Tractor-trailer trucks and automobiles have different sizes, weights and acceleration capabilities and sometimes form a hazardous combination on the nation's roads. But driving behind tractor-trailer trucks does have its advantages. It gives one the opportunity to read such captivating trailer tailgate messages as "How's My Driving?" and "Please Drive Safely." All kidding aside, driving behind and to the right of a tractor-trailer truck can be dangerous. When it makes a right-hand turn, it can hit and damage a car that is too close.
In this article, we are concerned with the design of truck warning signs that alert car drivers of trucks' wide right turns. These signs usually say "Caution - Wide Turns" or some variant. We are also concerned with the differences between the signs when there are no legal regulations governing their design. Over the past year or two, we have become aware of signs on the back of tractor-trailers alerting drivers to wide rights turns and have become intrigued with how many different signs there are and their merits. We therefore decided to study the signs to determine which we prefer from a human factors perspective.
Collecting Examples of Warning Signs
We evaluated the signs by taking pictures of them, ordering them according to various criteria, drawing conclusions about their effectiveness, and asking human factors researchers to evaluate them. While traveling to and from work over a two-week period, we photographed warning signs on the back of trucks parked at a truck stop on Interstate Route 95 near Boston. (Taking photos while driving behind trucks on highways or waiting for them at busy street intersections were not safe or time-efficient methods.)
Requirements for Signs
As part of our research, we spoke with various national trucking associations and federal agencies about these right-turn signs. We learned that the signs are voluntary and not regulated. A member of the staff of the National Highway Traffic Safety Administration said that the agency considers for regulation signs that are reflective, self-illuminated, or concerning hazardous cargo. Personnel at the American Trucking Association and National Transportation Safety Board provided similar comments.
Although it was apparent that the developers of the 25 signs we photographed used considerable conscientious effort, each of the signs only partially follows general human factors guidelines for warnings. According to one guideline, "at a minimum, a warning should contain the following fundamental elements: signal word, hazard, consequences, instructions" (Sanders & McCormick, 1993, p. 683). ANSI standard Z535.2 states that a warning sign should contain a signal word, a text message, and a pictorial (American National Standards Institute, 1991). Although some of the signs included a signal word, none of them described in text the possible consequences of ignoring the warning (i.e., a collision). However, many of the signs did depict a collision in their sketches.
Creating an Improved Sign
After viewing our 25 pictures, the five human factors researchers stated that none represented the best possible warning sign. Instead, they pointed out sign elements that they believed would best communicate the collision hazard. Combining their most frequent responses, we created a list of elements of an improved warning sign. The researchers reviewed the list and concurred that it was reasonable.