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

Transportation’s Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
Including induced demand effects changes the estimates significantly. Ramp metering
and incident management have moderate cost-effectiveness, ranging from $40-90 per
tonne for ramp metering and $40 to $170 per tonne for incident management (considering
implementation costs only); both strategies show net savings when vehicle operating costs
savings are included (up to -$120 per tonne for ramp metering and incident management
and lower deployment levels). All other strategies have direct costs of over $200 per tonne
(and in a few cases over $2,000 per tonne for road weather management and vehicle
infrastructure integration and maximum deployment levels), and show a net cost even
when vehicle operating cost savings are included (Cambridge Systematics, 2009).
Cobenefits
Traffic management strategies can have significant benefits in terms of delay reduction for
travelers and goods movement. For example, a review of various case studies of presettiming
traffic signal coordination suggests that travel-time reductions in the range of 8 to
25 percent are possible along a particular corridor. Studies of actuated traffic signal
coordination have found observed or simulated reductions in travel times from 8 percent
to as high as 41 percent, with delay reductions ranging from 14 to 44 percent compared to
baseline delay where the improvements have been applied (Cambridge Systematics, no
date). The Texas Transportation Institute reports that ramp metering in 25 cities reduces
delay by 29.4 million person hours, or approximately 2.4 percent of freeway delay (TTI
2007). Incident management practices have been estimated to reduce incident duration by
39 to 51 percent. 14 Various European countries have experienced a 3 to 7 percent increase
in peak period throughput and a 3 to 22 percent capacity increase along highway
corridors in which Active Traffic Management is applied (FHWA, 2007a).
Improved safety also is likely to be a by-product of some strategies; for example, crashes
may be reduced if motorists are informed of upcoming congestion or if stop-and-go traffic
is reduced. Incident management practices that decrease response time can save lives by
getting victims medical attention more quickly. Active Traffic Management has been
credited with significant reductions in incidents (up to 50 percent) in European
applications (FHWA, 2007a).
Traffic management strategies also should result in air quality benefits. Traffic actuated
signalization along corridors in three cities reduced hydrocarbon and carbon monoxide
emissions by 4 to 12 percent, although oxides of nitrogen increased slightly (by 4 percent)
in one location. An evaluation of preset ramp metering in Denver found a reduction in
emissions of 24 percent (Mitretek, 2005). These benefits are based on current vehicle
technologies and may be reduced in the future, especially if electric-drivetrain vehicles are
widely adopted. These estimates of air quality benefits also do not include any additional
emissions resulting from induced demand.
14 FHWA’s IDAS model provides default values of a 39 percent delay reduction for improved
incident response/management procedures alone, and 51 percent for combined incident
detection and response/management procedures.
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