Report No. FHWA/LA.13/508. University of Louisiana at Lafayette. Department of Civil and Environmental Engineering

Transcription

1 TECHNICAL REPORT STANDARD PAGE Report No. FHWA/LA.13/ Ttle and Subttle A Comprehensve Study on Pavement Edge Lne Implementaton 7. Author(s) Xaoduan Sun, Ph.D., P.E. Subassh Das 9. Performng Organzaton Name and Address Department of Cvl and Envronmental Engneerng Unversty of Lousana at Lafayette Lafayette, LA Sponsorng Agency Name and Address Lousana Department of Transportaton and Development P.O. Box Baton Rouge, LA Government Accesson No. 3. Recpent's Catalog No. 5. Report Date Aprl Performng Organzaton Code LTRC Project Number: 13-2P SIO Number: Performng Organzaton Report No. Unversty of Lousana at Lafayette 10. Work Unt No. 11. Contract or Grant No. 13. Type of Report and Perod Covered Fnal Report July 2012-June Sponsorng Agency Code 15. Supplementary Notes Conducted n Cooperaton wth the U.S. Department of Transportaton, Federal Hghway Admnstraton The prevous 2011 study Safety Improvement from Edge Lnes on Rural Two-Lane Hghways analyzed the crash data of three years before and one year after edge lne mplementaton by usng the latest safety analyss statstcal method. It concluded that placng pavement edge lnes on rural two-lane hghways n Lousana can not only change the lateral postons of the vehcles but also reduce crashes. The Crash Modfcaton Factor (CMF) for edge lne on narrow, rural twolane hghways s Consderng the decreasng trend n crashes n the state for the past three years, the modfed CMF s 0.83, whch mples that, on average, mplementng edge lnes can reduce 17% of crashes. As an extenson of the 2011 project, ths study not only used two more years of crash data for the after tme perod but also appled the Emprcal Bayes (EB) method n the analyss to estmate the crash reducton factors. Moreover, crash characterstcs analyss s performed n ths study to compare the dfference before and after edge lne mplementaton. Addtonally, ths project performed beneft and cost analyss. By consderng the safety trend n Lousana, the fnal estmated CMF s 0.85, whch means there s a 15% expected crash reducton n edge lne mplementaton on narrow, rural two-lane hghways. The statstcally estmated standard devaton for the CMF s The crash reducton s consstent n all crash types and partcularly sgnfcant n sngle vehcle crashes. Most of sngle vehcle crashes are ROR crashes, whch s the exact type of crash targeted by edge lne mplementaton. The benefts overwhelmngly offset the cost wth edge lne mplementaton. The most conservatve estmaton for beneft and cost rato s 19. Ths project recommends the use of edge lnes on narrow rural two-lane hghways whenever t s fnancally feasble and operatonally feasble. 17. Keywords Edge lnes, traffc safety, before-after studes, Emprcal Bayes method, beneft-cost analyss 18. Dstrbuton Statement Unrestrcted. Ths document s avalable through the Natonal Techncal Informaton Servce, Sprngfeld, VA Securty Classf. (of ths page) 20. Securty Classf. (of ths page) 21. No. of Pages: Prce

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3 Project Revew Commttee Each research project wll have an advsory commttee apponted by the LTRC Drector. The Project Revew Commttee s responsble for assstng the LTRC Admnstrator or Manager n the development of acceptable research problem statements, requests for proposals, revew of research proposals, oversght of approved research projects, and mplementaton of fndng. LTRC apprecates the dedcaton of the followng Project Revew Commttee Members n gudng ths research study to fruton. LTRC Admnstrator Zhongje Doc Zhang, Ph.D., P.E. Members Dan Magr, Had Shraz, Peter Allan, Jody Colvn, Krk Zerngue, Betsey Tramonte, and Jason Taylor Drectorate Implementaton Sponsor Rhett Desselle, P.E. Assstant Secretary Operatons

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5 A Comprehensve Study on Pavement Edge Lne Implementaton by Xaoduan Sun, Ph.D., P.E. Professor Subassh Das Ph.D. Student Cvl Engneerng Department Unversty of Lousana at Lafayette 254 Madson Hall 100 Rex Street Lafayette, LA LTRC Project No. 13-2P SIO No conducted for Lousana Department of Transportaton and Development Lousana Transportaton Research Center The contents of ths report reflect the vews of the author/prncpal nvestgator who s responsble for the facts and the accuracy of the data presented heren. The contents of ths report do not necessarly reflect the vews or polces of the Lousana Department of Transportaton and Development or the Lousana Transportaton Research Center. Ths report does not consttute a standard, specfcaton, or regulaton. Aprl 2014

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7 ABSTRACT The prevous 2011 study Safety Improvement from Edge Lnes on Rural Two-Lane Hghways analyzed the crash data of three years before and one year after edge lne mplementaton by usng the latest safety analyss statstcal method. It concluded that placng pavement edge lnes on rural two-lane hghways n Lousana can not only change the lateral postons of the vehcles but also reduce crashes. The Crash Modfcaton Factor (CMF) for edge lne on narrow, rural two-lane hghways s Consderng the decreasng trend n crashes n the state for the past three years, the modfed CMF s 0.83, whch mples that, on average, mplementng edge lnes can reduce 17% of crashes. As an extenson of the 2011 project, ths study not only used two more years of crash data for the after tme perod but also appled the Emprcal Bayes (EB) method n the analyss to estmate the crash reducton factors. Moreover, crash characterstcs analyss s performed n ths study to compare the dfference before and after edge lne mplementaton. Addtonally, ths project performed beneft and cost analyss. By consderng the safety trend n Lousana, the fnal estmated CMF s 0.85, whch means there s a 15% expected crash reducton n edge lne mplementaton on narrow, rural twolane hghways. The statstcally estmated standard devaton for the CMF s The crash reducton s consstent n all crash types and partcularly sgnfcant n sngle vehcle crashes. Most of sngle vehcle crashes are ROR crashes, whch s the exact type of crash targeted by edge lne mplementaton. The benefts overwhelmngly offset the cost wth edge lne mplementaton. The most conservatve estmaton for beneft and cost rato s 19. Ths project recommends the use of edge lnes on narrow rural two-lane hghways whenever t s fnancally feasble and operatonally feasble.

