Cover Image

Not for Sale



View/Hide Left Panel
Click for next page ( 37


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 36
36 CHAPTER 4 Managing Multimodal Tradeoffs-- Structuring Corridor Competition and Integration This chapter offers insights into the key tradeoffs that need Transit Versus Automobile to be made when planning, designing, building, and operating Corridor Orientation a new paradigm corridor. Close scrutiny of existing multi- The tradeoffs between freeways and transit lines involve the modal corridors suggests that the effectiveness of a transit facilities themselves as well as the corridors they inhabit. The line within a multimodal corridor depends on its design and orientation of a corridor's urban form (including land uses and the design of its adjacent freeway. The new paradigm offers urban design) and the design of the transit and freeway facil- insights into the competition between freeways and transit ities are important elements determining the relative success and how this competition can be structured to effectively carve of the corridor's transportation facilities (see Figure 4-1). out travel market niches in which each mode can thrive. This Transit-oriented corridors are designed to maximize non- chapter investigates the alternatives that should be considered automobilemobile access to land uses and transit stations. when planning a new paradigm corridor project. Land uses are generally high density with minimal parking. Walking is encouraged through the provision of dense, grid Multimodal Corridor Design street networks with wide sidewalks and streets designed for and Operational Tradeoffs pedestrian friendliness and moderate traffic speeds. The transit system and its surrounding circulation systems are all designed A new paradigm corridor is planned, designed, and operated to maximize access to transit stations by all modes of travel, to ensure an even playing field for competition between transit especially pedestrians. and freeway by segmenting the corridor's travel markets. Automobile-oriented corridors favor automobile mobility Segmented corridor markets--where transit and freeway are over nonautomobile station access. This typically leads to a each given a distinct travel market segment--can be encour- corridor with low-density, dispersed land uses that are difficult aged by the deliberate selection of combinations of planning, for pedestrians, bicycles, and transit to traverse while auto- design, and operational corridor components. These compo- mobiles can effectively, safely, and comfortably access these nents are discussed here as tradeoffs between performance and destinations. The freeway and its surrounding circulation design characteristics that help frame the discussion of the systems are designed to maximize automobile throughput new paradigm. (capacity), automobile travel speeds, and/or automobile Although these tradeoffs should be considered when plan- access to corridor land uses. If transit service exists at all in ning a multimodal corridor, a successful new paradigm cor- automobile-oriented corridors it generally supports auto- ridor uses the sum total of these tradeoff choices as building mobile circulation. Transit stations or stops are designed to blocks to yield a corridor that segments its travel market, maximize automobile access and parking. Park-and-ride lots giving both transit and freeway an advantage in serving a dominate the immediate station environments, and high- submarket. Segmented multimodal corridor markets can capacity road connections between station areas and the free- generally be classified as having either a transit or automobile way encourage peak-period commuters to reduce freeway orientation. The following section begins by describing transit congestion by parking their cars and transferring to transit. and automobile corridor orientation, followed by a discussion Few corridors are purely transit- or automobile-oriented; of the building block tradeoffs that contribute to them and most have a mixture of automobile- and transit-oriented ensure segmented travel markets. elements. These hybrid types can be placed somewhere along

