Investigation of the Safety Effects of Edge and Centerline Markings on Narrow, Low-Volume Roads

Lance Dougald Ben Cottrell Young-Jun Kweon In-Kyu Lim

• Background • Purpose • What we did • What we found • Next steps

Outline

2

Pavement Markings

3

Introduction and Background

Evolving Problem

– Increase in housing/retail development – Higher traffic volumes on nearby narrow roads without markings – Thought: Improve safety with low cost striping until higher cost design improvements could be implemented 4

Introduction and Background

•

VDOT Guidelines

: – Centerlines • ≥ 500 vpd, ≥18 ft width – Edgelines • Primary and Secondary routes w/no curb & gutter • Minimum 20 ft width • Centerlines present * where an engineering study indicates a need 5

Introduction and Background

•

MUTCD requirements

: – Centerlines • Urban arterials and collectors ≥ 20 ft width, ADT ≥ 6,000 vpd (recommended ≥ 4,000) • All two-way streets with 3+ traffic lanes – Edgelines • All freeways and expressways • Rural arterials ≥ 20 ft width, ADT ≥ 6,000 vpd (recommended ≥ 3,000) 6

Purpose and Scope

• Initially: to develop guidelines for marking edge and centerlines on low volume roads (≤ 3,000 vpd and 16-20 ft wide pavement) • Two phase process –

Phase I: investigate safety effectiveness of markings using cross-sectional crash data

– Phase II: before/after pilot study of edge and centerline applications at candidate sites and B/C analysis. 7

Methods

1. Conduct literature review (focusing on rural/suburban low volume roads) 2. Obtain information from other state DOTs 3. Develop inventory of current edge and centerline markings and database of crash history on narrow roads 4. Perform crash analysis (5 years of data – width, AADT, and presence of pavement markings) [cross-sectional analysis] 8

Lit Review and Survey Results

• Variability found in past research – Crashes – Speed – Lateral positioning • Variability in state DOT practices/policies – Majority follow MUTCD – Lower width/ADT thresholds from states that maintain secondary road system 9

Safety Impact of Edgelines on Rural Two-Lane Highways in Texas

• A before/after comparison study found edgelines reduced accident frequency up to 26% • highest safety impacts on curved roadways with lane widths of 9-10 ft 10

Benefit-Cost Analysis of Lane Marking

• paint costs $0.04 /linear-ft in rural areas and $0.07/linear-ft in urban areas • existing longitudinal pavement markings reduce crashes by 21% • edgelines on rural two-lane highways reduce crashes by 8 % 11

Lure of Low Cost Markings

Using $0.07 per linear-ft: • $740 per mile centerlines • $1,480 per mile center and edgelines VDOT HSIP average crash values • PDO: $9,000 B/C=6/1 • Injury :$55,000-$275,000 B/C=37/1-185/1 • Fatal :$5,000,000 B/C=33,784/1 12

Kentucky DOT Guidelines

Use of Edge Line Markings on Rural Two Lane Highways

. 2008. 13

Pavement Width (ft)

18

17 16 15 14 28 27 26 25 24 23 22 21 20

19

Lane Width (ft)

8

7.5

7 6.5

6 12 12 11 11 11 10 10 9 9

8

Centerline

Yes Yes Yes Yes Yes Yes Yes Yes Yes

Yes Yes

No No No No

Edgeline

Yes Yes Yes Yes Yes Yes Yes Yes Yes

No No

Yes Yes Yes Yes Paved Shoulder Width (ft)

2 1.5

2 1.5

1 1.5

1 1.5

1

1.5

1

1 1 1 1

State DOTs’ actions to increasing volumes on narrow roads

• Wyoming adds centerlines • Delaware was under pressure in two counties to establish a low AADT criterion for centerlines • Oregon adds edgelines if there are documented safety problems 15

Inventory/Crash History

• HTRIS – 3 subsystems – Roadway Inventory (200,000 segments) – Accident/Crash (FR-300) – Traffic Monitoring System (CCS) • 2004-2008 Crash Data – Eligible narrow and low volume segments – Presence of pavement markings (Google) 16

HTRIS Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Step 7 Step 8 Step 9 Step 10 RDI Subsystem Select segments maintained in 2004 - 2008 Select segments on Primary & Secondary Select segments Two-lane, Two way & Undivided Select segments pavement width 16ft - 20ft Join TMS to RDI Select segments with AADT 1 - 3,000 veh. Join ACC to RDI Compile RDI, TMS and ACC data Add Marking Inventory 2004 RDI 2005 RDI 2006 RDI 2007 RDI 2008 RDI TMS Subsystem 2004 TMS 2005 TMS 2006 TMS 2007 TMS 2008 TMS ACC Subsystem Select segments with crashes in 2004 - 2008 2004 ACC 2005 ACC 2006 ACC 2007 ACC 2008 ACC 17

Number of Lanes & Facility Type

Two-lane Undivided Total

Route System

Primary Secondary

Pavement Width (ft)

16 17 18 19

20

16 17 18 19 20

Length (mi)

20 11

Total Crash Frequency 2004-2008

66 8 162 68

1,456

122 9 351 32 285 2,516 536 218

5,182

252 12 327 40 166 6,807 18

Inventory/Crash History

• Matrix: – Pavement width (16’,18’,20’) – AADT band (<500, 501-3000) – Presence edge/centerlines – Number/length of segments – Crashes • Total • Road Departure • Density 19

Road Sections by Two AADT Bands and Presence of Pavement Markings AADT Bands

≤ 500 501-3,000 Total

Centerline Edgeline

No Yes No Yes No Yes No Yes No Yes No Yes

Number of Segments 1,910

12 27 232 171 6 212

2,227

4,797

Length (miles)

496 6 25 194 40 3 88 1,180 2,033 20

No Markings and Edgelines Only

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Centerlines Only and Both Markings 22

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Crash Analysis

Question: Are narrow roads with pavement markings safer than those without pavement markings?

