Degree Type


Date of Award


Degree Name

Master of Science


Civil, Construction, and Environmental Engineering

First Advisor

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.


Copyright Owner

Christian Ryan Sax



Date Available


File Format


File Size

171 pages