A historical crash analysis is completed to identify the types of crashes occurring at an interchange. A crash analysis is typically completed for each separate intersection of an interchange. See

Chapter 6

in this manual and Chapter 9 in the HSM for information on the data needed to complete a historical crash analysis, how to calculate an intersection crash rate, and how to create a collision diagram. The HSM tools described in more detail below can also be used to estimate the safety performance of an existing interchange.

The

ISATe

is useful for safety assessment of ramp terminals. It provides information about the relationship between roadway geometric design features and safety. This analysis uses design data, traffic control data, cross section data, and up to five years of crash data. The ISATe tool outputs include expected number of crashes for the study period and CMFs related to different geometric design features. It does not account for safety prediction of a frontage road ramp terminal and for roundabouts, nor SPUI’s.

Appendix L, Section 4

provides a reference to access this safety prediction tool.

The

IHSDM

can also be used to predict crash frequencies at ramp terminal intersections and compare safety effects of different geometric design features. Roundabouts at freeway ramp terminals can also be evaluated. The tool outputs predicted average crash frequencies for total and fatal/injury crashes.

Appendix L, Section 4

provides a reference to access this safety prediction tool.

Additional information related the HSM predictive method, SPFs, CMFs, SPICE, and IHSDM are provided in greater detail in

Chapter 5 and Chapter 6

of this manual and additional references are listed in

Appendix L, Section 4.