Crash Rate

R = \frac{A \times 1 0 ^{6}}{V D T} (segment), R = \frac{A \times 1 0 ^{6}}{MEV} (intersection)

Segment: crashes per million vehicle-miles. Intersection: per million entering vehicles. Compare with a critical rate before calling a site ‘high crash’.

$A$: Number of crashes in the period
$V D T$: Vehicle-miles of travel
$M E V$: Million entering vehicles

Step-by-step solved example

12 crashes in 3 years on 2 mi, AADT=8000. Segment R?

Crashes on a segment vs vehicle-miles of exposure.

1. VDT
8000×365×3×2=1.752e7 veh-mi.
2. R
12×1e6 / 1.752e7=0.68 / M VMT.

Answer: R ≈ 0.68 crashes / million VMT

10 practice questions

0/10 correct

1.Intersection rate uses entering volume not

2.AADT×365×years×length =

3.Severity index weights

4.10 crashes, 5 million VMT: R=

5.A critical-rate test accounts for

6.SPF / HSM predict

7.MEV for 4-leg, each AADT 5000, 1 year ≈

8.Night crash overrepresentation suggests

9.AADT=10000, 1 mi, 1 yr, 3 crashes: VMT=

10.10^6 in the formula makes the rate