STATE HIGHWAY ADMINISTRATION RESEARCH REPORT ENHANCEMENT OF FREEWAY INCIDENT TRAFFIC MANAGEMENT AND RESULTING BENEFITS

Transcription

1 MD-11- SP009B4Q STATE HIGHWAY ADMINISTRATION RESEARCH REPORT ENHANCEMENT OF FREEWAY INCIDENT TRAFFIC MANAGEMENT AND RESULTING BENEFITS WOON KIM AND MARK FRANZ GANG-LEN CHANG DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING UNIVERSITY OF MARYLAND COLLEGE PARK, MD SP009B4Q FINAL REPORT APRIL 2012

2 The contents of ths report reflect the vews of the author who s responsble for the facts and the accuracy of the data presented heren. The contents do not necessarly reflect the offcal vews or polces of the Maryland State Hghway Adnstraton. Ths report does not consttute a standard, specfcaton, or regulaton.

3 Report No. MD-11- SP009B4Q 4. Ttle and Subttle Techncal Report Docuentaton Page 2. Governent Accesson No. 3. Recpent's Catalog No. Enhanceent of Freeway Incdent Traffc Manageent and Resultng Benefts 5. Report Date Aprl Perforng Organzaton Code 7. Author/s 8. Perforng Organzaton Report No. Woon K, Mark Franz, and Gang-Len Chang 9. Perforng Organzaton Nae and Address Unversty of Maryland, Departent of Cvl and Envronental Engneerng, Maryland, College Park, MD Sponsorng Organzaton Nae and Address Maryland State Hghway Adnstraton Offce of Polcy & Research 707 North Calvert Street Baltore, MD Work Unt No. (TRAIS) 11. Contract or Grant No. SP009B4Q 13. Type of Report and Perod Covered Fnal Report 14. Sponsorng Agency Code (7120) STMD - MDOT/SHA 15. Suppleentary Notes 16. Abstract To prove traffc condtons on ajor hghways plagued by non-recurrent congeston, ost hghway agences have nvested ther resources n two prncpal operatonal progras: ncdent response and clearance, and traffc pact anageent. However, even wth the wde-spread pleentaton of such progras, effectvely nzng the traffc pact caused by ult-lane blocked ncdents reans a crtcal and challengng ssue for ost hghway agences. Ths research developed a ult-crtera decson-support syste for deternng the necessty of detour operatons durng ncdent anageent fro an overall soco-econoc beneft perspectve. The developed syste enables responsble agences to consder all assocated crtcal factors wth preferred weghts, ncludng the drect benefts and operatonal costs, safety and relablty, accessblty of detour, and acceptablty by travelers. Ths research s part of our developed ntegrated ncdent anagng syste for SHA that has varous essental functons, rangng fro predcton of ncdent duraton to estaton of operatonal benefts. Ths decson odule, based on the AHP (analytcal herarchcal process) ethodology, features ts coputng effcency and operatonal flexblty, allowng users to ake necessary revsons f ore data are avalable or ore crtera need to be ncluded. 17. Key Words Incdent, detour operatons, benefts, corrdor optzaton 19. Securty Classfcaton (of ths report) None 18. Dstrbuton Stateent: No restrctons Ths docuent s avalable fro the Research Dvson upon request. 20. Securty Classfcaton (of ths page) None 21. No. Of Pages 104 For DOT F (8-72) Reproducton of for and copleted page s authorzed. 22. Prce

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5 Table of Contents CHAPTER 1: Introducton Research Background Research Objectves Report Organzaton... 2 CHAPTER 2: Lterature Revew Introducton Incdent Response Strateges Coverng odels P-edan odels P-center odels Incdent Duraton Estaton Probablstc dstrbutons Condtonal probabltes Regresson odels Dscrete choce or classfcaton odels Decson or classfcaton trees Te sequental odels Detour Decson Support Syste CHAPTER 3: Revew of the FITM Progra and Operatons Introducton of the FITM Progra by SHA Crtera for Actvatng Detour Operatons A FITM Decson and Evaluaton Fraework Analyss of FITM-ncdents Closure v

6 CHAPTER 4: A Corrdor Control Model for Optzng Detour Operatons Introducton Forulatons of Network Traffc Flow Dynacs An Integrated Traffc Control Model Soluton Method Nuercal results CHAPTER 5: An Integrated Mult-crtera Support Syste for Assessng Detour Decsons Introducton The Detour Decson-Support Syste Syste fraework developent Suppleental odels for the syste Illustraton of the Syste Applcaton How relatve weghts for the evaluaton crtera affect the fnal results Concluson Recoendatons Bblography v

7 CHAPTER 1: Introducton 1.1 Research Background Although the ncdent response progra, naed Coordnated Hghways Acton Response Tea (CHART) by the Maryland State Hghway Adnstraton (SHA), has been well recognzed as one of the ost effcent ncdent response progras, the an prorty of CHART operators n response to detected ncdents has been anagng traffc at the ncdent scene and assstng drvers. However, CHART stll faces a challenge on how to effectvely strealne the traffc anageent actons for the hghway network pacted by a ajor accdent that deands the actvaton of a Freeway Incdent Traffc Manageent (FITM) plan. Concevably, effcently detourng vehcles durng the response operatons of ajor accdents to nze the foraton of traffc queues s a coplex task, as t necesstates good coordnaton aong agences responsble for varous crtcal actvtes. These nclude estatng the ncdent duraton and ts pact boundares, dentfyng the avalable detour routes, decdng where and what to dsplay on dynac essage sgns (DMS), and deternng how to accoodate the detoured traffc wth responsve sgnal settngs. Hence, the FITM plan wth the best plannng and proper executon ay yeld substantal benefts to both the network drvers and the entre socety. The pressve annual benefts reported by CHART, however, do not nclude the contrbuton fro the actvaton of the detour traffc anageent plans durng ajor ncdents. In vew of the dnshng resources and the pressng needs to nze the pacts of hghway accdents, a prorty task for SHA to further prove ts operatonal effectveness s to dentfy potental areas for CHART to enhance ts traffc ncdent anageent, especally durng pleentaton of the FITM plan. Such a task ncludes: (1) analyzng the spatal dstrbuton and nature of recent ncdents that requred SHA to pleent varous FITM plans; (2) understandng the nterrelatonshps between the duraton of detected ncdents, the congeston level, and SHA s decson to trgger a FITM plan; and (3) estatng the costs and benefts assocated wth soe of SHA s past FITM operatons. Due to the addtonal efforts and costs nvolved n detourng traffc, t s also peratve to have a relable decson-support tool that can assst SHA engneers n akng a relable and tely decson n a real-te operatonal envronent, based on the detected ncdent severty, estated clearance duraton, traffc 1

