weekend in his yard (Riemer 1999). These
40 trucks are idling for approximately 3,600 h
annually. In the absence of actual statistical
data, we present results as a function of
number of hours idled per year. Table 1 shows
estimates for total numbers of long-haul truck-
hours idling annually in the United States.
The location and the availability of
appropriate places to stop also influence truck
idling patterns. Truck drivers stop to rest at
public rest areas and private truck stops
(TRI 1996). Most truck drivers use free public
rest areas during the day and for short stops.
Nearly 1,500 public rest areas are scattered
throughout the contiguous 48 states and the
District of Columbia, offering some
25,000 truck parking spaces for the nearly
480,000 long-distance trucks (including those
that do not need to park overnight on the road).
Accessibility is an important concern, which
favors the public rest areas on interstate routes.
Therefore, the public facilities along the busy
interstate routes (such as I-5, I-10, I-40, I-80,
I-90, and I-95) become full early (TRI 1996).
Private truck stops provide approximately
184,000 additional parking spaces, and many
truck drivers use these, with new construction
projected to increase that number to 213,000
by the end of 1999 (TRI 1996). Although
many trucker drivers prefer not to pay user
fees, higher fuel taxes, or higher registration fees for parking, truck stops offer such services as
showers, laundry, and restaurants (TRI 1996). The truck stops along the busy interstate routes
report 90% occupancy levels. Drivers sometimes park at their customers' lots if the site is safe.
Drivers must balance their concerns for safety and cost in selecting a place to rest.
If there are 458,000 truck drivers who are likely to need to stop and sleep, and there are only
about 210,000 parking spaces at rest areas and truck stops, then a maximum of 46% of the heavy
long-haul trucks can be using them at any one time. Although trucks are out of service part of the
time for maintenance, there is peak utilization on weekdays, which increases the overcrowding.
Many truckers drive at night and sleep during the day.
Figure 2 Typical Sleeper