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low number. When net costs are computed on a per-trip basis, the two high-yield program types,
incentive and service/incentive, emerge as the most cost effective, with cost savings of $1.36 and
$0.63 per daily vehicle trip reduced, respectively. In contrast, neither the support nor the services
programs had avoidable costs to claim, and hence their net cost per trip reduced is the same as the
direct cost per trip (Comsis, 1994).
A "Trip Reduction Performance Program" sponsored by the Washington State Department of
Transportation (WSDOT) offers a window into 20052009 trip reduction costs under the state's
CTR regulations. Under this program entities ranging from employers to agencies contract with
WSDOT to deliver specified trip reductions. WSDOT sets an upper limit of a $460 annual cost per
average daily trip reduced, less than $2.00/day. Although many participants compete for funds at
this limit, other projects come in substantially lower (Hillsman, 2009).
One of several effectiveness measures relevant to TDM is congestion reduction. The Seattle I-5 cor-
ridor TDM-impact analysis described in the previous subsection estimated that study area peak
period ramp volumes would average about 4 percent higher without the existing CTR programs.
Traffic flow theory and observation indicate that it is the last few percentage points of traffic
growth that can move congestion from slowed traffic to traffic essentially at a standstill, and vehi-
cle trip reduction should have the opposite effect, unless counterbalanced by induced traffic.
Theory and experience were backed up by the analysis, which (using the CORSIM traffic simulation
model) determined that spatial congestion in the study area--measured in lane miles of congestion--
would increase by 23 percent in the 4-hour AM peak period and 44 percent in the 4-hour PM peak
period in the absence of current TDM programs. Similarly, it was determined that temporal conges-
tion expressed as the timespan during which 20 percent or more of the network is congested would
increase by 31 percent in the AM and 30 percent in the PM. With results such as these, it is possible to
see how Washington State's Commute Trip Reduction Task Force in 2005 estimated that Washington's
CTR programs were saving at least $24 million annually in reduced Puget Sound travel delay cost
(based on 2003 data). Workers at CTR sites were estimated to be saving $13.7 million in fuel costs. The
state's CTR program investment in 2005 was $2.7 million. This leverage was combined with additional
investment by local jurisdiction partners and participating employers (Georggi et al., 2007). The
employer contribution is understood to be in the $30 to $40 million range (Hillsman, 2009). A full-scale
cost-effectiveness evaluation would obviously fully quantify not only these additional cost contribu-
tions, but also additional societal and corporate/institutional costs and benefits.
Energy and Environmental Relationships
Because their purpose is to reduce vehicle trips and vehicle miles of travel, TDM strategies are fre-
quently considered as mechanisms to reduce energy use and vehicle emissions. The outcome for
both--energy used and pollutants emitted--is dependent not only on the number of vehicle trips
and travel miles. It is also dependent on the operating conditions under which the trips and travel
occur, as well as the state of engine and fuel technology. From the mid-1970s, as a result of con-
cerns about foreign petroleum dependency and growing problems with air pollution in American
cities, legislation has pushed vehicle manufacturers and petroleum companies to improve upon
the performance of their products. Beginning with the 1978 model year, foreign and domestic vehi-
cle manufacturers were obliged to meet federal standards and time schedules for corporate aver-
age fuel economy (CAFE standards) and rates of emissions (Hillsman, 2009). Hence, the domestic
vehicle fleet (light duty much more than heavy duty) has seen fuel economy and emissions perfor-
mance grow. Perhaps the biggest gains occurred in the 1990s following passage of the Clean Air
Act Amendments, and more may now be anticipated in the future.
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The purpose of this background is to convey the perspective that energy consumption and vehi-
cle emissions are derived outcomes depending heavily on the state of technology and fuels, which
have been evolving rapidly. Therefore, it can be potentially misleading to attempt comparisons
of the capabilities and cost-effectiveness of particular TDM strategies in reducing emissions or
fuel consumption using past data, given that there are so many context variables that contribute
to the outcome.
In spite of the fuel conservation efforts of the 1970s, as the real cost of fuel softened in subsequent
years, manufacturers lured consumers back to large, heavy, and high-horsepower vehicles. These
included light trucks and SUVs, which faced much less restrictive fuel economy and emissions
standards. Partially as a result, but also in response to increased driving overall, transportation
energy consumption rose markedly and has returned as a major policy issue. As such, it is a key
element of foreign petroleum dependency and global warming concerns.