8 condtons on avalable detour routes, estated traffc flow speeds on the prary and detour routes wth and wthout pleentng the FITM plan, and the resultng costs and benefts for varous traffc anageent strateges. 1.2 Research Objectves Ths research, proposed n response to the need to enhance the effcency of CHART s FITM operatons, has two prary objectves: (1) understand the nature of those ncdents that trggered pleentaton of the FITM plan over the past fve years; and (2) develop a decsonsupport syste that enables traffc engneers to deterne whether any detour operaton can be justfed. The decson support syste can also serve as an evaluaton tool for responsble staff to revew the past perforance of FITM operatons and reset soe decson thresholds based on avalable resources and personnel constrants. Note that the byproduct of such a decson-support tool ncludes the estated travel tes on the prary and detour routes and the resultng benefts such as reducton n delay, fuel consupton, and essons. Thus, wth soe addtonal traffc nforaton such as volues on the prary and detour routes durng the ncdent clearance perod, CHART can further estate the operatonal benefts produced fro annual FITM operatons and nclude these potentally large benefts n the annual CHART perforance evaluaton report. 1.3 Report Organzaton Based on the above objectves, the research results are organzed nto sx chapters. A bref descrpton of each chapter follows: Chapter 2 revews the lterature concernng ncdent response and anageent, dvdng all related studes nto three categores: ncdent response strateges, ncdent duraton estaton, and detour decson-support systes. Secton 2-2 presents those locaton coverage odels for best allocatng traffc response unts and housng avalable resources for eergency servce needs. Secton 2-3 suarzes state-of-the-art studes on predctng the duraton of a detected ncdent, the ost crtcal nforaton for estatng the resultng traffc pact boundares. Secton 2-4 brefly descrbes state of the practces on detour decson support systes, ncludng ther decson crtera, data needs, operatonal procedures, and potental areas for enhanceent. Results of the lterature revew serve as the bass for developng a ult-crtera decson-support 2

9 tool that allows responsble agences to ake a proper detour decson based on all assocated factors. Chapter 3 provdes an n-depth revew of SHA s FITM progra and dentfes potental areas for ts further enhanceent. Secton 3-2 copares the crtera used by SHA s FITM progra wth those eployed by other hghway agences, hghlghtng the need for an effectve decson-support syste for detour operatons. Secton 3-3 reports the analyss results of those ncdents trggerng the FITM operatons (called FITM-ncdents) between 2007 and 2010, ncludng the dstrbutons by locaton, ncdent nature, nuber of blocked lanes, truck nvolveent, clearance duraton, dfferent tes of the day, and dfferent days of the week. Chapter 4 ntroduces a freeway corrdor control odel desgned specfcally to optze the detour operatons durng non-recurrent congeston, ncludng the optal te-varyng detour rate, the actvaton and ternatng tes for detour operatons, and the sgnal te for each ntersecton n the detour route. Secton 4-2 presents the forulatons for odelng the coplex nteractons between freeway and surface traffc flows under varous detour control strateges, consderng the potental utual lane blockage at crtcal ntersectons due to the detourng traffc. Secton 4-3 dscusses ethods to specfy the objectve functon of the optal corrdor odel so that ts pleentaton can nze the total congeston and balance traffc condtons on the prary and detour routes. Secton 4-4 detals the soluton algorth desgned specfcally to enable traffc engneers to operate the developed odel n real te durng detour operatons. Secton 4-5 llustrates the case study results wth the optal corrdor control odel, hghlghtng the potental operatonal ssues and the resultng benefts. Chapter 5 presents a ult-crtera decson support syste for detour operatons, ncludng estaton of ncdent duraton, projecton of the traffc queue length, coparson between the traffc flow speeds wth and wthout detourng traffc, and a cost-beneft analyss for pleentng the FITM plan. Secton 5-2 llustrates the structure of an effectve syste for realte ncdent response and traffc anageent syste, focusng on the operatonal procedures and crtera to evaluate the need for detour operatons. Secton 5-3 analyzes the syste applcaton wth ncdent scenaros calbrated fro feld data, ncludng the senstvty of varous key paraeters on the decson outcoe, and prortzng ebedded crtera based on avalable resources and publc concerns. 3

10 Chapter 6 frst suarzes the research fndngs of ths study, hghlghtng the defcences of exstng practces n contendng wth non-recurrent congeston and potental areas for enhanceent. Ths secton s followed by recoendatons for SHA to advance ts FITM operatons n vew of the ncreasng frequency of ncdents and dnshng resources. 4

