Safety Impacts of Various Crash Countermeasures Safer Roads: A Guide to Road Safety Engineering....

Safety Impacts of Various Crash Countermeasures

Xiaoduan Sun

UL Lafayette

February 19, 2013

2013 Louisiana Transportation Conference

Outline

• Crash Countermeasures

• Converting urban undivided 4-lane roadway to five-lane roadway

• Edgeline on narrow rural 2-lane highways

• Raised pavement markers

Crash Countermeasures

• Eliminating all crash contributing factors

Pre-Event

Event

Post-Event

Human Vehicle Environment

Haddon Matrix- a useful framework for thinking about the complexities of a crash

Based on Interactive Highway Safety Design Model:

by Harry Lum and Jerry A. Reagan

Road

Environment

Factors (28%)

Vehicle

Factors (8%)

Human

Factors (95%)

4%

24% 67%4%

4%

Road

Environment

Factors (28%)

Vehicle

Factors (8%)

Human

Factors (95%)

4%

24% 67%4%

4%4%

24% 67%4%

4%

Keep in mind that everything we do must accommodate humans’ needs and match vehicles' capability

Eliminating crash contributing factors with crash countermeasures

Source: Safer Roads: A Guide to Road Safety Engineering. K.W. Ogden. Ashgate

Crash is not an accident, it is preventable. Crash reduction can not happen by chance

CMF from HSM

Chapter in HSM Part

D Content

# of CMFs Proven to be

effective

# of Crash Countermeasures

with Known Safety Effect

# of Crash Countermeasures with Unknown Safety Effect

13 Roadway Segments 36 43 72

14 Intersections 24 27 84

15 Interchange 4 8 25

16 Special Facilities and Geometric Situations

5 16 68

17 Road Network 3 16 5

Total 72 110 254

Developing CMF for Louisiana

• While the majority of crash countermeasures would be the same as the once used by other states, a few countermeasures will be unique in Louisiana

• Introducing few CMFs tailed to the unique situation in the state is the objective of this presentation

Outline

• Crash Countermeasures • Converting urban undivided 4-lane

roadway to five-lane roadway • Edgeline on narrow rural 2-lane highways • Raised pavement markers

9

Urban undivided multilane highways consistently exhibit low safety performance in the U.S.

Fatal Accidents

Injury

Accidents

Total

Accidents

RURAL

Number per

MVM

Number per

MVM

Number per

MVM

2 Lanes 0.07 0.94 2.39

4 or more lanes,

divided subtotal 0.063 0.77 2.09

Freeway 0.025 0.27 0.79

URBAN

2 Lanes 0.045 1.51 4.94

4 or more lanes,

undivided 0.04 2.12 6.65

4 or more lanes,

divided 0.027 1.65 4.86

Freeway 0.012 0.4 1.43

Representative Accident Rates by Location and Type of Road

10

– 1,530 miles of undivided multilane roadways under LADOTD system. 93% these roadways are in urban and suburban areas

11

Solutions?

• Expensive solution: installing physical separation either by barrier or by green space (boulevard) has been the most recommended crash countermeasure for the problem

12

• Inexpensive option: with sufficient pavement width, a four-lane undivided highway can also be easily changed to a five-lane roadway with the center lane for left-turns, which expectedly reduces rear-end collisions.

Solutions?

13

The five-lane design alternative including a center TWLTL in the median has, in the past 20 years, become a very common multilane design alternative for upgrading urban arterials. This design alternative has two through lanes of travel in each direction and a center TWLTL to provide for left-turn maneuvers at driveways and minor intersections. The total roadway width for a five-lane TWLTL section on an urban arterial ranges from 48 ft to 72 ft depending on the lane widths employed. From NCHRP 330, 1990

14

Pros and Cons of Two Options

• Physical barrier

– Better traffic (motorized or non-motorized) management

– Expensive

• Five lane

– Inexpensive with sufficient ROW

– Not recommended for new road in Louisiana

15

However

• Under the current budgetary situation, the expensive option is not financially feasible

• Going with the inexpensive but not perfect solution to reduce the crashes has been one option for the situation

• Several roadway segments in various LADOTD districts have implemented this inexpensive crash countermeasure in the past

