Introduction to TEAAS for Conducting Crash Analysis

Report
Low Cost
Solutions
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
• Evaluate the Effectiveness of Countermeasures
Corridor Reviews
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 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 Reviews
Crash Patterns of Reported Crashes on US 601
from the South Carolina State Line to US 74
Other
6%
Sideswipe
6%
Frontal Impact
20%
Animal
12%
Rear End
28%
Run-Off-Road
28%
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 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
• 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
• 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
• Determine Treatment and Intended Results
Treatment:
Intended Results:
Flashing Traffic Signal
Better Identify Traffic Control
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 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 Evaluation
Comparison Locations
Comparison
Intersections
Treatment
Intersection
Flasher Evaluation
Looking East on NC 210
Looking North on SR 1309
Looking West on NC 210
Looking South on SR 1309
Flasher Evaluation
Before Collision Diagram
Flasher Evaluation
After Collision Diagram
Flasher Evaluation
Results
•
•
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
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
• 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 Evaluation
Roundabout Evaluation
Before Collision Diagram
Roundabout Evaluation
After Collision Diagram
Roundabout Evaluation
Results
4-Way Stop Evaluation
• Location:
– SR 1001 (Shannon Rd) at SR 1505 (Old Lowery Rd) in Robeson
County
• Countermeasure:
– Convert Four Leg 2- Way Stop Control Intersection to
4-Way Stop Control
Treatment
Intersection
4-Way Stop Evaluation
Before Collision Diagram
4-Way Stop Evaluation
After Collision Diagram
4-Way Stop Evaluation
Results
•
Total Crashes
– Reduced 92 - 95 %
•
Target Crashes
– Reduced 91 - 95 %
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 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 Factors
• Crash Modification Factor - Overhead Flashers
D
R
A
F
T
D
R
A
F
T
• 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
Brian Murphy, PE
(919) 733-3915
[email protected]
Traffic Safety Unit Website:
http://www.ncdot.org/doh/preconstruct/traffic/TSU/default.html

similar documents