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9 ACKNOWLEDGMENTS The help and gudance from the project revew commttee s apprecated. The authors also wsh to express ther grattude to the engneers from all nne Lousana Department of Transportaton and Development (DOTD) dstrcts who mplemented the edge lnes for the study. v

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11 IMPLEMENTATION STATEMENT Lousana has about 5,600 mles of narrow, rural two-lane hghways. Inexpensve and feasble countermeasures are requred to be proposed to reduce the hgher percentage of crashes and fataltes assocated wth ths type of hghway. The fndngs of ths project present the outcome of an nexpensve countermeasure. The study recommends that use of edge lnes on narrow rural two-lane hghways whenever t s fnancally feasble and operatonally feasble. The provded recommendatons should help DOTD s future plan on mprovng the safety of rural two-lane hghways. Partcularly, each DOTD dstrct can use the outcomes of ths research n operatng and mantanng roadways under ther admnstraton. v

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13 TABLE OF CONTENTS ABSTRACT... ACKNOWLEDGMENTS... v IMPLEMENTATION STATEMENT... v TABLE OF CONTENTS... x LIST OF TABLES... x LIST OF FIGURES... x INTRODUCTION... 1 OBJECTIVE... 5 SCOPE... 7 METHODOLOGY... 9 Selecton of Segment and Edge Lne Implementaton... 9 Before and After Crash Analyss... 9 Improved Before and After Crash Analyss Emprcal Bayes Method Traffc Flow Characterstcs Crash Characterstcs Drver Characterstcs Correlaton between Contrbutng Factors DISCUSSIONS OF RESULTS Postve Safety Trend Beneft-Cost Anslyss CONCLUSIONS RECOMMENDATIONS ACRONYMS, ABBREVIATIONS, AND SYMBOLS REFERENCES APPENDIX A APPENDIX B x

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15 LIST OF TABLES Table 1 Secton length and no. of control sectons of the dstrcts... 9 Table 2 Results from the frst step Table 3 Results from the second step Table 4 Results from the thrd step Table 5 Results from the fourth step Table 6 Results from frst two steps Table 7 Results from the thrd step Table 8 Results from the fourth to sxth steps Table 9 Results from the seventh to nnth steps Table 10 Fatal crashes n before and after years Table 11 Lghtng condton n before and after years Table 12 Total crashes by year Table 13 Crash modfcaton factor wth confdence nterval Table 14 Decreasng trend of crashes on rural two-lane hghways Table 15 Estmated beneft-cost rato for edge lne nstallaton Table 16 The varables consdered for analyss of before-after study Table 17 Crash data wth AADT values for before and after perods Table 18 Table for mproved predcton calculaton Table 19 Table for Emprcal Bayes method x

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17 LIST OF FIGURES Fgure 1 Densty of AADT n before-after perods Fgure 2 Densty of estmated speed of the vehcles nvolved n crashes n before-after perods Fgure 3 Box and whsker plot of estmated speed of the vehcles nvolved n crashes n before-after perods Fgure 4 AADT vs. crash rate n before-after perods Fgure 5 Crash severty n before-after perods Fgure 6 Crash severty n before-after perods by type Fgure 7 Densty plot of crash hour n before-after perods Fgure 8 Surface condton n before-after years Fgure 9 Male and female drvers n traffc crashes Fgure 10 Drver age dstrbuton Fgure 11 Drver dstracton related crashes n before and after perod Fgure 12 Drver volaton nduced crashes n before and after perod Fgure 13 Correlaton between crash hour and estmated speed wth crash severty Fgure 14 Correlaton between crash hour and estmated speed wth weather condton Fgure 15 Correlaton between crash hour and estmated speed wth drver s lcense state Fgure 16 Correlaton between crash hour and estmated speed wth alcohol related crashes 32 Fgure 17 Correlaton between crash hour and estmated speed wth drugs related crashes.. 32 x

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19 INTRODUCTION Hghway safety s a crucal ssue n Lousana. Each year, approxmately 150,000 crashes occur, over 90,000 of whch are on the state-mantaned hghway system. In 2011, 677 people were klled and 70,354 were njured n hghway crashes n Lousana. Rural two-lane hghways n ths state carry one-thrd of the total vehcle mles traveled (VMT) and have experenced a consderably hgh percentage of fatal crashes. There were 12,467 crashes on rural two-lane hghways n Lousana n In that same year, approxmately 34% of fatal crashes and 35% of fataltes n the entre state occurred on rural two-lane hghways. Road departure crashes are consdered one of the most frequent and expensve types of crashes n the Unted States [1]. These crashes are more frequent on rural hghways, accountng for 60% of total crashes on rural two-lane roads [2]. Approprate pavement markngs s an nexpensve crash countermeasure to reduce road departure crashes. An edge lne generally provdes vsual gudance, whch helps to confne vehcles wthn the traveled lane to avod road departure. The mpact of edge lnes were documented n a number of studes. The Manual on Unform Traffc Control Devces (MUTCD) provdes gudelnes for the nstallaton of edge lnes. However, rural two-lane hghways wth narrow lane wdth are not always requred to have edge lnes. One of the major concerns s that the presence of edge lnes may nfluence drvers to operate closer to the centerlne whch then ncreases the rsks of head-on and sdeswpe crashes [3]. Whle DOTD makes efforts to comply wth the new MUTCD requrement, concerns arse on safety and beneft-costs of edge lnes on narrow, rural two-lane hghways. To nvestgate the mpact of edge lnes, the Lousana Transportaton Research Center (LTRC) sponsored a study n 2005 nvestgatng the vehcular lateral poston wth edge lne nstallaton, Impact of Edge Lnes on Safety of Rural Two-Lane Hghways. Ths project concluded that: Wth edge lnes, centralzaton of a vehcle s poston s more apparent durng nghttme, whch reduces the rsk of run-off-road (ROR) and head-on collsons. Edge lne markngs generally cause drvers to operate ther vehcles away from the road edge, rrespectve of the hghway algnment. The 2005 study also states that the magntude of the mpact of edge lne markngs s nfluenced by hghway wdth, operatng speed, tme of day, frequency of heavy vehcles, pavement condton, hghway algnment, and traffc volume from the opposte drecton. These conclusons were drawn based on the analyss of vehcular lateral poston data

