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Are They Sick? Evaluating Corridors from a Safety Health Perspective . Highway Safety Corridor Analysis Project . Bill Loudon and Bob Schulte, DKS Associates. Prepared by IDAHO TRANSPORTATION DEPARTMENT. April 3, 2013. Presentation Outline. Study Overview Network Screening Method

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are they sick evaluating corridors from a safety health perspective

Are They Sick? Evaluating Corridors from a Safety Health Perspective

Highway Safety Corridor Analysis Project

Bill Loudon and Bob Schulte, DKS Associates

Prepared by


April 3, 2013

presentation outline
Presentation Outline

Study Overview

Network Screening Method

Diagnosis of Safety Problems

Identification of Countermeasures

Evaluation of Potential Countermeasures

Summary of Benefits

study background
Study Background
  • Origins of Study
    • District 6 Corridor Health Assessment
    • District 6 Safety Needs Pilot Study
  • Statewide Application with District Orientation

What is the Highway Safety Manual?


Provide analytical tools and techniques for quantifying the safety effects of decisions made in planning, design, operations, and maintenance


Reduce the number and severity of crashes within the limits of available resources, science, technology, and legislatively mandated priorities

highway safety corridor analysis hsca project objectives
Highway Safety Corridor Analysis (HSCA) Project Objectives

Introduce use of a data-driven analytical process:

Identify the highest-priority locations for safety improvements

Identify improvement options for reducing crashes and crash severity

Evaluate and prioritize improvement options

Implement projects to construct the high-priority improvements

Evaluate the improvements

significant study outcomes
Significant Study Outcomes
  • Application of:
    • A District-wide and State-wide Safety Analysis Methodology
    • The Highway Safety Manual
  • Advanced use of GIS data to support planning and project prioritization
  • Advanced use of ITD Digital Video Logs
  • Advanced use of web-based tools – Google Earth
  • Gap Analysis of the Process
first stage screening priority safety segments
First Stage Screening - Priority Safety Segments

Safety Health Score =

.35*(% of State VMT for Category with Fatal Crash Rate greater than or equal to the Segment) +

.35*(% of State VMT for Category with Injury Crash Rate greater than or equal to the Segment) +

.3*(% of State VMT for Category with Total Crash Rate greater than or equal to the Segment)

safety priority rating
Safety Priority Rating

High– Safety score worse than or equal to 70% of the other segments of the same “Corridors of Importance” category.

Medium– Safety score better than 30% of the other segments but worse than 30%.

Low – Safety score better than or equal to 70% of the other segments.

itd corridors of significance classifications investment corridor analysis planning system icaps
ITD Corridors of Significance ClassificationsInvestment Corridor Analysis Planning System (ICAPS)
selection criteria for safety improvement locations
Selection Criteria for Safety Improvement Locations

Safety health score

Minimum of three crashes over five-year period

For crash clusters (segments), crash sites should be relatively close and have similar crash causes

steps in determining crash causality
Steps in Determining Crash Causality

Examine safety records

Identify physical features of roadway

Identify traffic operating characteristics

Consider information from Human Factors Guidelines

site characteristics
Site Characteristics

Rural setting

45-mph curve in middle of segment

Intersection located at end of 45-mph curve

Highway is relatively straight to north and south of segment

crash characteristics
Crash Characteristics
  • Total of 17 crashes
  • Crashes can classified into three groups:
    • Crashes on 45-mph curve (12 crashes)
    • Crashes at intersection (2 crashes)
    • Crashes on straight sections on either side of curve (3 crashes)
crash characteristics crashes on 45 mph curve
Crash Characteristics (Crashes on 45-mph Curve)

Lack of driver awareness of curve and curve characteristics was a contributing factor in over half of the crashes (i.e., inattention, speed too fast, drove left of center, overcorrection)

Eight out of 12 crashes occurred in ascending direction

In eight out of 12 crashes, vehicle ended up off of roadway (i.e., outside of ROW, in ditch, on embankment, etc.)

crash characteristics crashes at intersection
Crash Characteristics (Crashes at Intersection)

Speed too fast for conditions was contributing factor in both crashes

In both crashes, vehicle ended up off of roadway (i.e., in ditch or embankment)

crash characteristics crashes on straight sections
Crash Characteristics (Crashes on Straight Sections)

No apparent pattern, other than all of the crashes occurred on icy road surface with speed too fast for conditions

roadway environment
Roadway Environment

45-mph curve is at bottom of relatively steep downgrade (-2.6%) in ascending direction

roadway environment1
Roadway Environment

2 ft. shoulder

Curve is signed in advance with combination horizontal alignment/advisory speed signs

