October 1, 2006 Engineers have developed new pavement markings that give drivers the illusion that the car is moving faster than it really is. The markings, called optical speed bars, are series of lines painted at decreasing intervals on the road. Early tests show the bars are getting drivers to slow down.
RICHMOND, Va. -- A site along a Lee Chapel Road in Fairfax County, Virginia, is in memory of 18-year-old, Jamie "Allie" Grimsley, who died after losing control of her SUV.
She wasn't the first to die on this road...
"We've had two fatal accidents over the years on this particular stretch of road," says Bill Harrell, an engineer with the Virginia Department of Transportation in Richmond, Virginia.
Police believe high speed may have played a part in Allie's crash -- a common problem along this half-mile. When speed limit signs and expensive speeding tickets don't slow down drivers on curvy, dangerous roads like this, highway officials and engineers hope something a little different might get drivers to hit the brakes.
These new white lines, called optical speed bars, may do the trick.
Harrell says, "We want the traffic to slow down before they reach that particular section of road and then maintain that slower speed."
The series of lines is painted at decreasing intervals on the road. The markings give drivers the illusion that the car is moving faster than it really is, and the pattern of lines grabs drivers' attention so they slow down.
"The bottom line is to have another tool in our toolbox that we can use to try to influence speeds of traffic," Harrell says.
Does the illusion work? To find out, speed detectors will be installed along this road to monitor traffic.
The speed bars are in use and are being tested on roadways in New York and Virginia. Early tests show the bars are getting drivers to slow down.
BACKGROUND: The Virginia Department of Transportation is placing optical speed bars at regular intervals along Lee Chapel Road in Springfield, a stretch of pavement notorious for fast driving and traffic accidents. The bars are about two feet long and a foot wide, and are placed at intervals that narrow from 24 feet at the start to 15 feet at the end. This creates an optical illusion -- a flip book effect -- that tricks speeding drivers into thinking they are driving faster than are, causing them to slow down. A British study has shown that optical speed bumps reduced fatal and serious injury crashes, and the method has already been successfully tested in Texas, Kansas and Mississippi.
FLIPPING OUT: A flip book is simply a moving picture made as a small bound book whose pages show a series of movement -- broken down into individual images. When the pages are flipped quickly, the images look as if the scene is moving. This occurs because of an effect called "persistence of vision." Images in your will stay a fraction of a second longer than what is actually shown. Our eyes and brain retain a visual impression for about one-thirtieth of a second. Because of persistence of vision, we don't notice that a movie screen is dark about half of the time, or a TV image is little more than one bright, fast dot sweeping across the screen. Movies show one new frame every one-twenty-fourth of a second, and each frame is shown three times during this period. The eye retains the image of each frame long enough to give us the illusion of smooth motion.
BEFORE THE SILVER SCREEN: In the 19th century, a number of optical toys were created that also gave the illusion of motion from a rapid succession of still photos. The most well-known is the zoetrope, invented in 1834 by George Horner: A zoetrope is a cylinder with vertical slits cut into the sides. On the inner surface of the cylinder were images from a motion sequence. As the cylinder spins, the user looks through the slits at the images, producing an illusion of motion much like a movie.