Studies were conducted at two sites on rural roads with similar characteristics. The first site was 5.1 miles in length with an ADT of 6700. Over the year-long study period, 28 crashes occurred on this portion of roadway, five of them resulting in fatalities. The second site was a 11.2-mile section with an ADT of 5300. There were 32 crashes in this section with four crashes resulting in fatalities. Determine the total crash rate (all types of crashes) and the fatal crash rates for both locations, and discuss the implications.
What will be an ideal response?
Site 1 – Use Equation 5.27
RMVMT = A(100,000,000) / (ADT)(365 days)(length of road section)
RMVMT = (28)(100,000,000) / (6700)(365)(5.1)
RMVMT = 224.5
RMVMF = RMVMT (# of fatal / # of total)
RMVMF = 224.5(5/28)
RMVMF = 40.1
Site 2 – Use Equation 5.27
RMVMT = A(100,000,000) / (ADT)(365 days)(length of road section)
RMVMT = (32)(100,000,000) / (5300)(365)(11.2)
RMVMT = 147.7
RMVMF = RMVMT(# of fatal / # of total)
RMVMF = (147.7)(4/32)
RMVMF = 18.5
Although site 2 experiences more crashes, with a lower ADT, over the one
year period, the crash rate for that site is lower than for site 1. This is due to the
fact that the roadway section is more than twice longer for site 2, increasing the
total vehicle miles traveled and thereby reducing the rate per 100 million vehicle
miles traveled. Site 1 can be considered less safe than site 2 based on both crash
rate and fatality rate.
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