Elementary Units of Exposure
Abstract
Most road safety studies rely on summary measures of exposure. The term “summary measure” denotes any aggregate indicator of exposure that does not directly identify and count the number of opportunities for accidents to occur. This paper shows how elementary units of exposure can be developed on the basis of known aggregate measures, such as annual average daily traffic (AADT). An elementary unit of exposure refers to any event that generates an opportunity for an accident to occur. Four such events are identified: (a) encounters (i.e., vehicles passing each other in opposite directions of travel); (b) simultaneous arrivals at points of intersection between potentially conflicting directions of travel, in particular vehicles entering intersections at the same time or within a very short time interval; (c) change of travel lane on multilane highways; and (d) braking or stopping. These events describe traffic movements that occur before a wide range of crash types. The only major group of accidents that is not directly related to particular events is running off the road. The number of events expected to occur for each of the four types identified is estimated on the basis of the following assumptions: (a) AADT is known [when estimating the number of events, mean hourly volume (AADT/24) is used]; (b) vehicles or road users arrive at a point of potential conflict according to a Poisson process; and (c) simultaneous arrivals within a very short time interval (such as 1 s) have the potential to generate a conflict. The number of encounters and simultaneous arrivals in intersections increases considerably faster than AADT. The number of events that may generate conflicts involving lane changes, braking, or stopping increases more slowly than does AADT.
Get full access to this article
View all access and purchase options for this article.
References
1. Chapman R. The Concept of Exposure. Accident Analysis and Prevention, Vol. 5, 1973, pp. 95–110.
2. Council F. M., Stewart J. R., and Rodgman E. A. Development of Exposure Measures for Highway Safety Analysis. Report FHWA/RD-87/092. FHWA, U.S. Department of Transportation, 1987.
3. Hauer E., Ng J. C. N., and Lovell J. Estimation of Safety at Signalized Intersections. In Transportation Research Record 1185, TRB, National Research Council, Washington, D.C., 1988, pp. 48–61.
4. Hauer E. Exposure and Accident Rate. Traffic Engineering and Control, Vol. 36, 1995, pp. 134–138.
5. Mensah A., and Hauer E. Two Problems of Averaging Arising in the Estimation of the Relationship Between Accidents and Traffic Flow. In Transportation Research Record 1635, TRB, National Research Council, Washington, D.C., 1998, pp. 37–43.
6. Jonsson T., Ivan J. N., and Zhang C. Crash Prediction Models for Intersections on Rural Multilane Highways: Differences by Collision Type. In Transportation Research Record: Journal of the Transportation Research Board, No. 2019, Transportation Research Board of the National Academies, Washington, D.C., 2007, pp. 91–98.
7. Hauer E., Council F. M., and Mohammedshah Y. Safety Models for Urban Four-Lane Undivided Road Segments. In Transportation Research Record: Journal of the Transportation Research Board, No. 1897, Transportation Research Board of the National Academies, Washington, D.C., 2004, pp. 96–105.
8. Lord D., Geedipally S., Persaud B. N., Washington S. P., van Schalkwyk I., Ivan J. N., Lyon C., and Jonsson T. NCHRP Web Document 126: Methodology to Predict the Safety Performance of Rural Multilane Highways. Contractor's final report for NCHRP project 17-29. Web-only document 126. Transportation Research Board of the National Academies, Washington, D.C., 2008. onlinepubs.trb.org/onlinepubs/nchrp/nchrp_w126.pdf.
9. Hakamies-Blomqvist L., Raitanen T., and O'Neill D. Driver Ageing Does Not Cause Higher Accident Rates per km. Transportation Research Part F, Vol. 5, 2002, pp. 271–274.
10. Fontaine H. Driver Age and Road Accidents. What Is the Risk for Seniors? Recherche Transports Sécurité, Vol. 79, 2003, pp. 107–120.
11. Langford J., Methorst R., and Hakamies-Blomqvist L. Older Drivers Do Not Have a High Crash Risk—A Replication of Low Mileage Bias. Accident Analysis and Prevention, Vol. 38, 2006, pp. 574–578.