20 collected from 10 stes on the narrow, rural two-lane hghways that are wthn the DOTD Dstrct 03. Usng the latest safety analyss statstcal method, another LTRC sponsored study, Safety Improvement from Edge Lnes on Rural Two-Lane Hghways, completed n 2011, analyzed the crash data before and after edge lne mplementaton, and concluded that placng pavement edge lnes on rural two-lane hghways n Lousana can not only change vehcles lateral postons but can also reduce crashes [4]. The CMF for edge lnes on narrow, rural two-lane hghways s Consderng the decreasng trend n crashes n the state for the past three years, the modfed CMF s 0.83, whch mples that, on average, mplementng edge lnes can reduce 17% of crashes. As stated n the 2011 project report, pavement markngs have tradtonally been vewed by varous transportaton agences as an nexpensve crash countermeasure for mprovng hghway safety. Unlke other types of potental crash countermeasures, there has been a lmted number of studes conducted n the past on the safety mpact of edge lnes on narrow, rural two-lane hghways. The results of the nformaton revewed on the effectveness of edge lnes can be summarzed n three man categores: lateral poston of the travellng vehcle, crash reducton, and beneft-cost analyss. The followng revew s the same as n the 2011 report. The earlest study on vehcle poston was actually conducted n Lousana by I. L. Thomas n 1958 on a 24-ft. rural two-lane hghway n the state. He wanted to see f a broken or contnuous lne at varous dstances from the pavement edge had any sort of mpact on vehcles lateral poston. The research concluded that the tendency of vehcles to move towards the center of edge-strped pavements dd not appear consderably large enough to create any unusual hazard on a 24-ft. wde hghway [5]. In 1960, the same author repeated the study at dfferent locatons n Lousana, whch yelded the same concluson [6]. Other smlar studes on the vehcular lateral poston were conducted by the Mssour State Hghway Department n 1969 and Z. Y. Hassan n 1971 [7, 8]. These two studes agan gave the smlar conclusons. In 2000, research conducted by F. J. Steyvers et al. n the Netherlands used vdeo recordng equpment to observe vehcles poston changes before and after edge lne nstallaton on four unusually narrow rural hghways wth pavement wdths between 13.5 ft. and 14.8 ft. [9]. It was observed that drvers took a more central poston and approached the road edges less frequently when an edge lne was present. Interestngly, no problems were encountered wth oncomng vehcles on the edge lned hghways as the vehcles travelng n both drectons yelded to the sde whle passng. 2

21 J. V. Musck made a comparson of hghway crash occurrences before and after edge lne markngs on nne pars of rural two-lane hghways n Oho n The research showed that edge lne placement resulted n a consderable reducton n fatal and njury crashes [10]. A before and after study dentfed that edge lne placement contrbuted nearly a 20% reducton n crashes. Fataltes and njures reduced by 37%, and nghttme crashes decreased by 35%. A. J. Basle found a smlar trend to Musck s study when he conducted a before and after analyss on the hghways of Kansas n 1962 [11]. In Kansas, edge lnes were added to most of the rural two-lane hghways wth a pavement wdth of 20 to 26 ft. and a mnmum average daly traffc (ADT) of 1,000 vehcles per day (vpd). The study showed that edge lnes contrbuted to a 78% reducton n fataltes, and crashes at ntersectons or drveways were consderably decreased for both day and nght. In a 2005 study, A. R. Tsyganov et al. studed crash data from the Texas Department of Publc Safety to evaluate the current relatonshp between hghways wth and wthout edge lnes [12]. They revewed data from nearly 10,000 crashes on rural two-lane hghways for a four-year tme span. Lane wdth, shoulder wdth, and ADT were also consdered as sgnfcant attrbutes n the study. The results concluded that the expected crash reducton would be nearly 26%, and the best safety beneft was observed on horzontal curves and on hghways wth pavement wdths of 18 to 20 ft. The researchers descrbed that the decrease n speedng-related crashes at nght mght be a result of mprovng the drver s percepton of the travel path and speed of the vehcle. A study completed n 1991 by T. R. Mller quantfed the beneft-cost ratos of edge lnes for dfferent roadway condtons [13]. Analyzed crash data determned that pavement markngs contrbuted a 60:1 beneft-cost rato. Mller showed that, even on rural two-lane roads wth an ADT as low as 500 VPD, edge lnes provded a beneft-cost rato of 17:1. Research has repeatedly proven that the nstallaton of edge lne markngs reduces crash rates and mproves hghway safety. Some argue that f a 4- to 6-n. wde edge lne can contrbute to hghway safety, then a wder edge lne may offer addtonal safety benefts. A beneft-cost analyss conducted by W. E. Hughes et al. determned an annual decrease of eght edge lnerelated crashes for every 1,000 mles strped wth wde (8-n.) edge lnes [14].To compare the general low cost of edge lne markngs wth the overall cost of nstallng and mantanng roadways, t would be a reasonable step for the Department of Transportaton (DOT) to nvestgate the potental mprovements n safety from nstallng wder pavement markngs. B. H. Cottrell s study n 1987 can be consdered as one of the earlest safety evaluatons of wder edge lnes. The study analyzed crash data from three rural two-lane hghways n Vrgna [15]. At the three test sectons, the treatment stes were strped wth 8-n. wde edge 3

