Source: NCHRP-A (1999)
The crash frequencies are provided in Table 2. These percentages were found through a statistical study (Einstein Law 2004) of 6,289,000 reported auto crashes, 3,200,000 injuries related to auto crashes, and 41,345 deaths due to auto crashes in 1999:
Table 2. Frequencies of Each Type of Crash
Type of Crash
Proportion
Fatal Accident
0.01
Injury Accident
0.51
Property Damage
0.48
Source: Einstein Law (2004)
Awaiting additional data on the projects, the crash reduction factor is considered uniformly for all projects to lie in the range provided in Table 3. An analyst can change these values in the global variables section of the prototype prioritization software. For each project, a lower, median, and higher value of the benefit-cost ratio as well as the cost-effectiveness ratio is calculated to represent the uncertainty.
Table 3. Crash Reduction Factor
Median Estimate
Lower Estimate
Upper Estimate
0.1
0.05
0.15
Travel Time Savings This section describes a methodology for estimating annual savings in travel time. It is reasonable to assume that, by relieving congestion during peak hours through capacity enhancement, the reduction of vehicle operating time and associated reduction in vehicle operating costs could be significant.
The annual peak vehicle hours for each project location is derived by the following formula:
where
is the proportion of traffic that experiences peak period congestion
for each project location is derived by the following formula:
is the proportion of traffic that experiences peak period congestion