11 CHAPTER 2: Lterature Revew 2.1 Introducton Ths chapter suarzes the ajor studes concernng freeway ncdent traffc anageent over the past decades, focusng on crtcal ssues, exstng approaches, and potental research drectons. Ths chapter presents and dvdes the revew results nto the followng categores: Incdent response strateges: focusng on how best to use the avalable resources n response to detected and potental ncdents over the servce area durng a target te perod; Incdent duraton estaton: hghlghtng the data ssues and ajor strea of ethodologes to relably estate the duraton of a detected ncdent; and Detour decson support syste: evaluatng exstng crtera, strateges, or procedures used to deterne whether or not detour operatons are necessary. The reanng sectons present a bref suary of exstng studes related to each category n sequence. 2.2 Incdent Response Strateges A large body of traffc studes has ponted out the crtcal role of effcent response to the total delay ncurred by ncdents and concluded that an ncrease n ncdent response te ay contrbute to the lkelhood of havng secondary ncdents (Bentha, 1986; Brodsky and Hakkert, 1983; Mueller et al., 1988). The study results by Sanchez-Mangas et al. (2009) shows that a reducton of 10 nutes n eergency response te could result n 33 percent less probablty of ncurrng vehcle collson and fataltes. Most studes conclude that dspatchng eergency servces unts and clearng the ncdent scenes n a tely anner are the key tasks for nzng ncdent pact (Kepaptsoglou et al., 2011: Huang and Fan, 2011). In provng the effcency of eergency ncdent responses, both avalablty and accessblty of servce unts play essental roles. The avalablty of response unts can dffer dependng on the relatonshp between eergency response resources and the lkely dstrbuton of ncdents. Accessblty s usually easured n ters of transportaton costs (e.g., travel te, travel dstance, etc.) between dspatchng stes and ncdent locatons. For that reason, two vtal 5

12 questons arse n plannng and anagng eergency servces: how any response unts are needed, and where should they be allocated n response to the teporal and spatal dstrbuton of ncdents? The core ethodology for dealng wth ths ssue belongs to the category of faclty locaton assgnent. The core ssue of faclty locaton proble was to locate a sngle warehouse fro all canddate stes (Weber, 1929). Slar odels have also been developed and appled n a varety of felds, ncludng healthcare facltes, plants and warehouses, post offces, and landflls (Eselt, 2007; Owen and Daskn, 1998). Two an ssues assocated wth faclty locaton studes and the eergency ncdent response are: (1) allocatng eergency servce unts for recurrent eergency events and (2) plannng the locaton such as the response centers to house the resources for eergency servces and ncdent anageent. Typcally, the factors consdered when desgnng the locaton and dstrbuton of eergency servce resources nclude the total assets, operatonal costs, ncdent deand coverage, and ncdent response telness. The next three sectons suarze three categores of studes that can be used to optze ncdent response effcency: coverng odels, P-edan odels, and P-center odels Coverng odels Coverng odels, the ost wdely used approach for allocatng the stes of eergency servce unts, attept to provde coverage to all deand ponts, whch are consdered covered only f a response unt s avalable to provde servces to the deand ponts wthn a dstance lt. The lterature descrbes two ajor schools of ethods: the locaton set coverng proble (LSCP) and the axal coverng locaton proble (MCLP). The LSCP s an earler verson of the eergency faclty locaton odel by Toregas et al. (1971); t seeks to nze the requred nuber of faclty locatons that cover all deand ponts. To overcoe the defcences of the LSCP, several researchers (Church and ReVelle, 1974; Whte and Case, 1974; Schllng et al., 1979) developed the MCLP odel. That odel as to axze the coverage of deands subjected resource constrants and the nal servce standards so that t does not requre coverng all deand ponts. The MCLP and ts varants have been broadly appled to varous eergency servce probles. Such a study, by Eaton et al. (1985), nvolved plannng the locaton of eergency response vehcles n Texas. When pleented, ths plan actually decreased the average eergency response te. 6

13 The coverng ethodology for locatng eergency servces has also been extended to consder the stochastc nature of eergency events. One approach that reflects the coplexty and uncertanty of the response allocaton ssue uses chance-constraned odels (Chapan and Whte, 1974) that can guarantee a certan level of servce relablty. For nstance, Daskn (1983) estated the probablty that at least one server s avalable to serve the request fro any deand and forulated the axu expected coverng locaton proble (MEXCLP) to poston P facltes n order to axze the average of deand coverage. MEXCLP was enhanced later by ReVelle and Hogan (1986). Ther proposed odel, the probablstc locaton set coverng proble (PLSCP), uses an average server busy facton (q ) and a servce relablty factor (a) for deand ponts and then places the facltes to axze the probablty of servce unts beng free to serve wthn a partcular dstance. MEXCLP and PLSCP have been further odfed and proved for other EMS locaton probles by any researchers, and odelng detals of ther studes are avalable n the lterature (ReVelle and Hogan, 1989a; Banch and Church,1988; Batta et al.,1989; Goldberg et al., 1990; and Repede and Bernardo, 1994). Another approach taken to tackle the stochastc propertes of the eergency servce locaton ssue uses the scenaro plannng ethodology to handle ultple possbltes of a rando event by estatng possble paraeters that ay vary over dfferent eergency scenaros. In practce, responsble agences ay evaluate each scenaro ndvdually and then aggregate all strateges to develop scenaro-specfc solutons based on ostly engneerng judgents. For exaple, MCLP was extended by Schllng (1982) to ncorporate scenaros, ang to axze the deand coverage over all consdered scenaros. Schllng used ndvdual scenaros to dscover a range of good locaton decsons and then deterned the fnal locatons desgn coon to all scenaros based on a coprose decson. Although such an approach s conceptually and coputatonally sple, t ay not yeld relable results. Thus, Serra and Maranov (1999) developed a stochastc approach to represent the uncertanty of target paraeters. Soe other stochastc ethods reported n the lterature nclude stochastc prograng (SP) and robust optzaton (RO). In general, SP focuses on the expectaton of perforance easures so that t reles on the coplete probablty dstrbuton of rando paraeters, and thus havng less consderaton for the rsk (Brge and Louveaux, 1997). In contrast, RO places ore ephass on the worst-case scenaro, whch tends to yeld ore conservatve results. 7

