After rejecting the idea three years ago, and against the recommendation of the county's transportation engineers, the Prince William Board of County Supervisors will reconsider whether to allow speed humps to slow traffic in residential areas.

When the board adopted a residential traffic management guide in 2002, it voted against allowing speed humps because of safety concerns. At the time, fire and rescue officials said speed humps would increase response times, damage equipment and possibly exacerbate injuries to people being transported in ambulances as they bounced over the little hills.

At a board meeting Tuesday, the idea was back on the table at the request of Supervisor John D. Jenkins (D-Neabsco), who has fielded numerous proposals for speed humps and who had some installed in his district under a pilot program several years ago.

"We have humps on several streets," Jenkins said at the meeting, "and I've never heard of a single injury." On the other hand, Jenkins noted, his constituents have expressed concern about being injured by cars that speed through their neighborhoods.

The proposal would revise the county's traffic management guide to grant supervisors the authority to recommend speed humps and raised crosswalks on streets in their districts, to be paid with state and county transportation funds.

At the meeting, Tom Blaser, the county's transportation chief, opposed the measure for the same reasons the county rejected the idea initially.

"After conferring with the fire department, safety is still a concern, so the staff recommends no change" to the traffic management guide, Blaser said.

Specifically, Assistant Fire Chief Kevin McGee said, studies have shown that speed humps delay response times by eight to 12 seconds per hump. Anecdotally, McGee said, he has also heard of paramedics being thrown around in the back of ambulances as they try to attend to patients, who also run the risk of being tossed about.

The discussion of speed humps and bumps, which are different, was fairly brief Tuesday and momentarily Dr. Seuss-like.

"I personally don't know the difference between a hump and a bump," Supervisor Hilda M. Barg (D-Woodbridge) said. "Maybe we need a definition. How high is a hump? How high is a bump?"

A speed hump is wider, somewhat flatter and less abrupt than a speed bump, which is narrower and steeper and typically used to slow down traffic in commercial parking lots, county staff members said.

Supervisors decided to defer a decision on speed humps and raised crosswalks so they could study the matter further, in particular how they have worked in the Annandale area of Fairfax County.