UC Berkeley Earlier Faculty Research Title High Occupancy Vehicle Lanes: Not Always More Effective Than General Purpose Lanes Permalink https://escholarship.org/uc/item/1v11k99t Author Dahlgren, Joy Publication Date 2001 eScholarship.org Powered by the California Digital Library University of California High Occupancy Vehicle Lanes: Nat Always More Effective Than General Purpose Lanes Joy D~lgren Reprint UCTC No 504 The University of California Transportation Center Uraversity of Caldorma Berkeley, CA94720 The University of California Transportation Center The Umversity of Cdlforma Center actavmes Researchers Transportauon Center (UCTC) at other umversmes wlthm the Is one of t~n regional ur&s regaon also have oppormmnes mandated by Cong’mss and to collaborate with UCfaculty established in Fail 1988to on selected studies. supportresearch, education, and~ai~{ng in surfacetraas° UCTC’s edueauonal and portation.The UC Ccnrzr ~search progr’aras are focused servesfederal Reglon IX and on strategic planning for Is supported by matching xmprovmg metropohtan granr~ from the U.S Depart- aecessibzhty, with emphasxs men~ of Transpo~a~on, the on the spemalcondmons m California Departmcm of Regaon IX Particular attennon Transportation (C~dtrans), mud is d.urect~dto strategies for the Umversity. using transpormUon as an instrument of economic Based on the Berkeley developmenL while also ac- C~pus, UCTC draws upon commodatingto theregion’s exJstang capabihUes and persistentexpansion and resources of the Institutes of whileramntaz~ng and enhanc+ Tmnspormuen Sm&es at ing thequahty of life there Berkeley, Davxs, Irvme, and Los Angeles, the Insumte of The Center dastnbutes reports Urban and Regaon~d Deve|op- on its research in worlong merit at Berkeley, and several papers, monographs, and in academmdepartments at the reprints of published arlScies Berkeley, Davis, Irvine, and It also pubhshes Access, a Los Angeles campuses. magazane presenung sum- Faculty and smdems on other mariesof selectedsmdms For Umvermty of Cahforma a hst of publicationsm pnnt, campuses may participate m writeto theaddress below. Thecontents efthis repo~ reflect the views ofthe authors, whoare responsibleforthe facts an+ the +ecuracy ofthe information presented Unrversxtyof Cahforma herein,Thes document is disseminated underthe sponsorship ofthe Tra~or~at,onCenter Departmentoflransportatien, University Trensporta, +.Cem+r$ Program, in theinterest of information exchange. TheU.S. Government assumes no 108 NavalArehzlzeture Building liabihtyfar the contents oruse thereof. Berkeley, Cahforma94720 TcI. 5101643-7378 FAX:510./643-5456 The eom~a~of thls reportreflect the vmwsof theauthor whozs responmble forthe facts and aeeurazy of the dam presented herein. The conmnts do not aeeessmalyreflect the official v~ews or pohci~s of the State of Calffomm orthe U.SDepartment ofTransport~on. Tl’asreport does not eonsutute a ~and,~rd, specafiaaUot~or regulaUon High Occupancy Vehicle Lanes: Not Always More Effective Than General Purpose Lanes Joy Dahlgren Insutute of TransportahonStudies Umversltyof Cahfomta Berkeley, CA94720 Reprinted from Transportatzon Research A Vol 32A, no 2, pp 99-114 (1998) UCTCNo. 504 The Umversltyof CaliformaTransportation Center Urdversltyof California at Berkeley Transpn Rea-A, Vol 32, No 2, pp 99-114, 1998 © 1998 Etsevmr Science Ltd Pergamon All rights reserved Pnntcd m Great Bntmn 0963-8364/98$19 00 + 0 00 PII: S0965-8564(97)00021-9 HIGH OCCUPANCY VEHICLE LANES: NOT ALWAYS MORE EFFECTIVE THAN GENERAL PURPOSE LANES JOY DAHLGREN CahformaPATH, Headquarters, Instltute of Transportation Studies, UmversRyof Cahfornla, Berkeley, RichmondField Stauon, Bldg 452, 1357 S 46th Street, Rachmond,CA 94804-4698, U S A (Received15 October1996, in revised form 2 May1997) Abstract--Thesuccess of a haghoccupancy vehicle lane m motivatingpeople to shift to carpools and buses dependson maintaininga travel time differential betweenit and the adjacent general purpose1aries This differential, In turn, dependson the level of continuingdelay on the generalpurpose lanes Therefore,it is clear that a high occupancyvehicle lane that will motivatepeople to shift to high occupancyvehicles wII1not ehmmatecongestion Consequently,it is not clear that constructing a high occupancyvehicle lane will necessarilyreduce delay morethan constructaonof a generalpurpose lane Theobjectave of this researchis to determinethe circumstancesin whichthis wouldbe the case Thehypothesis is that such circumstanceswould be qtute llrruted, andthis provesto be the case Theintended benefits of high occupancylanes are definedas reducedperson-delay and reducedemtssmns A modelis developedto calculate these benefits for four alter- natives add a high occupancyvehMe lane, add a general purpose lane, convert an