The Oregon Department of Transportation (ODOT) is changing out speed advisory signs across the state, increasing the speed in many instances.
The effort will extend over the next three years on public roads with more than 1,000 vehicles per day traveling across them.
This shift is due to several reasons, including federal requirements to have consistent curve advisory speeds on public roads, meaning a speed on a curve in one county should “feel” like the same speed on a similar curve in another county.
Another reason for the updated speeds is vehicle capability, with new vehicles able to “corner” at higher speeds. Yet another reason is the increased used of advanced pavement materials providing smoother and safer pavements. Finally, the test used to determine top curve speeds, the ball bank indicator, was providing too much inconsistency in results. The method measured how far a liquid-suspended ball traveled in its arc on curves, and was impacted too much by road surfaces, rather than the curve itself.
“Today, ODOT employs GPS technology that allows an engineer to drive a curve fewer times and provides more consistent and reliable results,” the agency says. “Special software processes the data after each trip so engineers can set the correct advisory speed.”
As a result, many of the signs in Oregon will go up by 5 to 10 mph, with some even higher.
“Before, advisory speeds were very conservative and inconsistent,” ODOT Traffic Devices Engineer Eric Leaming says. “Now, these advisory speeds are going to be uniformly closer to the speeds drivers are comfortable traveling at through a curve. You won’t want to go faster than the advisory speed.”