Selecting Corridors for BRD Service
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Selecting Corridors for BRD Service

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This paper was adapted from my master's thesis for presentation at the 2004 Transportation Research Board conference.

This paper was adapted from my master's thesis for presentation at the 2004 Transportation Research Board conference.

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Selecting Corridors for BRD Service Selecting Corridors for BRD Service Document Transcript

  • Selecting Corridors for Bus Rapid Transit Using a Multicriteria MethodEric HolemanChicago Transit Authority120 N. Racine AvenueChicago IL 60607Tel. (312) 733-7000Fax (312) 432-7127Email: ehol@xmission.com
  • Eric Holeman 2ABSTRACTMany bus rapid transit (BRT) projects result from the availability of a single vacant corridor, such as an abandonedrail right of way. Deciding where to implement BRT service in an existing transit network, in the absence of anobvious corridor, is a more difficult question. Various factors, such as the potential rider density, possible travelspeed, and distance from other rapid transit corridors all weigh into the mix. Often the objectives tend to be mutuallyexclusive: a corridor that can provide fast travel times may offer few potential riders, while the corridor thatprovides the most riders may be along a traffic-clogged arterial. Where no one corridor is perfect, the best choice isnecessarily a compromise between varied and often conflicting objectives.Because of the conflicting objectives, a multicriteria method was chosen to address the question of identifyingpotential BRT corridors. Four alternatives were compared across a number of different criteria. The concordanceanalysis method was chosen because of its usefulness in evaluating alternatives where the differences are bothmeasurable and scalable. By placing different weights on the various objectives, the concordance analysis methodshow method does not result in the selection of one superior alternative, but instead shows how alternativescompare, given a particular set of priorities. Conversely, by showing how weighted alternatives rank, the methodreveals the priorities involved in the choice of a given alternative. The results point strongly to an alternative thatwas eventually chosen by the transit agency for a limited-stop BRT-type service.
  • Eric Holeman 3INTRODUCTIONThe Federal Transit Administration (FTA) has encouraged bus rapid transit (BRT) as a way to develop new rapidtransit projects at a low up-front cost. A number have of these projects have been undertaken by U.S. transitagencies. Many of those have typically taken advantage of the availability of a single corridor, such as Pittsburgh’suse of an old rail right of way, or Seattle’s use of high-occupancy vehicle (HOV) lanes along an Interstate highwaycorridor.Such corridors offer an obvious advantage in their ready availability. However, for an established urban transitsystem that wishes to overlay BRT services on an existing network, the question of how to select the corridor toupgrade becomes important. The goals of a BRT corridor typically involve providing a fast ride for a large numberof passengers, yet often the most densely populated transit corridors are those that provide the slowest busmovement. Conversely, corridors that offer quick vehicle movement are often found in areas of automobile-orienteddevelopment that aren’t likely to provide the number of riders needed to sustain a BRT service.This paper shows how a transit agency can identify and select bus rapid transit corridors using a multicriteriaanalysis method. The study compares a number of candidate corridors in an area of interest using various criteriaappropriate to the agency’s objectives in implementing a BRT service. Any corridor that is clearly superior to allothers may be identified as such. When no corridor is superior in all criteria, the corridors may be compared usingdifferent criteria weightings reflecting different prioritizations of the importance of the various objectives.DESCRIPTION OF CORRIDORSFour corridors were considered for evaluation in the part of Chicagos South Side, between the Dan Ryanexpressway and Lake Michigan. The area of interest of the corridors extends for five miles, between 63rd Street tothe north and 103rd street to the south. Corridors evaluated were limited to those north-south corridors with existingbus service. The corridors are described below and listed with a summary of their attributes in Table I. A map of thecorridors is provided in Figure 1.Each of the four corridors presents varying degrees of acceptability for BRT service. Martin Luther King Jr. Drive,though a broad boulevard for much of its length, narrows to two lanes through much of the area of interest. CottageGrove Avenue, a somewhat more commercially oriented corridor than King Drive, provides two traffic lanes in eachdirection for most of its length. Stony Island Avenue, a broad auto-oriented thoroughfare, provides barrier-separatedmultiple lanes for both north and southbound traffic. Like Cottage Grove, it is commercially oriented; though beingmuch wider, it has fewer residential buildings and minimal landscaping. Jeffery Boulevard is the narrowest of thecorridors, containing a single lane in each direction for all of its length. Although a narrow corridor like Jeffery isnot typically a candidate for BRT service, its high level of existing bus patronage merits its consideration in thisstudy.METHODThe concordance analysis method, as described by Giuliano (1) allows for the comparison of alternatives withdifferent, conflicting objectives. In applying the method, criteria are identified, and appropriate measures aredetermined for each of the criteria. Data are then collected for each measure of each alternative candidate. Thealternatives can then be ranked according to one or more weightings of the measures. Consistently unattractivealternatives can be readily identified and discarded, while the more attractive alternatives may then be comparedmore directly.Unlike a traditional cost-benefit approach, the concordance analysis method does not allow for the maximization ofa single outcome. Because of this, it is necessarily somewhat imprecise: several alternatives may emerge as viable,and the preferred alternative may end up being superior in no one single measure. Yet because the method enablesthe comparison of multiple favorable and unfavorable outcomes, the researcher may identify one or morealternatives that offer an acceptable combination of outcomes. The method is appropriate for the problem of transitcorridor selection because each alternative presents an assortment of costs and benefits that aren’t easily scaled todollar values.
