Consistency in Design for Low‐Volume Rural Roads

Abstract

The 2,000,000 miles of low‐volume rural roads in the United States are different than the high‐volume roads and should be designed differently. Traffic volumes on them are low, averaging about 110 vehicles/day or about one vehicle entering a given mile from both ends every three minutes during peak hours. This contrasts with one vehicle every four seconds at capacity. Geometries on many of these roads have not changed since they were built in the 1920s and 1930s. Today, road improvements should be based on designs that are consistent and safe, but economical, because needs are great and funds are scarce. Present‐day design practices for high volume roads require that each of their features meet a stipulated design speed set by modern surfaces and vehicles. This practice does not fit the low‐volume situation since, whenever possible, drivers will exceed any affordable design speed. They must be slowed down when situations warrant it. A consistent approach to design which realizes cheap but safe improvements to low‐volume roads is proposed. It involves integrating geometric design and positive guidance approaches. Positive guidance employs striping, signing, and other devices and strategies to mobilize drivers' senses so that they will drive sensibly. Selecting the less costly between geometry and positive guidance techniques will produce safer roads more cheaply.