Are They Sick? Evaluating Corridors from a Safety Health Perspective Bill Loudon and Bob Schulte,...

Are They Sick? Evaluating Corridors from a Safety Health

Perspective

Are They Sick? Evaluating Corridors from a Safety Health

Perspective

Bill Loudon and Bob Schulte, DKS Associates

Bill Loudon and Bob Schulte, DKS Associates

Prepared by

IDAHO TRANSPORTATION DEPARTMENT

Prepared by

IDAHO TRANSPORTATION DEPARTMENT

1April 3, 2013

Highway Safety Corridor Analysis Project

Presentation OutlinePresentation Outline

1. Study Overview

2. Network Screening Method

3. Diagnosis of Safety Problems

4. Identification of Countermeasures

5. Evaluation of Potential Countermeasures

6. Summary of Benefits

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1. Overview of Study1. Overview of Study

3

Study BackgroundStudy Background

Origins of Study

District 6 Corridor Health Assessment

District 6 Safety Needs Pilot Study

Statewide Application with District Orientation

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Corridor Health AssessmentCorridor Health Assessment

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Corridor Health ScoringCorridor Health ScoringFactor Weight Factor Score

Safety 40% .35*(% of State VMT for Category with Fatal Accident Rate greater than or equal to the Segment) + .35*(% of State VMT for Category with Injury Accident Rate greater than or equal to the Segment) + .3*(% of State VMT for Category with Total Accident Rate greater than or equal to the Segment)

Travel Timeand Delay

30% 1/LOS where LOS = .5 * (Link LOS for Average Peak Hour Conditions) + .2 * (Link LOS for Design Hour Volume) + .2 * (Int. LOS for Average Peak Hour Conditions) + .1 * (Int. LOS for Design Hour Volume)Where LOS = 1 for C or better, 2 for D, 3 for E and 5 for F

RideQuality

10% 1/PC where PC= 1 for Good, 2 for Fair, 3 for Poor and 5 for Very Poor Pavement Condition Rating

Points of

Access

10% =1-(Number of Access Points per mile) / (Number Allowed by Guidance for the Roadway Type)

Shoulder

Width

10% Average of Width/Guidance Standard up to 1

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What is the Highway Safety Manual?

•PurposeProvide analytical tools and techniques for quantifying the safety effects of decisions

made in planning, design, operations, and maintenance

•ObjectiveReduce the number and severity of

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

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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

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Significant Study OutcomesSignificant 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

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2. Network Screening Method2. Network Screening Method

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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 RatingSafety 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.

Priority Segments

Based Safety Health Score

Priority Segments

Based Safety Health Score

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ITD Corridors of Significance

Classifications

Investment Corridor Analysis Planning

System (ICAPS)

ITD Corridors of Significance

Classifications

Investment Corridor Analysis Planning

System (ICAPS)

Sample of Priority

Segments

All Routes

Sample of Priority

Segments

All Routes

Sample of Priority

Segments

Interstate and

StatewidePriority

Sample of Priority

Segments

Interstate and

StatewidePriority

Sample Priority Safety

Segment Information

Sample Priority Safety

Segment Information

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Second Stage Screening –

Priority Safety Improvement

Locations

Second Stage Screening –

Priority Safety Improvement

Locations

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

Selection of Safety Improvement Locations

Selection of Safety Improvement Locations

Picking the Highest Priority Locations for Analysis

Picking the Highest Priority Locations for Analysis

DistrictPriority Improvement Areas

District RegionalStatewid

e Interstate Total

1 1 7 6 7 21

2 0 7 7 0 14

3 0 7 13 2 22

4 1 5 7 6 19

5 0 8 0 5 13

6 3 4 6 9 22

Total 5 38 39 29 111

3. Diagnosis of Safety Problems3. Diagnosis of Safety Problems

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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

Crash Diagnosis (Crash Causality)

Crash Diagnosis (Crash Causality)

Example Safety Improvement LocationUS 95 @ MP 388.1 to MP 388.4 – District 1

Example Safety Improvement LocationUS 95 @ MP 388.1 to MP 388.4 – District 1

Site CharacteristicsSite 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 CharacteristicsCrash 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 EnvironmentRoadway Environment

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

Roadway EnvironmentRoadway Environment 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

2 ft. shoulder

Roadway EnvironmentRoadway Environment No left-turn lane at intersection

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

Roadway EnvironmentRoadway 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 FactorsHuman 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.

DiagnosisDiagnosis

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

DiagnosisDiagnosis

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

4. Identification of Countermeasures4. Identification of Countermeasures

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Identify Crash CountermeasuresIdentify Crash Countermeasures

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)


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



Place wide edge line markings through curve

Install continuous shoulder rumble strips

Install changeable speed warning signs



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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

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Monetary Impact of CrashesMonetary Impact of Crashes

Fatalities $6,053,567 Serious Injuries $301,473 Visible Injuries $84,441 Possible Injuries $55,972 Property Damage Only $6,480

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Sample Cost RateSample 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)

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Sample Cost RateSample 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

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Range of B/C RatiosRange of B/C Ratios Countermeasure Range Average

High B/C Protected Left-turn Signal 109.03 to 6713.27 3411.15

Dynamic Speed Warning 29.41 to 1226.96 628.19

Left-turn Lanes 10.86 to 167.29 83.49

Chevron signs for Curves 37.25 to 37.25 37.25

Right-turn Lanes 12.19 to 34.31 23.25

Consolidate Driveways 6.74 to 6.74 6.74

Roundabout 0.45 to 28.13 14.29

Widen Shoulders 0.27 to 28.14 6.11

Modify Curve 0.26 to 10.57 3.06

Convert to two 'T' Intersections 0.33 to 2.86 1.56

Add a passing lane 0.34 to 3.30 1.50

Reduce Skew Angle 0.11 to 4.32 1.27

Increase Median 0.94 to 0.94 0.94

Reduce Speed Limit 0.01 to 1.86 0.94

Low B/C Winter Maintenance 0.04 to 0.14 0.10

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Sample Countermeasure Information

Sample Countermeasure Information

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Remaining HSCA StepsRemaining HSCA Steps

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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

5. Summary of Benefits5. Summary of Benefits

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HSCA Benefits for DistrictsHSCA 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

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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

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HSCA Benefits AgencywideHSCA 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

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Are They Sick? Evaluating Corridors from a Safety Health Perspective Bill Loudon and Bob Schulte,...

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