Transportation's Role in Reducing U.S. Greenhouse Gas Emissions ...

Magnitude and Timing of GHG Reductions
Transportation’s Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
Most of the research quantifying the VMT and potential GHG benefits of traveler
information systems has examined highway and transit traveler information systems.
Even so, the evidence on the benefits of these strategies is quite limited as it has generally
been difficult to measure and quantify specific impacts. The diffuse nature of impacts
(spread across the transportation network) and the many ways in which travelers may
acquire and respond to information makes it especially challenging to evaluate the
impacts of improved information. Furthermore, some traveler responses, such as taking
longer routes to avoid congestion, may actually increase VMT and GHG.
Available literature suggests that road status information programs may cause an increase
in VMT that roughly offsets the benefits from reduced delay on the mainline (FHWA, no
date). However, the literature has been primarily qualitative rather than quantitative,
with the exception of one simulation study that predicted a statistically insignificant
(0.1 percent) systemwide reduction in VMT from advanced traveler information system
strategies and similarly insignificant (0.1 to 0.3 percent) reductions in emissions, compared
to a 1.5 percent reduction in overall vehicle-hours of delay (Wunderlich, Bunch, and
Larkin, 1999). On the other hand, another study using a computer simulation model
concluded that providing motorists in Seattle, Washington, with information about traffic
incidents and congestion could lead to a 1.8 percent reduction in average vehicle delay
and a 2 percent reduction in vehicle emissions for morning peak periods, as better
informed travelers were able to choose the most efficient mode and route to their
destination (Jensen et al., 2000).
The Moving Cooler study estimated that very modest net GHG reduction benefits would
accrue from traveler information systems, including 511 systems, a Web site, and
personalized information. The study assumed a 1 percent delay reduction for the lowest
level (511 and Web sites only) and 2.5 percent for more aggressive deployment, including
personalized information, but also accounts for increased GHG over the long run due to
induced demand effects from reduced delay. The overall magnitude of GHG reductions
that might be expected from further deployment of traveler information was estimated at
0.6 to 1.8 mmt CO2e in 2030, or only 0.1 to 0.5 mmt considering induced demand effects
(Cambridge Systematics, 2009). 19 Because these estimates were based on professional
judgment regarding delay reduction and because no assumptions on diversion were used,
they are subject to some uncertainty.
The impact of transit traveler information on mode shifting from auto to transit, and
therefore on reduced VMT and GHG emissions, has not been comprehensively studied.
Similarly, no reliable evidence yet exists on the potential benefits of real-time carpool and
19 The lower scenario assumes 511 and Web site only, and deployment along highway segments
with peak-period volume-to-capacity ratios greater than 1.05; the more aggressive scenario
includes personalized information and deployment along all highways with peak period volumeto-capacity
ratios greater than 0.95. The induced demand effects include the same adjustment
described in footnotes 5 and 7 under Section 4.2.1.
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