14 2.2.2 P-edan odels Another key ethod for evaluatng the effectveness of strateges for allocatng eergency servce stes nvolves easurng the average (or total) dstance between the facltes and ther deand stes. In general, as the average/total dstance decreases, the accessblty and effectveness of facltes ncrease. Hak (1964) used ths property n developng hs odel, ntroducng the P-edan ethod to locate P facltes n order to nze the average (or total) dstance between facltes and deands. The orgnal P-edan odel assued that the deands at each node and the travel dstances between nodes of the network are deternstc. ReVelle and Swan (1970) later odeled the P-edan proble as a lnear nteger progra and solved t wth a branch-and-bound algorth. Along the sae lne of research, Carson and Batta (1990) developed a P-edan odel to produce the dynac strategy that can best poston abulances to nze the average response te for a capus eergency servce. Berln et al. (1976) studed two P-edan odels to locate hosptals and abulances. Ther frst odel anly focused on patent needs and aed to nze the average dstance between the hosptals and deand ponts, as well as the average response te by abulances fro ther bases to the deand ponts. Ther second odel was desgned to enhance the perforance of the syste by addng a new objectve functon to nze the average dstance fro the abulance bases to the hosptals. Mandell (1998) adopted prorty dspatchng n a P-edan proble to optze the locatons of eergency unts for an EMS (eergency edcal servce) syste that conssted of advanced lfe support (ALS) unts and basc lfe support (BLS) unts. The P-edan odel has also been extended to account for uncertanty n travel tes and deand patterns. For nstance, Mrchandan (1980) took nto account stuatons where servce was unavalable for a deand and solved the proble usng a Markov process to create a syste whose states were characterzed by deand dstrbuton, servce and travel te, and servce unt avalablty. Serra and Maranov (1999) ntroduced the concept of regret and nax objectves n locatng a fre staton n Barcelona. Ther odel explctly tackled the uncertanty n deand, travel te, and dstance, usng scenaros to ntegrate the varaton of uncertan factors. Ther odel searched for a coprose soluton by nzng the axu regret over the dentfed scenaros. 8

15 2.2.3 P-center odels Whle the P-edan odel pays attenton to optzng the overall syste perforance, the P-center odel concentrates on nzng the worst syste perforance, ephaszng the portance of servce nequty rather than the average syste perforance. The P-center odel assues that a deand s served by the nearest faclty, thus akng full coverage for all deand ponts always possble by nzng the axu dstance between any deand and ts nearest faclty. However, unlke the full coverage offered by coverng odels, whch requres excessve resources, the P-center odel acheves ts as wth lted resources. The frst P-center odel, posed by Sylvester (1857) ore than a century ago, seeks to dentfy the center of a crcle wth the sallest radus that can cover all target destnatons. Snce then, ths odel has been extended to a wde range of faclty locaton applcatons, ncludng edcal (e.g., EMS centers and hosptals) and publc facltes. For exaple, Garfnkel et al. (1977) odeled ther proble wth nteger prograng and successfully solved t wth a bnary search technque and a cobnaton of exact tests as well as heurstcs. The forulatons by ReVelle and Hogan (1989b) for ther P-center proble sought to nze the axu dstance for avalable EMS unts wth a specfed relablty (α). They consdered syste congeston and derved the probablty of a servce unt beng busy to constran the servce relablty for all deands. The P-center odels have also been extended to consder ts stochastc aspect. For nstance, Hochbau and Pathra (1998) tred to nze the axu dstance on the network over all te perods. Snce the costs and the dstances between locatons dffer n each te perod, they used k fundaental networks to represent dfferent te perods and then developed a polynoal-te approxaton algorth to solve for each proble. Another nstance s the applcaton for locatng and dspatchng three eergency rescue helcopters for EMS deands due to accdents related to skng, hkng and clbng the north and south Alpne ountan durng holday seasons (Talwar, 2002). The proble was solved by usng effectve heurstcs n order to nze the worst response tes. In addton to the aforeentoned studes, a wde range of applcatons wth dfferent forulatons can be found n the lterature (Handler, 1990; Brandeau et al., 1995; Daskn, 2000; and Current et al., 2001). 9

16 2.3 Incdent Duraton Estaton Relable estaton of ncdent duraton has long been studed by researchers for several decades wth varous ethodologes. At the earler stage researchers used the descrptve statstcs of the data fro closed-crcut televson (CCTV) logs (1964), polce logs (1971), and the te lapse caera (1974) to estate the ncdent duraton dstrbuton. As ore advanced technologes for data collecton eerged over the past decades, traffc researchers have developed ore analytcal ethodologes. Most exstng approaches found n the lterature can be sorted nto the followng categores: (1) probablstc dstrbutons, (2) condtonal probabltes, (3) regresson odels, (4) dscrete choce or classfcaton odels, (5) decson or classfcaton trees, and (6) te sequental odels. The rest of ths secton dscusses each approach n detal Probablstc dstrbutons Probablstc odels, the frst category of approaches for estatng ncdent duratons that ths study wll revew, are relatvely straghtforward. These odels center on the dea of vewng an ncdent s duraton as a rando varable and atteptng to fnd a probablty densty functon (PDF) that can ft the data set. Golob et al. (1987) conducted ther research usng approxately 530 ncdents nvolvng trucks and found that they could odel ncdent duraton wth a log-noral dstrbuton. Ther fndngs were later supported by Gulano (1989), Garb et al. (1997), and Sullvan (1997) n ther studes of freeway ncdent duratons. Ozbay and Kachroo (1999) also found that the dstrbuton of ncdent duratons fro ther data set showed a shape very slar to the log-noral dstrbuton, although a few statstcal sgnfcance tests rejected ther hypothess. However, they realzed that when the study data set was subdvded by ncdent type and severty, these subsets followed a noral dstrbuton. Ths fndng has portant plcatons, snce t supports the theory that ncdent duraton s a rando varable (Sth and Sth, 2002). Slarly, Jones et al. (1991) dscovered that a log-logstc dstrbuton could be used to descrbe ther study data set fro Seattle. Na and Mannerng (2000) found that ther data set could be llustrated wth the Webull dstrbuton. However, Sth and Sth (2002) could not fnd an approprate probablty dstrbuton, ncludng log-noral and Webull dstrbutons, to ft the ncdent clearance tes for ther study data. 10