OCR for page 36
37 Transit-Oriented Auto-Oriented Objective: Max. Non- Objective: Max. Auto Auto Access to Transit & Access to Individual Activity Centers Land Uses Corridor Continuum Multimodal Corridor Continuum Multimodal Transit- Multimodal Auto- Oriented Oriented Objective: Emphasize Non- Objective: Emphasize Auto Auto Access to Transit Access to Employment Stations & Activity Centers Centers & Transit Stations Figure 4-1. The corridor and multimodal corridor continuums. the multimodal corridor continuum shown in Figure 4-1-- Transit corridor accessibility versus operating speed a subset of the corridor continuum. Under this framework, Freeway accessibility versus operating speed we can envision a range of multimodal corridor types. At Freeway capacity versus transit ridership one extreme, multimodal transit-oriented corridors generally Transit-oriented versus automobile-oriented urban form emphasize nonautomobile access to land uses and transit Local access versus intermodal transfer stations stations, but still provide sufficient parking and freeway-to- In-median and adjacent versus offset freeway alignment transit intermodal transfer capabilities to allow and encourage Supplementary versus complementary transit and freeway transfers between modes. At the other end of the spectrum, service multimodal automobile-oriented corridors emphasize auto- Fixed versus flexible transit routing mobile access to relatively dispersed land uses and to the Incremental versus concurrent corridor planning ap- freeway. proaches New paradigm corridors require deliberate mixtures of these components to create segmented travel markets favoring each Transit Corridor Accessibility mode. The critical choices made for a multimodal corridor's Versus Operating Speed design revolve around the advantages and disadvantages given to each mode. Often, tradeoffs must be made between modes. To a large extent, both transit coverage and operating speeds An advantage given to transit may come at the expense of the are a function of the number of stations provided on the performance of the freeway and vice versa. The degree to which transit line. The more stations per mile of transit line (that is, a corridor has optimized combinations of transportation the higher the density of stations) the more area the transit services and land uses will depend on the degree to which it was line will serve and the more accessibility transit riders will have intentionally and effectively planned and managed that way. to corridor land uses. However, the more stations a transit Therefore, the multimodal corridor continuum is best under- line has, the slower the speed of the transit vehicles will be and stood in relation to what we refer to later in this chapter as the the more difficult it will be for transit to compete with the "multimodal planning continuum" (see Figure 4-7). adjacent freeway in terms of travel times. The illustrations in Figure 4-2 show how a high frequency of stations and a circuitous alignment can increase transit Key New Paradigm Corridor Tradeoffs accessibility to local, corridor land uses at the expense of operating speeds, while low station frequencies and straight The selection of new paradigm corridor design and operat- alignments can offer higher operating speeds at the expense ing characteristics should be done within the context of how of transit accessibility to corridor land uses. these choices will affect the tradeoffs in performance among Transit lines generally are designed to either attract local, corridor modes. These tradeoff choices will, in turn, determine short-haul riders or long-haul, "through" riders. Transit corridor orientation and market segmentation. The follow- generally attracts local riders when the line and its surrounding ing is a list of critical tradeoffs that describe and determine the land uses are coordinated to provide high accessibility, while it relative success of a new paradigm corridor: attracts through passengers when it emphasizes fast operating

OCR for page 36
38 High Access/Low Speed Transit Line Low Access/High Speed Transit Line Figure 4-2. Transit corridor accessibility versus operating speed designs. Table 4-1. Transit corridor accessibility versus operating speed tradeoff outcomes. Transit Corridor Accessibility Transit Operating Speed Market Segmentation Local/Short-haul trips Regional/Long-haul trips Corridor Orientation Transit-oriented Automobile-oriented speeds. Table 4-1 suggests how this tradeoff can serve the operating speeds. Table 4-2 suggests how this tradeoff can serve purposes of developing a new paradigm corridor to have the purposes of developing a new paradigm corridor to have market segmentation and an optimized corridor orientation. market segmentation and an optimized corridor orientation. Freeway Corridor Accessibility Freeway Capacity Versus Versus Operating Speed Transit Ridership Performance Freeway systems with high interchange frequencies (that is, On transit lines that directly compete with freeways, rider- a large number of interchanges per mile) and circuitous right- ship can suffer when freeway capacity is maximized. If ample of-way alignments generally provide high levels of accessibility freeway capacity is available--for example, when a freeway to local, corridor land uses at the expense of operating speeds. has enough lanes to handle peak-period traffic demand-- These facilities are often more congested because more access freeway travel times will be short because of lower congestion points and curves along a freeway tend to slow traffic. levels and transit will not be an attractive alternative to driving. Figure 4-3 shows how a high frequency of interchanges and Table 4-3 suggests how this tradeoff can serve the purposes of a circuitous alignment can increase freeway accessibility to developing a new paradigm corridor to have market segmen- local, corridor land uses at the expense of operating speeds, tation and an optimized corridor orientation. while a low frequency of interchanges and straight alignments offer higher operating speeds at the expense of freeway acces- Transit-Oriented Versus sibility to corridor land uses.1, 2 Automobile-Oriented Urban Form Similar to transit lines, freeways are generally designed to attract either local short-haul patrons or long-haul "through" Urban form describes both the land uses and urban design patrons. Freeways tend to attract local trips when the freeway qualities of an urban environment. Transit-oriented urban form and its surrounding land uses are coordinated to provide high is typically defined as high-density, mixed-use, pedestrian- area coverage, while it attracts through (long-haul) passengers friendly land uses close to transit stations. Nonautomobile- when the facility and its corridor alignment emphasize high motive circulation is encouraged using dense, grid street networks and other design measures to slow automobile speeds. Automobile-oriented urban form has lower density, separated 1AASHTO (2004) AASHTO Green Book: A Policy on Geometric Design of Free- land uses with street pattern and urban design qualities ways and Streets, 5th Edition. 2Skabardonis, A., et al. Low-Cost Improvements for Recurring Freeway Bottle- intended to give priority to automobile circulation. Table 4-4 necks. NCHRP Project 03-83, anticipated publication in 2010. suggests how this tradeoff can serve the purposes of developing

