1. Creating a Critical Crash Rate Report Using Existing Tools and Available Information Heath Hoftiezer, P.E., P.T.O.E Civil Engineer/ P.E. (Traffic) City of Sioux Falls 2/19/08

2. WHY ?

3. Statistical Theory Average Crash Rate Outliers

4. Calculating Crash Rates Intersection Rates Rate per Million Entering Vehicles = (number of crashes) * (1 million) (number of years) * (ADT) * (365) Segment Rates Rate per Million Vehicle Miles = (number of crashes) * (1 million) (segment length) * (number of years) * (ADT) * (365) 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 ADT of all intersections or segments and if applicable the total of all segment lengths

5. Calculating Critical Crash Rates R c = R a + k * ( ) 2 - RaRaRaRamm0.5 R c = Critical Crash Rate R a = Average Crash Rate m = Vehicle Exposure During Study Period (ADT) * ( ) 3651000000, For intersections (ADT) * ( ) * length 3651000000, For segments k = Constant based on Level of Confidence

6. k and the Level of Confidence Level of Confidence 0.995 0.950 0.900 k 2.576 1.645 1.282

7. Intersection Categories Type of Control Volume of Traffic Intersection Geometry

8. Category I Signalized Intersections Both roads have an ADT of over 10,000 Category II Signalized Intersections One road has an ADT of over 10,000 Category III Signalized Intersections Both roads have an ADT of under 10,000 Categories Currently Used in Sioux Falls

9. Category V Un-signalized Intersections One road has an ADT of over 4,000 Category VI Un-signalized Intersections One road has an ADT of over 1,000 Category VII Un-signalized Intersections Both roads have an ADT of under 1,000 Category IV Un-signalized Intersections Both roads have an ADT of over 4,000

10. Existing Tools Used Microsoft Access Microsoft Excel Internet

11. Gathering Needed Information from the Internet ftp://ftp.state.sd.us/DPS/data_sharing/ IntersectionsState.mdb DPS_accident_sharing.mdb DPS_accident_sharing_ab.mdb