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Creating a Critical Crash Rate Report Using Existing Tools and Available Information. 2/19/08. Heath Hoftiezer, P.E., P.T.O.E Civil Engineer/ P.E. (Traffic) City of Sioux Falls. WHY ?. Outliers. Average Crash Rate. Statistical Theory. Calculating Crash Rates. Intersection Rates.

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Creating a critical crash rate report using existing tools and available information

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

2/19/08

Heath Hoftiezer, P.E., P.T.O.E

Civil Engineer/ P.E. (Traffic)

City of Sioux Falls


WHY ? and Available Information


Outliers and Available Information

Average Crash Rate

Statistical Theory


Calculating Crash Rates and Available Information

Intersection Rates

(number of crashes) * (1 million)

Rate per Million Entering Vehicles =

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

Segment Rates

(number of crashes) * (1 million)

Rate per Million Vehicle Miles =

(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


R and Available Informationa

0.5

Rc = Ra + k * ( )2 -

m

m

365

365

(ADT) * ( )

, For intersections

(ADT) * ( ) * length

, For segments

1000000

1000000

Calculating Critical Crash Rates

Rc = Critical Crash Rate

Ra = Average Crash Rate

m = Vehicle Exposure During Study Period

k = Constant based on Level of Confidence


k and the Level of Confidence and Available Information

Level of Confidence 0.9950.9500.900

k 2.5761.6451.282


Intersection Categories and Available Information

Type of Control

Volume of Traffic

Intersection Geometry


Categories Currently Used in Sioux Falls and Available Information

  • Signalized Intersections

  • Both roads have an ADT of over 10,000

Category I

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


Category IV and Available Information

Un-signalized Intersections

Both roads have an ADT of over 4,000

  • Un-signalized Intersections

  • One road has an ADT of over 4,000

Category V

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


Existing Tools Used and Available Information

Microsoft Access

Microsoft Excel

Internet


Gathering Needed Information from the Internet and Available Information

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

IntersectionsState.mdb

DPS_accident_sharing.mdb

DPS_accident_sharing_ab.mdb


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