There is a need to evaluate low-cost safety strategies that States may implement as part of their Strategic Highway Safety Plan. The Federal Highway Administration organized a Pooled Fund Study of 26 States to evaluate several low-cost safety strategies; reallocation of total paved width was one strategy selected. This study identifies whether it is ôsaferö to increase lane width or increase shoulder width given a fixed total width. Geometric, traffic, and crash data were obtained for more than 52,000 miles of roadway segments in Pennsylvania and Washington. A case-control approach was applied to evaluate the safety effectiveness of lane-shoulder combinations. The safety effects of total width, lane width, and shoulder width werecompared with previous studies to validate the modeling approach. There was a reduction in the odds ratio as total paved width, lane width, and shoulder width increase individually; this is consistent with previous research. Initial results did not indicate a clear trade-off between lane and shoulder width. In some cases, adding lane width is favorable where in othercases, adding shoulder width is favorable. Supplementing the results of this study with previous research, recommended crash modification factors (CMFs) are provided for several lane-shoulder combinations. The recommendedvalues present a more apparent trade-off, indicating a slight benefit to increasing lane width for a fixed total width. Importantly, the results differ from the Highway Safety Manual, which presents CMFs for lane and shoulder width separately. This raises the question of whether CMFs should be changed to reflect the interaction between lane and shoulder width.
Abstract