Environmental Engineering Reference
In-Depth Information
TABLE 8.1
1995 U.S. Transportation Vehicle Use
a
Number
Annual Miles
Miles per Vehicle
Miles per Gallon
Type
(million)
(Gmile/y)
(mile/y)
(mile/gal)
Passenger cars
132.2
1448
10,958
21.3
Light trucks, SUV
65.7
790
12,018
17.4
Trucks
6.72
178
26,500
6.2
Buses
0.69
6.4
9,312
6.6
Transit
0.12
3.6
30,900
4.7
Rail
1.22
30.4
24,900
8.7
Commercial air
0.0056
4.4
790,000
0.35
a
Data from Bureau of Transportation Statistics, U.S. Department of Transportation, 1999.
with the faster growth of vehicle population than highway miles, has aggravated the problem of
increasing highway congestion in U.S. cities.
Highway vehicle fuel consumption shows a growth proportionate to the vehicle population
(see Figure 8.1), but annual variations are larger, reflecting the tempering effects of variations in
economic activity and level of employment. In 1995, U.S. highway vehicle fuel consumption was
134.8 Ggal/y (510.2 GL/y), averaging out to 669 gallons per year (2532 L/y) per vehicle. Weighted
by the fuel heating value, this annual consumption is 16.3 Quad/y
0.54 TW.
A breakdown of the use of all transportation vehicles in the United States in 1995 is given in
Table 8.1. Small passenger vehicles (cars, light duty trucks, sports utility vehicles, vans) account
for 96% of all highway vehicles, 92% of highway vehicle miles, and 76% of highway fuel. These
privately owned vehicles clearly dominate highway travel and energy use. Public passenger travel,
by bus and transit on the ground and airplane above, accounts for only 0.6% of total transportation
vehicle miles annually.
Small passenger vehicles are used only a small fraction of the time, mostly for short trips.
Their average yearly mileage, about 12,000 miles per year, amounts to 33.7 miles per day, about an
hour per day of operating time. The average one-way trip length is less than 10 miles, so vehicles
do not move far from their home locations, on average.
In the United States, the manufacture, operation, and maintenance of highway vehicles and
the refining and distribution of their fuels is pervasively regulated by both federal and state govern-
ments. Two of the regulatory objectives are of interest here: control of exhaust and evaporative
emissions and vehicle fuel economy.
4
Other objectives include vehicle and passenger safety, op-
erator competence, and owner fiscal liability. The regulation of emissions and fuel economy falls
principally upon the vehicle manufacturer, to a lesser extent on the fuel supplier, and hardly at all
upon the vehicle owner, whose principal responsibility is to maintain control equipment during the
vehicle lifetime.
The problem of air pollutant emissions from transportation vehicles is primarily that associated
with the private passenger vehicle. Their emissions, principally carbon monoxide (CO), oxides
=
4
U.S. federal regulation of vehicle fuel economy was instituted after the oil crisis of the 1970s so as to reduce
the dependence of the national economy on the supply of imported oil. At present, there is no legislative
requirement that vehicle fuel economy should be regulated to reduce vehicular CO
2
emissions.
