Delivery people are sometimes surprised to find a single traffic light on the left side of this long driveway in Shadyside. Dark most of the time, it glows yellow for a few minutes and sometimes changes to a red X.

"I think everyone knows a red X means 'Stop,' " says the homeowner.

Delivery people, baby-sitters and other visitors do stop -- usually. If they don't, they get a scolding from the safety-conscious man who dreamed up this unique system to protect his nearly 2-year-old daughter and the family's 5-year-old dog.

The man, who asked not to be identified, worried about visitors' speed on his 150-foot-long driveway, which passes under an overhanging porte cochere on the side of the house and ends at the detached garage and parking pad. With the view obstructed, a driver would have no time to react if a child or dog stepped into the driveway from the back patio or yard. Backing out is even more dangerous, which is why the homeowner had another light installed facing the garage.

The driveways of many older homes in Pittsburgh and surrounding suburbs have similar blind spots. But the potential danger has less to do with the age of your home than what you drive. Backover accidents -- ones in which someone is injured or killed in a private driveway -- are increasing because Americans are driving more SUVs, which have larger blind zones front and back than smaller, lower vehicles.

Each week in the United States at least 50 children are struck in such accidents, said Janette Fennell, president and co-founder of Kids and Cars, a Kansas-based nonprofit safety organization. Two of those 50 children -- who are usually under the age of 5 -- die from their injuries. Last week, the 5-year-old adopted daughter of Christian singer Steven Curtis Chapman was killed by an SUV driven by her older brother in the driveway of the family home near Nashville, Tenn.

The federal government does not collect data on such accidents, but a 2002 Centers for Disease Control and Prevention study found that more than 9,160 children were treated in hospital emergency rooms due to nontraffic, auto-related incidents in a year, suggesting that the real number of backover accidents might be three times Kids and Cars' estimate.

Ms. Fennell had never heard of a system like the one installed in Shadyside. Most people focus on their cars, adding devices or buying models that have sensors or cameras that reveal what is behind a vehicle. The Kids and Cars Web site, www.kidsandcars.org, has a link to a 2005 Consumer Reports product review of such devices, which now start as low as $100.

"Consumer Reports plans to do another product review," said Ms. Fennell, who works closely with the consumer organization. "These devices keep getting better and less expensive."

One of the Shadyside homeowners' two vehicles has sensors and an alarm that alerts them to objects behind. But his biggest concern was the three or four vehicles that visited the house each day and the danger they posed to their daughter -- who is never outside unattended -- and their friendly female basset hound.

No statistics are available on how many family pets are hurt or killed in backovers. However, the number has likely declined as more Americans keep their pets indoors, said Merritt Clifton, editor of Animal People, a Washington state-based newspaper that covers animal-related issues.

"Most dogs and cats run away from a moving car," he said.

Mr. Clifton said the Shadyside safety light system reminded him of one he had seen on a well-traveled highway next to Yellowstone National Park. Motion detectors and lights alert motorists when moose, elk and other large animals cross the road.

With the dog in mind, the Shadyside homeowner and the system's designers opted for a contact switch on the back door that turns on the yellow caution light whenever the door is opened. The red X is illuminated when a motion detector senses movement within a 50-foot radius of its site next to the driveway. Both lights stay on 15 minutes and can be turned on manually from a switch in the kitchen. The low-voltage system's programmable relay and timer in the basement also have a battery backup in case of power outage.

The system's components cost about $1,500, and labor costs bring the total cost to around $3,000. Its design was a collaboration between the homeowner, electrical engineer Jeff Latcheran, electrician Bud Patton and Darrell Shick, project superintendent at Kirby Electric in Warrendale, the source of nearly all of the components.

The homeowner found the Industrial Traffic Solutions traffic signal on the Web. Although the LED signal has a green arrow that can be illuminated when there's no danger, he decided not to use it. He's pleased with the system's effectiveness and low maintenance.

"When your driveway becomes like Fifth Avenue, you've got to do something," he said.

His wife, meanwhile, likes the system and is amused by her husband's fascination with how it works.

"It must be a guy gadget kind of thing," she said.