Flashing lights - do they really slow traffic?

Flashing beacons (commonly called flashers or flashing lights) are frequently requested by communities in the belief that they will reduce vehicle speeds. Unfortunately, this is not necessarily the case. The following discussion of flashing beacons is offered in the interest of developing broader public understanding of what flashers can do and what factors must be considered before they should be installed.

EFFECTIVE USAGES OF FLASHERS
A flasher is generally installed at an intersection or in conjunction with a warning sign in advance of an area requiring greater than normal care by the average driver. Flashing beacons serve a useful purpose where the flashing yellow is used to alert drivers to unusual conditions that are not readily apparent, such as: obstructions in the roadway, uncommon roadway conditions, narrow bridges, or unusual conditions hidden from the motorists' view. One of the more common locations where a flasher can be used effectively is at a signalized intersection located just beyond a vertical or a horizontal curve, when the intersection is hidden from the view of approaching travelers. For any flasher to be effective, it must command the respect of the traveling public. In other words, immediately after seeing a flasher, the driver must consistently see an unusual condition which is being singled out for attention. Furthermore, the condition that the driver sees must be viewed as serious enough to justify his having been alerted.

UNJUSTIFIED FLASHERS
When flashers are used improperly and installed at locations where they are not warranted, they soon lose much of their effectiveness. They simply cease to command the respect of the drivers. What happens is that after continually being alerted to a condition which seldom, if ever, appears to be truly unusual, drivers actually stop "seeing" the flasher. When this happens, flashers which are truly needed may well be disregarded by drivers who have become conditioned to believe that flashers are just "window dressing." Because of this normal human reaction, even one improper usage greatly reduces the effectiveness of essential flashers.

In summary, when flashers are properly located, they serve a useful function. When they are used improperly and installed in locations where they are not warranted, they soon lose much, if not all, of their effectiveness. More seriously, improper usage greatly reduces the effectiveness of other flashers installed in areas where there is a real need. Above all, it is essential to prove that there is a problem which can be solved through the installation of a flasher before actually employing one. Too often, flashers are installed when someone assumes there is, or is going to be, a problem. It is of the utmost importance that flasher installation be held to a minimum in order to maintain a high degree of respect for the flasher installations that are truly needed.

back to traffic questions mainpage