Joe steers his
company's tractor-trailer rig to an interstate weigh station in Knox
County, Tennessee, for the required weight measurement and safety inspection.
As with his other three stops on weigh station scales that day, his
truck idles for about five minutes, wasting diesel fuel and precious
time. But his truck weight is once again found to be below the legal
limit, so he knows his company won't be ticketed and fined.
Joe's truck is
one of 500,000 carriers on the nation's highways that are checked four
times each day in the never-ending search for vehicles that are overloaded
and otherwise unsafe. The cost to the motor carrier industry and, subsequently,
to consumers of these mandated truck stops is estimated to be over $15
million daily. In addition, because weight enforcement activities are
slow and cumbersome, weigh stations are often overcrowded. Law enforcement
officials often face two choices that together can create unsafe conditions.
They can allow vehicles to back up in long lines near weigh station
entrance ramps. Or they can let carriers bypass stations without being
weighed or inspected.
Because the Knox
County weigh station, which is near the I-75/I-40 junction, is the second
busiest in the nation, about 70% of the 14,000 to 20,000 carriers traveling
toward it daily are allowed to bypass it. In the past, Joe has been
one of these. Some of these carriers legally bypass this station when
truck lines are short because their weight is considered acceptable
when they roll over an advanced, high-speed, weigh-in-motion (WIM) system
in the westbound lanes of I-75. This is one of more than 75 commercial
WIM systems embedded in the nation's highways that screen out commercial
vehicles that may be overweight. Each driver who participates in the
high-speed WIM program has a radiofrequency transponder for communication
with the weigh station. If the truck weight is near the allowable limit,
the driver is advised to stop at the upcoming weigh station for a more
accurate weighing of the vehicle.
The Knox County
system for weighing vehicles at high speeds is part of the National
High-Speed WIM Test Facility. With support from the Federal Highway
Administration and the Tennessee Departments of Transportation and Safety,
this facility was developed by ORNL's Engineering Technology Division
(ETD) in a cooperative research and development agreement with International
Road Dynamics (IRD), Inc., of Saskatchewan, Canada.
advanced WIM system for I-75 was designed, installed, and tested by
IRD and ORNL researchers David Beshears, Jeff Muhs, Matt Scudiere, and
others in ETD. The ORNL group developed an improved system for acquiring
and processing data from IRD's WIM hardware, which includes strain gauges
and transducers that measure how much the plates they're attached to
bend under the weight of truck tires, and then send corresponding electrical
signals to the data acquisition system. The researchers also installed
a small lab by I-75 for data collection and analysis. For the lab's
computer, which receives digitized signals from the WIM signal-processing
unit, they developed an advanced weight-determining algorithm. As a
result, the advanced system has an error rate that is 30% less than
that of a standard commercial WIM system for high-speed weight monitoring.
WIM systems pose several problems. "Installation of these systems is
expensive and requires extended lane closures, causing traffic jams,"
Beshears says. "Furthermore, these WIM systems are only 80 to 94% accurate.
That's not accurate enough for law enforcement, so the use of static
scales is required at weigh stations. Unless you get a truck weight
that is better than 99% accurate, you can't legally issue a citation
for a weight violation to a trucking company."
"We are now developing
a 'weight enforcement on the fly' technology that will weigh trucks
much more accurately at high speeds," Muhs says. "Its error rate will
be less than 1%. When used with a license plate reader and wireless
technology, this system will electronically identify and ticket overweight
trucks passing by without making them stop at weigh stations."
In the meantime,
the ORNL group is proposing that weigh station operators consider converting
static scales to low-speed WIM systems. Working with the Tennessee Department
of Safety and the Carlton Scale Company and using funding from the Defense
Advanced Research Projects Agency, the researchers have shown that it
is feasible to convert the static scales at the Knox County weigh station
into a high-accuracy, low-speed WIM system. This system was recognized
as an emerging technology at the American Museum of Science and Energy's
Tribute to Tennessee Technology Awards ceremony in 2000.
weight of a tractor (22,100 pounds) is displayed on the scale
meter. (Photo by Curtis Boles.)
"By using a static
scale platform that is 40 feet long, we have a large enough area and
a long enough time to sample the weight of the truck," Muhs says. "We
developed an algorithm that averages out the bounciness, or oscillations,
of truck tires as they alternately press heavily and lightly on the
platform of the scale. The algorithm allows us to weigh a truck moving
at 30 miles per hour with an error rate less than 1%, which is required
for law enforcement."
