Cathy Campbell did a double-take and tapped the brakes when she spotted what appeared to be a pointy-edged box lying in the road just ahead.
She got fooled.
It was a fake speed bump, a flat piece of blue, white and orange plastic that is designed to look like a 3-D pyramid from afar when applied to the pavement.
The optical illusion is one of the latest innovations being tested around the country to discourage speeding.
"It cautions you to slow down because you don't know what you are facing," Campbell said.
A smaller experiment two years ago in the Phoenix area found the faux speed bumps slowed traffic, at least temporarily. Now, in a much bigger test that began earlier this month, the National Highway Traffic Safety Administration wants to find out if the markers can also reduce pedestrian accidents.
The fake bumps are being tested on a section of road in a business and residential area in Philadelphia's northeastern corner. But soon they will also be popping up -- or looking that way -- on 60 to 90 more streets where speeding is a problem.
The 3-D markings are appealing because, at $60 to $80 each, they cost a fraction of real speed bumps (which can run $1,000 to $1,500) and require little maintenance, said Richard Simon, deputy regional administrator for the highway safety administration.
On one of three streets tested in the Phoenix trial, the percentage of drivers who obeyed the 25 mph speed limit nearly doubled. But the effect wore off after a few months.
"Initially they were great," said the Phoenix Police traffic coordinator, Officer Terry Sills. "Until people found out what they were."
Learning from the experience in Arizona, authorities are adding a publicity campaign in Philadelphia to let drivers know that the phony speed bumps will be followed by very real police officers, said Richard Blomberg, a contractor in charge of the study.
Even after motorists adjust, the fake bumps will act like flashing lights in a school zone, reminding drivers they are in an area where they should not be speeding, he said.
"After awhile the novelty wears off, but not the conspicuous effect," Blomberg said.