17 2.3.2 Condtonal probabltes Probablty odels for ncdent duraton can be extended to apply a condtonal probablty ethodology. The key dea of such odels s to fnd the probablty dstrbuton of ncdent duraton under certan gven condtons for exaple, the probablty that the ncdent duraton wll run over 30 nutes, gven that the ncdent has already lasted for ten nutes. It sees ntutvely clear that the probablty of an ncdent beng reoved wthn a gven perod of te would vary dependng on how long the ncdent has already lasted descrbed as duraton dependence by Na and Mannerng (2000) and the ncdent s characterstcs. One nterestng approach usng ths concept s the hazard-based duraton odel. Ths odel allows researchers to calculate ncdent duraton wth condtonal probablty odels. Such odels have been wdely used n boetrcs and ndustral engneerng to deterne causalty fro duraton data. Due to slartes wth the nature of traffc ncdent duratons, the theoretcal concepts and odels fro these felds have recently been appled to transportaton probles. Such approaches expand the focus fro sply estatng and predctng an ncdent s duraton to coputng the lkelhood that the ncdent wll be cleared n the next short te perod gven ts sustaned duraton. One representatve study usng ths ethodology (Na and Mannerng, 2000) used a two-year data set fro Washngton State. The study showed that each ncdent te (.e., detecton/reportng, response, and clearance tes) was sgnfcantly affected by nuerous factors, and dfferent dstrbuton assuptons were recoended for dfferent ncdent tes. They also found that the estated coeffcents were unstable through the two-year data used n odel developent. Na and Mannerng concluded that ths approach was ore useful for deternng whch varables have greater nfluence on ncdent duraton than for estatng or predctng the ncdent duraton for gven explanatory varables. Chung (2010) recently utlzed a slar approach, the log-logstc accelerated falure te (AFT) etrc odel, to estate/predct accdent duratons based on a two-year (2006 and 2007) accdent data set fro the Korean freeway syste. The estated duraton odel, based on year 2006 data, was valdated wth year 2007 data; the author concluded that the predctons of the developed odel were reasonably acceptable. He also tested the teporal transferablty of the proposed odel and concluded that the estated odel paraeters can be stable over te. 11

18 2.3.3 Regresson odels Another sple ethodology for predctng ncdent duraton uses regresson. These odels usually nclude a nuber of bnary varables as ndependent varables to ndcate ncdent characterstcs and a contnuous or categorcal varable as a dependent varable (.e., ncdent duraton). One of the best-known lnear regresson odels for ncdent duraton predcton was developed by Garb et al. (1997) usng 277 saples fro Calforna. The researchers used varous ndependent varables to represent ncdent characterstcs (e.g., ncdent type, nuber of lanes affected by the ncdent, nuber of vehcles nvolved, and truck nvolveent) and weather condtons (rany or dry). They also ncluded all possble cobnatons of the ndependent varables to optze the odel. Here s the fnal ncdent duraton odel fro ther research: ( ) = where Duraton = ncdent duraton (nutes) = nuber of lanes affected by the ncdent = nuber of vehcles nvolved n the ncdent = truck nvolveent (duy varable) = ornng or afternoon peak hour ndcator (0: ornng peak hour; 1: afternoon peak hour) = natural logarth of the polce response te (nutes) = weather condton ndcator (0: no ran; 1: ran) The logarth for of ncdent duratons ndcates that the ncdent duratons n ths data set follow a log-noral dstrbuton based on the Kologorov-Srnov test. Ths result s slar to those fro Golob et al. (1987) and Gulano (1988). Accordng to the authors, the polce response te was the ost sgnfcant factor affectng the ncdent duraton, followed by weather condtons, peak hour, truck nvolveent, and the cobned effect of the nuber of lanes and nuber of vehcles nvolved n the ncdent Dscrete choce or classfcaton odels Whle ost studes n the lterature have treated ncdent duraton as a contnuous varable, several researchers categorzed the contnuous varable of ncdent duraton nto dscrete te ntervals (e.g., 10 to 25 nutes) n order to apply dscrete choce or classfcaton 12

19 approaches. For nstance, Ln et al. (2004) developed a syste that ntegrates a dscrete choce odel and a rule-based odel to predct ncdent duraton. They adopted the ordered probt odels to frst predct ncdent duratons n a te nterval forat; then they developed and appled a rule-based suppleental odel to enhance the accuracy of predcton results. Boyles et al. (2007) also redefned ther orgnal ncdent duraton data nto an nterval forat n developng ther naïve Bayesan classfer (NBC), based on ncdent data fro the Georga Departent of Transportaton. They argued that the NBC has the followng dstnct advantages: (1) flexblty n accoodatng changeable aounts of nforaton (ncoplete nforaton or nforaton receved at dfferent ponts n te), (2) ncreased robustness to outlers than standard technques lke lnear regresson, (3) coputatonal splcty, (4) easy adaptablty as the nuber of saples for calbraton grows, and (5) relatve ease n nterpretng research results Decson or classfcaton trees Another approach frequently appearng n the ncdent duraton lterature, the decson or classfcaton tree odel, has proven qute useful for dscoverng patterns n a gven data set wthout consderng the fundaental probablstc dstrbuton (Sth and Sth, 2001). Ths property s very helpful, snce ost ncdent duraton data sets do not ft well to any coonly used dstrbuton. Sth and Sth (2001) also ponted out that the pattern-recognton odel has been used recently to develop ncdent duraton odels. One representatve odel, developed by Ozbay and Kachroo (1999) for the Northern Vrgna regon, began wth a odel to predct the clearance te usng lnear regresson based on a large saple sze. Unfortunately, the copleted analyss wth an unsatsfactory result (R ) showed that ther ncdent clearance te data followed nether a log-noral nor a log-logstc dstrbuton. As an alternatve ethod, they explored a decson tree odel and fnally generated relaton patterns (see Fgure 2-1) for use n predctng clearance tes. 13