OCR for page 36
39 High Access/High Congestion Freeway Low Access/Low Congestion Freeway Figure 4-3. Freeway corridor accessibility versus operating speed designs. a new paradigm corridor to have market segmentation and an modal transfer stations are designed to attract patrons arriving optimized corridor orientation. by car or bus transit from beyond the station's local neighbor- hood. Local-access stations provide excellent pedestrian, bicycle, and local circulator shuttle service access to station Local-Access- Versus entrances, unencumbered by park-and-ride lots, kiss-and-ride Intermodal-Transfer-Oriented Stations drop-off areas, and bus terminal facilities. Local-access-oriented stations are designed to accommodate Intermodal-transfer-oriented stations attract automobile- and attract patrons from nearby neighborhoods, while inter- and bus-to-transit transfer patrons by providing ample Table 4-2. Freeway corridor accessibility versus operating speed tradeoff outcomes. Freeway Corridor Accessibility Freeway Operating Speed Market Segmentation Local/Short-haul trips Regional/Long-haul trips Corridor Orientation Automobile-oriented Transit-oriented Table 4-3. Freeway capacity versus transit performance outcomes. Freeway Capacity Transit Ridership Performance Market Segmentation Freeway dominates corridor Transit has a potential to serve travel a secure travel market Corridor Orientation Automobile-oriented Transit- or Automobile- oriented Table 4-4. Transit- versus automobile-oriented urban form tradeoff outcomes. Automobile-Oriented Urban Transit-Oriented Urban Form Form Market Segmentation Nonmotorized transit station Automobile transit station access access Corridor Orientation Transit-oriented Automobile-oriented

OCR for page 36
40 Table 4-5. Local access versus intermodal transfer tradeoff outcomes. Local Access Intermodal Transfer Market Segmentation Nonmotorized transit station Automobile transit station access access Corridor Orientation Transit-oriented Automobile-oriented park-and-ride lots, quick and effective kiss-and-ride drop-off constructing them. Figure 4-4 illustrates the range of hori- facilities, and efficient, high-capacity bus terminal facilities to zontal multimodal corridor alignments. handle intermodal transfers. Intermodal stations are often In-median and adjacent alignments offer the greatest poten- located close to freeway ramp touchdown points, allowing tial for cost-savings in land acquisition and construction for quick freeway-to-transit intermodal transfers. Table 4-5 sug- the transit line (assuming it is the second facility built in the gests how this tradeoff can serve the purposes of developing corridor after the freeway) because they can take advantage of a new paradigm corridor to have market segmentation and any surplus right-of-way land in or next to the freeway. Offset an optimized corridor orientation. transit lines must often piece together vacant or otherwise available land to create a new right-of-way, potentially incur- In-Median and Adjacent Versus ring significant costs. Offset Freeway Alignment The adjacent alignment/offset stations option is a hybrid variant with potential to take advantage of some of the cost The alignment of the transit and freeway facilities has impli- savings possible from adjacent or in-median alignments while cations for the patronage of each mode as well as the costs of also avoiding the pedestrian and transit access impediments In-Median Alignment Adjacent Alignment Offset Alignment up to 1/2-mi. Adjacent Alignment up to 1/2-mi. /Offset Stations LEGEND Transit Line Transit Station Freeway Freeway Interchange Figure 4-4. The range of horizontal multimodal corridor alignments.

