Evaluation of a Low-Cost Program of Road System Traffic Safety Reviews for County Highways

Mendocino County is a large rural county in northern California with more than 1,000 centerline miles of county-maintained roads. The terrain is mountainous, with a few small inland valleys. During the 1990s, the Mendocino County Department of Transportation developed a program of road system traffic safety reviews to improve signing and markings on the arterials and collectors in the system. The effectiveness of the program was measured by comparing accident data for the reviewed roads with data for roads not included in, or influenced by, the reviews. To control for different groups of factors, two sets of control roads were selected—county-maintained roads not reviewed and state highways within the county. Over two consecutive 3-year review cycles, the number of accidents on the reviewed roads fell by 42.1%, while on the county-maintained roads not reviewed they increased by 26.5%, and on the state highways they fell by 3.3%. The total cost to conduct the reviews and implement the recommended changes was $ 79,300. The accident histories of the control roads were used to define the limits of the range of probable benefits. On the basis of average accident costs provided by the California Department of Transportation, calculated savings ranged from $ 12.58 million to $23.73 million, yielding a costs-to-benefits ratio between 1:159 and 1:299. The county is expanding the road system traffic safety review program to cover its entire maintained road system.