  • Eric Holeman 4A number of studies have examined the usefulness of concordance analysis in addressing transportation issues.Giuliano provided a demonstration of the method that compared transportation improvement alternatives.Hastak and Abu-Mallouh (2) provided an example of using concordance analysis to prioritize transit stationimprovement projects. Both studies strongly suggest the usefulness of concordance analysis as a tool to evaluatetransit corridors in situations where no single criterion is paramount—provided sufficient criteria to be optimizedcan be measured and scaled.Applying the Concordance Analysis Method to the problem BRT Corridor SelectionOnce the criteria for comparing BRT corridors are identified, they can be evaluated using available measures. It isassumed that the objectives of a transit operator, in implementing a BRT project include increasing patronage in thecorridor, improving service quality, minimizing operating costs, and avoiding competition with existing routes.Increased PatronageFor the desired outcome of increased patronage, it is assumed that a high-ridership corridor has some residualdemand that may be served by providing BRT service. The capacity for patronage increase is therefore assumed tobe greatest in corridors that already have high ridership, and the current ridership in the corridor is assumed to be auseful measurement of that potential. It is further assumed that customers prefer faster buses and are more likely to patronize a faster service.Because a service that operates in relatively uncongested conditions is more likely to benefit from BRT conversionthan a service that is operating in crowded streets, the current operating speed of the bus will be used as a measure ofthe corridor’s ability to attract increased ridership.Improved Service Quality/Reduced Operating CostThe outcome of improved service quality is somewhat harder to define, and not all aspects of it are necessarilyrelated to the corridors in which the service runs. However, it will be assumed that for purposes of selecting acorridor that faster is better. For the transit agency, operating costs are directly related to operating speed—fasterbuses mean lower costs. The measures of potential service improvement are also applicable to the objective ofminimizing operating cost, and will hereafter be treated as the same criterion. The current operating speed of theexisting bus service in a corridor, already identified as a measure for the potential of increased patronage, will alsoserve as a measure of potential for improved service quality and reduced operating cost. The possibility of improving service further by adding lane restrictions is also considered, with theassumption that such a service improvement is more possible if there are more lanes available. Therefore, thenumber of traffic lanes in the corridor will provide another measures relating to service quality improvement.Avoiding Competition with Existing ServiceThe chosen corridor is expected to avoid redundancy with existing rapid transit services. It is assumed that thelikelihood of service cannibalization is related to the distance to a competing service. For the corridors underconsideration, the nearest competing CTA rapid transit service is the parallel Red Line service. Distance from theRed Line is therefore an appropriate measure of the likelihood of service cannibalization. However, there is alsocompeting Metra commuter rail service near the corridors, and it is possible that Metra customers may be less likelyto consider a CTA service, as they already enjoy a rapid transit-style service with stops approximately half a mileapart. The distance to the nearest parallel Metra service, then, may also be considered an appropriate measure of thepossibility of service competition.DATA AND DATA COLLECTIONOnce measures for the criteria were defined, data could be collected. A field survey of the corridors determined thenumber of lanes in each direction along the length of each corridor. CTA provided schedules and ridership reports,and the agency’s map was used to determine the distance to competing services.
