Turner-Fairbank Highway Research Center

« back to the list

Difficulties with Quasi-Induced Exposrue when Speed Varies Systematically by Vehicle Type

Product Type

Journal Article


Jiang, X. and R.W. Lyles



Full citation

Jiang, X. and R.W. Lyles. Difficulties with Quasi-Induced Exposrue when Speed Varies Systematically by Vehicle Type. In Accident Analysis and Prevention, Vol. 39, No. 4, Pergamon Press, Oxford, NY, July 2007, pp. 649-656


The attractiveness of quasi-induced exposure lies in the simplistic nature of its theory and application. As opposed to vehicle miles of travel, quasi-induced exposure is developed solely from the accident data themselves. Involvement ratios (IRs) are used to describe the relative over- or under-involvement of different drivervehicle combinations in traffic accidents. The issue of systematic bias in the involvement ratios is explored, and it is shown both theoretically and empirically that the variation in average speeds between vehicle types can affect relative accident involvement ratios. For vehicle types that routinely travel faster, the IRs will likely be underestimated; while for slower-moving vehicle types, the IRs will be overestimated. In the case of speed, the magnitude of the effect on the IRs is dependent both on the magnitude of the speed differential and the percentage of slower vehicles in the traffic stream. Conclusions can be extended to whenever there are speed or other behavior disparities associated with the drivervehicle combinations in the traffic stream. Other examples include the speed discrepancy caused by different drivers (e.g., younger versus older drivers). Caution must be used in interpreting results from applications of the quasi-induced technique whenever such biases might be encountered.

Available From

Accident Analysis and Prevention

Link To Journal Article

Difficulties with Quasi-Induced Exposrue when Speed Varies Systematically by Vehicle Type


Accident analysis
Accident data
Accident exposure
Accident rates
Motor vehicles
Traffic accidents
Vehicle characteristics
Vehicles by speed

« Back to the List

HSIS Summaries

HSIS Summary Reports are two to eight pages in length and include a brief description of the issue addressed, data used, methodology applied, significant results, and practical implications.

Read More

Research Reports

A variety of research studies have been performed using data from HSIS. Many of the final reports prepared are now available electronically.

Read More

Technical Summaries

Research reports are often summarized in executive summaries, technical briefs, or other abbreviated formats. Included here are those road safety summaries that involved research using HSIS data.

Read More

Safety Analysis Tools

In addition to conducting research, HSIS resources are also used to develop products that can be used by practitioners in the analysis of safety problems.

Read More

Other Projects

HSIS data are sometimes used in research studies that result in other types of finished products, such as dissertations, theses, and conference proceedings.

Read More