Accidents on Suburban Highways—Tennessee's Experience

As part of a larger effort to develop guidelines for the design of arterial roads in areas undergoing suburbanization, a safety analysis of median design was undertaken using Tennessee data. The two median designs investigated were continuous two-way left-turn lanes (TWLTLs) and raised medians. All study sections had four basic through-lanes and were located in areas with various degrees of typical suburban commercial development (i.e., strip development). Several statistical techniques (analysis of covariance and multiple regression analysis) were used to determine the relative safety of the two designs. The study limited itself to highways where average daily traffic volumes were less than or equal to 32,500 vehicles per day. For this volume range, the study concluded that medians are generally safer than TWLTLs, but certain conditions exist where TWLTLs would have a more favorable safety experience (high driveway densities and low to medium traffic volumes). Regression analysis revealed that driveway density is an important contributor to accidents for medians but not for TWLTLs.