On the section of Interstate 10 through central Phoenix, crash frequency consistently ranked high on the Arizona Department of Transportation (ADOT) highway system. High traffic volume, in conjunction with substantial weaving associated with two system interchanges, continuous HOV lane access and a tunnel, contributed to the relatively high crash frequencies. Identifying causal factors and assessing the potential impact of improvements was difficult due to the complexity of corridor operations and roadway geometry. Existing tools and methods were insufficient to perform a quantitative safety performance evaluation.


Kittelson applied AASHTO Highway Safety Manual (HSM) freeway crash predictive methods to quantitatively assess safety performance, which involved identifying sites with a high potential for crash reduction, identifying and assessing potential countermeasures, and analyzing benefit/cost of improvement projects. Kittelson conducted a detailed diagnostic assessment of safety performance within the freeway corridor, as well as developed calibration factors so that the HSM methodology better reflected local conditions in the Phoenix metro area.

The Outcome

Tailoring National Guidance to Local Needs

The study identified high priority segments within the corridor for safety improvement. Countermeasures were recommended based on an evaluation of the potential benefit to reduced crash frequency and severity. The crash prediction calibration factors developed with the study can be used for the evaluation of safety performance on urban freeways throughout Arizona.






Phoenix, AZ