Also, while vehicles have become less polluting of ozone-contributing gasses (VOC, NOx, and
CO), the past focus has not been on greenhouse gas emissions. The greenhouse gas pollutants,
primarily CO2, are directly tied to fossil fuel combustion. Conventional emissions control technol-
ogy cannot effectively mitigate the greenhouse gas effects of high rates of motor vehicle use. Only
fossil fuel consumption reduction--a function of fuel efficiency enhancement and VMT reduction--
can lower CO2 emissions.
There have been many studies where TDM measures have been considered and analyzed for adop-
tion as Transportation Control Measures (TCMs) to mitigate pollution impacts. In a Transportation
Research Board study of the benefits of the U.S. government's Congestion Mitigation and Air
Quality (CMAQ) program published in TRB Special Report 264, a literature review examined scores
of Metropolitan Planning Organization (MPO) and academic research studies that attempted to
estimate the travel and emissions effects of TCMs. It was found, however, that virtually all of these
studies were limited in that they were modeling efforts and not empirical studies. Consequently,
only a small number of studies provided the basis for the CMAQ review. The selected studies had
the characteristic that their travel impacts were based on empirical observation, though emissions
models were necessary to estimate the travel impact effects on emissions.
Perhaps the most substantial resource used by the TRB/CMAQ study was a set of demonstration
projects conducted in California under various sponsors in the 1990s. The common denominator
of these studies was the way their impacts were determined. Each of the projects had been closely
monitored through before-and-after data collection, accompanied by detailed tracking of costs and
operating characteristics. The three different programs involved were the Los Angeles County
Metropolitan Transportation Authority (MTA) TDM Demonstration program, which funded more
than 170 TDM projects to test the costs and effectiveness of eight categories of projects in reducing
vehicle trips, VMT, and emissions; California law/program AB2766, which provided $60 million
in funding from vehicle registration revenues toward 250 projects aimed at reducing vehicle air
pollution; and the San Diego-Coronado Bridge Toll Revenue Program, which used bridge toll rev-
enue to finance projects to increase bridge capacity and reduce congestion and improve air qual-
ity (Committee for the Evaluation of the Congestion Mitigation and Air Quality Improvement
Program, 2002). A summary covering these three programs has been presented in a 1998 TRB paper
(Pansing, Schreffler, and Sillings, 1998). Results of this assessment are shown in Table 19-37.
The table shows the range of impacts on vehicle trips and travel, four key pollutants, and the cor-
responding cost associated with reducing each. Unfortunately, while overall travel impacts were
measured, underlying modal shares were not reported for these projects. Predictably, the range of
impacts across all strategy categories--both for travel and emissions--is so broad as to preclude
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strong conclusions about relative cost-effectiveness, since the impact is substantially controlled by
the scale (cost) of the project. Even when normalized in relation to cost, one still observes a consid-
erable range in the cost-based performance for most of the strategies, likely related in part to ambi-
ent conditions. The biggest ranges in performance are associated with the alternative-fuel-vehicle
measures and the transit improvements, while the core TDM measures (with the exception of
telecommunications) seem more stable in their measured performance. Generally what can be
observed from these data is the rather favorable performance of the TDM strategies (except
telecommunications and to some extent vanpools) in reducing VMT and emissions.
Largely but not entirely similar conclusions were reached in the TRB/CMAQ evaluation itself.
Table 19-38 offers a summary of the emissions cost-effectiveness taken from Table E-4 of the CMAQ
study. The median values shown are also derived from a fairly wide range of impacts found in the
representative projects (Committee for the Evaluation of the Congestion Mitigation and Air Quality
Improvement Program, 2002).
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Table 19-37 Comparative Travel, Emissions, and Cost-Effectiveness of Transportation Control Measures--
Three California Programs
Cost per Travel Cost per
Travel Impacts Emissions Impacts (Lbs.) Impact Emissions
Cost per Cost per Reduction
Project Category VTR VMTR HC/ROG NOx CO PM-10 VTR VMTR (per Lb.)
