Slow moving vehicle sign not recognized by drivers

May 27, 2003

In the first evaluation of motorist comprehension of the Slow Moving Vehicle (SMV) sign, a Penn State researcher found that less than 30 percent of the drivers knew what it meant.

The emblem, which has been in use for over 40 years, is currently required by 41 state motor vehicle codes. Most of these codes require farm equipment, construction and maintenance machinery and animal-drawn vehicles, such as Amish buggies, to display the symbol.

Philip M. Garvey, research associate at Penn State's Pennsylvania Transportation Institute who directed the study, says, "The reasons why so few of the drivers in our study recognized the SMV emblem include its uncontrolled misuse, poor driver education, the sign's inconsistent day/night appearance, and potential confusion with other roadway symbols."

The current SMV sign is a solid orange triangle during the day but appears to be a hollow red triangle at night when it also looks like the warning triangle used by drivers of stalled trucks.

Garvey notes, "About 30,000 slow moving farm equipment crashes, alone, are reported to occur annually on U.S. roads, suggesting that the emblem is not meeting the safety needs of either the general motoring public or SMV operators."

Garvey details his findings in a paper, "Motorist Comprehension of the Slow-Moving Vehicle (SMV) Emblem," in the current issue of the quarterly Journal of Agricultural Safety and Health. (

In the study, Garvey showed an image of the SMV sign in both its daytime and nighttime appearance to groups of older and younger drivers. There were 51 younger drivers, ages 18 to 40, and 55 older drivers, 64 to 84.

When shown the nighttime image, the older group correctly identified it more than twice as often as the younger group. However, overall, only slightly more than half of the 74 people who had a response to both the day and night appearance of the SMV sign recognized that the daytime and nighttime images were different versions of the same symbol. Incorrect responses included "biohazard," "stop," and "emergency vehicle."

"The recent upsurge of new low-speed vehicles, such as neighborhood electric vehicles and modified golf carts, will increase interactions between vehicles that travel at or below 25 mph and the rest of traffic," says the Penn State researcher. "Requiring these new vehicles to display the SMV sign, as the National Highway Traffic Safety Administration proposes, will only be effective in preventing accidents if the emblem's comprehensibility is improved through more consistent and accurate motorist education, increased enforcement and emblem modification."

Penn State

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