16

Four segments selected for the analysis

District Control Section

Length (mi) Installation

Year

Estimated # of

Driveways Location

LA 3025 D3 828-23 1.228 2003 45 Lafayette

LA 182 D3 032-02 1 2007 50 Opelousas

LA 28 D8 074-01 0.92 2005 45 Alexandria

LA 1138 D7

810-06

1.07 1999 50 Lake Charles

17

Roadway Configuration

LA3025

18

LA 3025 (from 2012 Google Earth)

19

LA182

20

LA182 (from 2012 Google Earth)

21

LA1138

LA28

(from 2012 Google Earth)

22

Summary of Crashes (3 years before and after)

Before After Percentage Change

Crashes Average

Crash Rate

Crashes Average

Crash Rate

Crashes Crash Rate

LA3025 358 10.05 147 4.59 -59% -54%

LA182 178 8.12 85 3.53 -52% -51%

LA28 206 7.38 99 4.09 -52% -45%

LA1138 260 16.01 167 10.63 -36% -34%

23

Changes by Crash Type

LA182

0

20

40

60

80

100

Head-O

n

Left

Turn

-e

Left

Turn

-f

Left

Turn

-g

Non Coll

Rear-E

nd

Right T

urn-h

Right T

urn-i

Rt. Angl

e

Sides

wipe (O

D)

Sides

wip (S

D)

Blank

Oth

er

Cra

sh F

req

ue

ncy Before

Total

AfterTotal

LA3025

0

50

100

150

200

250

Head-O

n

Left

Turn

-e

Left

Turn

-f

Left

Turn

-g

Non Coll

Rear-E

nd

Right T

urn-h

Rt. Angl

e

Sides

wipe (O

D)

Sides

wipe (S

D)

Blank

Oth

er

Cra

sh F

req

ue

ncy Before

Total

AfterTotal

24

Changes by Pavement Surface Condition

LA182

0

20

40

60

80

100

120

140

160

180

Dry Wet

Pavement Surface Condition

Cras

h Fr

eque

ncy

BeforeTotal

AfterTotal

LA3025

0

50

100

150

200

250

300

Dry Wet


Cras

h Fr

eque

ncy

BeforeTotal

AfterTotal

LA28

0

20

40

60

80

100

120

140

160

Dry Wet


Cra

sh F

req

ue

ncy

BeforeTotal

AfterTotal

LA1138

0

50

100

150

200

250

Dry Wet


Cra

sh F

req

ue

ncy

BeforeTotal

AfterTotal

25

Changes by Time of the Day

LA 3025

0

40

80

120

160

200

6am-

12pm

12pm-

6pm

6pm-

12am

12am-

6am

Cras

h Fr

eque

ncy

BeforeTotal

AfterTotal

LA 182

0

20

40

60

80

100

120

6am-

12pm

12pm-

6pm

6pm-

12am

12am-

6am

Cras

h Fr

eque

ncy Before

Total

AfterTotal

LA 1138

0

20

40

60

80

100

120

140

160

6am-

12pm

12pm-

6pm

6pm-

12am

12am-

6am

Cras

h Fre

quen

cy

BeforeTotal

AfterTotal

LA 28

0

20

40

60

80

100

120

6am-

12pm

12pm-

6pm

6pm-

12am

12am-

6am

Cras

h Fre

quen

cy

BeforeTotal

AfterTotal

26

Changes by Crash Severity

Crashes by

Severity

LA3025 LA182 LA28 LA1138

Before After %

Change Before After

% Change

Before After %

Change Before After

% Change

Total 358 147 -58.90% 178 85 -52.30% 206 99 -51.94% 260 167 -35.77%

PDO 277 105 -62.10% 124 63 -49.20% 148 76 -48.68% 172 119 -30.81%

Injury Crashes

81 40 -50.60% 54 22 -59.30% 58 23 -60.34% 88 48 -45.45%

Fatal 0 2 increase 0 0 0% 0 0 0% 0 0 0%

27

Benefit/Cost Ratio

• Benefit—saving from reduced crashes

• Cost – striping

• B/C=166!