Alternative Fuel 441 13,716 23 23 192 72 $0.22 $0.03 $3.06
Vehicles 594,080 4,752,641 12,806 9,269 121,067 26,649 $18.70 $1.23 $1,351.00
TDM
Bicycle Facilities 3,480 11,760 46 38 668 6 $0.43 $0.02 $0.83
33,840 486,174 864 845 7,503 2,546 $4.04 $0.71 $26.00
Financial Incentives 40,858 1,292,760 2,130 2,301 18,979 668 ($0.44) ($0.01) ($0.63)
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141,600 6,056,880 8,865 10,089 77,881 2,804 $7.04 $0.37 $19.98
Organizational TDM 53,760 950,400 1,632 1,744 16,435 440 $2.65 $0.18 $7.85
63,360 966,800 1,678 1,760 17,506 448 $3.48 $0.19 $9.23
Telecommunications 0 40,800 80 80 895 19 $1.13 $0 ($4.56)
95,520 5,966,880 9,120 10,553 76,921 2990 $3,236.00 $17.00 $661.00
Vanpools 14,227 737,528 735 713 6,420 237 $1.33 $0.03 $1.45
143,500 6,880,000 9,420 10,168 79,031 32,782 $20.49 $0.48 $46.67
Transit Improvements
Line Haul 1,344 21,360 137 (55) 975 5 $0.22 $0.03 $3.06
594,080 4,752,641 12,806 9,269 121,067 26,649 $35.00 $2.20 $1,117.00
Shuttle 1,984 9,950 187 6 2,376 14 $3.68 $0.05 $6.52
35,713 835,380 1,019 1,100 10,056 286 $75.60 $27.70 $610.00
Source: Pansing, Schreffler, and Sillings (1998).
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Table 19-38 Emissions Reduction Cost-Effectiveness of TDM
and Other CMAQ-Funded Strategies
Median Cost Median Cost
CMAQ Strategy per Ton CMAQ Strategy per Ton
Inspection and maintenance $4,500 Modal subsidies and vouchers $125,400
Regional rideshare programs $18,500 Park-and-ride (transit and rideshare) $127,500
Charges and fees $27,900 Bicycle/pedestrian programs $206,600
Vanpool programs $30,400 New transit capital systems/vehicles $208,000
Miscellaneous TDM $34,100 Shuttles, feeder, paratransit $214,700
Traffic signalization $35,200 Freeway/incident management $240,900
Alternative fuel vehicles $53,000 HOV facilities $316,200
Employer trip reduction $56,900 Alternative fuel buses $355,700
Conventional fuel bus replacement $63,200 Telework $743,200
Conventional transit service $64,600
upgrades
Note: Effectiveness measure is median cost per ton of emissions reduced (VOCs + NOx).
Source: Committee for the Evaluation of the Congestion Mitigation and Air Quality Improvement Program (2002).
Two important conclusions were reached by the TRB/CMAQ study:
· The success of any strategy depended greatly on its being applied in an appropriate context.
· Several of the strategy categories that had favorable cost-effectiveness in reducing emissions
were of the TDM genre.
While inspection and maintenance ranked as the most cost-effective of all strategies, well above
average cost-per-ton performance was found in the TDM categories of regional ridesharing pro-
grams, charges and fees, vanpool programs, miscellaneous TDM, and employer trip reduction.
Conversely, among the least cost-effective TDM strategies were telework programs, transit shut-
tles or feeder lines, and bicycle/pedestrian facilities and programs. Also less cost-effective than
the top 10 strategies for reducing emissions were such widely popular Transportation System
Management (TSM) measures as park-and-ride lots, freeway/incident management programs,
and HOV facilities (Committee for the Evaluation of the Congestion Mitigation and Air Quality
Improvement Program, 2002).19
The two areas where conclusions differed markedly between the California-based studies and the
TRB/CMAQ study were with respect to vanpools and bicycle facilities. Note that while vanpool-
ing exhibits a tendency toward disappointing cost-effectiveness in the summary of California
studies (see Table 19-37), the cost spread is wide, and it places a respectable fourth out of 19 for
19 A significant limitation affecting single-objective/single-function cost-effectiveness (or cost-benefit) analyses
such as these is that other benefits to individuals or society are not considered. This issue is expanded upon
with respect to non-motorized transport (NMT) facilities in Chapter 16, "Pedestrian and Bicycle Facilities."
See "Economic and Equity Impacts" in that chapter's "Related Information and Impacts" section.
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