Question

5-8 A local jurisdiction has determined that for a given set of geometric conditions, a maxi- mum rate of 8 crashes/million entering vehicles can be tolerated. At an intersection of two roadways with ADTs of 10,000 and 7500, how many crashes can occur before cor- rective action must be sought? 5-10 A 5.4-mile segment of highway has the following traffic and safety data: 2005 2006 2007 17,400 15,200 16,300 Annual average daily traffic (AADT) Number of fatal crashes Number of crashes 29 Determine the fatal crash and total crash rates (per 100 million VMT) for each year and for the entire three-year period. Comment on and qualify the results as necessary. Highway Crash Rate Problem A stretch of highway is 18 miles long. Over a period of 12 years, the ADT has been 1500 vehicles. During that same period, there have been 7 fatal accidents, 16 nonfatal personal injury accidents, and 23 property damage only accidents. What is the accident rate per 100 million vehicle miles (RMVM)?

Answer 1

5-8

Considering the maximum rate of 8 crashes/million entering vehicles

Here, the number of vehicles entering the intersection is 10000 + 7500 = 17500

$\therefore$ Considering the maximum crashes it will take before action has to be taken in a week

1 million - 8 crashes

17500 - 0.14 crashes - ((8*17500)/1000000) (Daily)

Now, 1/0.14 = 7.14 ( Approximately a week)

Which means 1 crash per week in the given intersection is what it takes before corrective action has to be taken.

5-10

The crash rate on a roadway is calculated as -

R = (C × 100000000)/(V × 365 × N × L)

Where,

• R = Roadway Departure crash rate for the road segment expressed as crashes per 100 million vehicle-miles of travel,
• C = Total number of roadway departure crashes in the study period
• V = Traffic volumes using Average Annual Daily Traffic (AADT) volumes
• N = Number of years of data
• L = Length of the roadway segment in miles

Therefore now using the above equation -

1) For year 2005

Fatal Crash Rate = (3×100000000)/(15200×365×1×5.4) = 10 per 100 million VMT

Total Crash Rate = (29×100000000)/(15200×365×1×5.4) = 97 per 100 million VMT

2) For year 2006 -

Fatal Crash Rate = (2×100000000)/(16300×365×1×5.4) = 6 per 100 million VMT

Total Crash Rate = (31×100000000)/(16300×365×1×5.4) = 96 per 100 million VMT

3) For year 2007 -

Fatal Crash Rate = (3×100000000)/(17400×365×1×5.4) = 9 per 100 million VMT

Total Crash Rate = (27×100000000)/(17400×365×1×5.4) = 79 per 100 million VMT

Now for entire three year period -

Fatal Crash Rate = (8×100000000)/(48900×365×1×5.4) = 8 per 100 million VMT

Total Crash Rate = (87×100000000)/(48900×365×1×5.4) = 90 per 100 million VMT

Highway Crash Rate Problem:

Again the crash rate is calculated using the formula from above, i.e

R = (C × 100000000)/(V × 365 × N × L)

Here,

C = 7 + 16 + 23 = 46

V = 1500

N = 12

L = 18

Now, R = (46 × 100000000)/(1500×365×12×18) = 39

$\therefore$  Accident Rate is 39 per 100 million VMT