20 Fgure 2-1: A Part of the coplete decson tree to predct clearance Te by Ozbay and Kachroo (1999) Note that an ncdent tree coprses a seres of decson varables. Ths s another advantage of the tree-type ethodologes ther self-explanatory nature, whch s rooted n the tree-structure. Users can easly understand the output by followng the branches related to the condtons of varables. For nstance, the tree uses an ncdent type as the frst varable to decde f the detected ncdent type s known or not. Once t s classfed as an unknown type, then the tree edately provdes an estate of 45 nutes for the average clearance te. Otherwse, t oves to the next level to deterne the type of ncdent. Sth and Sth (2001), nspred by the study of Ozbay and Kachroo, tred to develop a slar classfcaton tree. They concluded that such a tree, developed on the bass of a relable and suffcent database, perfors well even though thers yelded unsatsfactory results due to poor data qualty. To enhance ts adaptablty to ncoplete nforaton n real-te predcton, Yang et al. (2008) developed a Bayesan decson tree, whch can predct ncdent duraton wth ssng or nconsstent nforaton. They nserted Bayesan nodes followng every decson node to ask whether the requred nforaton s avalable. If the nforaton s avalable, no 14

21 further calculaton wll occur for that node. Otherwse, the odel uses Bayesan theory to copute the value of the node. Then, the coputed Bayesan node value s used to estate the te nterval class to whch the detected ncdent belongs. Ther odel reportedly outperfored the tradtonal classfcaton tree odel developed on the sae data set the Bayesan decson tree and classfcaton tree yelded 74 and 46 percent predcton accuraces, respectvely Te sequental odels Khattak et al. (1995) realzed that the full set of varables for ncdent forecasts would be avalable at the oent the ncdent was cleared. Although predcton odels based on ths total set of varables would be ore accurate and relable, they are less practcal for use n real-te ncdent anageent operatons precsely because a full set of varables would only becoe avalable after clearng the ncdent. Thus, they ntroduced a te sequental odel that focuses on predctng real-te ncdent duraton under partal nforaton. Ther odel consders ten dstnct stages of ncdent duraton, based on the avalablty of nforaton. Each stage estates dfferent ranges of ncdent duraton wth a separate truncated regresson odel. As the odel oves to the next stage, t ncludes progressvely ore varables to explan the stage s duraton. Despte ts orgnalty and reasonablty, ths odel was not tested or valdated due to the lack of feld data. The authors also entoned that the purpose of ther study was to ntroduce and deonstrate the te sequental odel rather than to prove ts perforance n traffc operatons. Snce then, ther approach has been extended and enhanced by several researchers. For nstance, We and Lee (2007) proposed an adaptve procedure whch ncludes two artfcalneural-network-based odels for sequentally forecastng an ncdent s duraton. The frst odel, the so-called Model A, was desgned to predct the duraton of the detected ncdent at ts notfcaton, at whch pont Model B takes over and updates the duraton at ultple perods untl clearance of the ncdent. The perforances of these odels were evaluated wth ean absolute percentage error (MAPE) for predcted ncdent duratons at every forecast te perod; ost results were less than 40 percent, plyng that the proposed odels are capable of yeldng reasonable forecasts. Later, they proved ther odel by addng a procedure to select a bestperforng subset of features usng genetc algorths (GAs) (Lee and We, 2010). They found that reducng the densonalty of nput features can decrease the cost of acqurng data and ncrease the nterpretablty and coprehensblty of odel outputs. Furtherore, they claed that data splfcaton can elnate rrelevant data whch can slead the learnng process and 15

22 par developent of the fnal odel. In fact, they reported that the MAPE for forecasted ncdent duraton at each te perod dropped, ostly fallng below 29 percent after they appled ther proposed feature selecton ethod. Q and Teng (2008) also developed a te sequental procedure whch dvdes the ncdent anageent process nto ultple stages, dependng on the avalablty of specfc nforaton. They developed a hazard-based duraton regresson odel for each stage, wth dfferent varables representng dfferent nforaton avalable. The reanng ncdent duraton, then, could be predcted onlne usng the truncated edan of ncdent duraton and the estated paraeters and coeffcents. Ther study concluded that predcton accuracy ncreased as ore nforaton was ntegrated nto the developed odels. Although varous technques produce acceptable results, ost research fndngs are not drectly applcable to other locatons. Because each odel was developed usng dfferent ncdent data sources and descrptve varables, and each yelded soewhat dfferent results. Therefore, any target applcaton requres ether a recalbraton of exstng odels n the lterature to adjust the paraeters to the new data source or the developent of a new odel whch can outperfor any exstng odels wth the avalable data set. 2.4 Detour Decson Support Syste Contendng wth non-recurrent congeston has long been a prorty task for ost hghway agences. A recent study (Lndley, 1987) ponted out that non-recurrent traffc congeston due to ncdents, hghway constructon zones, and specal events has contrbuted up to 60 percent of the total freeway corrdor delay n the Unted States. Under ost ncdent scenaros, f proper dverson plans can be pleented n te, otorsts can crcuvent the congested segents and best use the avalable corrdor capacty. To contend wth ths vtal operatonal ssue, transportaton professonals have proposed a varety of advanced dverson control and route gudance strateges (Pavls and Papageorgou, 1999; Morn, 1995; Papageorgou, 1990; Messer and Papageorgou, 1995; Wu and Chang, 1999; Lu et al., 2011) to optally balance the volues between the freeway and the arteral systes. Certanly, those strateges have ade nvaluable contrbutons to provng ncdent anageent n freeway corrdors. Nevertheless, before pleentng any detour strategy, traffc operators ust justfy ts necessty based on varous factors, snce such operatons usually deand substantal aount of 16