Segment Total Benefits ($) Total Cost ($) B/C Ratio

LA 3025 2,753,868 14,100 195

LA 182 1,913,808 11,500 166

LA 28 2,110,212 10,600 199

LA 1138 2,317,488 12,300 188

LA 3025 LA 182 LA 28 LA 1138

Reduction Reduction Reduction Reduction

PDO 172 61 72 53

Injury 41 32 35 40

Severity

Level

28

CMF Results

Expected

Crash Reduction

Standard Deviation

Estimated the CMF

Standard Deviation

LA3025 175 27.62

0.45

0.051

LA182 110 20.53

0.43

0.062

LA28 111 21.28

0.47

0.062

LA1138 87 25.42

0.65

0.075

29

Roadway Estimated

CMF Standard Deviation

CMF+ 3*Standard Deviation

LA3025 0.45 0.051 0.60 LA182 0.43 0.062 0.62 LA28 0.47 0.062 0.66

LA1138 0.65 0.075 0.88

CMF Value0.88

0.9989

0.65

Probabilty Distribution

LA1138

CMF Value0.60.45

0.9984

Probability Distribution

LA3025

CMF Value0.620.43

0.9989


LA182

CMF Value0.660.47

0.9989


LA28

What does the result mean? A certainty in crash reduction

30

Results Discussion

• The crash reduction by the re-striping/lane conversion projects is striking and the estimated CMF is impressive (crash countermeasures, as listed in the first edition of the HSM, seldom yield CMF values smaller than 0.5)

• The estimated CMF and standard deviation on all roadway segments indicate a certainty that a re-striping project reduces crashes.

31

• Reductions are consistent cross crash category • It is a very cost-effective crash countermeasure • Demonstrating the need for flexibility in selecting

the best safety improvement project under the existing constraints (financial or otherwise).

• If and when funds do become available and sufficient right-of-way (ROW) can be obtained, these two 5-lane roadway segments can be converted to a boulevard roadway type, a concept very much promoted today in urban and suburban areas in Louisiana

Results Discussion

32

Sustainable crash reduction

LA3025

0

50

100

150

2000 2001 2002 2004 2005 2006 2008 2009 2010

Year

Cra

sh F

req

ue

ncy

3 years after

3 years before

3 years after after

33

3 years after

3 years after

3 years after after

3 years after after

3 years before

3 years before

Hurricane Rita

34

CMF as a function of AADT

AADT vs. Estimated CMF

y = 3E-09x2 - 0.0001x + 1.8028

R2 = 0.996

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

10,000 15,000 20,000 25,000 30,000

AADT

CM

F

35

Due to the huge success of the lane-conversion project, more segments from LADOTD District 3 have been recently re-striped:

• LA 14-Bypass in Abbeville

• LA 14 in Abbeville

• US 190 in Eunice

• LA 93 in Sunset

• LA 14 in New Iberia

Acknowledgement

• Mr. Nick Fruge from District 3

• Ms. Bridget Webster from District 8

• Mr. Jason Roberson from District 4

• Mr. Tyson Thevis from District 7

Outline

• Project background




• Raised pavement markers (delineation purpose)

Setting

(Road Type)

Traffic Volume

(AADT)

Crash Type

(Severity) CMF Std. Error

≤ 20,000 1.13 0.2

20,001-60,000 0.94 0.3

>60,000 0.67 0.3

Rural

(Four-lane Freeways)

Nightime

All Types

(All Severities)

The need to have Louisiana CMF on Raised Pavement Markers (RPM)

Should the state continue the practice?

CMF from the HSM

Ref: Bahar, G., C. Mollett, B. Persaud, C. Lyon, A. Smiley, T. Smahel, and H. McGee. National Cooperative Highway Research Report 518: Safety Evaluation of Permanent Raised Pavement Markers. NCHRP, Transportation Research Board, National Research Council, Washington, DC, 2004.