  • Eric Holeman 5Schedule DataSchedule data were used to calculate the average current travel speed, providing a measure of the capacity of abilityof buses to quickly move through the corridors. For each bus route along each of the corridors, recent publishedCTA schedules were consulted to determine average speed along the corridor during AM rush hours for inboundservice and during PM rush hours for outbound services. While buses do not always travel according to theirschedules, it was assumed that the published schedules provide an approximation of the travel time, if not an exactmeasure.Ridership DataCurrent ridership counts provide a measure of the corridor’s support of the current bus service, a measure that isused as a proxy for potential BRT ridership. CTA’s ridership data provides the number of passenger boardings perweekday per route. This provides a crude measure of the route patronage; however, it should be noted that theridership figures are not available for time of day. Further, only boarding counts for the entire length of each routecould be obtained, though it would have been preferable to isolate boardings that occurred within the area ofinterest. The ridership counts for all the services in each corridor were combined, including both local and expressservices.Corridor DataThe width of each corridor was determined by a field survey. Each of the four corridors was traveled along its entirelength, from 63rd Street to 103rd Street. For each half mile (i.e., four numbered streets) the number of lanes in eachdirection was noted at the midpoint. Each corridor runs for five miles through the area of interest, so a total of tenmeasurements were made. From these ten measurements, the average width of each corridor was computed. Onlyone corridor, Jeffery Boulevard, was of uniform width along the entire five miles. Parking lanes and turning laneswere not included in the lane measurements.Competitive Service (“Cannibalization”) DataData measuring the distance between the proposed alternatives and competing CTA and Metra commuter railservice were taken from the CTA’s route map. For CTA service, the only competing service is the Red Line railservice between 63rd and 95th Streets. The nearest Metra service to all corridors is the Metra Electric main branchservice. The distance between the candidate corridor and the potentially competing rail corridor was measured alongthe connecting east-west street at the location of the rail station, and averaged out over the length of the competingcorridors.DATA ANALYSISFive measures are available for the analysis, representing the various criteria. The raw data for each of the measuresfor the four candidate corridors is shown in Tables I and II. A summary of the associations of measures with criteriais shown in Table III.To compare the alternatives across different measures, the measures must be are normalized to values between 0 and1, as shown in Table IV. A graphic illustration of how the normalized measures of the corridors compare is shown inFigure 2. Examining the relative values of the measures among the alternatives, no one alternative emerges as trulysuperior or inferior to all others, however, the King Drive alternative emerges as inferior in all measures but one: theseparation from the Metra corridor.Selecting Weightings for Corridor ComparisonTo compare the various alternatives, a relative percentage weight is assigned to each measure, with the criteriaweights summing to 100%. For the initial analysis, three weightings are applied. Each of these initial weightingsassumes that one of the outcomes is of primary importance, and that the other two are of equal secondaryimportance. For computational simplicity, the total weighting of the measurements of the primary criterion is set at
  • Eric Holeman 660%, and the secondary criteria weightings are set to 20% each. The initial weightings of each measurement underthese scenarios are shown in Table V. Some assumptions must be made within these basic weightings. As the measurement of current servicespeed is considered a measure of both potential ridership increase and improved travel time, it is “double” weightedin all scenarios, assigned a weight that allows for its significance to both of these criteria. In addition, the criterion ofavoiding conflict with existing corridors has two measures, one relating to competing CTA service and anotherrelating to competing Metra service. The importance of avoiding conflicting CTA service is arbitrarily assumed tobe three times more important than avoiding conflicting Metra service. A greater assumption is made in thederivation of the weightings. Ideally, the process of deriving weightings would involve interested stakeholders theagency and from the community. For the sake of expedience in this study, arbitrary weightings are used. In the scenario emphasizing ridership improvement, the current ridership is weighted at 30%, for one halfof the needed 60% weighting. Service speed is weighted at 30% toward improving ridership, completing the needed60% emphasis on that criterion, but it is also weighted another 10%, to account for its importance as half of themeasurement of the criterion of improving travel time. The number of lanes is weighted 10%, as the other half ofthis criterion measurement. The 20% weight for avoiding service redundancy is split at 15% for the CTAmeasurement and 5% for the Metra measurement, per the 3:1 ratio already assumed. Figure 3 provides a graphicsummary of the weight assignments of this scenario.Assignment of Weights to Scaled Measures and Ranking of AlternativesFor each scenario, the various weights are then assigned to the scaled measures. The resulting scores are thensummed, and the alternatives can then be ranked according to how they score under that particular weightingscenario.Ridership Emphasis ScenarioUsing the weights for the increased ridership emphasis scenario yields the results shown in Table VI. The ridership-emphasis scenario, which places a heavy emphasis on the measures of current ridership and current speed,unsurprisingly favors the Jeffery and Cottage Grove corridors, each of which score high in both measurements.Interestingly, although the current ridership measurement for the Stony Island corridor is much lower than that ofKing Drive, the heavy weighting on travel time makes the two corridors almost equally preferred under thisscenario.Travel Time Improvement Emphasis ScenarioUnder the travel time improvement scenario, the weights fall heavily on the measures of corridor speed and numberof lanes. Existing ridership receives only a 10% weight in this scenario. Unsurprisingly, the Stony Island corridor,with its high number of lanes and correspondingly high travel times emerges as the preferred alternative. However,the Cottage Grove corridor actually posts a higher score under corridor speed, and outweighs Stony Island by afactor of two in the discounted measure of existing ridership. A summary of the results of the travel time emphasisscenario is shown in Table VII.Corridor Conflict Avoidance ScenarioThe final initial scenario explores the results of a weighting scheme that emphasizes avoidance of competition withexisting service. The greatest emphasis, a 45% weight, is placed on avoiding CTA service duplication. Lesseremphasis (15%) is placed on avoiding Metra service duplication. The results of the competition avoidance scenario are found in Table VIII, and as might be predicted, thetotal scores are proportionate to the distance from the CTA Red Line corridor. The lowest scores are found in theKing Drive corridor, which runs a scant half-mile from the Red Line, and along Cottage Grove, a full mile from theRed Line but bordering a Metra line for much of its length. Interestingly, the Jeffery corridor, which features a highlevel of service and the second-highest ridership of all the corridors, scores best in this scenario. This finding isconsistent with CTA policy of avoiding duplicating service where possible.