existing lane to a high occupancyvehicle lane, and do nothing The model takes into account the mmalcondmons, the dynamic nature of the travel time differential betweenthe high occupancyvehicle lane and other lanes, and the uncertainty regarding the extent to whichpeople will shift modesIt combinesqueuemg theory and mode chozce theory and provides a robust methodfor companngalternatives using a small amountof easily observeddata Apphcatlonof the modelm typical situations showsthat with initial delays on the order of 15 mmor more,adding a high occupancyvehicle lane wouldprovide substantial reductions m delay and some reduction in emissionsHowe~,er, in a w~derange of such situations, addinga general purposelane wouldbe evenmore effective Onlyif the initial delay is long andthe mltmlproportion of high occupancyvehicles falls in a rather narrowrange, wouldan addedhigh occupancyvehicle lane be moreeffective Thepropomon of high occupancyvehacles must be suchthat it allowsgood utilization of the h~ghoccupancy vehicle lane while maintaininga sufficient travel time differential to motivatea shift to busesor carpoolsAdding a high occu- pancyvehicle lane to a three lane freewaywill be moreeffectwe than addinga generalpurpose lane only if the mmalmaximum delay Is on the order of 35 mmor moreand the proportion of high occupancyvehJcles is on the order of 20%Federal potlcles encourageconstruction of high occupancyvehmle lanes and restrict fundingfor general purposelanes mareas that havenot attained air quality standards Thefindings of this research suggesta needto reconsiderthese policies © 1998Elsevier ScienceLtd All rights reserved Keywords high occupancy vebacle, hlgh occupancy vehicle lane, carpool Iane I INTRODUCTION Thebenefits of constructing a high occupancyvehicle (HOV)lane are obviousby providing incentive for peopleto shaft fromautomobiles w~th one or twooccupants to carpoolsor buses, the HOVlane reducesvehicle-trips, therebyreducing congestion and air pollutmn.Less obvious~s the fact that mmany situations the benefits wouldbe as great or greaterif the newlane werea general purposelane instead. The reasons for thas are s~mpleThe umquebenefits of an HOVlane as comparedto a general purposelane~that ~t motwatesa shaft to HOVsand gives pnontyat the bottleneck to HOVs--do net arise unless delay continueson the general purposelane. If delay ~s ehminatedwhen the HOV lane is constructed,there will be no incentive to shift to an HOVBut evenff delay continueson the generalpurpose lanes, twofactors limit the extentof the modeshaft. In-vehicle travel time has been foundto have a weakeffect on modechoice. Small(1977) founda minuteof out-of-vehicle walt time to be valuedat almost10 minutesof m-vehicle time anda transfer, at 13.6nunutesof in-vehicle time. Kollo(1986), in updatingthe travel model for the MetropohtanTransportatmn Commissmn m the San Franctsco Bay Area, foundeven less sensmwtyto in-vehicle travel time than Small 99 I00 J Dahlgren (b) The mot:vat:on to shaft mode depends on the &fferentaaI m travel times on the HOVlane and the other freeway lanes. As people stnft to HOVs,th:s &fferential is eroded. Therefore, regardless of how muchoverall traffic :ncreases, there :s an upper hmat on the travel time dafferentlal and the propomonof people who will be motavated to shaft to an HOVlane. Furthermore, af the mmal propomon of HOVsis greater than the propomon of capacity that w111be devoted to HOVsafter the HOVlane is added, the HOVtane w~ll be as con- gested as the general purpose lanes and will offer no travel time advantage. The key questaon :s under what carcumstances does constructang an HOVlane result in less delay and lower emass:ons than constructing a general purpose lane* To answer this question, the effects of constructing either type of lane are identified and a modelto comparethe benefits of the each as developed Constructing an HOVlane has several anterrelated effects (Fag 1) The most significant effect the shaft of current HOVsto the HOVlane Thas shaft reduces delay on the general purpose lanes, perhaps ehmmatmgat altogether If delay remains on the general purpose lanes, some people shaft to HOVs,further reducing delay on the general purpose lanes The reduced delay for both HOVs and non-HOVs(hereafter referred to as LOVs--low occupancy ve~cles) motavates some people traveling on the shoulders of the peak to shaft their trip to the peak It also motivates people to sh~ft from other routes that are nowslower. It mayreduce traps by people who prev:ously dad not travel because of the delay In the long run, the reduced delay may result an more developmentand trips than wouldhave otherw:se been the case. These last four effects offset the original reductions m delay. Except for the shaft to HOVs,constructing a general