Schedule Adherence Support


Schedule Adherence applications assist the driver to maintain his/her position relative to schedule or to planned intervals. They assist the driver to micro-manage the progress of his/her vehicle, while the broader service management and co-ordination is performed by an operations management system such as CAD/AVM. The degree of driver autonomy varies from one system to another. In some cases, there remains a strong degree of interaction between the dispatchers and the drivers, and the application is merely an aid. In other cases, the driver is expected to be quite autonomous and the interaction between dispatcher and driver is intentionally minimised.

These applications are based on or more of four typical features:

1) Display the current position of the vehicle relative to the schedule. This is usually in “+/-“ mode, showing the number of minutes in delay or advance of the scheduled position. The information may be colour-coded to highlight when the service is outside the tolerance range. Operating ahead of the scheduled time is usually the most distinctive colour, as early-running is considered undesirable. The driver is required to maintain position relative to schedule. This may include slowing down or holding for a few minutes at designated locations if he/she is operating ahead of schedule.

2) Display the intervals to the vehicles ahead and behind. This is typically shown in minutes, and may also be colour-coded. The driver is required to keep the interval as even as possible. This feature is most common where the service is operated to regular intervals rather than to a timetable. It also used for timetabled services where the CAD/AVM dispatcher regulates the departures from the terminal, and it is then the responsibility of the drivers to maintain service intervals along the route.

3) Display route, timing and transfer information to the driver. This is a simpler form of assistance that provides the driver with useful information, but does not present the real-time timekeeping status or relative intervals.

4) Dynamic recalculation of the schedule or headways may be performed and transmitted to individual vehicles or to all vehicles operating on the route. This adjusts the information displayed to the driver, so that he/she drives according to information rather than to the planned timetable. In case of diversion, the route file, stop sequence and timings may be updated.

Additional features may be included where the route is flexible. This is most noted in Demand Responsive Transport where pre-booked passengers must be collected or dropped-off at designated points and times.

Technologies, data and resources

Schedule Adherence applications are implemented within a broader CAD/AVM or other operations management system. The technologies used are:

  • Display screen for the driver. This may be integrated into the driver’s radio system (especially for simpler +/- information) or as a screen option in the on-board unit.
  • Route reference data, stored in the on-bus computer, drivers display unit, or the fare collection system
  • Vehicle location unit (e.g. GPS) to generate the current location of the vehicle
  • Mobile communications, for transfer of relevant real-time information to the vehicle

The data requirements are typically:

  • Reference data for the route – route taken, bus stops, transfer points, holding point
  • Schedule data for the route, including departure times, intermediate times, sectional journey times, transfer timing
  • Real-time information from the CAD/AVM system, including recalculated routes and schedules, intervals to other vehicles, interchange/transfer information

Advantages and Cautions

The primary advantages of Schedule Adherence support applications are to:

  • assist the driver to maintain schedule and/or relative position to other vehicles. This is especially important on longer routes where significant deviations can occur along the route.
  • provide the driver with a greater degree of responsibility and autonomy
  • reduce the tendency of drivers to operate ahead of schedule, as the deviation is clearly indicated
  • assist drivers to manage timed interchange/transfers with other routes and modes
  • provide the driver with the information to make minor, imperceptible adjustments to keep the service on schedule, thus avoiding the development of significant deviations which in turn require intervention to resolve
  • minimise voice interaction between dispatcher and drivers, and the number of instructions or interventions made by the dispatcher
  • provide a tool to adapt to disruption or degraded service conditions

The principal cautions in relation to Schedule Adherence support are:

  • displaying delay information may encourage drivers to drive fast in order to make up time. The expectations and responsibilities of the driver need to be made clear
  • sectional journey times need to be accurately calculated, taking account that the travel speed will vary along the route, by time of day, and by peak and counter-peak direction. Assuming a uniform speed will provide unrealistic information to the driver, and render the system of little value

Relevant Case Studies

Dublin, Prince William County, Zurich