  • Eric Holeman 7Summary of All Weighting ResultsThe different weighting scenarios place a high emphasis on a few measures, with very predictable results. In eachscenario, one measure is typically weighted at 40%, with two measures accounting for up to 70% of the total weight,resulting in a very coarse identification of the category leaders for each criterion. A summary of initial results can befound in Table IX. The low ranking for King Drive in all scenarios is consistent with the initial observation that this corridormay constitute an inferior solution. In the raw measure values, it was outranked by Cottage Grove in all measuresexcept for distance from Metra, a value that has not been weighted heavily in any scenario. Among the higher scoring corridors, few emerge as choices without compromise. The Jeffery corridorleads in two scenarios, confirming its status as the current leader in ridership and competition avoidance, but doesn’tshow up particularly well in travel time improvement potential. Moreover, its width of only one lane through thelength of the corridor would make it an unattractive candidate for BRT service. The Stony Island corridor scored thehighest in the travel time improvement scenario, yet its low current ridership would tend to suggest that the samefactors that make its buses move quickly—fast travel times and high number of lanes--also make it an unattractivedestination for bus riders. An interesting result is noted in the second-place scoring. Cottage Grove, the second ranking finisher in thetravel time and ridership improvement scenarios, emerges as unattractive only under the service conflict avoidancescenario. However, its current ridership score—highest of all corridors—shows that the corridor is already attractiveto bus riders.CONCLUSIONSApplying the concordance analysis methodology is a straightforward process, yet it necessitates a number ofassumptions. Most of these assumptions result from the difficulty in obtaining needed information. The limitedscope of the study further necessitates assumptions. However, as these assumptions may be addressed by obtainingmore complete data and including it in the study, they do not detract from the usefulness of the method.The four generalized criteria are likely sufficient for evaluating corridors from the agency’s perspective, which isconsistent with the scope of this study. It is assumed that other factors, such as residents’ concern regarding impactsresulting from the implementation of BRT service, would necessarily be addressed in a different study.While the results of this study should be considered in light of the data used, these concerns involve only the dataused, and not the method used to analyze the data. The concordance analysis method has previously shown to beuseful in selecting among transportation alternatives. Given a wider variety of more specific data inputs, the methodcan be readily adapted to the question of BRT corridor selection.ACKNOWLEDGEMENTSFinancial assistance for the study was provided through the “Making CTA More Competitive as it Moves into the21st Century” program, subcontracted through the Great Cities Urban Data Visualization Program and the UrbanTransportation Center of the University of Illinois at Chicago, and through URS Corporation and the ChicagoTransit Authority.REFERENCES1. Giuliano, Genevieve. “A Multicriteria Method for Transportation Investment Planning.” Transportation Research, vol. 19A, no. 1, February 1985, pp 29-41.2. Hastak, Makarand and Maher M. Abu-Mallouh. “MSRP: Model for Station Rehabilitation Planning.” Journal of Infrastructure Systems, vol. 127, no. 2, June 2001, pp. 58-66.
