Robert Herling, PlannerRobert Herling, PlannerDuluth-Superior Metropolitan Interstate CouncilDuluth-Superior Metropolitan Interstate Council

rherling@ardc.orgrherling@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 2006:

First assessment done in 2006: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 2006 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:

5crashes2002 + 2003 + 2004 + 2005 + 2006( ) ÷

Average number of crashes per yearAverage number of crashes per year

““Quantity measure” for safety:Quantity measure” for safety:

propertydamagecrashes

( x 1) injurycrashes( x 2) fatality

crashes( x 3)

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:

x [ + + ]total years x 365 days x intersection AADT

1,000,000vehiclesentering

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

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

– ∆2003∆2003 + ∆2004 + ∆2005 + ∆2006( ) ÷ 4[ ]

AADT per lane (factored by traffic control type)AADT per lane (factored by traffic control type)

““Quantity measure” for mobility:Quantity measure” for mobility:

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

x traffic control device factornumber of lanes( )÷AADT2006

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:

Where FC is: Major arterial = 5

Minor arterial = 4

Major collector = 3

Major collector = 2

Local road = 1

( )FC1 + FC2 +…

FCn+ ( 100) ÷

AADT2006 - AADT2002

AADT2002

• 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

worstseverity

rate( ]best

severityrate )_[ worst

severityrate

)( _ location’slocation’sSeveritySeverity

raterate

• Indexing Ij = -100(X/R)+100

÷-100 x

+100

example:

• Composite scoringn

C = Σ(Ij)j - 1

index value for LOS( )index value

for AADTper lane mi

( ) index value for % change

in AADT( )

index value for % changeIn crash rate

( )index value for crashfrequency

( ) index value for severity

rate( )+ +

+ ++

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

¯* Inadequate sight distances

• 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: rherling@ardc.org

Duluth-Superior Metropolitan Interstate Council (MIC): www.dsmic.org