Does 24+0=22+2? An Intro to HSM Methods

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Does 24+0=22+2? An Intro to HSM Methods. Jason J. Siwula, PE – Safety Engineer. Does 24+0=22+2?. On the surface it appears that 24=24 Sometimes items are not as simple as they seem…. 24 = 24. I see you x!. Placement makes a world of difference!.

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### Does 24+0=22+2?An Intro to HSM Methods

Jason J. Siwula, PE – Safety Engineer

Does 24+0=22+2?
• On the surface it appears that 24=24
• Sometimes items are not as simple as they seem…

24 = 24

Placement makes a world of difference!

Edgeline on edge of pavement with no room for shoulder

Edgeline placed with room for shoulder

Example Case Study

Source: Hillary Isebrands (FHWA Office of Safety)

Example Case Study (continued)
• Q: When resurfaced, can we influence safety on this roadway without utilizing any additional funds to do so?
• A: Yes, with the HSM we can examine different lane/shoulder combinations to determine the best layout of the markings for safety performance.
Example Case Study continued

Existing Conditions

11 ft. lanes, 1 ft. shoulders

What does that mean?

Using the SPF for 2 lane rural highways for a 10 miles segment with 10,000 vpd we would estimate a base number of crashes to be 26.72 crashes per year.

Existing Conditions

11 ft. lanes, 1 ft. shoulders

26.72*1.29=34.47 crashes per year

(344.7 crashes in 10 years)

26.72*1.26=33.66crashes per year

(336.6 crashes in 10 years)

That’s a predicted savings of 8.1 crashes over 10 years!

What is the HSM?
• The Highway Safety Manual (HSM) introduces a science-based technical approach that takes the guesswork out of safety analysis
• Provides tools to conduct quantitative safety analyses, allowing for safety to be evaluated alongside other transportation performance measures

Source: http://www.highwaysafetymanual.org/Documents/HSMP-1.pdf

HSM Part C – Predictive Method
• Introduces Safety Performance Functions (SPFs)
• Predictive method for estimating expected average crash frequency of a:
• Network
• Facility
• Individual Site
HSM in Kentucky?
• Utilize HSIP funds to purchase HSMs for each District as well as the Central Office
• Utilize HSM predictive methods in project evaluation and prioritization for new projects
• KYTC Safety Engineers are evaluating the accompanying software package SafetyAnalyst for possible future implementation
Interested in the HSM?
• http://www.highwaysafetymanual.org
• http://safety.fhwa.dot.gov/hsm/
• http://www.cmfclearinghouse.org