Besides increasing enforcement
efficiency, this approach will let trucks go through weigh stations
faster but allow inspectors time to determine whether a vehicle should
be pulled out of line and checked for brake problems or additional safety
violations. Traffic simulations of ORNL's low-speed WIM system indicate
the average delay for a motor carrier can be reduced by a factor of
seven, from 280 seconds to 40 seconds, eliminating traffic bottlenecks
that cause trucks to bypass weigh stations. Such a system also could
be used to weigh trucks as they enter and leave depot areas, such as
grain elevators and landfills.
Capps, leader of the Transportation Technology Development and
Demonstration Team in ORNL's Engineering Technology Division,
chats with Ralph Long, retired Exxon-Mobil truck driver, while
the tractor (minus its trailer) is being weighed on the static
weigh-in-motion scale at the NTRC. (Photo by Curtis Boles and
enhanced by Vicki Beets.)
A low-speed WIM
system using a static scale is located at the NTRC. The ORNL group is
using it for research and demonstrations.
Muhs spearheaded the development
of a fiber-optic WIM in 1989, but the project was abandoned a few years
later because the fiber used by the ORNL group was no longer being fabricated.
So the group focused on a different WIM technology. In 1996 in partnership
with the Tennessee Air National Guard, the ORNL group developed, tested,
and evaluated a portable WIM system for the U.S. Air Force. The system
was demonstrated at McGhee-Tyson Airport in Knoxville and at two military
of the Tennessee Air National Guard at McGhee-Tyson Airport (including
Colonel Fred Forster, right front) test ORNL's portable weigh-in-motion
system for the U.S. Air Force. This automated system uses plates,
strain gauges, and an advanced data acquisition system and algorithm
to weigh and determine the center of balance of military vehicles
in motion before they are loaded onto cargo aircraft for rapid
vehicle data acquisition (AVDAC) system, which uses plates and strain
gauges, weighs and determines the center of balance of trucks, tanks,
and other military vehicles in motion for rapid deployment by aircraft
into and out of a theater of operation. The goal is to make sure that
military aircraft and their cargo arrive safely and on schedule to help
meet a humanitarian need, provide assistance during a regional conflict,
or help protect the national security.
"If the center
of balance of the aircraft is not in the right zone, it cannot take
off safely," Beshears says. "That's why military vehicles must be weighed
so it can be determined where to put them and how best to distribute
the load in the cargo plane." The AVDAC system, which has been licensed
to Intercomp, Inc., in Minnesota, combines a weight-determining algorithm
and an electronic data acquisition system developed by ORNL with hardware
that converts tire forces into electrical signals. It could replace
the manual method of using small portable scales, a calculator, and
a tape measure to determine number of axles, axle weight, axle spacing,
gross weight, and center of balance. Because the AVDAC system is fully
automated, it is not subject to operator error and it is safer to use.
"Our AVDAC system
cut the error rate in half for WIM systems," Beshears says. "It greatly
simplifies the weighing operation and increases productivity by 500%,
saving 40 minutes per aircraft. Over 10 years this technology could
save the Air Force $45 million and prevent the loss of at least one
$200 million C-17 cargo aircraft."
Saving time and
money is not just a whim, but it may be a benefit of tomorrow's WIM
researchers and Air Force officials have envisioned a WIM system
for automatically weighing, marking, and loading an entire battalion
of military vehicles onto a military aircraft. This system integrates
wireless technology with load-planning software. Each vehicle
has a distinctive radiofrequency (rf) signature, which is identified
by an rf reader as the vehicle passes over a WIM scale. The vehicle's
weight and center of balance are measured and transmitted with
its rf identification to a computer, which has load-planning software.
The computer decides where on the aircraft each vehicle should
go to give the aircraft the proper center of balance so it can
take off safely. The driver of each vehicle (see above) follows
computer-controlled guide lights on the aircraft that tell him
where to park the vehicle.
Muhs (left) and David Beshears conduct research on energy (e.g.,
hybrid lighting) as well as transportation projects. (Photo by
Curtis Boles and enhanced by Jane Parrott.)
Engineering Technology Division
Department of Safety
American Museum of Science
Defense Advanced Research
Air National Guard