Developing CMF for RPM

• Data

– Annual RPM and striping ratings

– Crash

• Analysis

– By setting (urban vs. rural)

– By time (nighttime vs. daytime)

• Three condition ratings:

– ‘G’ as Good

– ‘P’ as Poor

– ‘F’ as Fair

• Rating ‘C’ as Construction

Ratings

2002 2003 2004 2005 2006 2007 2008 2009 2010

Control Section

Section Length

450-91 2.54 G G P G G F F F P

450-92 1.36 F F G G G F F F P

450-93 3.40 F F G G G F F F P

450-94 1.17 F F G G G F F F P

450-95 0.13 F F G G G F F F P

450-96 0.38 F F G G G F F F P

Summary

Freeway

Number of Segments in Each Rating Group in Nine years

GG GF GP FG FF FP PG PF PP

Rural 606 85 171 63 110 140 75 31 285

Urban 1,028 189 280 156 214 266 141 88 734

Total 1,634 274 451 219 324 406 216 119 1,019

Average Crash Rate by Combined Ratings on Rural freeways

Rural and night hours

0.159 0.163

0.196

0

0.05

0.1

0.15

0.2

0.25

GG FF PP

Striping and RPM rating

Avg

. C

rash

Ra

te

Rural and 24 hours

0.666

0.7600.817

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

GG FF PP


Avg

. C

rash

Ra

te

23% increase 23% increase

Average Crash Rate by Combined Ratings on Urban freeways

Urban and 24 hours

2.1132.005 2.077

0

0.5

1

1.5

2

2.5

GG FF PP


Avg

. Cra

sh R

ate

Urban and Night hours

0.3840.406

0.369

0

0.1

0.2

0.3

0.4

0.5

GG FF PP


Avg

. Cra

sh R

ate

Average crash rate by single rating on rural freeways

Rural and 24 hours

0.6580.692 0.706

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

G F P

RPM rating

Avg

. Cra

sh R

ate


0.1520.165 0.168

0

0.05

0.1

0.15

0.2

0.25

G F P

RPM rating

Avg

. Cra

sh R

ate


0.1610.180 0.178

0

0.05

0.1

0.15

0.2

0.25

G F P

Striping rating

Avg

. Cra

sh R

ate

Rural and 24 hours

0.6750.724

0.760

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

G F P

Striping rating

Avg

. Cra

sh R

ate

Striping RPM

Results of Statistical Test (Average Crash Rate between Good and Poor)

Roadway Type

Feature Crash

Rate at

t-test for Equality of Means

t df Mean

Difference Std. Error Difference

95% Confidence Interval of the Difference

Lower Upper

AADT ≤ 20,000

Rural RPM Night -1.781 489 -0.033 0.018 -0.069 0.003

Rural RPM 24 Hrs -1.101 489 -0.065 0.059 -0.181 0.051

Rural RPM+Striping Night -2.603 309 -0.063 0.024 -0.110 -0.015

Rural RPM+Striping 24 Hrs -2.591 309 -0.212 0.082 -0.373 -0.051

20,000≤AADT ≤ 60,000

Rural RPM Night -2.665 816 -0.038 0.014 -0.066 -0.010

Rural RPM 24 Hrs -3.249 816 -0.142 0.044 -0.228 -0.056



AADT ≤ 60,000

Rural RPM Night -2.128 1339 -0.025 0.012 -0.049 -0.002

Rural RPM 24 Hrs -2.573 1339 -0.102 0.040 -0.180 -0.024



CMF Development

Highway

Type Feature

Crash

Hour Rating N Mean CMF

AADT≤ 20,000

Rural RPM Night Good 291 0.139 0.81

Poor 200 0.172

Rural RPM 24 Hrs Good 291 0.635 0.91

Poor 200 0.7

Rural RPM+Striping Night Good 225 0.138 0.69

Poor 86 0.201

Rural RPM+Striping 24 Hrs Good 225 0.644 0.75

Poor 86 0.856

20,000 ≤ AADT≤ 60,000


Poor 382 0.179


Poor 382 0.738


Poor 165 0.195


Poor 165 0.77

AADT≤ 60,000


Poor 596 0.178


Poor 596 0.757


Poor 285 0.2


Poor 285 0.841

• Crash rate is used for the analysis

• Only “Good’’ ratings and “Poor” ratings are considered

• Nine years data is used for both ratings

Results Discussion

• RPM does offer safety benefit to the state rural freeways based on all analysis methods

• Because of combined effects of two ratings, it is hard, if not impossible, to accurately estimate CMF for RPM