OCR for page 36
41 of these approaches. By running the transit line primarily in However, the proximity of transit and freeways in multi- the freeway ROW while locating the stations as far as possible modal corridors often cause operational conflicts for both from the freeway, benefits for pedestrian, bicycle, and feeder modes. These conflicts can be minimized by effectively dividing transit access to the stations can be realized, but often at the the corridor's travel market into long- and short-haul trips expense of transit operating speeds and travel times along and then designing the transit line and the freeway to cater the corridor due to the circuitous route the transit line must exclusively to one or the other. follow. Although it is understood that traditionally the spacings of The range of possible corridor horizontal alignments freeway interchanges are keyed to street patterns and design also has significant performance implications. In-median standards, while the spacings of rapid transit are keyed to bus alignments have the most potential for operational conflicts routes, development densities, and street patterns, the effects of between the transit stations and the freeway and its inter- multimodal coordination can affect operations and patron- change ramps. The freeway is a physical barrier to pedestrians age, without respect to the original intentions of the systems' and bicyclists accessing both adjacent and in-median stations. designers. Traffic going to and from the freeway via its interchange ramps Multimodal corridor transit and freeway facilities are gen- pose a safety hazard to pedestrians and bicycles attempting erally either coordinated in a supplementary or complementary to access the stations and tend to make a transit-unfriendly fashion. environment. Transit lines offset from their freeway neighbors can operate Supplementary coordination means that the additional in greater isolation from the freeway and its automobile traffic, infrastructure in terms of lanes, track, ramps, and stations potentially taking advantage of a more pedestrian-friendly will supplement the capacity of the corridor, increasing environment. As a result, adjacent or in-median transit lines access and mobility. Supplemental effects improve the must depend more on automobile and bus access to their corridor capacity additively. stations, potentially limiting the ridership performance of Complementary coordination results from the fact that their systems. In-median and adjacent transit alignments also the transit and freeway components of the corridor may have performance implications for freeways, since the traffic exhibit different though complementary characteristics, associated with station access can disrupt the smooth oper- outcomes, and benefits. Complementary benefits would ation of freeway interchange ramps and reduce the carrying occur from the integration of modes within a multimodal capacity of the freeway itself. corridor. Transit and freeway facilities can coexist in the Table 4-6 suggests how this tradeoff can serve the purposes same corridor, but may not work in a coordinated fashion. of developing a new paradigm corridor to have market seg- The various modes in a corridor might be coordinated mentation and an optimized corridor orientation. through a common payment system, a traveler infor- mation system with comparative travel times by mode, or a coordinated, real-time congestion management system Multimodal Coordination: Supplementary Versus that adjusts the capacity and service deployments of one Complementary Transit and Freeway Services mode to compensate for the capacity constraints of another. A truly multimodal corridor is designed to maximize the intermodal relationships between the freeway and transit Corridors that have either a combination of long station facilities in the corridor. Ideally, either automobile-to-transit spacings and short interchange spacings, or the opposite, offer or nonautomobile-to-automobile transfers will be seamless complementary travel services in a multimodal corridor and and as effortless as possible. In this way, transit and freeway tend to carry more total passengers. So-called supplementary systems complement each other, providing a combined level corridors that have similarly spaced stations and interchanges of service for corridor trips that exceeds the summed capacity will compete directly with each other for the same corridor and performance of its component parts. trips, and performance of the entire corridor suffers as a result. Table 4-6. In-median and adjacent versus offset alignment tradeoff outcomes. In-Median/Adjacent Alignment Offset Alignment Market Segmentation Intermodal transfers/Transit as High level of segmentation congestion relief to freeway possible Corridor Orientation Automobile-oriented Transit-oriented

