A Side Object Detection System (SODS) for transit buses was cost-effective with a baseline benefit-cost ratio of 1.43 and a ratio range of 0.37-3.55.
Made Public Date


United States

Assessing the Business Case for Integrated Collision Avoidance Systems on Transit Buses

Summary Information

Transit buses are involved in approximately 100,000 collisions annually, resulting in a collision rate (i.e., taking into account the number of transit buses) that is up to four times higher than other modes. (With an average of 100 fatalities and 7,500 injuries per year resulting from a transit bus collision, the likelihood of injury or death is far less than it is for other surface transport modes.) Transit agencies employ a broad array of activities targeted at improving the safety and security of passengers and operators including driver training, maintenance planning, accident reporting, etc. However, the nation’s fleet of transit buses has not significantly adopted collision avoidance, in contrast to the relatively robust deployment of in-vehicle safety systems for passenger vehicles and heavy trucks.

The operating conditions of transit buses, characterized by low-speeds, frequent stops and pulling in and out of traffic in a frequently dense urban environment, may not be amenable to the kinds of collision avoidance systems designed for high-speed operations of passenger vehicles and heavy trucks. To help determine the potential for collision warning systems for reducing transit bus collisions, the U.S. DOT sponsored a study of the business case assessment for (or against) seven safety systems:

  • Forward Collision Warning Systems
  • Rear Collision Warning Systems
  • Side Object Detection Systems
  • Forward Object Detection Systems
  • Rear Object Detection Systems
  • Lane Departure Warning systems
  • Pedestrian Detection Systems

The study estimated the potential effectiveness of these systems by comparing their capability of preventing frequently occurring collision scenarios (e.g., side-swipe, forward, rear). The benefit-cost ratio of each of these systems as a stand-alone and bundled system was based on the installation, training and maintenance costs to the potential savings from collisions avoided.


Results showed that the Side Object Detection System (SODS) was the only cost-effective system, with a benefit-cost ratio ranging from 0.37 to 3.55. The cost-effectiveness of SODS is attributable to the fact that sideswipe collisions occur relatively frequently, and a high proportion of them are avoidable, rendering the potential for savings relatively high. In contrast, forward, rear, and angle collisions occur less frequently and are not as avoidable. Bundled systems only showed a potential for savings if they included SODS, and Pedestrian Detection Systems were cost-effective only for operators with above-average collision rates or high collision costs.

The table below shows the range of benefit-cost ratios for the systems.

In-vehicle Safety System
Estimated Purchase Price
Forward Collision Warning
Rear Collision Warning
Side Object Detection
Forward Object Detection
Rear Object Detection
Lane Departure Warning
Pedestrian Detection