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

Transportation’s Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
Improving System Efficiency by Improving Utilization
System efficiency has many facets, but perhaps the most important element in system efficiency is
the system’s load factor, sometimes called capacity factor or system utilization. When a transit
agency dispatches a 50-passenger transit bus on a route, the cost of the bus, the driver, the
maintenance/repair back-up, and fuel/emissions are all essentially fixed. If there is only one
passenger, the transit bus is a poor investment from the point-of-view of both economics and the
environment. On the other hand, if the bus is full or nearly full, there is a reasonable prospect that
fares can pay the costs of the run, while the emissions savings from removing 40 or 50 cars off the
road are immense.
Put another way, if there is excess capacity, the economic and emissions cost of adding an extra
passenger is essentially zero. This same phenomenon applies to both freight and passenger
modes, and (because of high operating costs) is particularly important to aviation. Available data
suggests that system efficiency for aviation and freight rail is high and has been improving rapidly
in recent years. For example, according to data from the Bureau of Transportation Statistics (BTS,
2009), freight rail energy efficiency (measured per ton-mile) improved by an average of 3.4 percent
annually in the 1980s, and 1.5 percent annually since then—even though locomotive technology
has changed little. For domestic air travel, energy efficiency per passenger-mile has improved by
2.9 percent annually since 1990*, due to increased passenger load factors, increased fuel efficiency,
and improved technologies and operational procedures to reduce fuel burn and emissions.
Improvements in these privately-operated modes have been driven by economic pressures.
However, due to saturation in improvement that can be maximally attained, this trend will likely
continue but at the lower pace. Operational gains estimated through 2035 range between 2.5 and 6
percent.
System efficiency for passenger rail and personal automobiles, on the other hand, has been low
and stagnating. Transit energy efficiency per passenger-mile declined in the 1980s and increased
by only 0.8 percent annually since then; Amtrak efficiency has not changed since 1990.
Automobile efficiency has increased by only 0.5 percent annually since 1990 (BTS, 2009). Average
vehicle occupancies have continued to decline (and are only slightly higher than 1.0 for work trips.
The implication is that there is considerable scope for improvement in the efficiency of surface
passenger transportation modes, and that improvements could potentially generate large
increases in transportation services without increases in emissions.
System efficiency strategies that improve freight utilization are considered in various subsections
of this section. Strategies that improve passenger vehicle utilization, such as transit and
ridesharing, are discussed in Section 5.0, Reducing Carbon-intensive Travel Activity.
*Calculated from data in Volume 1 Section 2.2.
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