Signs advising drivers to slow down while approaching a curve are being changed across Oregon.

Tom Fuller, spokesman with the Oregon Department of Transportation, said 50 to 75 percent of the signs on state-managed roads will be changing over the next three to four years, with most seeing the recommended speed increase by 5 to 10 mph.

Fuller said the recommended speeds currently posted date to the 1930s and ’40s in many cases. A dashboard-mounted instrument that allowed a ball suspended in a vial of liquid to travel to the right or left was used to set suggested speeds, Fuller said, but road managers often took a more conservative approach, dropping the recommended speed following accidents.

These conservative recommendations and the habits they’ve ingrained in drivers present a potential problem as ODOT and others begin replacing the signs, Fuller said. Drivers who’ve become accustomed to going 40 mph around curves posted for 30 mph are likely to find themselves traveling too fast if they apply that standard on newly posted curves.

“If I’m going around a corner, I usually know, in my car, how much faster I can go, but it’s those corners you don’t drive very often or have never driven that can pose a problem,” Fuller said.

The change is the result of a federal push to achieve consistency in such signs across the country, Fuller said. The new federal standards apply to all public roads traveled by at least 1,000 vehicles a day, meaning city and county road departments will also be updating their signs.

“The Federal Highway Administration wants consistency, so the corner in Portland, Oregon, is going to be the same as a corner in Portland, Maine,” Fuller said.

More modern equipment will play a part in setting the new suggested speeds. Instead of the ball in a vial of liquid, ODOT now uses GPS information to plot the shape of a curve and set a recommended speed.

The new signs will offer drivers a clue that something has changed, but it’s subtle — a slightly brighter shade of yellow, and a perforated steel post in place of wood.

Many of the signs along highways in Central and Eastern Oregon have already been replaced, said ODOT community liaison Abbey Driscoll.

Driscoll said as part of ODOT’s updating of speed limit signs across much of the eastern half of the state — on March 1, speed limits increased to 65 mph and 70 mph on more than 1,500 miles of highway — the suggested speed signs on those highways’ curves were replaced as well.

Driscoll said the remaining curve speed signs under ODOT’s control in Central and Eastern Oregon are scheduled to be replaced by 2018.

— Reporter: 541-383-0387, shammers@bendbulletin.com