12. Alvarez F. J., and Fierro I. Older Drivers, Medical Condition, Medical Impairment and Crash Risk. Accident Analysis and Prevention, Vol. 40, 2008, pp. 55–60.
13. Hauer E. Left Turn Protection, Safety, Delay and Guidelines: A Literature Review. Toronto, Ontario, Canada, 2004. www.roadsafetyresearch.com.
14. Martin J.-L., and Quincy R. Crossover Crashes at Median Strips Equipped with Barriers on a French Motorway Network. In Transportation Research Record: Journal of the Transportation Research Board, No. 1758, TRB, National Research Council, Washington, D.C., 2001, pp. 6–12.
15. Fridstrøm L. Econometric Models of Road Use, Accidents, and Road Investment Decisions, Vol. II. Report 457. Institute of Transport Economics, Oslo, Norway, 1999.
16. Elvik R. Laws of Accident Causation. Accident Analysis and Prevention, Vol. 38, 2006, pp. 742–747.
Cite article
Cite article
Cite article
OR
Download to reference manager
If you have citation software installed, you can download article citation data to the citation manager of your choice
Information, rights and permissions
Information
Published In
Article first published online: January 1, 2009
Issue published: January 2009
Authors
Metrics and citations
Metrics
Journals metrics
This article was published in Transportation Research Record: Journal of the Transportation Research Board.
VIEW ALL JOURNAL METRICSArticle usage*
Total views and downloads: 59
*Article usage tracking started in December 2016
Altmetric
See the impact this article is making through the number of times it’s been read, and the Altmetric Score.
Learn more about the Altmetric Scores
Articles citing this one
Receive email alerts when this article is cited
Web of Science: 0
Crossref: 32
- Microscopic Traffic Risk Assessment at Signalized Intersections of a B...
- Effect of vehicle size on crash risk in a heterogeneous traffic scenar...
- Specifying Autonomous Driving Scenarios
- The ‘safety in density’ effect for cyclists and motor vehicles in Scan...
- Cyclists at Roundabouts: Risk Analysis and Rational Criteria for Choos...
- Observations on the Relationship between Crash Frequency and Traffic F...
- Event-based road safety assessment: A novel approach towards risk micr...
- Traffic volume and crashes and how crash and road characteristics affe...
- Towards linking driving complexity to crash risk
- Nighttime safety evaluation for signalized intersections at the signal...
- Transferability of real-time safety performance functions for signaliz...
- Risk Analysis and Safer Layout Design Solutions for Bicycles in Four-L...
- Safety Problems in Urban Cycling Mobility: A Quantitative Risk Analysi...
- Using HLM to investigate the relationship between traffic accident ris...
- Geometrical and Functional Criteria as a Methodological Approach to Im...
- Traffic conflict models to evaluate the safety of signalized intersect...
- Safety Performance Evaluation of a Three-Leg Unsignalized Intersection...
- Bayesian estimation of conflict-based safety performance functions
- Modeling spatial relationships between multimodal transportation infra...
- Conflict-Based Safety Performance Functions for Predicting Traffic Col...
- Applications of Generalized Additive and Bayesian Hierarchical Models ...
- Exposure-based Road Traffic Fatality Rates by Mode of Travel in France
- Some implications of an event-based definition of exposure to the risk...
- Road crash fatality rates in France: A comparison of road user types, ...
- Can it be true that most drivers are safer than the average driver?
- Evaluation of Postencroachment Time as Surrogate for Opposing Left-Tur...
- Exposure to lateral collision in signalized intersections with protect...
- Are rural older drivers subject to low-mileage bias?
- Extended prediction models for crashes at roundabouts
- Are Age-Based Licensing Restrictions a Meaningful Way to Enhance Rural...
- Large-Scale Automated Analysis of Vehicle Interactions and Collisions
- Exploratory Study of Mechanisms by Which Exposure Influences Accident ...
Figures and tables
Figures & Media
Tables
View Options
Get access
Access options
If you have access to journal content via a personal subscription, university, library, employer or society, select from the options below:
loading institutional access options
Alternatively, view purchase options below:
Purchase 24 hour online access to view and download content.
Access journal content via a DeepDyve subscription or find out more about this option.
