely used. These track circuits indicate whether the distance between a set of points is clear or occupied. Switching is then enabled or disabled accordingly. This changeover protection function can be enhanced and provides significantly more reliable information when combined with an axle counting system. 3.3 Flank Protection

Flank protection equipment is used to prevent “flank collisions”, which can occur when a vehicle merges onto the same route as another vehicle. This threat exists at track intersections, and during shunting operations. There are various types of flank protection equipment, including protection switches, track blocks and blocking signals. Axle counting track sections can be used in conjunction with blocking signals. 3.4 CBTC (Communication Based Train Control)

CBTC is a type of and security system. Permission to travel and control commands are not indicated using signals, but instead via data communication between track vehicles and track equipment. CBTC fall back systems are required in case communication to one or more trains goes down. Secondary train detection is also required in case non-CBTC equipped maintenance vehicles and “mixed traffic” (CBTC and non-CBTC) are sharing the same routes. When an axle counting system is being utilized to detect track clear/occupied status, this system would be characterized as a viable and vital fall back plan.

4. Modern Solutions for Urban and Mass Transit Transportation Systems

Since urban and mass transit transportation systems vary greatly, they require precise, individually designed wheel detection and axle counting systems. Years ago, Frauscher recognized the need for reliable and readily available solutions in this category of railroad, making it a developmental focal point, which continues today. Specific solutions have been created for use in urban & mass transit transportation systems. 4.1 Custom Designed Evaluation Algorithms

Various problems can occur due to the large variety of vehicle types that exist in this category of railroad. The differences in the vehicles and their impact on track-mounted sensors represent a critical challenge. Low- hanging electromagnetic track breaks, which can be mounted very close to the wheel, represent a specific problem.

By evaluating the analog wheel sensor signals, Frauscher can adapt the evaluation algorithms and trigger thresholds on an individual basis. This provides a clear differentiation between an axle and an electromagnetic brake when traversing the wheel sensor. Adjusting the algorithms and trigger thresholds ensures reliable and secure wheel detection. Various hardware and software components are available (SIL 3/SIL 4).

Figure 6: Electromagnetic brakes can create a challenge for wheel detection and axle counters

4.1.1 Counting Head Control

Metallic objects such as worker steel-toe boots, trash, metallic dirt, bicycles, etc. can damp a wheel detection point and trigger an unwanted “occupied” signal within a track section, which erroneously reduces the availability of the system. This effect can be counteracted with the counting head control function.

If the track clear/occupied detection sections adjacent to a wheel detection point are clear, the wheel detection point can be set essentially to a “stand-by” mode. In this mode, an unlimited number of different incidences of damping caused by metallic items such as those listed above can be suppressed. When damping is caused by these configured situations, no “occupied” status signal will be given, and the reset control is omitted. Approaching trains will automatically switch off the “stand-by” mode and will be reliably and safely detected. 4.1.2 Supervisor Track Sections (STS)

A supervisor track section is an overlaid section for two or more “regular” track sections, allowing automated correction of designated external interferences. In the case of a miscount, a supervisor section indicating “clear” has the authority to reset the corresponding track sections. Similarly, a faulty supervisor track section can be automatically reset if the two corresponding track sections are clear.

STS functionality increases availability without any additional equipment. Further STS functionality is vital according to SIL 4 requirements.

The application of a supervisor section can also be referred to as synchronization.

Figure 7: Supervisor Track Sections

4.1.3 Speed Measurement

The ability to determine train speed is increasing in importance for public transportation systems, following several speed-related fatal accidents over the past few years. The Frauscher VEB measuring system provides information regarding speed, status and diagnostics, cost-effectively and in real-time via a CAN interface. The evaluation of the traversing speed is recorded with a single wheel detection point, accurate to within +/-3%

Speed measurement capabilities can also be used for speed testing equipment, derailment protection, passenger warnings on platforms and at speed-dependent grade crossings. 4.1.4 Reset Procedure

A wide variety of reset procedures are necessary, depending on the operator and the system, including:

 Direct reset  Restricted reset  Preparatory direct reset  Preparatory restricted reset

There are more than 13 different reset procedures that can be configured with the Frauscher Advanced Counter FAdC, according to the customer’s needs.

4.1.5 Wheel Rock

In circumstances where railcars stop at a sensor, normal operation would put the adjacent track section into occupied status. Operators may prefer that this occupancy status be suppressed when this “partial traversing” occurs. Each Frauscher wheel sensor consists of 2 sensing points, which recognize and evaluate these wheel rock events. As a rule, if complete traversing takes place, the partial traversing indicator is reset to clear status. If complete traversing does not occur after this wheel rock, the track section remains in occupied status. The section must be reset by the station manager.

Depending on the configuration of the Frauscher axle counting system, one or more partial traversing procedures can be suppressed. The track section remains in clear status, changing to occupied status only following a complete traversing. The number of partial traversing events permitted can be freely configured.

4.2 Mechanical Environment

4.2.1 Grooved Rail Claw Assembly

The use of grooved rails and an enclosed superstructure requires special mechanical solutions for mounting wheel detection points. In this situation, the lip of the grooved rail will interfere with the detection of the wheel flange. Therefore, during installation of the wheel sensor, the grooving must be removed over a length of about 15 ¾” (40 cm), to ensure wheels are reliably and safely detected.

Figure 8 illustrates the correlation between grooved rails, wheel flanges, grooved rail claws and wheel sensor mounting. It shows an RSR180 wheel sensor installed with a grooved rail claw. Grooved rail claws are custom made for the respective track profile, with claw variants clamped, welded or connected with screws, depending on customer requirements. If required, a traffic-compatible cover is available (illustrated in Figure 3).

Figure 8: Rail claws for use in grooved rails

4.2.2 Special Plug Terminal

In most situations, there is limited space available near the track. Since Frauscher’s wheel sensors do not require evaluation electronics on the track, the space required for the wheel detection point is minimal. Clamping units for cable connections (wheel sensor signal cable for indoor equipment) can be designed as a simple plug terminal. For installations where grooved rail claws are used, a waterproof plug terminal protects the clamping element.

4.3 Planning, Operation and Maintenance

4.3.1 Scalable Complete System and Flexible Integration

The wide variation in requirements of urban and mass transit rail transportation systems for wheel detection and axle counting systems is matched by a wide variation in the and control systems required. Simple, scalable systems are required for flexible integration. Frauscher wheel detection and axle counting systems offer a choice of relay, optocoupler or serial interfaces. 4.3.2 Installation, Maintenance and Diagnosis

In contrast to technology, wheel detection systems can be assembled and installed even during railway operation. Since no drilling of holes into the rail is required by utilizing the Frauscher rail claw, the installation of wheel sensors does not interfere with existing installed track circuits.

Railway operators and maintenance staff are being faced with increasingly complex systems, so whenever possible it is best to provide a simple and compact structure, as well as intuitive operation. The meeting of this goal begins during the planning and design phase, throughout the configuration and commissioning phase, and continues throughout the operation and maintenance phase. Of increasing importance to railroad operators is the reduction of overall maintenance costs, which is possible via preventative maintenance and expedient and efficient elimination of faults. Frauscher systems can be equipped with modern diagnostic systems, as required by the needs of the operator.