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...
TRANSCRIPT
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 | [email protected] | 919.334.5602
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