Clear Zone - A synthesis of practice and an evaluation of the benefits of meeting the ten-foot clear zone goal on urban streets

摘要

In urban communities, there are often limited amounts of right-of-way available for establishinga large setback distance from the curb for fixed objects. Urban communities must constantlyweigh the cost of purchasing additional right-of-way for clear zones against the risk of fixedobject crashes. From 2004 to 2006, this type of crash on curbed roads represented 15% of allfatal crashes and 3% of all crashes in the state of Iowa. Many states have kept the currentminimum AASHTO recommendations as their minimum clear zone standards; however, otherstates have decided that these recommendations are insufficient and have increased the requiredminimum clear zone distance to better suit the judgment of local designers.This thesis presents research on the effects of the clear zone on urban curbed streets. Theresearch was conducted in two phases. The first phase involved a synthesis of practice thatincluded a literature review and a survey of practices in jurisdictions that have developmentaland historical patterns similar to those of Iowa. The second phase involved investigating thebenefits of a 10 ft clear zone, which included examining urban corridors in Iowa that meet or donot meet the 10 ft clear zone goal. The results of this study indicate that a consistent fixed objectoffset results in a reduction in the number of fixed object crashes, a 5 ft clear zone is mosteffective when the goal is to minimize the number of fixed object crashes, and a 3 ft clear zone ismost effective when the goal is to minimize the cost of fixed object crashes.