22 lnes, and the comparson stes were restrped wth 4-n. wde edge lnes. The before and after study consdered crash data from three years before and two years after placng the treatment. That study specfcally focused on ROR crashes and the researcher theorzed that a sgnfcant reducton n ROR crashes would warrant the use of wder edge lnes. The result showed nearly a 14% reducton n both ROR and opposte-drecton (OD) crashes. But crash reductons from wder edge lnes were not statstcally sgnfcant when compared to the comparson stes. At the end, the researcher concluded that there was no substantal proof to consder that 8-n. wde edge lnes usage sgnfcantly reduced the nvestgated crash rates. Another study from New Mexco by J. W. Hall n 1987 used 530 mles of rural two-lane hghway to evaluate the ROR and OD crash rates [16]. The study appled 8-n. edge lnes on 176 mles of the studed roadway, and the remanng sectons used 6 n. for comparson purposes. The fndngs showed that crash rates decreased approxmately 10% at the treatment locatons and 16% at the comparson sectons. A recent 2010 study by J. D. Mles et al. evaluated the potental benefts of usng wder and brghter edge lne markngs [17]. The crash data analyss conducted n the study supports the mplementaton of wde edge lne pavement markngs to mprove safety along rural hghways. In the recently publshed frst edton of the Hghway Safety Manual (HSM), there are CMFs for placng standard and wde edge lne markngs on rural two-lane hghways (wthout mentonng the wdth of pavement) [18].The CMF value of the edge lne placement (from HSM) s wthn the range of 0.90 to However, ths CMF value from HSM cannot be used drectly. Although nvestgatons were conducted on the effectveness of edge lne mplementaton as revewed above, none of these studes were done for the narrow, rural two-lane hghways n Lousana. There s a need to contnue the 2011 study not just wth more crash data but also wth the well accepted crash analyss methodology. It s mportant to nvestgate crash characterstcs analyss of before and after years and beneft-cost rato for edge lne mplementaton on narrow, rural two lane hghways. 4

23 OBJECTIVE The goal of ths project was to nvestgate the safety mpact of pavement markngs on rural two-lane hghways n Lousana. Specfcally, the research objectves were: Conduct a complete before-and-after crash analyss wth three years before and three years after crash data to estmate the crash reducton factors wth EB method. Conduct crash characterstcs analyss. Conduct beneft-cost analyss. 5

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25 SCOPE To meet the objectves of ths project, ths study was conducted on selected narrow, rural two-lane hghways wth pavement wdth less than 22 ft. from all DOTD dstrcts. It was done wth the collaboraton of all DOTD dstrcts for edge lne mplementaton. The annual crash frequences of sx years (2005, 2006, 2007 as the before perod, and 2009, 2010, 2011 as the after perod ) from each ste were used. The mproved safety predcton and Emprcal Bayes (EB) methods are used n the analyss. 7

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27 METHODOLOGY The study conssts of three basc steps: selecton of the segments, edge lne mplementaton, and before-after crash analyss. Snce the frst two steps are already descrbed n detal n the 2011 study report, n ths secton focus wll be gven to the before and after study wth EB method, thorough analyss on the traffc flow characterstcs, crash and drver characterstcs, correlaton between the contrbutng factors, and beneft-cost analyss. Selecton of Segment and Edge Lne Implementaton As n the report Safety Improvement from Edge Lnes on Rural Two-Lane Hghways, the total length of the study sectons was mles [4]. After nvestgatng the condton of pavement markngs, two control sectons were excluded from ths study due to the fadng edge lnes. The fnal lst of the analyzed segments s gven n Table 1. Table 1 Secton length and no. of control sectons of the dstrcts DOTD No. of Secton Length Dstrct Control Sectons Average Before and After Crash Analyss The objectve of an unbased observatonal before-after study s to evaluate a treatment where the hghways and facltes are unchanged (ncludng AADT) except for the mplementaton of the treatment. However, t s mpossble to control the changes of other factors n a hghway safety study. Theoretcally speakng, the true mpact of a treatment 9

28 should be the dfference between the predcted safety after the treatment and the predcted safety n the after perod f the treatment were not mplemented. Two methods are used n the analyss. Improved Before and After Crash Analyss To account for the change n traffc volume, the followng procedure, ntroduced by E. Hauer, was used n estmatng the unbased crash changes before and after nstallaton of the edge lne [19]. Step One: Estmatng the safety f the edge lne was not nstalled durng the after perod,, and the safety wth the edge lne project N (1) r tf where, N K tf r A B avg avg K = Estmated expected number of crashes n the after tme perod wth the edge lne = Observed annual crashes after edge lne project = Estmated expected number of crashes n the after perod wthout the edge lne = Observed annual crashes before the edge lne project = Traffc flow correcton factor A = B avg avg = Average traffc flow durng the after perod = Average flows durng the before perod (2) The results of ths applcaton are lsted n Table 2. 10

29 Table 2 Results from the frst step DOTD Dstrct Secton Length No. of Control Sectons ˆ , ,967 34, ,187 2, ,200 18, ,977 4, ,047 3, ,967 5, ,923 7, ,270 27, All , , ,026 Â avg Bˆ avg rˆ tf ˆ Step Two: Estmatng the varance VAR } and VAR } { { { VAR VAR { r tf } N } r tf v { Aavg} v { B avg} VAR { } rd r tf K K VAR { r tf } where, VAR {ˆ} = Estmated varance of r d = Rato of tme duraton of after perod to tme duraton of before perod v = The percent coeffcent of varance for AADT estmates = number of count - days AADT 82 (Number of count-days s consdered as 3 n calculaton.) VAR { } = Estmated varance of (3) (4) (5) 11

