Collision warning and avoidance


Collision warning and avoidance is a set of direct supports to the driver to assist safer driving. It covers two distinct sets of applications:

  • Collision warning, which provides information to the driver, but it remains up to the driver whether to use that information and what action to take.
  • Collision avoidance, which triggers an avoidance response (e.g. deceleration) when a potential collision is detected. To date, collision avoidance remains in the developmental stage for general vehicles, and for freight and public transport vehicles. There are rare cases where it is currently used in bus services (e.g. detection of obstacle on guided busway), but otherwise it is a technology not yet in deployment in the sector. It is not considered further in this toolkit.

Collision warning applications can be broadly clustered in three groups:

  • Warnings against minor collisions and scrapes (which may have severe consequences for pedestrians or cyclists). This includes object detection for reversing and when manoeuvring through narrow spaces (e.g. bus parking lots, narrow streets), and pedestrian detection (emerging, not yet widely deployed).
  • Warnings against major collisions including major impacts and loss of control. This includes forward-facing proximity detectors, vision enhancement, blind-spot detectors, lane-keeping assistance, roll stability control, and driver fatigue alerts.
  • Warnings against known hazards. For urban public transport, the most relevant application is low-bridge detection.

Technologies, data and resources

This review does not consider general vehicle safety features, stability systems, engine management systems, etc., and only considers ITS-related features.

Applications and technologies for collision warning and avoidance generally emerge from the auto industry and the freight sector, and are then migrated to the public transport sector through the vehicle manufacturers, either as standard or as options.

The principal technologies used for collision warning are:

  • Edge-of-vehicle sensors
  • Obstacle detection systems
  • Vision enhancement systems
  • Navigation aids, including low-bridge location databases
  • Audio or visual alarms

Currently, the bus transport sector uses only systems that are self-contained within the vehicle. Neither the Intelligent Highway nor Co-operative Driving initiatives are yet relevant to the sector, although they will become relevant as such services become available to general traffic.

Advantages and Cautions

The primary advantages of Collision Warning and Avoidance applications are to:

  • reduce, or ideally eliminate, reversing collisions. Of particular importance is to eliminate hazard of reversing over pedestrians or other vulnerable users
  • significantly reduce the number of scrapes and minor collisions which, although of low casualty risk, are expensive and time-consuming to repair, and which degrade the visual appearance of the fleet
  • assist operation in confined locations – e.g. busways, narrow streets
  • assist drivers to avoid major collisions, shunts

The principal cautions in relation to Collision Warning and Avoidance are:

  • drivers needs to be adequately trained in their use
  • drivers need to maintain a sense of vigilance, and to avoid over-reliance on the support systems and warnings

Relevant Case Studies