SAFETY EFFECTS OF CROSS-SECTION DESIGN FOR TWO-LANE ROADS - VOLUME I - FINAL REPORT

Abstract

This study was intended to quantify the benefits and costs resulting from lane widening, shoulder widening, shoulder surfacing, sideslope flattening, and roadside improvements. Detailed traffic, accident, and roadway data were collected on 4,951 miles of two lane roads in seven states. An accident predictive model and statistical tests were used to determine expected accident reductions related to various geometric improvements. Factors found to be most related to reduced accidents were wider lanes and shoulders, improved roadside conditions, and flatter sideslopes. Paved shoulders were found to have a marginal safety benefit compared to unpaved shoulders. Detailed accident analyses were also conducted for roadside features. Factors associated with increased fixed object accidents include higher traffic volumes, greater numbers of roadside objects, and closer distance of roadside objects to the road. Roadside objects associated with high accident severities include culverts, trees, utility and light poles, bridges, rocks, and earth embankments. Construction cost data from several states were used to develop a cost model for numerous types of roadway and roadside projects. This volume contains the final report and four appendixes. The final report contains detailed information on data collection and data analysis and conclusions and recommendations. The appendixes contain detailed information on the literature review, photographs used for the rural and urban roadside hazard scales, and economic analysis inputs (a).