Robert Herling, PlannerRobert Herling, PlannerDuluth-Superior Metropolitan Interstate CouncilDuluth-Superior Metropolitan Interstate Council
[email protected]@ardc.org(218)–529-7573(218)–529-7573
A Quantitative Assessment MethodA Quantitative Assessment MethodFor System Safety & EfficiencyFor System Safety & Efficiency
September 18, 2008September 18, 2008
• NOT scientific
• NOT statistically significant
• IS a way to measure relative performance
• IS inexpensive
• IS fair & balanced
The methodology is…The methodology is…
****
Transportation in Duluth-SuperiorTransportation in Duluth-Superior
Goal of Transportation Goal of Transportation Systems Management (TSM):Systems Management (TSM):
Improved safety & efficiency through low-cost, Improved safety & efficiency through low-cost, high-benefit solutionshigh-benefit solutions
• perform a system-wide assessmentperform a system-wide assessment
• prioritize locations by needsprioritize locations by needs
• provide a method of monitoringprovide a method of monitoring
MIC Project ObjectivesMIC Project Objectives
• 3 crashes per year
• Reduced crash rate
• High severity rate
• 3 Crashes per year
• Moderate crash rate
• Low severity rate
YEAR 1YEAR 1
• 6 Crashes per year
• High crash rate
• High severity rate
Strategy: identify, quantify, and monitor…
YEAR 3YEAR 3 YEAR 5YEAR 5
• running a system-wide analysis with any frequency
• balancing safety and efficiency needs
• balancing spot locations and road segments
• comparing needs between two states
Challenges:
Solutions:• thresholds to limit number of locations analyzed• address spot locations and road segments separately
• do two separate assessments (MN & WI)
Started with a previous concept:
Adjusted Scale
5 year crash trend
Current crash severity
Level of service
Functional class
1 2 3 4 5 6
0 2 4 6 8 10
A B C D E F
Major/Major
Major/Minor
Major/Collector
Minor/Minor
Minor/Collector
Collector/Collector
• Only analyzed spot locations
• Safety threshold: 3 or more crashes in most recent year
• Mobility threshold: LOS D or poorer
• Did not compare MN results with WI results
Initial attempt in 2005:
First assessment done in 2005:Locations ranked with Locations ranked with weight valuesweight values (LOS given more influence) (LOS given more influence)
For each location, analysis of For each location, analysis of conditions contributing to poor safety conditions contributing to poor safety & capacity& capacity
• Too simplified
• Crash rate not the best measure
• Too much emphasis put on LOS
Problems with 2005 assessment:
Suggested improvements:• Use similar measures for both capacity and safety
• Use same number of measures for both
• Get rid of the weights
• Crash frequency (Quantity)
• Crash severity rate (Severity)
• Average increase in crash rate (Change)
Safety performance measures:
Mobility performance measures:
• AADT per lane mile (Quantity)
• LOS (Severity)
• % change in AADT (Change)
Improved methodology:Improved methodology:
(crashes2002 + 2003 + 2004 + 2005 + 2006) / 4
Average number of crashes per yearAverage number of crashes per year
““Quantity measure” for safety:Quantity measure” for safety:
Number of equivalent property damage crashes per million vehiclesNumber of equivalent property damage crashes per million vehicles
““Severity measure” for safety:Severity measure” for safety:
total crashes xpropertydamagecrashes( x 1) injury
crashes( x 2) fatalitycrashes( x 3)+ +[ ]
total years x 365 days x AADT
0.5
0
1 year
0.5
0
Ch
ang
e i
n R
ate
5 yr Avg.5 yr Avg.