Chevrons and post-mounted delineators are located on curve

Intersection warning sign located on curve

Narrow shoulder widths – 2 feet

roadway environment2
Roadway Environment

No left-turn lane at intersection

Narrow approach and lane widths on minor road at intersection – 20 feet

roadway environment3
Roadway Environment

CMF for horizontal curve is 1.48

CMF for narrow shoulder widths is 1.172

Composite CMF for this section is 1.734

traffic operating environment
Traffic Operating Environment

No other locations for several miles to north and south where drivers must slow down – either straight sections or wide radius curves

60 mph speed limit, so many vehicles likely traveling at 65 mph+

human factors
Human Factors

HFG indicates that driver expectations about a curve are an important factor in drivers’ judgments about the curvature and corresponding speeds

Expectations, in turn, are significantly influenced by drivers’ experience with previous curves and tangents

HFG also states that advisory/message signs should not be placed on curves – direct information only should be provided via lane markings, raised markers, etc.


In curve crashes, there was inadequate driver awareness of the curve and curve characteristics

This was likely influenced by the lack similar curves on both sides of this section (previous driver experience)

Misjudgment of speed on curve in ascending direction could also be affected by downgrade prior to curve


Narrow shoulders likely contribute to the high percentage of vehicles ending up to side of the highway

This limits the likelihood of recovery and the driver’s ability to bring the vehicle to a safe stop on the shoulder

Turning crashes may be related to the higher speeds on US 95 combined with the lack of a turn lane and the narrow minor road approach

alternative countermeasures higher cost
Alternative Countermeasures(Higher Cost)

Modify horizontal curve – increase radius and length of curve, add spiral transitions

Widen lanes through curve

Widen shoulders through entire section

Add left-turn lane at intersection

Widen turn radii and lane widths on minor road at intersection

alternative countermeasures lower cost
Alternative Countermeasures(Lower Cost)

Install oversize horizontal alignment warning signs

Install horizontal alignment warning signs with beacons

Place large arrow signs on curve

Install snowplowable, permanent raised pavement markers through curve

Relocate intersection warning sign away from curve

alternative countermeasures lower cost1
Alternative Countermeasures(Lower Cost)

Place wide edge line markings through curve

Install continuous shoulder rumble strips

Install changeable speed warning signs

create a simple benefit cost ratio
Create a Simple Benefit/Cost Ratio

Benefits = Reduced Annual Fatalities * Monetary Value of a Fatality +

Reduced Annual Injuries * Monetary Value of an Injury

Reduced Annual PDO Crashes * Monetary Value of a PDO Crash

Cost = Units of Countermeasure Element * Cost Rate for Element

B/C Ratio = Annual Monetary Value of Crash Reduction/

Annualized Cost of Countermeasure

monetary impact of crashes
Monetary Impact of Crashes

Fatalities $6,053,567

Serious Injuries $301,473

Visible Injuries $84,441

Possible Injuries $55,972

Property Damage Only $6,480

sample cost rate
Sample Cost Rate
  • CMF2r Shoulder Width/Type
    • Length of roadway to modify
    • Additional width of shoulder
    • Shoulder type
      • Unit Cost Rate - $33,333/mile-feet of shoulder width for paved shoulder
      • (Based upon $400,000 a lane mile)
sample cost rate1
Sample Cost Rate
  • CMF3r Horizontal Curves (Length, Radius, Spiral)
    • Desired Length
    • Terrain type
      • Unit Cost Rate - $/Curve (by type of terrain – flat, rolling, mountainous)
      • $50,000/flat curve
      • $100,000/rolling curve
      • $400,000/mountainous curve
remaining hsca steps
Remaining HSCA Steps
  • Complete Identification of improvement options (countermeasures)
  • Evaluate Benefits of Improvement Options using the HSM procedures
  • Estimate B/C Ratios
  • Evaluate Project Priorities
  • Final Assessment of Process
hsca benefits for districts
HSCA Benefits for Districts

Within each district, helps ensure that highest need locations are being addressed

Represents an accepted, defensible and repeatable process

Uses latest techniques for identification of crash causality and countermeasures (HSM and HFG)

Relatively low-cost to apply – all data is already available from existing sources such as TAMS, WebCARS, and video logs

more hsca benefits for districts
More HSCA Benefits for Districts

Information on countermeasures can be used as a first step in the project development process

Analysis files serve as an historical record for safety improvement identification process

Input data forms a rich database that can be used for other purposes within districts

hsca benefits agencywide
HSCA Benefits Agencywide

Places ITD in-line with FHWA directives for data- driven, performance-based safety decision-making processes

Helps ensure best return statewide on scarce safety improvement dollars

Process is consistent with and can be integrated with other statewide initiatives underway such as ICAPS, statewide travel model, TAMS, and IPLAN

Process removes bias from allocation of safety dollars across the state