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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
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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
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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
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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
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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.
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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
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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
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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-ŕ-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
