Selecting Corridors for Bus Rapid Transit Using a Multicriteria Method

Eric Holeman

Chicago Transit Authority 120 N. Racine Avenue Chicago IL 60607 Tel. (312) 733-7000 Fax (312) 432-7127 Email: ehol@xmission.com

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ABSTRACT

Many bus rapid transit (BRT) projects result from the availability of a single vacant corridor, such as an abandoned rail right of way. Deciding where to implement BRT service in an existing transit network, in the absence of an obvious corridor, is a more difficult question. Various factors, such as the potential rider density, possible travel speed, and distance from other rapid transit corridors all weigh into the mix. Often the objectives tend to be mutually exclusive: a corridor that can provide fast travel times may offer few potential riders, while the corridor that provides the most riders may be along a traffic-clogged arterial. Where no one corridor is perfect, the best choice is necessarily a compromise between varied and often conflicting objectives. Because of the conflicting objectives, a multicriteria method was chosen to address the question of identifying potential BRT corridors. Four alternatives were compared across a number of different criteria. The concordance analysis method was chosen because of its usefulness in evaluating alternatives where the differences are both measurable and scalable. By placing different weights on the various objectives, the concordance analysis method show method does not result in the selection of one superior alternative, but instead shows how alternatives compare, given a particular set of priorities. Conversely, by showing how weighted alternatives rank, the method reveals the priorities involved in the choice of a given alternative. The results point strongly to an alternative that was eventually chosen by the transit agency for a limited-stop BRT-type service.

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INTRODUCTION

The Federal Transit Administration (FTA) has encouraged bus rapid transit (BRT) as a way to develop new rapid transit projects at a low up-front cost. A number have of these projects have been undertaken by U.S. transit agencies. Many of those have typically taken advantage of the availability of a single corridor, such as Pittsburgh’s use of an old rail right of way, or Seattle’s use of high-occupancy vehicle (HOV) lanes along an Interstate highway corridor. Such corridors offer an obvious advantage in their ready availability. However, for an established urban transit system that wishes to overlay BRT services on an existing network, the question of how to select the corridor to upgrade becomes important. The goals of a BRT corridor typically involve providing a fast ride for a large number of passengers, yet often the most densely populated transit corridors are those that provide the slowest bus movement. Conversely, corridors that offer quick vehicle movement are often found in areas of automobile-oriented development 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 multicriteria analysis method. The study compares a number of candidate corridors in an area of interest using various criteria appropriate to the agency’s objectives in implementing a BRT service. Any corridor that is clearly superior to all others may be identified as such. When no corridor is superior in all criteria, the corridors may be compared using different criteria weightings reflecting different prioritizations of the importance of the various objectives.

DESCRIPTION OF CORRIDORS

Four corridors were considered for evaluation in the part of Chicago's South Side, between the Dan Ryan expressway and Lake Michigan. The area of interest of the corridors extends for five miles, between 63rd Street to the north and 103rd street to the south. Corridors evaluated were limited to those north-south corridors with existing bus service. The corridors are described below and listed with a summary of their attributes in Table I. A map of the corridors 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. Cottage Grove Avenue, a somewhat more commercially oriented corridor than King Drive, provides two traffic lanes in each direction for most of its length. Stony Island Avenue, a broad auto-oriented thoroughfare, provides barrier-separated multiple lanes for both north and southbound traffic. Like Cottage Grove, it is commercially oriented; though being much wider, it has fewer residential buildings and minimal landscaping. Jeffery Boulevard is the narrowest of the corridors, containing a single lane in each direction for all of its length. Although a narrow corridor like Jeffery is not typically a candidate for BRT service, its high level of existing bus patronage merits its consideration in this study.

METHOD

The concordance analysis method, as described by Giuliano (1) allows for the comparison of alternatives with different, conflicting objectives. In applying the method, criteria are identified, and appropriate measures are determined for each of the criteria. Data are then collected for each measure of each alternative candidate. The alternatives can then be ranked according to one or more weightings of the measures. Consistently unattractive alternatives can be readily identified and discarded, while the more attractive alternatives may then be compared more directly. Unlike a traditional cost-benefit approach, the concordance analysis method does not allow for the maximization of a 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 enables the comparison of multiple favorable and unfavorable outcomes, the researcher may identify one or more alternatives that offer an acceptable combination of outcomes. The method is appropriate for the problem of transit corridor selection because each alternative presents an assortment of costs and benefits that aren’t easily scaled to dollar values.

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A 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 station improvement projects. Both studies strongly suggest the usefulness of concordance analysis as a tool to evaluate transit corridors in situations where no single criterion is paramount—provided sufficient criteria to be optimized can be measured and scaled.