OCR for page 36
42 Transit-Oriented Complementary Auto-Oriented Complementary Supplementary Figure 4-5. Multimodal coordination hypothetical complementary and supplementary corridors. Analysis suggests that corridors will carry the most total A corridor with automobile-oriented complementary passengers (transit riders and freeway passengers) if they are coordination has long station spacings on its transit facility designed with complementary coordination, and a combi- and relatively short interchange spacings on its freeway com- nation of either a transit-oriented urban form pattern and ponent. This provides a low level of local accessibility and transit-oriented station access services, or automobile-oriented higher speeds for transit, and lower speeds and higher acces- urban form and automobile-oriented station access. sibility for automobiles via the freeway. Based on these findings, we further propose three multi- Table 4-7 suggests how this tradeoff can serve the purposes modal coordination configurations (illustrated in Figure 4-5): of developing a new paradigm corridor to have market seg- transit-oriented complementary, automobile-oriented com- mentation and an optimized corridor orientation. plementary, and supplementary. A corridor with transit-oriented complementary coordina- Fixed Versus Flexible Transit Routing tion has long interchange spacings on its freeway component and relatively short station spacings on its transit line. This One of the most important advantages automobiles have provides a high level of local accessibility and slower speeds for over traditional transit services is their flexibility--wherever transit, and higher speeds and lower accessibility for auto- roads go, cars can go. Fixed-rail transit vehicles only go where mobiles via the freeway. tracks are installed. This means fixed-rail transit operates at a Table 4-7. Multimodal coordination tradeoff outcomes. Supplementary Automobile-Oriented Transit-Oriented Complementary Complementary Market Segmentation Low levels of Freeway: Local/Short- Transit: Local/Short-haul segmentation haul trips trips Transit: Regional/Long- Freeway: Regional/Long- haul trips haul trips Corridor Orientation Automobile-oriented Automobile-oriented Transit-oriented

OCR for page 36
43 Source: Courtesy Washington State Department of Transportation and IBI Group, I-405 South Corridor Bus Rapid Transit Pre-Design, Final Report. Figure 4-6. Two routing alternatives for the proposed I-405 South Corridor Bus Rapid Transit System for the Puget Sound Region illustrates the flexible routing capabilities of bus rapid transit. disadvantage vis--vis a freeway because automobiles can cover nal systems and are subject to congestion. Therefore, while much more territory within the same corridor. However, flexibility of routing can be an advantage for BRT, it can also BRT is not dependent on fixed right-of-way infrastructure and lower transit's quality of service due to signal and congestion therefore offers flexible routing as well as the carrying capacity delays when not running exclusively in a dedicated lane. and speed advantages of fixed rail. BRT operating in separate Table 4-8 suggests how this tradeoff can serve the purposes facilities in or alongside a freeway median may enter and leave of developing a new paradigm corridor to have market seg- the freeway at selected locations, and distribute to other areas. mentation and an optimized corridor orientation. With rail lines, this usually requires a transfer to buses. The flexible routing capabilities of BRT are illustrated in Figure 4-6. Planning Multimodal Corridors: However, just as BRT can offer some of the routing flexibil- Concurrent Versus Incremental Approaches ity advantages similar to automobiles, it can also suffer from some of the same disadvantages that automobiles face. Auto- To understand how a multimodal corridor functions and mobiles can operate at a disadvantage to fixed rail and exclu- its relative success, it is necessary to understand something sive lane BRT transit services because they are slowed by sig- about its history and the process by which it was planned, Table 4-8. Fixed versus flexible transit routing tradeoff outcomes. Fixed Transit Routing Flexible Transit Routing Market Segmentation High level of segmentation Intermodal transfers/Transit possible as congestion relief to freeway Corridor Orientation Transit-oriented Automobile-oriented