• It is conservative to say CMF on RPM is about 0.90

• No safety benefit of RPM is detected on urban freeways

• Project background




Outline

Edgeline Requirement

Previous

MUTCD

(1994)

Updated

MUTCD

(2000)1

Current LaDOTD

Policy (1994)2

Road

Width No Requirement 20-ft or Wider 22-ft or Wider

AADT No Requirement Greater than

3,000 No Requirement

Research Investigation

• The 2007 study on 10 segments of narrow rural 2-lane highways proved that: – With the edge line, vehicles tend to move away from

the road edge; thus, the risk of having a running-off-roadway crash is likely to be reduced

– The implementation of edge lines is likely to reduce the head-on and sideswipe collisions at night because of the reduced number of vehicles crossing the centerline in the nighttime.

• The impact of edge line on crashes is also investigated on the selected segments from all LaDOTD districts

Control Section

(District 3)

Highway Number

Log from and to

Suggestion

Mile post (Log Mile)

823-27 0087

0-1.89

Starting at milepost 4.0 for 3 miles (0.25 mile before the

control section)

before

after

• 389-01

Control Section

(D3)

Highway Number

Log from and to

Suggestion

Milepost (Log Mile)

389-01 0098

2.59-7.15

Starting at milepost 27 for 6 miles (log-mile 2 for 6 miles)

before

after

Control Section

(D4)

Highway Number

Log from and to

Suggestion

Milepost (Log Mile)

048-02 0169

4.72-8.29

Starting at milepost 22 for 5 miles (log mile 4.5 for 5 miles)

before

after

• Crash data analysis

• Three years before and three years after

2005 2006 2007 2008 2009 2010 2011

Before Installation Year After

Total Crashes

2005 2006 2007 2009 2010 2011

DOTD

District Total Total Total Total Total Total

2 23 34 24 19 8 17

3 86 68 67 81 85 68

4 12 16 8 12 5 6

5 84 74 85 90 99 72

7 21 30 14 10 14 17

8 16 13 15 10 14 10

58 5 3 4 2 4 1

61 32 36 17 15 15 20

62 85 103 83 71 62 63

Total 345 346 295 290 299 263

Results

Before 3 Years- After 3 Years

Naïve B-A Method 2 Improved Prediction

DOTD

District

(No. of CSECT)

Reduction in

Crashes

Index of

Effectiveness

Reduction

in Crashes

Index of

Effectiveness

2 (1) 4 0.58 10 0.38

3 (9) -13 1.05 -17 1.07

4 (2) 13 0.62 18 0.54

5 (4) -18 1.07 1 0.99

7 (2) 24 0.62 14 0.72

8 (2) 9 0.77 13 0.69

58 (1) 5 0.54 2 0.69

61 (3) 35 0.58 44 0.52

62 (4) 75 0.72 108 0.64

Results

Before 3 Years- After 3 Years

Improved Prediction Method

Estimated

Expected

Reduction

Stdev. CMF Stdev.

194 48 0.81 0.041

Result Interpretation

0.868 0.701 1.0278

2

Benefit-Cost Analysis

Severity

Type

2004-2007

(Before

Years)

2009-2011

(After

Years)

Change

Including Loss

of

Quality of Life

Safety

Benefit ($)

Fatal 12 13 -1 4,376,304 -4,376,304

Injury 424 341 83 71,139 5,904,537

PDO 550 498 52 3,292 171,184

Total Benefit 1,699,417

Cost ($0.15 per

foot) Benefit B-C Ratio

All Control

Sections 86,835 1,699,417 19.57

Putting together

• Our Analysis 0.81

Safety Trend for the Narrow Rural 2-lane

-5.6%

Final Estimated CMF 0.87

HSM

CMF for Rural Two Lane

Source: Highway Safety Manual (1st Edition), Vol. 3, 2010

Results Discussion

• Implementing edge line is most likely to reduce number of crashes based on our crash analysis

• The expected reduction is estimated 13%

Summary

A very effective short-term crash countermeasure for urban undivided 4-lane roadway

Reducing crashes on rural freeway

Results in lower crash rate

Thank You and Questions?

Safety Impacts of Various Crash Countermeasures Safer Roads: A Guide to Road Safety Engineering....

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