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Low Cost Solutions. TRAFFIC SAFETY SYSTEMS MANAGEMENT SECTION -. Brian Murphy, PE North Carolina DOT - Traffic Engineering Branch. Missouri Traffic & Safety Conference May 17, 2006. Mendocino Themes. Treat Sites as a System - Not a Spot Start Simple

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Low cost solutions

Low Cost Solutions

TRAFFIC SAFETY SYSTEMS MANAGEMENT SECTION -

Brian Murphy, PE

North Carolina DOT - Traffic Engineering Branch

Missouri Traffic & Safety Conference

May 17, 2006


Mendocino themes

Mendocino Themes

  • Treat Sites as a System - Not a Spot

  • Start Simple

  • Evaluate the Effectiveness of Countermeasures


Corridor reviews

Corridor Reviews


Corridor reviews1

Corridor Reviews

  • Road Safety Audits

    • The N.C. Board of Transportation passed a resolution for the development of a program to reduce crashes, fatalities, and injuries on two-lane highway facilities with higher than average crash rates

    • Traffic Safety Unit identifies sections and takes lead role in investigation

    • Multidisciplinary team

      • Law Enforcement

      • Traffic Engineers from other districts

      • FHWA

      • Roadway Design Engineer

      • Locals (e.g. GHSP Safe Community Representative)


Corridor reviews2

Corridor Reviews

US 601 From US 74 to the South Carolina State Line

Regional Perspective

Overall Crash Rate 35% lower than Statewide Average.

Fatal Crash Rate 60% higher than Statewide Average.


Corridor reviews3

Corridor Reviews


Corridor reviews4

Corridor Reviews

  • General Findings

    • Very Straight Road

    • Rolling Terrain

    • Poor Intersection Visibility

    • Poor Driveway Visibility

    • Redundant Low Volume Intersections

    • Poor Intersection Alignment

    • Unforgiving Roadside

    • Narrow Right-Of-Way


Corridor reviews5

Corridor Reviews

  • Recommendations

    • 18 General Recommendations for the Corridor

    • 23 Recommendations at Specific Intersections or Driveways

    • 7 Recommendations for Specific Segments

  • Example Recommendations

    • Install arrow board signs at all "T" type intersections

    • Clear sight triangles at 5 intersections

    • Install stop bars at all intersections on US 601

    • Install continuous shoulder rumble strip on one section


Evaluation

Evaluation


Evaluation1

Evaluation

  • Why Evaluate?

    • Need to know if countermeasures we implement actually work

      • Typical way this is measured: “If phone stops ringing, treatment worked”

    • Need good safety data to make informed decisions

      • Spend limited taxpayer money wisely

  • Safety Evaluation Group

    • Evaluated 130+ projects last year

      • http://www.ncdot.org/doh/preconstruct/traffic/Safety/ses/projects/completed.html

    • Evaluate low cost countermeasures, work zone issues, enforcement programs, safety systems (e.g. median barrier)

    • Develop crash reduction factors based on NC data


Example spot safety evaluation

Example Spot Safety Evaluation

  • Location:

    • NC 210 at SR 1309 (Old Fairground Rd) in Johnston County

  • Countermeasure:

    • Installation of a Flashing Traffic Signal

    • Cost: $15,000

Treatment Intersection


Flasher evaluation

Flasher Evaluation

Intended Results:

Better Identify Traffic Control

Treatment:

Flashing Traffic Signal

  • Determine Treatment and Intended Results


Flasher evaluation1

Flasher Evaluation

  • Determine Measures of Effectiveness

    • Total Crashes

    • Frontal Impact Crashes (Target Crashes)

      • Left turn same roadway, left turn different roadway, right turn same roadway, right turn different roadway, head on, and angle

      • Specifically looking for crashes where vehicles ran Stop Sign control on SR 1309 (Old Fairground Rd)


Flasher evaluation2

Flasher Evaluation

  • Set up Evaluation Study

    • Determine Analysis Dates

      • Project Completion Date: 4/25/1997

      • Before Period: 12/1/1990 - 2/28/1997(6 Years, 3 Months)

      • After Period: 7/1/1997 - 9/30/2003(6 Years, 3 Months)

    • Pick Comparison Sites

      • Criteria:

        • Similar characteristics to Treatment Location (geometry, volume, etc.)

