Understanding of Heavy-Vehicle Encroachment Frequency

• Published in: Transportation research record 2014-01, Vol.2437 (1), p.20-26
• Main Authors: Carrigan, Christine E., Ray, Malcolm H., Johnson, T. Olaf
• Format: Article
• Language: English
• Subjects: Crashes; Heavy vehicles; Passengers; Risk analysis; Roadsides; Transportation; Vehicles
• ISSN: 0361-1981; 2169-4052
• DOI: 10.3141/2437-03

Encroachment data gathering in the past explicitly excluded heavy vehicles; this exclusion compelled assumptions to be made about the frequency at which heavy vehicles encroached onto the roadside. This paper examines the assumption that heavy vehicles encroach onto the roadside at the same rate as passenger vehicles. This assumption may be untrue for several reasons. In general, heavy vehicles are driven by trained professionals, who operate with additional restrictions on operating hours. Driver behavior and the performance characteristics of heavy vehicles differ from those of passenger vehicles. In this study, four data sets were analyzed: a national sample, two statewide samples, and a regional sample. The results challenged the long-held assumption that heavy vehicles encroached at the same frequency as passenger vehicles. The findings indicated that heavy vehicles encroached at approximately 30% of the rate of all vehicles. Although the causes of this reduced encroachment rate remain speculative, the examined data demonstrate that a difference does exist and should be accounted for in the modeling of run-off-road crashes for roadside safety benefit–cost and risk analyses.