APPLYING SAFETY AND OPERATIONAL EFFECTS OF HIGHWAY DESIGN FEATURES TO TWO-LANE RURAL HIGHWAYS

Rural 2-lane highways constitute a majority of the mileage of public roads in the U.S. Rural 2-lane highways have 40% of the total travel but experience 60% of the highway fatalities. The fatality rate for 2-lane rural highways in the U.S. is 2.39 per 100 million vehicle miles vs. 1.43 per 100 million vehicle miles for the interstate system. During the 1980s and 1990s, research was conducted in the U.S. to quantify the safety and operational effects of various key geometric design features including: Lane and Shoulder Widths, Roadside Safety, Horizontal and Vertical Alignment, Sight Distance, and Rural Intersections. Study and analysis of the safety and operational benefits of these various key geometric design features has resulted in a series of reports and findings which include Transportation Research Board Special Report 214, State of the Art Report 6, NCHRP 247, 362, 374, 376, 383, 400, 430, 439, and 440, NCHRP Synthesis 299, FHWA Program Reports (1998 Flexibility in Highway Design, Prediction of the Expected Safety Performance of Rural Two-Lane Highways, 2001 Older Driver Highway Design Handbook, 2000 Roundabouts; an Informational Guide, 2002 Safety Effectiveness of Intersection Left- and Right-Turn Lanes), 1999 ITE Traffic Safety Toolbox, AASHTO Roadside Design Guide, and the new AASHTO 2001 Policy on Geometric Design of Highways and Streets as identified in the bibliography for this paper. Aggregating this research has resulted in a compendium of the safety benefits of certain geometric design features for 2-lane rural highways which links design standards and safety. This aggregated research information offers a basis for software analysis of proposed highway designs to assess their expected safety performance and traditional capacity performance. Application of these benefits and effects achieves a numerical methodology for safety in a similar manner as is often performed for capacity. This compendium of the safety and operational benefits of highway design features is being deployed in the U.S. to state highway departments in advance of the release of the software-based analysis system.