Computer Aided Dispatch


CAD/AVM systems assist the processes of dispatching revenue service vehicles. They are primarily concerned with managing the dispatch of buses from their terminal points. In some cases, the CAD/AVM also supports the dispatch of vehicles from the depot.

The objectives of a CAD/AVM systems are usually:

  • To dispatch vehicles according to the operational plan.
  • To dispatch the vehicle at the scheduled time; or
  • To dispatch vehicles according to a headway plan (e.g. vehicles at 5 minute intervals in the peak, 8 minutes in the inter-peak, 15 minutes in the evenings)
  • In case of late arrival of incoming vehicles and/or other disruptions, to arrange the departures as close as possible to the service plan, and maintain proper intervals
  • In case of more serious disruptions, to manage the departures to provide the best service possible with the resources available
  • In case of one or more vehicles being unavailable, to smooth the intervals
  • To liaise with support services for replacement vehicles and/or drivers
  • To record all departures for administration, analysis, planning and intervention measures

Two distinguishing traits of CAD/AVM systems are observed:

1) Centralisation: Some transport operators establish a single centralised control centre, from which all of the operations management and dispatching is performed. Other transport operators decentralise the operations management, so that dispatching capacity is established at depot-level, at main bus stations, or at terminals.

2) Hierarchy: The majority of dispatching systems are operated without a hierarchical structure. The control centre (whether centralised or decentralised) conducts the operations management in autonomous fashion. In some systems, the individual dispatcher points perform the regular dispatching, while a central console oversees co-ordination and steps when required (e.g. in case of severe disruption, road blockage, events, etc). In a relatively small number of systems, the contracting transport authority has oversight of the dispatching centres of the operators, and will intervene where services deviate from the required performance, or instruct the operator to do so.

CAD/AVM systems provide the following core functions to assist the dispatcher in the operations management and dispatch functions:

  • Display the routes and/or terminal points in graphical format
  • Present the current locations of the vehicles operating on the relevant routes, usually with indication of the their status (early/late)
  • Provide supporting information on schedules, dispatching sequence, vehicle availability
  • Provide status information and alerts about actual and missing departures
  • Support voice and data communication with drivers, vehicles and support staff to facilitate on-time departure
  • Capture data on all departures

The CAD/AVM application is typically integrated with other operations management functions.

Technologies, data and resources

CAD/AVM systems utilise the following technologies:

  • Software
  • Hardware platform (server, displays, printers)
  • GIS/mapping
  • Voice and data communications with drivers/vehicles and with operations support personnel

The principal data required for the CAD/AVM systems are:

  • Schedules and route information
  • Real-time data on bus locations and on vehicle status
  • Real-time and pre-planned information on vehicle and driver assignment

Advantages and Cautions

The principal advantages of CAD/AVM systems are improved ability to:

  • gather and present a wide range of real-time, plan and support information, and present it to dispatchers in usable format
  • better manage and implement dispatch strategies, in particular when vehicles are in delay
  • manage multiple routes per dispatcher and save resources
  • record all departures

Key cautions in relation to CAD/AVM systems are:

  • The importance of the operations management plan is often underestimated. The CAD/AVM software facilitate improved dispatching, but it cannot substitute for proper processes.
  • Procedures need to be well developed and documented, and fully consistent with the CAD/AVM software platform
  • CAD/AVM systems do not run themselves, they require significant human input. An adequate number of dispatchers is required, with permanent cover throughout the operating period.
  • Dispatchers need clear objectives in relation to active management of the service. There is a risk that they become ‘observers’ and rather passive.
  • Selection and training of the dispatchers is highly important.

Relevant Case Studies

Dublin, Florence, Prince William County, Zurich