Reduced
visibility caused by spray from large trucks can frighten drivers and jeopardize
their safety. To address this problem, the AAA Foundation for Traffic Safety
funded Texas Transportation Institute (TTI) to identify and evaluate commercially
available technologies purported to reduce spray from large trucks in wet weather
conditions. These technologies were either some type of “fender, brush or flap”
system. The study found that:
- The addition of the after market
devices does not significantly reduce spray by large trucks in wet weather
- Improved vehicle aerodynamics
of the newer tractor-trailer significantly reduces the amount of spray generated
“These
findings underscore the importance of motorists using good “share-the-road“
strategies around large trucks and giving them a wide berth,” says J. Peter
Kissinger, President & CEO of the AAA Foundation for Traffic Safety. He
added, “Given the improved performance of the newer aerodynamic trucks, I also
hope the industry will do whatever it can to accelerate the retirement of the
older, less effective vehicles.”
Five
spray suppression devices, representing all known products introduced after
1990 and on the market at the time of the study were evaluated to identify which
is the most effective. Each device was mounted on a 1985 Freightliner tractor-trailer
combination. This older, non-aerodynamic tractor-trailer configuration was chosen
to evaluate more effectively any differences among the devices. Pilot testing
consisted of performing 8 runs for each device in a right crosswind at 55 mph
(88.5 kph).
Subsequently, four configurations were tested to indicate which
configuration, if any, produced the least amount of spray, whether the spray
treatment was effective at a variety of vehicle speeds, and the role of vehicle
aerodynamics in the production of spray. Configuration 1 was a 1997 Freightliner
tractor-trailer (representing the newer, more aerodynamic designs) with no spray
suppression devices. Configuration 2 was the same 1997 Freightliner tractor-trailer
outfitted with the most effective spray device from pilot testing. Configuration
3 was a 1985 Freightliner tractor-trailer outfitted with no spray devices, and
configuration 4 was the same 1985 Freightliner tractor-trailer outfitted with
the most effective spray device from pilot testing.
At
the lower vehicle speed, regardless of the wind condition, the addition of spray
reduction devices to the newer and more aerodynamic tractor-trailer configuration
did not result in a significant reduction of spray. Consistent with these results,
testing at the higher vehicle speed also indicated no significant differences
between the improved aerodynamic tractor-trailer without spray reduction devices
and the improved aerodynamic tractor-trailer with such devices, for any wind
condition.
For
the less aerodynamic 1985 tractor-trailer the addition of the spray reduction
devices did slightly reduce spray at lower speeds in non-stringent wind conditions.
However, more significantly, the devices provided no benefits at higher speeds.
The
evaluation used two measurement methods based on SAE standards simultaneously,
a laser-based method and a modified video-based method. Results showed that
laser- and video-based measurement methodologies produce highly correlated results.
The AAA Foundation for Traffic Safety is an independent,
publicly funded, 501 (c)(3) charitable research and educational organization
established in 1947 by the American Automobile Association (AAA). The AAA Foundation’s
mission is to prevent traffic deaths and injuries by conducting research into
their causes and by educating the public about strategies to prevent crashes
and related injuries. All AAA Foundation research can be found at www.aaafoundation.org.
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