30 The results of ths applcaton are lsted n Table 3. DOTD Dstrct Secton Length No. of Control Sectons Table 3 Results from the second step VAR {ˆ} { A ˆ } avg v v B ˆ } { avg VAR {ˆ } { rˆ tf } All Step Three: Estmatng the crash dfference and the rato (6) VAR where, 1 VAR { } 2 = Estmated safety mpact of the project = Estmated unbased expected crash modfcaton factor (7) The results of ths applcaton are lsted n Table 4. 12

31 Table 4 Results from the thrd step DOTD No. of Secton Length Dstrct Control Sectons ˆ ˆ All Step Four: Estmatng the standard devaton of and ˆ { ˆ} { } ( VAR ˆ { ˆ} VAˆ R{ ˆ}) VAR { } VAR { } 2 2 VAR 1 2 { } The results of ths applcaton are lsted n Table 5. (8) (9) 13

32 DOTD Dstrct Secton Length Table 5 Results from the fourth step No. of Control Sectons ˆ { ˆ} var ance ˆ { ˆ} All var ance Emprcal Bayes Method The EB method s a statstcal method that combnes the observed crash frequency wth the predcted crash frequency usng the Safety Performance Functon (SPF) to calculate the expected crash frequency for a ste of nterest. Ths method can account for the effect of regresson-to-the-mean along wth changes n traffc volume and other changes not due to the treatment n crash frequences. It has been consdered a statstcally defensble safety evaluaton tool n observatonal before-after studes for more than two decades [20]. In an EB method, SPFs are used to estmate the expected crash frequences at the treated stes had treatments not been appled [19]. Generalzed lnear regresson models, specfcally negatve bnomal regresson models, are often used to derve the SPFs [21]. It s mportant to note that, n ths evaluaton, safety performance functons were calbrated for each year of the before and after perods rather than just for each perod. Step One: The frst step was to develop a SPF. Researchers used the SPF of HSM for rural two-lane hghway segments as gven below: ˆ 6 ( 0.312) E( k ) AADT L36510 y e (10) 14

33 where, E(k y )= predcted total crash frequency for roadway segment base condtons; AADT = average annual daly traffc volume (vehcles per day); L = length of roadway segment (mles). After developng the SPF functon, researchers estmated the expected number of crashes for each year n the before perod at each treatment ste. Step Two: The second step was to compute the sum of the annual SPF predctons for each treatment ste durng the before perod by: y 1 O k y y1 P Eˆ( ) (11) where, y 0 denotes the year durng whch the edge lne was nstalled at ste. The results of frst two steps are lsted n Table 6. Table 6 Results from the frst two steps DOTD No. of Secton Length Dstrct Control Sectons P All Step Three: The thrd step was to obtan an estmate of the expected number of crashes (M ) before mplementaton of the countermeasure at each treatment ste and an estmate of varance of M. The estmate M was gven by combnng the sum of the annual SPF predctons durng the before perod (P ) wth the total count of crashes durng the before 15

34 perod as follows: M w P ( 1 w ) K (12) where, K s the total crash counts durng the before perod at ste and the weght w s gven by: 1 w (13) P 1 k where, k s the estmated over dsperson parameter of the negatve bnomal regresson model that s a functon of the roadway segment length as specfed n HSM. The closer the over dsperson parameter s to zero, the more statstcally relable the SPF s. The value s calculated as: k (14) L where, k = over dsperson parameter; L = length of roadway segment (mles). An estmated varance of M s gven by: Var ( M ) (1 w ) M (15) As the relatonshp s lnear, the M value of each dstrct was calculated by summng up all consecutve control sectons. I M 1 Mˆ (16) I Var ˆ ( Mˆ ) Var( ) (17) 1 M The results of step three are shown n Table 7. 16

35 Table 7 Results from the thrd step DOTD No. of Secton Length Dstrct Control Sectons M Var(M ) All Step Four: The fourth step was to determne SPF predctons E ˆ( ) for each year n the after perod at each treatment ste, and compute C (the rato of the sum of the annual SPF predctons for the after perod, Q and the sum of the annual SPF predctons for the before perod, P ). C y yyo1 yyo1 y1 Eˆ( k Eˆ( k y y ) Q ) P k y (18) Step Fve: The ffth step was to obtan the predcted crashes and ts estmated varance durng the after perod that would have occurred wthout mplementng the countermeasure. The predcted crashes ( ˆ ) are gven by: ˆ CM (19) The estmated varance of ( ˆ ) s gven by: 2 2 V ar ˆ ( ) C Var ˆ ( M ) C (1 w) M (20) Step Sx: The sxth step was to compute the sum of the predcted crashes over all stes n a treatment group of nterest and ts estmated varance by: I ˆ (21) 1 17

36 I Var ˆ ( ˆ) Var( ˆ ) (22) 1 where, s the total number of stes n a treatment group of nterest. The results of step four to step sx are shown n Table 8. DOTD Dstrct Table 8 Results from the fourth to sxth steps No. of Secton Length Control C ˆ Var (ˆ ) Sectons All ,016 1, Step Seven: The seventh step was to compute the sum of the observed crashes over all stes n a treatment group of nterest by: L I L 1 where, L s the total crash counts durng the after perod at ste. (23) Step Eght: The ndex of effectveness of the countermeasure was estmated by: ˆ 1 L VAR { } 2 where, = Estmated unbased expected crash modfcaton factor. (24) Step Nne: The nnth step was to compute the estmated varance and standard error of the 18