2002 to 2003
State Hwy 194 & Mesaba Ave E 4th St & 6th Ave E
2002 to 2003
[(∆2003 + ∆2004 + ∆2005 + ∆2006) / 4] – ∆2003
Average change in crash rate vs. base year’s change in crash Average change in crash rate vs. base year’s change in crash rate (2002 to 2003)rate (2002 to 2003)
“Change measure” for safety:
-0.5 -0.5
- 0.34
+ 0.20C
han
ge
in
Rat
e
1 year
AADT per lane (factored by traffic control type)AADT per lane (factored by traffic control type)
““Quantity measure” for mobility:Quantity measure” for mobility:
AADT2006 / number of lanes( ) x traffic control device factor
where:
No control (not an intersection) = .01
Roundabout = .02
Signal (protected L-turn for all) = .03
Signal (protected L-turn for some) = .04
Signal (no protected L-turns) = .05
Stop or Yield = .06
1
2
3
4 56
7
8
910
LOS as identified by TP Plus modelLOS as identified by TP Plus model
““Severity measure” for mobility:Severity measure” for mobility:
A, B, C, D, E, F( )
LOS A = 1
LOS B = 2
LOS C = 3
LOS E = 5
LOS F = 6
LOS A = 4where:
% change in AADT from 1% change in AADT from 1stst year to last year (adjusted by func. class) year to last year (adjusted by func. class)
“Change measure” for mobility:
(AADT2006 - AADT2002) / AADT2002][ (FC1 + FC2 +… FCn) / 100+
where: Major arterial = 5
Minor arterial = 4
Major collector = 3
Major collector = 2
Local road = 1
• Indexing
How can these things be compared?How can these things be compared?
• Composite scoring
Ij = -100(X/R)+100
n C = Σ(Ij)
j - 1
Creates an individual score between 0 - 100Creates an individual score between 0 - 100
Combines all individual scores for a final score Combines all individual scores for a final score between 0 - 600 between 0 - 600
• Indexing Ij = -100(X/R)+100
/-100 x [
worstseverity
rate( ]bestseverity
rate )_+100
worst severity
rate )( _ location’slocation’sSeveritySeverity
raterate
example:
• Composite scoringn
C = Σ(Ij)j - 1
+index value for % changeIn crash rate( )index value
for crashfrequency
( ) index value for severity
rate( ) +
index value for LOS( )index value
for AADTper lane mi( )
index value for % change in
AADT( )+ ++
0
50
100
150
200
250
300
350
E 4th St & 6thAve E
Arrowhead Rd& Kenwood Ave
US Hwy 2 &State Hwy 194
Skylin Pkwy &W 7th St
State Hwy 194& Mesaba Ave
Can prioritize locations by composite Can prioritize locations by composite scorescore
INTERSECTIONSINTERSECTIONS
CO
MPO
SIT
E S
CO
RE
CO
MPO
SIT
E S
CO
RE
Or analyze locations in how they rank by Or analyze locations in how they rank by safety or efficiencysafety or efficiency
0
50
100
150
200
250
300
350
E 4th St & 6thAve E
Arrowhead Rd& Kenwood Ave
US Hwy 2 &State Hwy 194
Skylin Pkwy &W 7th St
State Hwy 194& Mesaba Ave
Safety MeasuresMobility Measures
INTERSECTIONSINTERSECTIONS
CO
MPO
SIT
E S
CO
RE
CO
MPO
SIT
E S
CO
RE
E 4th St - Heading NE
6th Ave E - Heading SW
E 4E 4thth St & 6 St & 6thth Ave E: Mobility Issues Ave E: Mobility Issues
0 50 10025FeetE
4E
4thth S
t S
t
66 thth Ave E
Ave E
LOS DLOS D
LOS CLOS C
¯* Lack of protected L-turns on E 4th St
W 7
th S
t
Skyl
ine
Pkw
y
W 7th St - Heading SW
Skyline Pkwy - Heading NE
Skyline Pkwy & W 7Skyline Pkwy & W 7thth St: Safety Issues St: Safety Issues
¯* Sight distance issues
• NOT scientific
• NOT statistically significant
• IS a way to measure relative performance
• IS inexpensive
• IS fair & balanced
The methodology is…The methodology is…
Questions?Questions?
Robert Herling, Planner: [email protected]
Duluth-Superior Metropolitan Interstate Council (MIC): www.dsmic.org