Finally: A splash-and-spray study that’s not all wet
After several studies and attempts by legislators to mandate spray-reduction devices on trucks, the AAA Foundation for Traffic Safety released a study that shows what can really be done to help solve visibility problems caused by trucks traveling on wet roads

About 20 years ago, former U.S. Sen. John Danforth, R-MO, attempted to mandate the use of splash-and-spray devices on commercial trucks. The Owner-Operator Independent Drivers Association said such an effort would do more harm than good.

That’s because in OOIDA’s view, the devices tend to build up chunks of ice during cold weather — the result of such a mandate would likely be large chunks of ice bounding around the highway.

Now, after several splash-and-spray studies by various groups, the AAA Foundation has taken a new look at the problem by releasing “Evaluation of Splash and Spray Suppression Devices on Large Trucks.”

The paper makes two important conclusions:

  • The addition of aftermarket devices does not significantly reduce spray by large trucks in wet weather; and
  • 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 ... especially in wet weather conditions,” said J. Peter Kissinger, president and 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.”

More on study methods
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 eight 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, the study said.

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 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. 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.

—by Dick Larsen, senior editor

Dick Larsen can be reached at