23 resources and anpower. In ths regard, very lted nforaton s avalable n the lterature to assst decson akers n assessng the benefts and costs of pleentng detour operatons, although nuerous traffc safety and operaton anuals (e.g., Delaware DOT, 2011; State Polce NJ, 2010; Unv. of Kentucky, 2009; FHWA, 2009; Wsconsn DOT, 2008) have addressed the need of properly dvertng traffc flows durng ajor ncdents or eergences. One source offerng gudance for detour plan developent, the Alternate Route Handbook (2006), provdes coprehensve and general gudelnes for how to plan and execute the detour operatons nvolvng varous stakeholder agences. Accordng to ths docuent, the key factors to consder nclude ncdent duraton, nuber of lanes blocked, observed traffc condton, te of day, and day of the week. The capacty of the proposed alternatve route and ts background traffc are also crtcal factors. Table 2-1 suarzes the crtera used n several states to decde whether or not to execute the predeveloped alternate route plan. Notce that the Florda DOT Dstrct IV operates ts detour plan when two or ore lanes are closed for at least two hours. On the other hand, ost states requre an ncdent duraton of longer than 30 nutes or the coplete closure of the roadway to pleent detour plans. The Manual on Unfor Traffc Control Devces (MUTCD) (2009) states that ajor and nteredate ncdents lastng ore than 30 nutes usually requre traffc dverson or detourng for road users, due to partal or full roadway closures, whle traffc dverson ay not be necessary for nor ncdents usually cleared wthn 30 nutes. In revewng the lterature, t becoes evdent that a relable tool for traffc control operators to decde when and how to pleent detour operatons has yet to be developed. 17

24 Table 2-1: Crtera for decdng the pleentaton of detour plans n varous states AGENCY North Carolna DOT an offce North Carolna DOT Charlotte regonal offce North Carolna DOT Charlotte regonal offce New Jersey DOT Oregon DOT New York State DOT Regon 1 Florda DOT Dstrct IV ARTIMIS (Oho/Kentucky) Ada County, Idaho CRITERIA Coplete closure of the hghway n ether drecton s antcpated for 15 nutes or longer. No acton or dscusson occurs untl 15 nutes after the ncdent. After 15 nutes, an alternate route plan s deployed only f the hghway s copletely closed (all lanes closed, ncludng the shoulder) and closure s expected to last at least an addtonal 15 nutes (30 nutes total). No acton or dscusson occurs untl 15 nutes after the ncdent. After 15 nutes, an alternate route plan s deployed only f the hghway s copletely closed (all lanes closed, ncludng the shoulder) and closure s expected to last at least an addtonal 15 nutes (30 nutes total). Level 1: Lane closures on a state hghway that are expected to have a prolonged duraton and pact on traffc. Level 2: Coplete closure of a hghway that s antcpated to last ore than 90 nutes. Incdent wth two or ore lanes blocked, or Incdent wth one lane blocked and expected to last ore than 20 nutes. Ipleented only when the hghway s copletely closed. Wll not be pleented f at least one lane(or even the shoulder) s open. Two or ore lanes blocked for at least two hours. Ths plan has a detaled table wth four dfferent levels, based on soe present crtera, such as: - Durng the ornng and afternoon peak hours, an advsory alternate route s deployed n the event of a two-lane closure for ore than two hours or a closure of ore than two lanes for less than 30 nutes. - Mandatory alternate routes are deployed durng the peak hours when ore than two lanes are closed for at least 30 nutes. Ths plan specfes dfferent levels of severty, ncludng: - Levels C and D requre pleentaton of a dverson route. - Level C s an ncdent takng 30 to 120 nutes fro detecton to full recovery of the traffc flow. - Level D s an ncdent takng over two hours fro ts detecton to full recovery (ncludng full freeway closure n one or both drectons). Wsconsn DOT (Blue Route) Incdent causes delays that wll exceed 30 nutes. Source: Alternate Route Handbook (2006) 18

25 In vew of the benefts and ltatons n the exstng studes and the addtonal functonal requreents for real-world syste applcatons, ths study as to acheve the followng goals so as to tgate ncdent pacts on freeways: Provde relable gudelnes and tools to help responsble agences when they desgn, deterne, and operate traffc anageent plan/progra under non-recurrent congeston. Delver a sold, ntegrated freeway traffc anageent syste whch can be utlzed as a prototype and/or appled n real-te traffc operatons 19

26 CHAPTER 3: Revew of the FITM Progra and Operatons 3.1 Introducton of the FITM Progra by SHA To prove traffc condtons on ajor hghways plagued by non-recurrent congeston, ost hghway agences have nvested ther resources n two prncpal operatonal progras: ncdent response and clearance, and traffc pact anageent. The forer ncludes effectve detecton of ncdents, effcent response, and well-coordnated clearance operatons; the latter focuses on nzng ncdent pacts va dssenaton of traffc nforaton and pleentaton of necessary control strateges such as rap closures or detour operatons. However, even wth the wde-spread pleentaton of such progras, effectvely nzng the traffc pact caused by ult-lane blocked ncdents reans an especally crtcal and challengng ssue for ost hghway agences. The FITM progra developed by SHA as to provde the gudelnes for detour operatons durng the clearance of ajor ncdents. FITM s a set of locaton-specfc routng plans to detour vehcles fro an ncdent-pacted hghway segent to a pre-selected neghborng parallel arteral and then gude traffc back to the sae route. For all ajor hghway corrdors covered by the CHART progra, the FITM progra offers a detaled operatonal anual for each roadway lnk when detour operatons n response to a severe ncdent are justfed. Fgure 3-1 llustrates an exaple of the detour plan provded by the FITM operatons anual for the roadway lnk between exts 7 and 9 of I-495 on the Captal Beltway. It s notceable that the ap-based routng plan for an dentfed ncdent locaton shows clearly where to ext and return to the prary route, the nuber of ntersectons on the detour route, and soe key geoetrc or control features on those detour lnks that ay affect the operatonal effcency. The operatonal anual also provdes a detaled lnk-based navgaton n a table forat and the eergency contact phone nubers for detourng travelers (see Table 3-1). Snce the detour traffc certanly wll cause a volue surge on the detour route and deand the ntersecton sgnals to accoodate wth a responsve tng plan, the FITM operatonal anual also lsts the affected sgnals and ther phases that need to be adjusted durng the perod of ncdent response and traffc anageent. 20