        • Located near Treatment Location (weather, jurisdiction)

        • Not affected by Treatment being evaluated

      • Compare crash trends of Comparison Location to the Treatment Location. If trends are not similar, choose different Comparison Locations.


Flasher evaluation3

Flasher Evaluation

Comparison Locations

Comparison Intersections

Treatment Intersection


Flasher evaluation4

Flasher Evaluation

Looking East on NC 210

Looking North on SR 1309

Looking West on NC 210

Looking South on SR 1309


Flasher evaluation5

Flasher Evaluation

Before Collision Diagram


Flasher evaluation6

Flasher Evaluation

After Collision Diagram


Flasher evaluation7

Flasher Evaluation

  • ADT increased over 50 %

  • In After Period

    • Approximately 90% of all crashes occurred during AM and PM peak periods

    • Appears increasing commuter traffic creates problem for motorists crossing NC 210

    • Vehicles not stopping at STOP sign

      • Before: 5 out of 14 crashes

      • After: 2 out of 19 crashes

      • Therefore, 17 of 19 Frontal Impact Crashes in the After Period were caused by another factor

Results


Flasher evaluation8

Flasher Evaluation

  • Results / Discussion (cntd)

    • The prevalent crash problem does not appear to have been caused by a lack of recognizing the Stop Sign control condition (as was stated in the Project Justification sheet)

    • Problem seems to be more gap selection

    • Access points located close to intersection

      • Sight distance problems

      • Problems with vehicles turning into driveway

        Proper problem identification is key!


Roundabout evaluation

Roundabout Evaluation

  • Location:

    • NC 751 at SR 1307 (Old Erwin Rd) in Durham County

  • Countermeasure:

    • Convert Four Leg Stop

      Control Intersection to a

      Roundabout

    • Cost: $265,000

Treatment Intersection


Roundabout evaluation1

Roundabout Evaluation


Roundabout evaluation2

Roundabout Evaluation

Before Collision Diagram


Roundabout evaluation3

Roundabout Evaluation

After Collision Diagram


Roundabout evaluation4

Roundabout Evaluation

Results


4 way stop evaluation

4-Way Stop Evaluation

  • Location:

    • SR 1001 (Shannon Rd) at SR 1505 (Old Lowery Rd) in Robeson County

  • Countermeasure:

    • Convert Four Leg 2- WayStop Control Intersection to

      4-Way Stop Control

Treatment Intersection


4 way stop evaluation1

4-Way Stop Evaluation

Before Collision Diagram


4 way stop evaluation2

4-Way Stop Evaluation

After Collision Diagram


4 way stop evaluation3

4-Way Stop Evaluation

  • Total Crashes

    • Reduced 92 - 95 %

  • Target Crashes

    • Reduced 91 - 95 %

Results


Crash modification factors

Crash Modification Factors

  • Goal:

    • Develop crash modification factors based on North Carolina crash data

      • Reflects roadway / driver / weather / reportability conditions in North Carolina

      • Reflects decisions that Traffic Engineers North Carolina are making


Crash modification factors1

Crash Modification Factors

  • Overhead Flashers

    • Site Criteria

      • Rural

      • Intersection of two two-lane roads

      • No turn lanes

      • STOP sign control

      • At least three years of ‘after’ period crash data available

    • Resulted in 34 Treatment Sites


Crash modification factors2

Crash Modification Factors

D

R

A

F

T

D

R

A

F

T

  • Crash Modification Factor - Overhead Flashers

PRELIMINARY NUMBERS

  • Safety Performance Function (Minnesota / HSM)

  • N = Ci e (-9.34 +0.60 ln (ADT1) + 0.61 ln (ADT2))

  • Where:

  • ADT1 = Average Daily Volume on Major Road

  • ADT2 = Average Daily Volume on Minor Road

  • Ci = Calibration Factor Based on Local Crash Data = 1.92 NC

    • Emperical Bayes / Reference Sites

      • Used same criteria as treatment sites

      • 170 sites chosen


  • Contact information

    Contact Information

    Brian Murphy, PE

    (919) 733-3915

    [email protected]

    Traffic Safety Unit Website:

    http://www.ncdot.org/doh/preconstruct/traffic/TSU/default.html


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