Do Road Hazard Signs Like “Deer Crossing” and “Falling Rocks” Actually Prevent Accidents?
Warning of an upcoming curve, playing kids, falling rock, icy roads and, of course, deer, traditional static warning signs litter the sides of our roadways to the point where they have just become white noise. Often placed arbitrarily, many road warning signs, which can be extremely expensive to install (see Bonus Fact below), are erected more for their ability to shield government from liability than to improve public safety. Ignored by drivers and not supported by scientific research, other than a few limited (and well-planned) exceptions, there seems to be little reason for most traditional road hazard signs.
The most useless static signs are those that warn against occasional perils, such as an icy bridge, deer, or falling rock. In a 2006 study conducted in Kansas, researchers examined 45 different variables in 15 Kansas counties and compared crash rates before and after the installation of deer warning signs. After their exhaustive study (and 149-page report), the researchers concluded that: “there is little or no relationship between deer warning signs and crash rates. . . . static deer warning signs as they have been used in Kansas are not an effective measure for mitigating deer-vehicle crashes.”
Similarly, studies of ice warning signs have been found to be equally feeble: “ice-warning signs do not have a statistically significant impact on the frequency or severity of vehicular accidents that involve ice.”
Aside from the possibility that static hazard signs, by their nature, may simply be an ineffective way to control driver behavior, the authors of these studies have identified two other problems: (1) over-signage; and (2) arbitrary placement. As it was noted in one study: “Too many signs or ice-warning signs posted at potentially inappropriate locations . . . where the ice hazard is rarely present . . . can desensitize drivers, thereby negating any safety enhancement the signs may have.”
Perhaps surprisingly, the reason so many signs are in “inappropriate locations” is due to the fact that the decision-making processes for their placement are, according to one report “vague and arbitrary at best.” In fact, in a survey of 28 state departments of transportation, it was determined that 93% “had not done any evaluation of the effectiveness” of static signs warning of occasional hazards.
So why do they put up the signs? Lawyers and lawsuits. The survey report noted that 20% of the agencies who answered it admitted that “tort liability and litigation [had] an important role in the decision,” to place the signs of infrequent hazards.
It’s important to note that the pointlessness of many road signs is not limited only to those that warn of occasional hazards. In a 2004 report, the National Cooperative Highway Research Program (NCHRP) identified that signs warning of upcoming curves also suffered from over-proliferation (causing desensitization), arbitrary placement and overall ineffectiveness; as with other static signs, the report revealed that “many highway agencies prefer to use traditional advance warning and curve signs even if research indicates [they] may be ineffective . . . because of tort liability concerns.”
Regardless of the frequency of the hazard, the ineffectiveness of all of these signs is troubling. In a 2007 report summarizing research of the effectiveness of “Children at Play” and similar signs, the authors revealed that, “there is no evidence that special warning signs of this sort reduce driver speeds or crash rates. This is the unanimous conclusion of many credible sources we located on this topic.” Startlingly, these authors also noted that rather than improving public and child safety, because the signs give drivers little guidance, they may actually make things worse: (1) by giving a false sense of security to parents and children in those areas where signs are posted; and (2) by giving the impression that there aren’t children playing in areas that don’t have signs.
All that said, there is some evidence that, in certain situations, judiciously adding signs can reduce accidents. Between 1992 and 1998, Mendocino County, CA saw a 42.1% reduction in crashes after installing new signs. How?
Although it’s not entirely clear why Mendocino County’s signs were so effective when so many others were useless, there were a few unique factors to the California program that may explain the difference: (1) it appears that prior to their 1990s efforts, few signs had been posted; (2) the county’s roads were particularly treacherous; and, perhaps most importantly, (3) significant thought and research went into the placement of each sign.
Located about 100 miles north of San Francisco, Mendocino County was mostly rural with a relatively small population (90,000) when the program began. Criss-crossed by many secondary, curvy roads, some with no centerlines or shoulders, before the signs went up, the county saw a lot of motor vehicle accidents (601 in 1992).
To deal with the problem, the county retained the services of a civil engineer who established a comprehensive system of review of the county’s roads. For each area studied, the reviewer examined each crash report for that stretch of road during the preceding three years. By doing so, they determined not only why crashes occurred, but also where a sign could helpfully warn of any hazards. Remarkably successful, after the signs went up, in 1998 there were only 348 crashes; the county later estimated it had saved more than $12 million by not having to respond to the avoided accidents.
- Why Some Countries Drive on the Right and Some Countries Drive on the Left
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- Why Don’t They Bother Putting the Apostrophe in “DONT WALK” signs?
- The Origin of the Green, Yellow, and Red Color Scheme for Traffic Lights
- Installing street signs is an incredibly expensive affair in many places for a variety of reasons. For instance, in 2011 the Washington State Department of Transportation claimed it costs anywhere from $30,000 to $75,000 per sign, though they later clarified those were worst case and most expensive scenarios and sometimes the signs and installation can ring in only around $10,000. Bronlea Mishler of the DOT explained, “Installing a sign along a highway isn’t quite as simple as pounding some posts into a ground and bolting on a sign — that’s why the cost is so variable. There are two ways to replace a sign. One way allows us to install it under old rules; the second way requires us to follow new federal standards… The old rules apply if we are just fixing something, not building something new. Installing a sign alongside the road counts as fixing something — basically, just giving drivers more information. If we install a sign on the side of the road, it would cost: $2,000 to make the sign, buy the beams and rivets; $8,000 for two steel posts and concrete; $5,000 to clear brush and other landscape work before and after installation; $15,000 for maintenance crews to set up traffic cones, work vehicles, program highway signs and spend the evening doing the work. Total: $30,000…. The new rules apply if we’re doing a new construction project. Costs would be higher because we would have to bring everything up to the current highway code. These often involve putting up a sign bridge, a steel structure that spans the entire freeway to hold up multiple signs. Typical costs include: $2,600 to make the sign, buy the beams and rivets because the sign must be bigger; $75,000 for the sign bridge. Total: $77,600.” WSDOT Deputy Regional Administrator Bill Vleck also stated, beyond many of these signs needing to be special ordered and often being much larger than most sign makers make, drastically increasing cost, some of the seemingly exorbitant costs are due to special features of the signs few know about. For instance, “If there’s an auto accident, if a car hits that sign post and there’s any kind of injury involved, the state is going to be liable, so we’re looking potentially at a multi-million dollar settlement in those kind of situations… [So] it would have to be a breakaway type sign post, and it has to be specially fabricated so that if a car hits that sign, it reacts appropriately and doesn’t come down and basically take out the occupants.”
- Assessing the Effectiveness of Deer Warning Signs (Meyer)
- Effectiveness of “Children at Play” Warning Signs (CTC II)
- Effectiveness of Traffic Signs on Local Roads (CTC)
- Guide for Reducing Collisions on Horizontal Curves (NHRP)
- Signs Show the Way to Cost-Effective Rural Safety
- Static Warning Signs of Occasional Hazards: Do They Work? (Al-Kaisy et al)
- The $77,000 question (AKA, adventures in confusion and clarity)
- WSDOT Defends the Cost of Signs
 Meyer at 101
 CTC at 6
 CTC at 6
 Al-Kaisy at 41
 Al-Kaisy at 41
 NCHRP at V-8, V-9.
 CTC II at 1
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