Vehicle to and from stop/shelter
Communications between vehicles and stops is most often related to the provision of real time information or for the transfer of automatic vehicle location information in roadside detector systems.
In the most common roadside detector systems, the electronic sign at the roadside contains a transmitter which continuously sends a radio signal with information identifying the stop number or location. As the vehicle passes the roadside beacon, an on-board receiver picks up this transmission. The receiver is connected to the radio system, generally through the on-board computer, which transmits the vehicle position and a time-stamp of when the stop was passed to the control centre.
RTPI is usually provided via display units at roadside stop locations. These are typically pole mounted LED displays that show customers the minutes to arrival of particular routes and the route destination. In terms of RTPI the communication process usually involves the following steps:
- Satellite signals are continuously received by the in-vehicle GPS system which is connected to the on-board computer.
- The on-board computer sends updated location information to the control centre AVL system via the on-board radio system on a regular basis, approximately every 10 to 60 seconds.
- Where the scheduled arrival time at a stop is different to the actual estimated arrival time, data is transmitted to the radio receiver in the RTPI display at the stop. This is transmitted via the radio system, which is typically GPRS, from the control centre. TETRA digital PMR systems can also be used for RTPI data transfer.
Rather than transferring location data from vehicles to RTPI displays via the control centre, some systems are capable of directly sending information from the vehicle to the RTPI display. These systems allow for faster updates and also use the in-vehicle radio to broadcast information to a radio receiver in the RTPI display.
Communications links between vehicles and stops are mainly operated for the purposes of providing RTPI but can also be used for AVL systems with additional integration with the operations control centre.
Benefits and cautions
The provision of RTPI through the use of communications connections between vehicles and roadside stops vastly improves customer service by removing passenger uncertainty as to when their service will arrive. This improves the attractiveness and usability of the network for existing passengers and therefore increases the likelihood that new customers will be attracted to the service.
The use of vehicle-to-roadside communications for the purposes of AVL has a number of drawbacks. With this type of system there is not continuous monitoring of vehicle location, so accurate RTPI cannot be provided. Also tracking is limited to infrastructure coverage, which means that it may be limited to specific routes as it may not be feasible to provide full network coverage.
Relevant case studies