37 ndex of effectveness and the approxmate 95% confdence nterval for. The estmated standard error of the ndex of effectveness are gven by: { } 1 Var { } L Var { } The results of step seven to step nne are shown n Table 9. (25) DOTD Dstrct Secton Length No. of Control Sectons Table 9 Results from the seventh to nnth steps L ˆ sd (ˆ ) ˆ 3 * sd ( ˆ ) ˆ 3 * sd ( ˆ ) All Traffc Flow Characterstcs In addton to the CMF development, traffc characterstcs were also analyzed to see f sgnfcant changes exst between the before and after tme perods. It s noted the AADT ncreased by 4% on average durng the after perod. The densty plot of AADT s presented n Fgure 1, whch ndcates two spkes n AADT durng the after perod. Fgure 2 represents the densty plot of estmated operatng speed n before-after perods, whch shows denstes of the moderate speed (50-65mph) are ncreased n the after years. Edge lnes helped the drvers to keep ther vehcles n proper lane; at the same tme, drvers ncrease the speed because of the nature of behavoral adaptaton. The box and whsker plot n Fgure 3 clearly shows the ncreased average speed. 19

38 Fgure 1 Densty of AADT n before-after perods Fgure 2 Densty of estmated speed of the vehcles nvolved n crashes n before-after perods 20

39 Fgure 3 Box and whsker plot of estmated speed of the vehcles nvolved n crashes n beforeafter perods Fgure 4 plots the relatonshp between crash rate and AADT for the two study perods. Under same or smlar AADT, crash rates were generally hgher n the before perods than the after perods. Crash Rate Before Years AADT Fgure 4 AADT vs. crash rate n before-after perods After Years 21

40 Crash Characterstcs In addton to the change n traffc characterstcs, researchers also nvestgated the change n crash characterstcs. Fgure 5 shows the crash severtes by year. Number of Crashes TOTAL PDO INJURY Fgure 5 Crash severty n before-after perods There s a slght ncrease n the fataltes manly due to a hgh number n 2010 as shown n Table 10. Table 10 Fatal crashes n before and after years Severty Type Fatal crashes The occurrence of a fatal crash s an extremely rare event consderng the magntude of AADT. Annual fatal crashes are hghly random. Therefore, the ncrease n 2010 could be a varaton from the mean. The njury crashes n the after perod decreased by 19.6% and Property Damage Only (PDO) crashes decreased by 9.5%. 22

41 It s always nterestng to see the changes n type of collsons n the before and after perods. Fgure 6 gves the changes n types of collson durng before and after perods. Sngle vehcle crashes are seen as the most sgnfcant type of collsons. SIDESWIPE RIGHT TURN COLLISION TYPE After COLLISION TYPE Before LEFT TURN RIGHT ANGLE HEAD-ON REAR-END SINGLE VEHICLE Yearly average crashes Fgure 6 Crash severty n before-after perods by type Clearly, sngle vehcle crashes reduced after the edge lne nstallaton. These crashes are commonly nvolved n road departures. Overall, sngle vehcle crashes decreased by 13%, rear-end crashes decreased by 4%, and rght angle crashes decreased by 20% n the after tme perod. On the other hand, left-turn crashes ncreased by 16%. The crash data also shows that the road departure crashes reduced nearly by 17% n the after perod whch clearly specfes the postve safety mpact of edge lne markngs. Fgure 7 shows a densty plot of crash hour n the before-after perod of edge lne nstallaton. Mnor changes n the nght-tme crashes are vsble from ths plot. 23

42 Fgure 7 Densty plot of crash hour n before-after perods Table 11 lsts the number of crashes under dfferent lghtng condtons. The majorty of crashes happened n daylght. As shown n Table 11, daylght crashes decreased by 14% and nght tme crashes (wth no street lght) decreased by 12%. But crashes under the proper lghtng condton seemed to ncrease. The number of crashes ncreased by 16% for roadway segments wth the proper lghtng. The hgher operatng speed caused by behavoral adaptaton n a more vsble zone may have affected ths result. Table 11 Lghtng condton for before and after years DAYLIGHT DARK - NO STREET LIGHTS DARK - CONTINUOUS STREET LIGHT DARK - STREET LIGHT AT INTERSECTION ONLY

43 Fgure 8 represents the crash scenaro based on the surface condton. Under wet and dry surface condtons, fewer crashes were seen durng the after years. When pavement s wet, edge lne markngs are not as clearly vsble as under dry condtons. The neglgble decrease n wet pavement surface justfes ths crteron (14.90% decrease n dry condton and 8.20% decrease n wet condton). SURFACE CONDITION After WET SURFACE CONDITION Before DRY Yearly average crashes Fgure 8 Surface condton n before-after years Drver Characterstcs Human factor s consdered as a practcal, scentfc dscplne that tres to enhance the relatonshp between devces and systems and the user. The man focal pont of ths dscplne n hghway safety s the roadway user. Drvng errors such as wrong perceptons, slower reactons, and poor decson makng are the products of a poor match between the needs and capabltes of drvers and the task demands on the roadway. To lnk drver, vehcle, roadway, and envronmental factors to specfc crtera of drver behavor and performance s the mportant task to mprove overall road safety. Drver related factors can be dvded nto four broad categores: background factors (experence, tranng, professon, etc.); demographc factors (age, gender, lcense state, etc.); physologcal factors (drvng behavor, physcal and mental health, vson, hearng, etc.); and socal factors (lfe qualty, socal health, etc.). The behavors of drvers depend on these factors. The drvng task lke 25