Applying the Concordance Analysis Method to the problem BRT Corridor Selection

Once the criteria for comparing BRT corridors are identified, they can be evaluated using available measures. It is assumed that the objectives of a transit operator, in implementing a BRT project include increasing patronage in the corridor, improving service quality, minimizing operating costs, and avoiding competition with existing routes.

Increased Patronage

For the desired outcome of increased patronage, it is assumed that a high-ridership corridor has some residual demand that may be served by providing BRT service. The capacity for patronage increase is therefore assumed to be greatest in corridors that already have high ridership, and the current ridership in the corridor is assumed to be a useful 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 conversion than a service that is operating in crowded streets, the current operating speed of the bus will be used as a measure of the corridor’s ability to attract increased ridership.

Improved Service Quality/Reduced Operating Cost

The outcome of improved service quality is somewhat harder to define, and not all aspects of it are necessarily related to the corridors in which the service runs. However, it will be assumed that for purposes of selecting a corridor that faster is better. For the transit agency, operating costs are directly related to operating speed—faster buses mean lower costs. The measures of potential service improvement are also applicable to the objective of minimizing operating cost, and will hereafter be treated as the same criterion. The current operating speed of the existing bus service in a corridor, already identified as a measure for the potential of increased patronage, will also serve 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 the assumption that such a service improvement is more possible if there are more lanes available. Therefore, the number of traffic lanes in the corridor will provide another measures relating to service quality improvement.

Avoiding Competition with Existing Service

The chosen corridor is expected to avoid redundancy with existing rapid transit services. It is assumed that the likelihood of service cannibalization is related to the distance to a competing service. For the corridors under consideration, the nearest competing CTA rapid transit service is the parallel Red Line service. Distance from the Red Line is therefore an appropriate measure of the likelihood of service cannibalization. However, there is also competing Metra commuter rail service near the corridors, and it is possible that Metra customers may be less likely to consider a CTA service, as they already enjoy a rapid transit-style service with stops approximately half a mile apart. The distance to the nearest parallel Metra service, then, may also be considered an appropriate measure of the possibility of service competition.

DATA AND DATA COLLECTION

Once measures for the criteria were defined, data could be collected. A field survey of the corridors determined the number 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.

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Schedule Data

Schedule data were used to calculate the average current travel speed, providing a measure of the capacity of ability of buses to quickly move through the corridors. For each bus route along each of the corridors, recent published CTA schedules were consulted to determine average speed along the corridor during AM rush hours for inbound service and during PM rush hours for outbound services. While buses do not always travel according to their schedules, it was assumed that the published schedules provide an approximation of the travel time, if not an exact measure.

Ridership Data

Current ridership counts provide a measure of the corridor’s support of the current bus service, a measure that is used as a proxy for potential BRT ridership. CTA’s ridership data provides the number of passenger boardings per weekday per route. This provides a crude measure of the route patronage; however, it should be noted that the ridership figures are not available for time of day. Further, only boarding counts for the entire length of each route could be obtained, though it would have been preferable to isolate boardings that occurred within the area of interest. The ridership counts for all the services in each corridor were combined, including both local and express services.

Corridor Data

The width of each corridor was determined by a field survey. Each of the four corridors was traveled along its entire length, from 63rd Street to 103rd Street. For each half mile (i.e., four numbered streets) the number of lanes in each direction was noted at the midpoint. Each corridor runs for five miles through the area of interest, so a total of ten measurements were made. From these ten measurements, the average width of each corridor was computed. Only one corridor, Jeffery Boulevard, was of uniform width along the entire five miles. Parking lanes and turning lanes were not included in the lane measurements.

Competitive Service (“Cannibalization”) Data

Data measuring the distance between the proposed alternatives and competing CTA and Metra commuter rail service were taken from the CTA’s route map. For CTA service, the only competing service is the Red Line rail service between 63rd and 95th Streets. The nearest Metra service to all corridors is the Metra Electric main branch service. The distance between the candidate corridor and the potentially competing rail corridor was measured along the connecting east-west street at the location of the rail station, and averaged out over the length of the competing corridors.

DATA ANALYSIS

Five measures are available for the analysis, representing the various criteria. The raw data for each of the measures for the four candidate corridors is shown in Tables I and II. A summary of the associations of measures with criteria is shown in Table III. To compare the alternatives across different measures, the measures must be are normalized to values between 0 and 1, as shown in Table IV. A graphic illustration of how the normalized measures of the corridors compare is shown in Figure 2. Examining the relative values of the measures among the alternatives, no one alternative emerges as truly superior or inferior to all others, however, the King Drive alternative emerges as inferior in all measures but one: the separation from the Metra corridor.