27 Fgure 3-1: An exaple of the detour plan on I-495 provded by the FITM anual 21

28 Table 3-1: An exaple of the detour plan on I-495 provded by the FITM anual Note that the FITM progra by SHA currently covers only the followng ajor routes: - Interstate hghways: I-70, I-81, I-83, I-97, I-270, I-695, I-495, and I-95; - State routes: MD100, MD295, MD404; and - US routes: US13, US50, US113, US

29 For a detected ncdent, SHA traffc engneers are nstructed to use the followng crtera to deterne whether or not an FITM plan should be pleented: - The estated ncdent duraton exceeds one hour; or - The ncdent nature and ts clearance cause a coplete lane blockage. However, the FITM operatonal anual does not address a ethod to dynacally adjust sgnal tes n response to the te-varyng detourng traffc flows, nor does the current progra dscuss such crtcal operatonal ssues as: - Where are the locatons to place portable DMS to gude the detourng travelers? - What essages should be dsplayed to nfor the approachng roadway users? - How should the ntal estate of the clearance duraton be provded for a detected ncdent and ts pact boundares? - How should the ncdent anageent progress be updated for travelers wthn the ncdent pact area? - How should the ost effectve traffc control and anageent plan be selected for the sae ncdent locaton but at dfferent tes of a day such as peak versus off-peak perods? - Should the detour operatons be sustaned when the clearance operaton has recovered the roadway fro a coplete blockage to the partal lane-open status? - What percentage of traffc should be detoured durng dfferent stages of the clearance operatons (e.g., one lane or two-lane open) to avod excessve congeston on the detour route? - When wll be the optal te to ternate the detour operatons, consderng both the approachng traffc volue on the prary and the detour routes? Asde fro dealng wth the above ssues, the current FITM progra does not nclude soe essental operatonal steps to coordnate wth local agences responsble for anagng traffc and controllng sgnals on the detour route. 23

30 3.2 Crtera for Actvatng Detour Operatons Aong all the crtcal ssues to be addressed by the FITM progra, the ost dffcult one s when to actvate the detour operatons, because ts effectve pleentaton needs not only suffcent equpent for nforaton dssenaton and control anageent, but also vast huan resources to ensure drver coplance. Hence, all those hghway agences wth an actve ncdent response progra have adopted ther own crtera to actvate detour operatons. The last chapter on lterature revew has reported those crtera used by nne hghway agences. Notably, all such crtera vary wdely, though anly based on the ncdent duraton and lane blockage level. Nevertheless, they can be classfed nto two categores; Category-1: Ipleent the andatory detour operaton only f - All lane closure and the ncdent duraton are expected to last ore than 15 nutes (e.g., North Carolna state an center), 30 nutes (North Carolna), or 90 nutes (e.g., New Jersey); - Ether All-lane closure or the ncdent duraton are expected to last ore than 60 nutes (e.g. Maryland); - Roadway closure for two lanes or ore (Oregon) and for ore than two hours (Florda, Idaho); and - Roadway closure of ore than two lanes for ore than 30 nutes durng the peak hours (Oho and Kentucky); Category-2: Actvate the advsory detour operaton only f - One-lane closure for ore than 20 nutes (Oregon); - Two-lane closure for ore than two hours or ore than two-lane closure for less than 30 nutes (Oho and Kentucky); and - Delays caused by the detected ncdent exceed 30 nutes. In general, those states that experenced ore heavy recurrent congeston are less wllng to pleent detour operatons durng the duraton of ncdent clearance. For exaple, New York wll not actvate ts traffc dverson progra as long as one or the shoulder lane reans open, and SHA would actvate ts FITM operatons only f the ncdent duraton exceeded one hour. 24

31 3.3 A FITM Decson and Evaluaton Fraework Despte the dscrepances aong varous crtera for detour operatons, ost hghway agences share the followng two coon prncples n contendng wth non-recurrent congeston: - Detour operatons deand well-desgned plans n advance and need vast personnel and resources to pleent effectvely and n a tely anner; and - Care should be exercsed to ensure that drvers coplyng wth the ncdent anageent nstructons wll not suffer excessve and undue delays on the suggested alternate route. The challenge for hghway agences n contendng wth ths ssue s that durng the partal-lane closure scenaro drvers ay encounter unexpectedly long travel tes and congeston on the alternatve route f proper essages, route gudance, and sgnal accoodaton have not been placed n te to gude the traffc flow. Otherwse, very often those stayng on the prary route durng the partal-lane closure perod ay actually experence a shorter travel te, and drvers wll consequently lose confdence n traffc nforaton or nstructons dsplayed va DMS or any eans of advanced transportaton nforaton systes (ATIS). Ths s one reason that ost hghway agences are reluctant to dvert traffc unless the need and benefts are too obvous to gnore. Concevably, a successful operaton of any detour plan durng a ajor ncdent needs full cooperaton between otorsts and the responsble agences. Whle the latter should have a wellprepared plan and suffcent resources to accoplsh the objectve of nzng the total socetal cost durng the ncdent clearance perod, the forer should be wllng to follow the nstructons to reduce ther delays ncurred by the accdent and clearance operatons. Unfortunately, developng such utual confdence and cooperaton between otorsts and traffc agences at the desrable level s a dffcult task and uch reans to be done n ncdent anageent practce. The followng secton presents a fraework for an ntegrated FITM syste n response to such a need. Undoubtedly, a relable and effcent FITM syste needs to frst wn the trust or confdence of otorsts who can be convnced that any essage or nstructon fro responsble hghway agences durng the ncdent-plagued perod can lead the to experence less travel 25