44 speed and headway selecton, lane mantenance, lane changng vares wth dfferent drver profles (normal, aggressve, dstracted, mpared, drowsy, reckless, cautous, etc.). About 52% of Lousana s lcense holders are female. Although males were nvolved n more crashes, they were also engaged n more vehcle mles travelled. The breakdown of the crashes by male and female offenders over the perod of nvestgaton s shown n Fgure 9. It s seen that female nvolvement n crashes does not change much after the nstallaton of edge lnes. In the crash database, about 5% of the records have no drver gender nformaton, whch explans why the sum of male and female crashes doesn t add up to the total number of crashes. Drvers nvolved Male Female Fgure 9 Male and female drvers n traffc crashes It s well known that drvers n dfferent age groups behave dfferently. The very young and the very old have the hghest crash rates but for dfferent reasons. To see the effect of edge lnes by age group, the crash frequency was dvded by age group as youths (15-24), mddleaged drvers (25-54), and senors (55 and above). The mddle-aged groups were subdvded nto 10-year age groups (25-34, 35-44, and 45-54). The dstrbuton of crashes based on drver s age was plotted n Fgure 10. Young drvers (15-24) were seen to be nvolved n fewer crashes after the placement of edge lnes. Although t s not surprsng to see small varatons between the before and after perods due to the regresson-to-the-mean effect, the 17% drop n the age group was engrossng. On the other hand, crashes ncreased n age group by 8%. 26

45 Before Years ( ) After Years ( ) No. of crashes or Above Drver's age Fgure 10 Drver age dstrbuton Fgure 11 and Fgure 12 show the mpact of drver dstracton and volaton n traffc crashes n the selected segments n before and after years. Over the last 20 years, the concept of drver dstracton has been consdered as a key focus n the feld of human factor related research. A large and expandng body of research has documented the myrad ways n whch dstracton can mpact on drvng performance and safety. Edge lne nstallaton ndcates a reducton n the number of crashes caused by dstracted and volaton drvng. The possble reason s the edge lne markngs help the drvers n daylght or n dark to mantan ther proper guded way. 27

46 UNKNOWN DRIVER DISTRACTION After DRIVER DISTRACTION Before NOT DISTRACTED CELL PHONE Yearly average crashes Fgure 11 Drver dstracton related crashes n before and after perod NO VIOLATIONS VIOLATIONS After VIOLATIONS Before CARELESS OPERATION FOLLOWING TOO CLOSELY FAILURE TO YIELD Yearly average crashes Fgure 12 Drver volaton nduced crashes n before and after perod 28

47 Correlaton between Contrbutng Factors Varous categorcal and numercal varables were consdered for analyss n ths study. A complete lst of the analyzed varables s gven n Appendx A. The challenge was to select the approprate varables for observng the mpact of edge lne markngs n rural two-lane hghways. The sgnfcant varables nvestgated n ths secton are: AADT, drver s age, posted speed, estmated speed, and crash hour. Estmated drvng speed (drver s operatng speed) and crash hour are consdered as two mportant numercal varables because of ther sgnfcant mpact on the safety outcome of edge lne markngs. Fgures provde nformaton on the relatonshp between the assocaton factors. In these fgures, t s mportant to note that any mssng value aganst any partcular crash number doesn t generate data ponts. Fgure 13 llustrates the dstrbuton of operatng speed by crash severty and crash hour for the before and after tme perods. Fgure 13 Correlaton between crash hour and estmated speed wth crash severty It s a close correlaton between crash hour and estmated operatng speed n fatal crashes. The hgher speed s the key reason for the crash occurrence durng the before perod. In after years, two fatal crashes were seen to have occurred under lower speed at nght. For njury and PDO crashes, hgh speed drvng has hgher concentraton of crash occurrences. 29

48 Fgure 14 shows the correlaton between crash hour and estmated operatng speed n comparson wth weather condton. The fgure ndcates that a hgher speed s the sgnfcant factor for crash ncdents n cloudy and rany weather. Fgure 15 shows the correlaton between crash hour and estmated speed n comparson wth drver s lcense state. Most crashes are assocated wth the local lcense holders whle the non-local drvers are seen to be nvolved n crashes when the operatng speed s hgher n before years. A closer look at the fatal crashes n before-after perod, t was seen that non-lousana drvers n before perods were nvolved n fatal crashes when the operatng speed was hgher. Fgure 14 Correlaton between crash hour and estmated speed wth weather condton 30

49 Fgure 15 Correlaton between crash hour and estmated speed wth drver s lcense state Both alcohol and drug mpared drvers are more lkely to cause a fatal or severe njury crash than sober drvers. Alcohol s more often nvolved n rural-area crashes than n urban-area crashes. In 2011, alcohol was nvolved n 45% of rural and n 34% of urban fatal crashes n Lousana. Fgure 16 and Fgure 17 shows the relatonshp between mpared drvng speed and crash occurrence hours. Impared drvers are seen to be nvolved n more fatal or njury crashes when the operatng speed s hgher n both before and after years. From the fgures, t can be nferred that edge lne nstallaton has lttle effect on the lane-keepng tendency for the mpared drvers, whch resulted n traffc crashes. 31

50 Fgure 16 Correlaton between crash hour and estmated speed wth alcohol related crashes Fgure 17 Correlaton between crash hour and estmated speed wth drugs related crashes 32

51 DISCUSSIONS OF RESULTS Postve Safety Trend Although the results show a declne n crashes, the overall crash reducton trend n the last few years should be consdered, excludng the year For the past several years, Lousana along wth the entre country has been experencng a steady declne n annual crash frequences. The total traffc fataltes n the Unted States has declned from 42,708 n 2006 to 41,259, 37,423, 33,808 and 32,788 n 2007, 2008, 2009 and 2010, respectvely [22].In 2011, Lousana experenced 630 fatal crashes (decreased by 2.02% from 2010), 677 persons klled (decreased by 5.97% from 2010), 43,343 njury traffc crashes (ncreased by 2.06% from 2010)[23]. As llustrated n Table 12, the number of crashes n Lousana has also decreased snce 2006 except Durng the study perod, the total crashes reduced by 5.6% from the before years ( ) to the after years ( ). Table 12 Total crashes by year Year Total Crashes Percentage Change , , % (ncrease) , % (decrease) , % (decrease) , % (decrease) , % (decrease) , % (ncrease) (total) 480, (total) 453, % (decrease) Table 13 summarzes the results from both of the methods. Two columns are shown n the table to evaluate the confdence nterval. By observng the results, t s seen that all of the dstrcts experenced a postve safety mpact from edge lne nstallaton except Dstrct 03. The Emprcal Bayes results show tghter values than the mproved predcton n most of the dstrcts. 33