Selecting Weightings for Corridor Comparison

To compare the various alternatives, a relative percentage weight is assigned to each measure, with the criteria weights summing to 100%. For the initial analysis, three weightings are applied. Each of these initial weightings assumes that one of the outcomes is of primary importance, and that the other two are of equal secondary importance. For computational simplicity, the total weighting of the measurements of the primary criterion is set at

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60%, and the secondary criteria weightings are set to 20% each. The initial weightings of each measurement under these scenarios are shown in Table V.

Some assumptions must be made within these basic weightings. As the measurement of current service speed is considered a measure of both potential ridership increase and improved travel time, it is “double” weighted in all scenarios, assigned a weight that allows for its significance to both of these criteria. In addition, the criterion of avoiding conflict with existing corridors has two measures, one relating to competing CTA service and another relating to competing Metra service. The importance of avoiding conflicting CTA service is arbitrarily assumed to be three times more important than avoiding conflicting Metra service. A greater assumption is made in the derivation of the weightings. Ideally, the process of deriving weightings would involve interested stakeholders the agency 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 half of the needed 60% weighting. Service speed is weighted at 30% toward improving ridership, completing the needed 60% emphasis on that criterion, but it is also weighted another 10%, to account for its importance as half of the measurement of the criterion of improving travel time. The number of lanes is weighted 10%, as the other half of this criterion measurement. The 20% weight for avoiding service redundancy is split at 15% for the CTA measurement and 5% for the Metra measurement, per the 3:1 ratio already assumed. Figure 3 provides a graphic summary of the weight assignments of this scenario.

Assignment of Weights to Scaled Measures and Ranking of Alternatives

For each scenario, the various weights are then assigned to the scaled measures. The resulting scores are then summed, and the alternatives can then be ranked according to how they score under that particular weighting scenario.

Ridership Emphasis Scenario

Using 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 of King Drive, the heavy weighting on travel time makes the two corridors almost equally preferred under this scenario.

Travel Time Improvement Emphasis Scenario

Under the travel time improvement scenario, the weights fall heavily on the measures of corridor speed and number of 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 a factor of two in the discounted measure of existing ridership. A summary of the results of the travel time emphasis scenario is shown in Table VII.

Corridor Conflict Avoidance Scenario

The final initial scenario explores the results of a weighting scheme that emphasizes avoidance of competition with existing service. The greatest emphasis, a 45% weight, is placed on avoiding CTA service duplication. Lesser emphasis (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, the total scores are proportionate to the distance from the CTA Red Line corridor. The lowest scores are found in the King Drive corridor, which runs a scant half-mile from the Red Line, and along Cottage Grove, a full mile from the Red Line but bordering a Metra line for much of its length. Interestingly, the Jeffery corridor, which features a high level of service and the second-highest ridership of all the corridors, scores best in this scenario. This finding is consistent with CTA policy of avoiding duplicating service where possible.

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Summary of All Weighting Results

The different weighting scenarios place a high emphasis on a few measures, with very predictable results. In each scenario, 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 be found in Table IX.

The low ranking for King Drive in all scenarios is consistent with the initial observation that this corridor may constitute an inferior solution. In the raw measure values, it was outranked by Cottage Grove in all measures except 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 corridor leads in two scenarios, confirming its status as the current leader in ridership and competition avoidance, but doesn’t show up particularly well in travel time improvement potential. Moreover, its width of only one lane through the length of the corridor would make it an unattractive candidate for BRT service. The Stony Island corridor scored the highest in the travel time improvement scenario, yet its low current ridership would tend to suggest that the same factors that make its buses move quickly—fast travel times and high number of lanes--also make it an unattractive destination for bus riders.

An interesting result is noted in the second-place scoring. Cottage Grove, the second ranking finisher in the travel time and ridership improvement scenarios, emerges as unattractive only under the service conflict avoidance scenario. However, its current ridership score—highest of all corridors—shows that the corridor is already attractive to bus riders.

CONCLUSIONS

Applying the concordance analysis methodology is a straightforward process, yet it necessitates a number of assumptions. Most of these assumptions result from the difficulty in obtaining needed information. The limited scope of the study further necessitates assumptions. However, as these assumptions may be addressed by obtaining more 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 is consistent with the scope of this study. It is assumed that other factors, such as residents’ concern regarding impacts resulting 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 data used, and not the method used to analyze the data. The concordance analysis method has previously shown to be useful in selecting among transportation alternatives. Given a wider variety of more specific data inputs, the method can be readily adapted to the question of BRT corridor selection. ACKNOWLEDGEMENTS Financial assistance for the study was provided through the “Making CTA More Competitive as it Moves into the 21st Century” program, subcontracted through the Great Cities Urban Data Visualization Program and the Urban Transportation Center of the University of Illinois at Chicago, and through URS Corporation and the Chicago Transit Authority. REFERENCES

1. 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.

