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

Transportation’s Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
Magnitude and Timing of GHG Reductions
The VMT reduction effects of congestion pricing can be calculated using the same elasticity
assumptions as for other pricing measures addressed in this study. Further assuming that
a congestion fee is applied to all freeways and arterials operating at level of service E or
worse, the proportion of VMT subject to congestion pricing is estimated to be 29 percent in
urban areas and 7 percent in rural areas across all functional classes of roads. 11
It should be noted that this is a very rough approximation. It does not account for any
increases in off-peak travel if people simply shift the time of their trip rather than forgoing
it or choosing an alternative mode. Sophisticated regional models are needed to analyze
more sensitively the necessary congestion fees and their impacts, which would vary
substantially by facility and by time of day.
5-26
Applying
an average fee of 65 cents per mile, which is the price estimated to be necessary to improve
level of service to D on these roads, the result is approximately a 20 percent reduction in
peak period traffic levels or an overall VMT reduction of 3.1 percent. Accounting for fuel
savings from reduced delay as well, this results in a GHG reduction of 35 mmt CO2e in
2030. Lesser reductions would be achieved at lower fee levels, or if congestion pricing
applications are not universal.
Regional simulations using travel demand models have been conducted in a few
metropolitan areas. A study in the Washington, D.C., region concluded that a
comprehensive distance-based toll, with tolls varying by time of day, would result in an
average cost of 3.3 cents per mile and an overall VMT reduction of 7.1 percent. Just
applying the variable toll to freeways would reduce VMT by 2.1 percent (Harrington,
Houde, and Safirova, 2007). Another study for the U.S. Department of Energy used travel
demand models in Minneapolis–St. Paul and Seattle, in conjunction with speed-fuel
efficiency relationships, to evaluate the combined benefits of travel reductions and
operating efficiencies from areawide systems of managed lanes. 12
The results from
different scenarios ranged from an 0.1 percent impact on fuel consumption and GHG
emissions to 2.5 percent depending upon the scenario. Extrapolating these results to a
national level based on projected 2030 congestion levels in different urbanized areas led to
an overall estimated reduction in national fuel consumption ranging from 0.5 to
1.1 percent (EEA, 2008), which would correspond to a reduction of 9 to 21 mmt CO2e in
2030.
11 “Level of service” is a measure of roadway performance that ranges from A (best) to F (worst). It
is based on traffic volumes for freeways, and on intersection delay for arterial streets. The
estimate of future mileage operating at level of service E or worse is based on forecasts of
congestion by FHWA under various scenarios (U.S. DOT, 2006).
12 These systems included high-occupancy/toll (HOT) lanes on freeways, in which drivers of singleoccupancy
vehicles can use the lane if they pay a fee which depends upon the congestion on the
nontolled travel lanes. Depending upon the scenario, either existing/planned high-occupancy
vehicle (HOV) lanes were converted to HOT lanes, or a new HOT lane was constructed alongside
an existing/planned HOV lane to form two HOT lanes.