52 Table 13 Crash modfcaton factor wth confdence nterval Improved predcton method Emprcal Bayes method Secton No. of ˆ ˆ 3 * sd ( ˆ ) ˆ 3 * sd ( ˆ ) ˆ ˆ 3 * sd ( ˆ ) ˆ 3 * Length Control Sectons All DOTD Dstrct sd ( ˆ ) The crash reducton s also nvestgated by the pavement wdth of a rural two-lane hghway as shown n Table 14. Table 14 Decreasng trend of crashes on rural two-lane hghways Year Less than 20' Less than 22' and bgger than or equal to 20' 22' More than 22' Total ,747 2,847 6,794 12, ,741 2,891 7,041 12, ,993 3,070 7,480 13,765 Average 189 2,827 2,936 7,105 13,057 ( ) ,686 2,965 6,816 12, ,892 2,966 6,397 12, ,796 2,910 6,496 12,408 Average 226 2,791 2,947 6,570 12,534 ( ) Change 19.58% -1.27% 0.37% -7.53% -4.01% Accordng to the crash record, the crash reducton s nearly 4.01% for rural two-lane hghways of all pavement wdths and s 1.3% for narrow hghways (less than 22 ft. and bgger than or equal to 20 ft.) durng the study perod. Most of the studed control sectons were n the less than 22 ft. and wder than or equal to 20 ft. group. For the safety trend analyss, the safety mprovement of ths group was calculated. Consderng ths fact, the 34

53 estmated crash modfcaton factor would be estmated as 0.85 ( ) wth a standard devaton That means the range of the CMF s {0.73, 0.96}. Beneft-Cost Analyss The cost for nstallng 6-n. waterborne edge lnes vares based on the agency rate and product. Accordng to the Lousana estmates, the average cost for a fatal cost s $4,376,304, for an njury crash s $137,670, and for a PDO s $3,292. Installng edge lnes reduces njury and PDO crashes, thus the average cost of crashes would be consdered as a safety beneft. The observed reducton of crashes s consdered here for the beneft-cost analyss. One fatal crash ncrease n after years s excluded from the calculaton because the number of annual fatal crashes s hghly random wth a small sample sze. The estmated beneft-cost rato for edge lne nstallaton ranges from to per lane mle based on agency rate and materal. The beneft-cost estmatons are shown n Table 15. Table 15 Estmated beneft-cost rato for edge lne nstallaton Fatal Crash Injury Crash PDO Crash Reducton Cost ncludng loss of qualty of lfe 4,376, ,670 3,292 Savngs from averted crashes 11,426, ,184 Total Beneft 11,597,794 Pant (DOTD) Pant (Contractor) Thermoplastc (Contractor) Cost per lane mle $450 $700 $2800 Total cost $98,676 $153,496 $613,984 Beneft-cost rato

54

55 CONCLUSIONS Based on the analyss results and dscusson, the followng conclusons can be drawn: 1. Placng pavement edge lnes on rural two-lane hghways n Lousana can not only change vehcle lateral postons but can also reduce crashes. 2. Based on the Emprcal Bayes method, the most relable CMF for edge lnes on narrow, rural two-lane hghways (pavement wdth less than 22 ft. and wder than or equal to 20 ft.) s Consderng the safety trend n Lousana, the fnal estmated CMF s 0.85, whch means there s a 15% expected crash reducton n edge lne wth mplementaton on narrow, rural two-lane hghways. The statstcally estmated standard devaton for the CMF s The CMF range (0.73, 0.96) ndcates a certanty n crash reducton wth edge lnes. 5. The crash reducton s consstent n all crash types and s partcularly sgnfcant n sngle vehcle crashes. Most of sngle vehcle crashes are ROR crashes. 6. The benefts overwhelmngly offset the cost wth edge lne mplementaton. The most conservatve estmaton for beneft and cost rato s

56

57 RECOMMENDATIONS Ths project recommends the use of edge lnes on narrow, rural two-lane hghways whenever fnancally and operatonally feasble. Snce each DOTD dstrct bears the responsblty of mplementng pavement markngs, DOTD may want to establsh a polcy askng each dstrct to mplement edge lnes f suffcent resources are avalable. Under fnancal or operatonal constrants, roadways wth hgher traffc volumes should have prorty to have edge lnes mplemented. 39

58 40

59 ACRONYMS, ABBREVIATIONS, AND SYMBOLS AADT ADT AASHTO CMF CRF DOT EB FHWA HSM ITS DOTD LTRC MUTCD NCHRP OD PDO ROR RPM SHSP SPF VMT VPD Annual Average Daly Traffc Average Daly Traffc Amercan Assocaton of State Hghway and Transportaton Offcals Crash Modfcaton Factor Crash Reducton Factor Department of Transportaton Emprcal Bayes Federal Hghway Admnstraton Hghway Safety Manual Intellgent Transportaton Systems Department of Transportaton and Development Lousana Transportaton Research Center Manual of Unform Traffc Control Devces Natonal Cooperatve Hghway Research Program Opposte Drecton Property Damage Only Run-off Road Rased Pavement Marker Strategc Hghway Safety Plan Safety Performance Functon Vehcle Mle Traveled Vehcles Per Day 41