Virginia, like many other states, has used truck lane restrictions on parts of its interstate system in an attempt to improve mobility and safety. The Code of Virginia currently specifies two types of lane restrictions. First, trucks may not travel in the left-most lane of interstates with three or more lanes by direction (1) when the speed limit is 65 mph or higher, (2) along all of I-81, and (3) along interstates in the Virginia Department of Transportation’s (VDOT) Northern Virginia District. Second, trucks may not travel in the left lane of two-lane directional interstate segments when their speed is below the posted speed limit; this restriction was enacted in 2007 and was intended to reduce cases of trucks impeding traffic flow on steep grades in the western part of the state.
This report describes Phase II of a 2007 study that found that the safety impact of the first type of restriction appeared to be affected by traffic volume. Safety was enhanced on low- volume roads (i.e., annual average daily traffic [AADT] less than 10,000 vehicles per day per lane [vpdpl]) but degraded on high-volume roads (i.e., AADT above 10,000 vpdpl). Given that most of the high-volume interstates investigated were in Northern Virginia, there was a need to re-examine the safety analysis to ensure that the findings were not a product of the growing congestion in the region but rather were attributable to the effects of the truck lane restrictions.
The purpose of this study was to provide a detailed assessment of the safety and mobility impacts of Virginia’s truck lane restrictions, expanding on the Phase I study. First, crashes on high-volume interstates with three or more lanes by direction noted in the Phase I study were re-examined. Individual crash reports were reviewed, and any crashes that were not influenced by the restriction were removed from subsequent analysis. An empirical Bayes analysis was then used to re-assess safety using the screened crashes. Second, the operational and safety impacts of the restriction on two-lane segments of interstate were examined. Third, the effect of an enforcement campaign on compliance with the restriction for two-lane segments was determined.
The crash analysis for the high-volume, three-lane segments confirmed that crashes were higher than expected after the restriction was put in place and thus were not merely the products of growing congestion. The safety and operational impacts of the restriction for two-lane interstates revealed no significant benefits, likely because the level of non-compliance with the restriction was high. With regard to the effect of the concentrated enforcement campaign, compliance improved, but the improvement was relatively modest.
The study recommends that VDOT (1) pursue a legislative modification to remove truck lane restrictions on high-volume interstates with three or more lanes in each direction; (2) determine if signing could be modified to improve compliance; (3) partner with the Virginia State Police and the Virginia Trucking Association to increase compliance on the two-lane directional segments of interstate; and (4) direct a study to re-evaluate the effectiveness of the two-lane restrictions once at least 3 years of “after” crash data are available. Removal of the truck restrictions on the specified high-volume interstates should create crash reduction benefits. If crash costs are converted into dollars, an estimated $266,996 of crashes would be eliminated statewide annually through removal of these restrictions. Those costs accrue to drivers. Additional direct savings to VDOT would occur through the reduction of signing.