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Table I: Selected Attributes of Corridors

Corridor Daily

Boardings

Mean Number of

Lanes

Distance to nearest

CTA rail service (miles)

Distance to nearest Metra service (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

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Table II: Average Current Bus Travel Speeds in Candidate Corridors

Corridor

AM Peak Travel Speed (mph)

Northbound

PM Peak Travel Speed (mph) Southbound

Mean Peak Travel Speed (mph)

Martin Luther King Drive Cottage Grove Avenue Stony Island Avenue Jeffery Boulevard

10.9 10.4 10.0 10.0

10.0 12.0 7.5 8.6

10.5 11.2 8.8 9.3

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Table III: Summary of Criteria and Respective Measures

Criteria Increased ridership

Shorter travel time

Maximize distance from existing service

Current ridership X Current service speed X X Number of lanes X Distance from Red Line X

M

easu

re

Distance from Metra Lines X

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Table IV: Summary of Normalized Measures

Corridor Ridership

Speed Through Corridor

Mean Number of Lanes

(each direction)

Mean Distance to CTA rail service (miles)

Mean Distance to

Metra service (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

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Table V: Summary of Measurement Weights Under Initial Weighting Scenarios

Measurement

Current ridership

Current service speed

Number of lanes

Distance from Red Line

Distance from Metra Lines

Increasing ridership

30% 40% 10% 15% 5%

Travel Time improvement

10% 40% 30% 15% 5%

Wei

ghti

ng S

cena

rio

Em

phas

is

Avoiding competition with existing service

10% 20% 10% 45% 15%

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Table VI: Analysis Results, Ridership Emphasis Scenario

Corridor Ridership (30%)

Corridor Speed (40%)

Number of Lanes (10%)

Distance to CTA (15%)

Distance to Metra (5%) Sums

Martin Luther King Drive

0.23 0.37 0.03 0.03 0.03 0.699

Cottage Grove Avenue 0.30 0.40 0.05 0.06 0.01 0.826

Stony Island Avenue

0.13 0.33 0.10 0.12 0.03 0.709

Jeffery Boulevard 0.29 0.31 0.03 0.15 0.05 0.834

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Table VII: Analysis Results, Travel Time Emphasis Scenario

Corridor Ridership

(10%) Corridor Speed

(40%) Number of

Lanes (30%)

Distance to CTA

(15%)

Distance to Metra (5%) Sums

Martin Luther King Drive

0.08 0.37 0.10 0.03 0.03 0.615

Cottage Grove Avenue

0.10 0.40 0.16 0.06 0.01 0.732

Stony Island Avenue

0.04 0.33 0.30 0.12 0.03 0.825

Jeffery Boulevard 0.10 0.31 0.09 0.15 0.05 0.703

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Table VIII: Analysis Results, Service Conflict Avoidance Scenario

Corridor Ridership

(10%) Corridor Speed

(20%) Number of

Lanes (10%)

Distance to CTA (45%)

Distance to

Metra (15%) Sums Martin Luther King Drive

0.08 0.19 0.03 0.09 0.09 0.484

Cottage Grove Avenue 0.10 0.20 0.05 0.18 0.04 0.572

Stony Island Avenue

0.04 0.17 0.10 0.36 0.09 0.762

Jeffery Boulevard 0.10 0.16 0.03 0.45 0.15 0.884

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Table IX: Summary of Overall Rankings under Initial Weighting Scenarios

Highest Score Second Highest Score Lowest Score Increasing Ridership Jeffery Cottage Grove King Drive

Travel Time Improvement

Stony Island Cottage Grove King Drive

Avoiding Competition with Existing Service

Jeffery Stony Island King Drive

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Figure 1: Map of Corridors and Rail Service

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Figure 2: Graphic Summary of Normalized Data

0%

50%

100%

Ridership Speed MeanNumberof Lanes

Distanceto CTA

Rail

Distanceto Metra

Perc

ent o

f M

axim

um V

alue

Martin LutherKing Drive

Cottage GroveAvenue

Stony IslandAvenue

JefferyBoulevard

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Figure 3: Weights for Ridership Improvement Emphasis Scenario

Distance from Metra

Distance from CTA

Number of Lanes

Current Speed

Current Ridership

Current Speed

Improving Ridership

Improving Travel Time

Avoiding CompetingService