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

Outline Background Purpose What we did What we found Next steps 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 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 13 Use of Edge Line Markings on Rural Two Lane Highways

Pavement Width (ft) Lane Width (ft) CenterlineEdgeline Paved Shoulder Width (ft) 2812Yes Yes Yes Yes Yes Yes Yes 1 219Yes Yes 1 198YesNo YesNo NoYes1 167NoYes NoYes1 146NoYes1

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) Crash Data –Eligible narrow and low volume segments –Presence of pavement markings (Google) 16

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Number of Lanes & Facility Type Route System Pavement Width (ft) Length (mi) Total Crash Frequency Two-lane Undivided Primary ,4565,182 Secondary Total2,5166,807 18

Inventory/Crash History Matrix: –Pavement width (16’,18’,20’) –AADT band (<500, ) –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 CenterlineEdgeline Number of Segments Length (miles) ≤ 500 No 1, Yes126 Yes No2725 Yes ,000 No Yes63 No21288 Yes2,2271,180 Total 4,7972,033 20

No Markings and Edgelines Only 21

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 SegmentsEdgelines AbsentPresent Centerlines Absent2,08118 Present2392,459 26

Crash frequency and marking presence Crash Frequency (5-year crashes per segment) Edgelines AbsentPresent Centerlines Absent Present

Crash density and marking presence Crash Density (5-year crashes per 0.5 mile) Edgelines AbsentPresent Centerlines Absent Present

Crash Rate by marking presence Crash Rate (5-year crashes per 0.5 mile per 1,000 vehicles) Edgelines AbsentPresent Centerlines Absent Present

Number of segments by marking presence and pavement width Number of SegmentsEdgelines AbsentPresent 16 feetCenterlines Absent1184 Present feetCenterlines Absent7379 Present feetCenterlines Absent12265 Present

Crash frequency by marking presence and pavement width Crash Frequency (5-year crashes per segment) Edgelines AbsentPresent 16 feetCenterlines Absent Present feetCenterlines Absent Present feetCenterlines Absent Present

Crash rate by marking presence and pavement width Crash Rate (5-year crashes per 0.5 mile per 1,000 vehicles) Edgelines AbsentPresent 16 feetCenterlines Absent Present feetCenterlines Absent Present feetCenterlines Absent Present

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 3 segment groups appear different 36

Crash Analysis SPF results for 95% upper limit However, 3 curves are statistically identical 37

Study sites vs all VDOT roads no. road miles no. crashes study sites 2,0334,797 VDOT roads 60,066251,609 % 3.4%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.VDOT’s Traffic Engineering Div. should consider developing a statewide process for a pavement marking inventory. 2.VDOT’s TED should consider asking the Office of the Attorney General for an interpretation/opinion of the term “appropriate” in HJR

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. 45

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