Creating a Critical Crash Rate Creating a Critical Crash Rate Report Using Existing Tools and Report Using Existing Tools and

Available InformationAvailable Information

Heath Hoftiezer, P.E., P.T.O.EHeath Hoftiezer, P.E., P.T.O.ECivil Engineer/ P.E. (Traffic)Civil Engineer/ P.E. (Traffic)

City of Sioux FallsCity of Sioux Falls

2/19/082/19/08

WHY ?WHY ?

Statistical TheoryStatistical Theory

Average Crash RateAverage Crash RateOutliersOutliers

Calculating Crash RatesCalculating Crash RatesIntersection RatesIntersection Rates

Rate per Million Entering Vehicles =Rate per Million Entering Vehicles =(number of crashes) * (1 million)(number of crashes) * (1 million)

(number of years) * (ADT) * (365)(number of years) * (ADT) * (365)

Segment RatesSegment Rates

Rate per Million Vehicle Miles =Rate per Million Vehicle Miles =(number of crashes) * (1 million)(number of crashes) * (1 million)

(segment length) * (number of years) * (ADT) * (365)(segment length) * (number of years) * (ADT) * (365)

To calculate an average crash rate use the total number of all crashes for the To calculate an average crash rate use the total number of all crashes for the intersections or segments that the average is desired for along with the total intersections or segments that the average is desired for along with the total ADT of all intersections or segments and if applicable the total of all segment ADT of all intersections or segments and if applicable the total of all segment

lengthslengths

Calculating Critical Crash RatesCalculating Critical Crash Rates

RRcc = R = Raa + k * ( ) + k * ( )22 - - RRaa

mm mm0.5 0.5

RRcc = Critical Crash Rate = Critical Crash Rate

RRaa = Average Crash Rate = Average Crash Rate

m = Vehicle Exposure During Study Periodm = Vehicle Exposure During Study Period(ADT) * ( )(ADT) * ( )

365365

10000001000000, For intersections, For intersections

(ADT) * ( ) * length(ADT) * ( ) * length365365

10000001000000, For segments, For segments

k = Constant based on Level of Confidencek = Constant based on Level of Confidence

k and the Level of Confidencek and the Level of Confidence

Level of Confidence Level of Confidence

0.9950.9950.9500.9500.9000.900

k k

2.5762.5761.6451.6451.2821.282

Intersection CategoriesIntersection Categories

Type of ControlType of Control

Volume of TrafficVolume of Traffic

Intersection GeometryIntersection Geometry

Category ISignalized IntersectionsSignalized IntersectionsBoth roads have an ADT of over 10,000Both roads have an ADT of over 10,000

Category IISignalized IntersectionsSignalized Intersections

One road has an ADT of over 10,000One road has an ADT of over 10,000

Category IIISignalized IntersectionsSignalized IntersectionsBoth roads have an ADT of under 10,000Both roads have an ADT of under 10,000

Categories Currently Used in Sioux Falls

Category VUn-signalized IntersectionsUn-signalized IntersectionsOne road has an ADT of over 4,000One road has an ADT of over 4,000

Category VIUn-signalized IntersectionsUn-signalized Intersections

One road has an ADT of over 1,000One road has an ADT of over 1,000

Category VIIUn-signalized IntersectionsUn-signalized IntersectionsBoth roads have an ADT of under 1,000Both roads have an ADT of under 1,000

Category IVUn-signalized IntersectionsUn-signalized Intersections

Both roads have an ADT of over 4,000Both roads have an ADT of over 4,000

Existing Tools UsedExisting Tools Used

Microsoft AccessMicrosoft AccessMicrosoft ExcelMicrosoft Excel

InternetInternet

Gathering Needed Information Gathering Needed Information from the Internetfrom the Internet

ftp://ftp.state.sd.us/DPS/data_sharing/ftp://ftp.state.sd.us/DPS/data_sharing/

IntersectionsState.mdbIntersectionsState.mdb

DPS_accident_sharing.mdbDPS_accident_sharing.mdb

DPS_accident_sharing_ab.mdbDPS_accident_sharing_ab.mdb