cmfs in cpms/spfs · 10 1.01 15 1.00 20 0.99 25 0.98 30 0.97 note: cmfs apply to urban/suburban...

CMFs in CPMs/SPFs

Presented by

Frank Gross December 8, 2015

Overview

Part C: Predictive Method

Part D: CMFs

Integrating CMFs (Part D) in the Predictive Method (Part C)

What is the Predictive Method (Part C)?

Quantitative method to estimate safety performance of a site, facility, or network

Predicts crashes for given set of geometric conditions, traffic control, and traffic volumes

Simple SPF

N = AADT * L * 365 * 10-6 * e-.312

Complex SPF

N = exp[-9.34 + 0.60*ln(Maj. ADT) + 0.61*ln(Min. ADT) + 0.13*Driveways + 0.0054*Skew]

Purpose of the Predictive Method (Part C)

Quantify the safety performance of existing or proposed facilities

Compare the safety performance of various design alternatives

Evaluate the economic and safety effectiveness of constructed projects

Justify design exceptions based on safety impacts

What are CMFs (Part D)?

Quantitative method to estimate change

in safety performance associated with

change in site conditions

Source: Highway Safety Manual

Median Width (ft) CMF

10 1.01

15 1.00

20 0.99

25 0.98

30 0.97

Note: CMFs apply to urban/suburban arterials without a median barrier.

Purpose of CMFs (Part D)

Estimate change in crashes as a result of treatment

CMFs in the Predictive Method

SPFs calculate predicted crash frequency

For given traffic volume

For given base conditions

N = AADT * L * 365 * 10-6 * e-.312

CMFs provide adjustments to the predicted crash frequency

Adjust base conditions (adjustment factors)

Adjust for treatments or other features

N = AADT * L * 365 * 10-6 * e-.312 * CMFS.R.S.

Feature Base

Condition

Lane width (LW) 12 feet

Shoulder width (SW) 6 feet

Shoulder type Paved

Roadside hazard rating (RHR) 3

Driveway density (DD) 5 per mile

Horizontal curvature None

Vertical curvature None

Centerline rumble strips None

Passing lanes None

Two-way left-turn lanes None

Lighting None

Automated speed enforcement None

Grade Level 0%

Part C Example

A design engineer wants to calculate the

predicted safety performance of a proposed 1

mile section of rural two-lane road with 6,000

AADT.

For Base Conditions:

N = AADT * L * 365 * 10-6 * e-.312

N = 6000 * 1.0 * 365 * 10-6 * e-.312

N = 1.6 crashes per year

Feature Base

Condition Proposed Condition

Lane width (LW) 12 feet 11 feet

Shoulder width (SW) 6 feet 2 feet

Shoulder type Paved Paved

Roadside hazard rating (RHR) 3 3

Driveway density (DD) 5 per mile 5 per mile

Horizontal curvature None None

Vertical curvature None None

Centerline rumble strips None None

Passing lanes None None

Two-way left-turn lanes None None

Lighting None None

Automated speed enforcement None None

Grade Level 0% 0%

Part C Example

What is the predicted safety performance of a

1 mile rural two-lane road with 6,000 AADT,

11-ft lanes, and 2-ft paved shoulders?

For Base Conditions:

N = AADT * L * 365 * 10-6 * e-.312

N = 1.6 crashes per year

With Part C Adjustment Factors:

N = 1.6 * CMFL.W. * CMFS.W.

N = 1.6 * 1.05 * 1.30

N = 2.2 crashes per year

Lane

Width

Average Annual Daily Traffic (veh/day)

< 400 400 to 2,000 > 2,000

11 feet 1.01 1.01 + 2.5 x 10-5 x (AADT – 400) 1.05

≥12 feet 1.00 1.00 1.00

Shoulder

Width

Average Annual Daily Traffic (veh/day)

< 400 400 to 2,000 > 2,000

2 feet 1.07 1.07 + 1.43 x 10-4 x (AADT – 400) 1.30

6 feet 1.00 1.00 1.00

Part D – Countermeasure Example

A traffic signal is proposed at a rural, two-way, stop-

controlled intersection.

Crashes with treatment

= CMF * crashes without treatment

= 0.56 * 5.0 = 2.8 crashes per year (with treatment)

Crash reduction

= Crashes without – Crashes with

= 5.0 – 2.8 = 2.2 crashes per year

Input Value

10-yr total crashes 50

Crashes per year (without treatment)

5.0

CMF (total crashes) 0.56

**Note: ‘crashes without treatment’

can be estimated using observed

crash history or predictive methods

Integrating Part D into Predictive Method

A design engineer wants to estimate the safety effect of shoulder rumble strips on a 1 mile section of rural two-lane road with 6,000 AADT.

For Base Conditions:

N = AADT * L * 365 * 10-6 * e-.312

N = 1.6 crashes per year

With Part C Adjustment Factors:

N = 1.6 * CMFL.W. * CMFS.W.

N = 1.6 * 1.05 * 1.30

N = 2.2 crashes per year

Feature Base

Condition Proposed Condition

Lane width (LW) 12 feet 11 feet

Shoulder width (SW) 6 feet 2 feet

Shoulder type Paved Paved

Roadside hazard rating (RHR) 3 3

Driveway density (DD) 5 per mile 5 per mile

Horizontal curvature None None

Vertical curvature None None

Centerline rumble strips None None

Passing lanes None None

Two-way left-turn lanes None None

Lighting None None

Automated speed enforcement None None

Grade Level 0% 0%

Integrating Part D into Predictive Method

A design engineer wants to estimate the safety effect of shoulder rumble strips on a 1

mile section of rural two-lane road with 6,000 AADT.

CMFs for Installing Shoulder Rumble Strips

CMF Crash Type

Crash Severity

Area Type

Number of Lanes

State Minimum

Traffic Volume Maximum

Traffic Volume

1.06 All All Rural 2 MN,MO,PA 782 10386

1.14 All All Rural 2 MN 782 10386

1.4 All All Rural 2 MO 861 6205

0.76 All All Rural 2 PA 948 9067

Source: CMF Clearinghouse

Integrating Part D into Predictive Method

A design engineer wants to estimate the safety effect of shoulder rumble strips on a 1 mile section of rural two-lane road with 6,000 AADT.

For Base Conditions:

N = AADT * L * 365 * 10-6 * e-.312

N = 1.6 crashes per year

With Part C Adjustment Factors:

N = 1.6 * CMFL.W. * CMFS.W.

N = 1.6 * 1.05 * 1.30

N = 2.2 crashes per year

With Part C Adjustment Factors and CMF from CMF Clearinghouse:

N = 2.2 * CMFS.R.S. N = 2.2 * 0.76

N = 1.7 crashes per year

Wrap-Up

Do Don’t

Apply Part C adjustment factors to applicable SPFs

Apply Part C adjustment factors to other SPFs

Apply Part D CMFs to applicable scenarios

Apply Part D CMFs to inapplicable scenarios

Frank Gross | fgross@vhb.com | 919.334.5602

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Offices located throughout the east coast