Many states have implemented truck lane restrictions in an attempt to improve safety and mobility on freeways. These restrictions typically prohibit trucks from traveling in the median (left-most) lane of multilane highways; the restriction potentially increases passing opportunities and reduces negative interactions between slow-moving trucks and faster-moving vehicles. Virginia has restricted trucks from the median lane of some interstates with three or more lanes by direction since 1997, but no systematic evaluation of the safety impact of the restrictions has been conducted. Evaluations of similar restrictions in other states have yielded contradictory findings, but those studies often used a limited data set. An empirical Bayes' analysis of Virginia's restrictions was performed by using 6 years of crash data from 22 sites with restrictions and 16 similar sites without restrictions. The analysis showed that a breakpoint in safety performance occurred around 10,000 vehicles per day per lane. Facilities where the volume was below this threshold had significantly fewer crashes than anticipated, averaging a 13% reduction in total crashes and a 32% reduction in fatal and injury crashes. Sites where the volume exceeded this threshold had increases in total crashes and fatal or injury crashes of 28% and 23%, respectively. A detailed analysis of crashes on the higher-volume roads was conducted to screen out crashes in which the restrictions likely played no role. That analysis showed that the number of truck-involved crashes was still significantly higher than predicted, indicating that safety on higher-volume roads may be negatively affected by truck lane restrictions.
Fontaine, M.D., C.S. Bhamidipati, and L.E. Dougald. Safety Impact of Truck Lane Restrictions on Multilane Freeways. In Transportation Research Record: Journal of the Transportation Research Board, No. 2096, Transportation Research Board, National Research Council, Washington, D.C., 2009, pp. 25-32.