Date of Award
Master of Science
Civil, Construction, and Environmental Engineering
Thomas H. Maze
In urban communities, there are often limited amounts of right-of-way available for establishing
a large setback distance from the curb for fixed objects. Urban communities must constantly
weigh the cost of purchasing additional right-of-way for clear zones against the risk of fixed
object crashes. From 2004 to 2006, this type of crash on curbed roads represented 15% of all
fatal crashes and 3% of all crashes in the state of Iowa. Many states have kept the current
minimum AASHTO recommendations as their minimum clear zone standards; however, other
states have decided that these recommendations are insufficient and have increased the required
minimum 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. The
research was conducted in two phases. The first phase involved a synthesis of practice that
included a literature review and a survey of practices in jurisdictions that have developmental
and historical patterns similar to those of Iowa. The second phase involved investigating the
benefits of a 10 ft clear zone, which included examining urban corridors in Iowa that meet or do
not meet the 10 ft clear zone goal. The results of this study indicate that a consistent fixed object
offset results in a reduction in the number of fixed object crashes, a 5 ft clear zone is most
effective when the goal is to minimize the number of fixed object crashes, and a 3 ft clear zone is
most effective when the goal is to minimize the cost of fixed object crashes.
Christian Ryan Sax
Sax, Christian Ryan, "Clear Zone - A synthesis of practice and an evaluation of the benefits of meeting the ten-foot clear zone goal on urban streets" (2008). Graduate Theses and Dissertations. 10932.