• Compared roads with: – No markings – Centerline markings only – Edge-line markings only – Edge and centerline markings 24

Crash Analysis

ANOVA: • Developed individual models for widths: – 16’, 18’, 20’ • Crash frequency (# of crashes) • Crash density (crashes/mile) • Crash rate (crashes/mile/vehicles) 25

Number of segments and marking presence

Number of Segments

Centerlines Absent Present

Edgelines

Absent Present 2,081 239 18 2,459 26

Crash frequency and marking presence

Crash Frequency (5-year crashes per segment)

Absent Centerlines Present

Edgelines

Absent Present 0.13

1.43

0.28

2.03

27

Crash density and marking presence

Crash Density (5-year crashes per 0.5 mile)

Centerlines Absent Present

Edgelines

Absent Present 0.15

1.16

0.19

1.48

28

Crash Rate by marking presence

Crash Rate (5-year crashes per 0.5 mile per 1,000 vehicles)

Absent Centerlines Present

Edgelines

Absent Present 0.77

1.11

0.96

1.11

29

Number of segments by marking presence and pavement width

Number of Segments

16 feet Centerlines 18 feet Centerlines 20 feet Centerlines Absent Present Absent Present Absent Present

Edgelines

Absent Present 118 21 737 4 56 9 61 1226 157 284 5 2119 30

Crash frequency by marking presence and pavement width

Crash Frequency (5-year crashes per segment)

16 feet Centerlines Absent Present 18 feet Centerlines 20 feet Centerlines Absent Present Absent Present

Edgelines

Absent Present

0.42

2.62

0.20

1.70

0.05

1.16

0.25

2.66

0.33

1.77

0.20

2.04

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Crash rate by marking presence and pavement width

Crash Rate (5-year crashes per 0.5 mile per 1,000 vehicles)

Absent 16 feet Centerlines Present 18 feet Centerlines 20 feet Centerlines Absent Present Absent Present

Edgelines

Absent Present

1.69

2.66

1.11

1.58

0.47

0.72

0.41

2.01

1.65

1.56

0.17

1.03

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Crash Analysis Results

ANOVA: • No statistical difference found for crash frequency, density, and rate for each of the 4 marking scenarios • Shortcoming: accounting for AADT, segment length 33

Safety Performance Function (SPF)

A safety performance function (SPF) is an equation used to predict the average number of crashes per year at a location as a function of exposure and, in some cases, roadway or intersection characteristics (e.g., number of lanes, traffic control, or median type) SPF estimated by the negative binomial model 34

Crash Analysis

• Separate SPFs developed for 4 cases: • No lines present • Centerlines only • Edgelines only • Both lines present 35

Crash Analysis

• SPF results 8 7 6 2 1 5 4 3 0 0 500 1,000 1,500 2,000 2,500 3,000 AADT • 3 segment groups appear different 36

Crash Analysis

• SPF results for 95% upper limit 16 14 12 10 4 2 8 6 0 0 500 1,000 1,500 2,000 2,500 3,000 AADT • However, 3 curves are statistically identical 37

Study sites vs all VDOT roads

study sites VDOT roads % no. road miles 2,033 no. crashes 2004-2008 4,797 60,066 3.4% 251,609 1.9% 38

Pavement Marking Inventory

• how districts maintain a pavement marking inventory in terms of software, format, data quality and frequency of updating the inventory vary • 2 districts did not have an inventory for these roads • a uniform, up to date pavement marking inventory may have value 39

Discussion: Perspectives

• HJR 243: – “the Virginia Department of Transportation be requested to revise its standards for the provision of centerline pavement markings to include all

appropriate

secondary roads having a pavement width of 18 feet or more where official traffic counts indicate a minimum of 500 vpd .” 40

Discussion: Perspectives

• The term “appropriate” may allow for guidance to be developed on what roads to mark and how to mark them • Flexibility in HJR 243 to mark more roads? Mark fewer roads?

• Interpretation on the word “appropriate” is needed 41

Limitations

• Before/after Empirical Bayes study ideal – Select and mark roads then wait for after data – Low number of crashes typical – Large number of road sections = impractical • Driver’s behavior not addressed – Exploratory study utilizing data from VTTI’s naturalistic driving study 42

Conclusions

• High variability exists in state DOT practices for installing pavement markings on narrow roads • Based on cross-sectional analysis of crash frequency, density, rate, and SPF prediction, there appears to be no statistical difference between segments with and without centerlines and/or edgelines 43

Recommendations

1.

2.

VDOT’s Traffic Engineering Div. should consider developing a statewide process for a pavement marking inventory.

VDOT’s TED should consider asking the Office of the Attorney General for an interpretation/opinion of the term “appropriate” in HJR 243.

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Recommendations

3. VCTIR staff should consider an exploratory study to determine if data from VTTI’s naturalistic driving study may be used to evaluate driver behavior on narrow roads with and without centerlines and/or edgelines.

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Investigation of the Safety Effects of Edge and Centerline Markings on Narrow, Low-Volume Roads

http://www.virginiadot.org/vtrc/main/online_reports/pdf/14-r3.pdf