The 2010 Evaluation of Low Cost Safety Improvements Pooled Fund Study

Technical Advisory Committee Meeting

March 2010

Thomas M. Welch, P.E.State Transportation Safety EngineerOffice of Traffic and SafetyIowa Department of Transportation 515 239-1267tom.welch@dot.iowa.gov 1

Horizontal Curve Fatal Crashes

37

63

51

25

97

173 140

334

390

187

127

153

164

808

177

49298

23

DC

72 209

30

183

35

497

64

487

138

35

675

500

155

385

534

318

27

321

66

77

343

59

89

258

35

84

226208

163

256

166

101

DC=3

2006-2008 Average

From: FHWA Roadway Departure Team2

Percent of Fatal Crashes at Horizontal Curve

54

17

42

37

36

22 22

27

46

35

29

27

41

23

18

13

26

24

DC

29 20

25

29

30

34

39

35

21

16

22

35

32

36

18

35

40

32

17

35

43

40

24

30

26

25

3921

44

27

21

44

DC=8

2006-2008 Average

From: FHWA Roadway Departure Team3

Primary Highway Curve Crashes

•Statewide average = 1.1 / MVM (avg radius = 2850 ft., avg length = 870 ft.) •Top 30 average = 11.7 (7.2*) / MVM (avg radius = 1780 ft., avg length = 807 ft.) •Worst (of top 30) = 78 / MVM•5% of crashes occur at top 30 locations (1% of curves)•11% of fatals occur at top 30 locations * Weighted average

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10

15

20

25

30

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Radius (ft)

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(MV

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10

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20

25

30

0 500 1000 1500 2000 2500 3000

Length (ft)

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(MV

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Low Cost Curve Improvements

• Super elevation: add or correct

• Pave shoulders: outside & inside

• Shoulder rumble strips

• Flatten outside slope

• Remove objects outside curve

• Delineate, chevron, RPM’s (raised pavement markers)

• Advisory speed plate, ball bank advisory

• Center line rumble stripe

• Larger/brighter chevrons5

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District Installed Treatments

• 43 rural curves have been selected that have had improvements in the last three years, statewide.

• Improvements were mainly new Chevrons and larger/brighter chevrons.

• Curves will be cataloged by radius, ADT, etc.

• 75 to 150 control curves will be selected for comparison.

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Evaluation of Treatments to reduce speeds and crashes on high crash horizontal curves

(FHWA funded: Dr. Shauna Hallmark @ Iowa State University PI)

RoadUpstream Intersection

Downstream Intersection County Comments Speed/Crash

Potential Treatments

Final Treatment AADT

L-35/221st St Deacon Rd Eastman RD Mills

US 275 (has existing Chevrons)

50 mph advisory; speed problem both directions (85th); 10 crashes, 3 NB/2 SB All

Larger Chevrons or

LED 2410

Loess Hills Trail Kermit PL York Rd Harrison No Chevrons

35 mph advisory; speeding both directions; 26 crashes; 12 NB/10 SB Pvmt Mkg Pvmt Mkg 1880

IA 141 L-32 Spruce Ave Monona Has Chevrons

35 mph advisory; speeding both directions; 8 crashes; 2 NB/2 SB All

Larger Chevrons 830

US 52 Clay Hill Rd Sherrill Rd Dubuque

Possibly large Chevrons (lots of these exist)

40 mph advisory; speed problem 85th both directions; 13 crashes; 4 NB/3 SB Reflectors

Reflectorized Strip 2280

DMC 99H-50/Stony Hollow Rd 150th St

Des Moines No chevrons

no advisory; speed problem 85th SB; 14 crashes; 5 NB/1 SB Pvmt Mkg Pvmt Mkg 1430

115 Ave/Y-52Allens Grove Rd 230 St Scott

Chevrons (small) exist

40 mph advisory; speed problem both directions; 10 crashes; 2 NB/7 SB All but LED

Reflectorized Strip 1710

Great River Road (X 56) Larriet Rd Larriet Rd Clayton

Existing chevrons

45 mph advisory; speed problem 85th both directions; 9 crashes; 3 NB/2 SB

Reflector or LED

Larger Chevrons or

LED 1130

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Full Post Chevron (adding reflectorized strip to post) --- chevron is already in place, reflector strip is added to post

Pavement Markings (Curve Sign or "SLOW")

Solar Powered in-pavement RPM

Larger Chevrons

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FY 2011 State of Iowa Funded Safety Program

• 16 Low Cost Curve Improvement Projects– speed advisory plates– bigger/brighter chevrons– paved shoulders/shoulder rumble strips– centerline rumble strips– 25-30 curve improvements

• $70,000 - Improve signing at “Top 30” Curves

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