Public Transportation vehicles preference at crossroads/junctions

The principle of controlling public transportation vehicles preference

To ensure preference of public transportation vehicles at crossroads it is necessary to assess the position of the vehicle in relation to the crossroads and to affect the algorithm controlling the traffic lights at the crossroads accordingly (this is not the absolute priority of  ambulance, fire department and police vehicles).

The crossroads algorithm can be affected so that:

• there is no change (the vehicle is not delayed or there is a number of preferred vehicles coming from various directions),
• the drive-through time is shortened in order to free another direction sooner,
• it lengthens the drive-through time in order to allow another public transportation vehicle to drive through in the same direction,
• a new cycle is inserted, i.e. the order of the cycles is changed,
• if the vehicle is waiting at the stop close to the crossroads it sends information regarding the coming green light into the vehicle to ensure that the doors are closed and the vehicle leaves the stop in time,
• the system assigns green lights at special independent crossings.

The affecting of algorithms is performed by scanning vehicles as they pass through checkpoints. To ensure correct control, it is necessary that there are multiple checkpoints – for example: log on, log on check, log off, log off correction, stationing, etc., and it is also necessary for the information to get to the crossroads control unit in time. We have to realize that a vehicle going 50km/h covers the distance of 13,89m in one second from which follows that if the log on point is for example 70 m in front of the crossroads a vehicle going 50 km/h will get to the crossroads in 5 seconds.

According to our experience the message from the vehicle must get to the crossroads control unit  0,5 seconds after the vehicle goes through the checkpoint (the position assessment itself can be delayed by one second because of GPS position assessing – performed  1x per second). Because there is a possibility of tailbacks at crossroads the vehicle must communicate with the crossroads control unit multiple times and its position assessment must be made more accurate. The vehicle-control unit communication system must take these two factors into account.

Ways of monitoring vehicle position at checkpoints:

• with the help of a GPS module and a control unit with the possibility of position assessment (now with 2,5 m accuracy) sending the vehicle position information via radio,
• the checkpoint itself monitors the vehicle going through it (contact or contactless methods). This way is usually more costly because it is necessary to build checkpoints in front of the crossroads (for example – infrared sensors – the vehicle transmits infrared codes which are received at the given place and transported (for example via cables) to the control unit).

Possibilities of solving radio transmissions:

• using the induction  automatic system for throwing  switches BSV - this method is suitable mainly for track vehicles (dependent traction) which throw switches (however, it can be used generally). The radio framework transmitted from the vehicle carries the preference information. The receiver loop must be placed far enough in front of the crossroads (it does not usually use position corrections).
• using radio transmissions on a reserved radio channel on the 170 MHz band or the 430 MHz band in the TAIT radio network or in our   FD NET radio network  performed by  EPIS 4.0x on-board computers.  This way allows using a multiple checkpoint system and it requires only one vehicle radio station.
• using radio transmissions on a reserved radio channel. This method requires using another vehicle radio modem of a price similar as in the preceding point and if there are similar frequencies a special antenna diplexer must be used as well. This system can be integrated in the  FD NET radio network.
• using radio transmissions on a free band – this method requires using a specialized preference control modem in the vehicle. Since there is a danger of another vehicle using this band at the same time, successful communication cannot be ensured.
• using GPRS/UMTS transmissions - we do not recommend this method because it is not possible to ensure successful vehicle-control unit communication in a required time interval.
• using radio transmissions via the TETRA system – we do not have practical experience regarding the vehicle-control unit-vehicle information transfer speed.
• using infrared beacons –  this method is similar to our BSV system. However, it requires an investment in providing the vehicle with a new system.

We have been dealing with the issue of public transportation vehicle preference at crossroads since 2003 and the above solutions are the result of our work in this field.

Public transportation vehicle preference at crossroads using the BSV system

This method uses the BSV induction system for contactless throwing of switches and it is based on transmitting to the crossroads information regarding the position of the vehicle in relation to the schedule. This information is included in every data packet sent form the vehicle to the rails (trams) or to the trolleybus line (trolleybuses). Information regarding the number of the vehicle is transmitted together with information regarding a delay of the vehicle. The information regarding the delay is acquired from position data sent to the dispatching (this information is transferred via the vehicle bus every second or every 10 seconds).

Transferred vehicle-schedule states:

• the vehicle travels according to the schedule - there is no need for vehicle preference (0 to -2 minutes),
• the vehicle is mildly delayed - it will help if the vehicle is preferred (-2 to -5 minutes),
• the vehicle requires preference - the vehicle is delayed therefore it is necessary to speed up its driving through the crossroads (-5 to -10 minutes),
• reserve state – the delay is so significant that it is not necessary to deal with it.

The crossroads control unit must be equipped with a BSV receiver and a BSV loop and with the BSV-PU switch control unit. The information is transmitted to the control unit by two one-bit inputs. If needed the vehicle number can be transferred via a serial line.

Public transportation vehicle preference at crossroads using radio transmissions

The method of sending vehicle position information to the crossroads control unit using radio transmissions on a reserved band is included in our complex vehicle system -  EPIS 4.0X on-board computer and in our   FD NET radio network control. This method prevents the necessity of using another communication infrastructure in the vehicle and the communication (both voice and radio) including crossroads control is controlled by one vehicle radio station which can be equipped with fast channel switching. This solution decreases expenses because it already is a part of the supplied vehicle technology and there is no need for additional space for new units in the vehicle. Data for the on-board computer are created by a special SW which is a part of the supplied product and can be controlled intuitively.

The proposed communication protocol (the data transfer itself) is in accordance with the RTIGT008-1.5 recommendation and therefore with international standards. Transferring data to the crossroads unit via radio is required by the company protocol and it follows the behavior of the FD NET radio network. The system installation schema can be seen in the following picture:

Our company has also developed a public transportation vehicle preference system for the TAIT radio network. In this case redefined behavior of the TM 8255 radio station is used for the purposes of communication.

Crossroads control units and systems

Our company produces two types of crossroads control units and systems using different types of radio network:

• for the TAIT radio network, where the controlling function is performed by UCU 01 units ( versatile communication units) and by a TAIT radio station using the THSD module. This preference type is included in the  EPIS 4.0. on-board computer.
• for systems using the FD NET radio network, where the control function is performed by RMU 10 units (radiomodem units). This preference type is integrated in  the EPIS 4.0A. on-board computer.

Communication units for the RMU 10 crossroads control unit

Our RMU 10 communication unit consist of a basic TAIT radio station and our MRS 10 built-in unit which is installed directly in the radio station. The MRS 10 unit processes commands sent by the EPIS 4.0A on-board computer  from the vehicle and it transmits it to the crossroads control unit. Simultaneously it works as a fast radio modem.

Control and setting components:

• a DIP switch is used to set the crossroads control unit address.
• a USB output is used to reprogram the FW internal modem of the control unit.

The following picture shows a crossroads control unit receiver unit working on a reserved band.

Program for creating crossroads data – JunctionPrefEditor

The JunctionPrefEditor program edits crossroads data at the basis of which it is possible to create links needed for crossroads preference. Another function of the SW is creating exports from the assembled data for the EPIS 4.0A on-board computer.

Vehicle behavior at crossroads is set according to a map with coordinates of the displayed map sector. Individual points are then placed on the map and assigned functions (log on, log on check, . . .). The character of vehicle behavior can be assigned to the points as well (for example the type of the sector between stops, preference type, traction behavior, etc.).

The result of these actions is a file which is uploaded via depot update systems to the on-board computer. The on-board computer then behaves according to the commands set by the