Assessment of the effectiveness of proposed “Keep Right Pass Left – It’s the Law” signs on two lane rural freeways

Abstract

This study focuses on the problem of unlawful left-lane usage on non-congested two-lane rural freeways in Michigan. According to the Michigan Vehicle Code, vehicles shall remain on the right lane of two-lane sections of rural freeways when not passing other vehicles. While drivers are currently reminded of this rule by signs stating “Slower Traffic Keep Right” installed as part of the normal post-interchange sign sequence, traffic observations suggest that many motorists do not to follow this rule. As part of an effort to entice drivers to abide by existing rules, this study investigates a proposal to replace current “Slower Traffic Keep Right” signs with new explicit signs stating “Keep Right Pass Left – It’s the Law”. To assess the effectiveness of this replacement, traffic behavioral data were collected at four rural sites along I-96 in Michigan, first with the existing sign in place and then with the proposed new sign. Tube counters data were collected to compare lane-specific traffic volumes and speed distributions in the presence of each sign. Video data were further collected to obtain information about individual passing events and develop statistics about the validity of left-lane usage by individual vehicles and about left-lane vehicle groupings caused by slow moving vehicles in the freeway left lane. Results of the analyses provide no indication that replacing existing “Slower Traffic Keep Right” sings would effectively improve left-lane usage behavior on two-lane rural freeways. Depending on the sites considered, either improvements or deteriorations in left-lane behavior were observed following the sign replacement. In all cases, statistical tests further indicate that the observed changes are not statistically significant.