  • Eric Holeman 8 Table I: Selected Attributes of Corridors Distance to Distance to nearest nearest Mean CTA rail Metra Daily Number of service service Corridor Boardings Lanes (miles) (miles) Cottage Grove Avenue 28,848 1.10 0.52 .82 Jeffery Boulevard 27,961 1.70 1.02 .32 Martin Luther King Drive 22,066 3.20 2.02 .82 Stony Island Avenue 12,147 1.00 2.52 1.32
  • Eric Holeman 9 Table II: Average Current Bus Travel Speeds in Candidate Corridors AM Peak Travel Speed PM Peak Travel Mean Peak Travel (mph) Speed (mph) Speed Corridor Northbound Southbound (mph) Martin Luther King Drive 10.9 10.0 10.5 Cottage Grove Avenue 10.4 12.0 11.2 Stony Island Avenue 10.0 7.5 8.8 Jeffery Boulevard 10.0 8.6 9.3
  • Eric Holeman 10 Table III: Summary of Criteria and Respective Measures Criteria Increased Shorter travel Maximize distance from ridership time existing service Current ridership X Measure Current service speed X X Number of lanes X Distance from Red Line X Distance from Metra Lines X
  • Eric Holeman 11 Table IV: Summary of Normalized Measures Mean Distance to Mean Speed Mean Number CTA rail Distance to Through of Lanes service Metra service Corridor Ridership Corridor (each direction) (miles) (miles) Martin Luther King Drive 0.76 0.93 0.34 0.21 0.62 Cottage Grove Avenue 1.00 1.00 0.53 0.41 0.24 Stony Island Avenue 0.42 0.83 1.00 0.80 0.62 Jeffery Boulevard 0.97 0.78 0.31 1.00 1.00
  • Eric Holeman 12 Table V: Summary of Measurement Weights Under Initial Weighting Scenarios Measurement Current Current service Number Distance from Distance from ridership speed of lanes Red Line Metra Lines Increasing Weighting Scenario ridership 30% 40% 10% 15% 5% Emphasis Travel Time 10% 40% 30% 15% 5% improvement Avoiding competition with 10% 20% 10% 45% 15% existing service
  • Eric Holeman 13 Table VI: Analysis Results, Ridership Emphasis Scenario Corridor Distance Ridership Speed Number of Distance to to Metra Corridor (30%) (40%) Lanes (10%) CTA (15%) (5%) Sums Martin Luther 0.23 0.37 0.03 0.03 0.03 0.699 King Drive Cottage Grove 0.30 0.40 0.05 0.06 0.01 0.826 Avenue Stony Island 0.13 0.33 0.10 0.12 0.03 0.709 Avenue Jeffery Boulevard 0.29 0.31 0.03 0.15 0.05 0.834
  • Eric Holeman 14 Table VII: Analysis Results, Travel Time Emphasis Scenario Ridership Corridor Speed Number of Distance to CTA Distance to Corridor (10%) (40%) Lanes (30%) (15%) Metra (5%) SumsMartin Luther 0.08 0.37 0.10 0.03 0.03 0.615King DriveCottage Grove 0.10 0.40 0.16 0.06 0.01 0.732AvenueStony Island 0.04 0.33 0.30 0.12 0.03 0.825AvenueJeffery Boulevard 0.10 0.31 0.09 0.15 0.05 0.703
  • Eric Holeman 15 Table VIII: Analysis Results, Service Conflict Avoidance Scenario Ridership Corridor Speed Number of Distance to Distance to Corridor (10%) (20%) Lanes (10%) CTA (45%) Metra (15%) SumsMartin Luther 0.08 0.19 0.03 0.09 0.09 0.484King DriveCottage Grove 0.10 0.20 0.05 0.18 0.04 0.572AvenueStony Island 0.04 0.17 0.10 0.36 0.09 0.762AvenueJeffery Boulevard 0.10 0.16 0.03 0.45 0.15 0.884
  • Eric Holeman 16 Table IX: Summary of Overall Rankings under Initial Weighting Scenarios Highest Score Second Highest Score Lowest Score Increasing Jeffery Cottage Grove King Drive Ridership Travel Time Stony Island Cottage Grove King Drive Improvement Avoiding Competition with Jeffery Stony Island King Drive Existing Service
  • Eric Holeman 17 Figure 1: Map of Corridors and Rail Service
  • Eric Holeman 18 Figure 2: Graphic Summary of Normalized Data 100% Martin Luther King Drive Cottage Grove Percent of Maximum Value Avenue 50% Stony Island Avenue Jeffery Boulevard 0% Ridership Speed Mean Distance Distance Number to CTA to Metra of Lanes Rail
  • Eric Holeman 19 Figure 3: Weights for Ridership Improvement Emphasis Scenario Current Speed Current Speed Number of Lanes Improving Ridership Improving Travel Time Distance from CTA Avoiding Competing Distance from Service Current Metra Ridership