Study Details

Study Title: Developing Safety Performance Functions for Diamond Interchange Ramp Terminals

Authors: Wang et al.

Publication Date: JAN, 2011

Abstract: The objectives of this research were to identify factors contributing to ramp terminal crashes and develop safety performance functions for four-leg diamond interchange ramp terminals. Four-leg diamond interchange ramp terminals in Wisconsin were sampled to construct two datasets. The first dataset was comprised of 60 pairs of interchange ramp terminals and was used to do general analysis and identify the effects of geometric factors. The other dataset was comprised of only signalized diamond interchange ramp terminals and was used to study the effect of signal timing. The major factors considered included traffic volume, traffic control, and geometric design. For signalized interchange ramp terminals, yellow and all-red clearance intervals were also considered as factors. The presence of cross road median is negatively correlated with average crash frequency. For signalized interchange ramp terminals, the crash frequency increases with deficient yellow or all-red intervals and decreases if there is an exclusive right turn phase. Decreasing the deficient yellow clearance interval by one sec was found to reduce the crashes by 84 percent. While decreasing the deficient all-red clearance interval by 0.5 sec was found to reduce crashes by 39 percent. These findings indicate that providing adequate clearance times at signalized ramp terminals can significantly improve their safety performance. Validation of these SPFs for signalized ramp terminals with an expanded dataset is recommended.

Study Citation: Wang, H., Chitturi, M., and Noyce, D., "Developing Safety Performance Functions for Diamond Interchange Ramp Terminals." Presented at the 90th Meeting of the Transportation Research Board, Washington, D.C., (2011).


CMFs Associated With This Study

Category: Interchange design

Countermeasure: Change number of lanes on cross road at diamond interchange ramp from X to Y

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation CRF Equation 3 Stars All All Principal Arterial Other Freeways and Expressways

Countermeasure: Change spacing distance between two ramp terminals at diamond interchange from X to Y feet

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation CRF Equation 3 Stars All All Principal Arterial Other Freeways and Expressways
CMF Equation CRF Equation 3 Stars Rear end All Principal Arterial Other Freeways and Expressways
CMF Equation CRF Equation 3 Stars Angle All Principal Arterial Other Freeways and Expressways

Countermeasure: Divided vs. undivided cross road at diamond interchange ramps

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.53 47.2 3 Stars All All Principal Arterial Other Freeways and Expressways

Category:Intersection geometry

Countermeasure: Presence of exclusive right turn phase at diamond interchange ramps

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.27 73.3 3 Stars All All Principal Arterial Other Freeways and Expressways
0.37 62.6 3 Stars Rear end All Principal Arterial Other Freeways and Expressways
0.13 87.5 3 Stars Angle All Principal Arterial Other Freeways and Expressways

Category:Intersection traffic control

Countermeasure: Change difference between actual and ITE-recommended red clearance interval from X to Y seconds at diamond interchange ramps

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation CRF Equation 3 Stars All All Principal Arterial Other Freeways and Expressways
CMF Equation CRF Equation 3 Stars Rear end All Principal Arterial Other Freeways and Expressways
CMF Equation CRF Equation 3 Stars Angle All Principal Arterial Other Freeways and Expressways

Countermeasure: Change difference between actual and ITE-recommended yellow change interval from X to Y seconds at diamond interchange ramps

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
CMF Equation CRF Equation 3 Stars All All Principal Arterial Other Freeways and Expressways
CMF Equation CRF Equation 3 Stars Rear end All Principal Arterial Other Freeways and Expressways
CMF Equation CRF Equation 3 Stars Angle All Principal Arterial Other Freeways and Expressways