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Oregon uses new technology to upgrade curve advisory speed signs to meet new FHWA requirements

Over the course of the next three years, the Oregon Department of Transportation (ODOT) will use new technology to update curve advisory speed signs around the state, to take into account the dynamic advances in modern vehicles.

The agency estimates that some 50-75% of all the state’s curve speed advisory signs will change over the next three to four years, with most seeing an increase in the advisory speed of 5-10mph (8-16km/h) to better match each individual curve. There are three main reasons for ODOT’s program:

• New federal requirements improve safety and create consistency, with updated Federal Highway Administration (FHWA) procedures requiring consistency of curve advisory speeds on all public roads. Consistency in curve signing means that a bend with an advisory speed of 40mph in the Willamette Valley will feel similar to a 40mph curve in Baker County or a 40mph curve in another state;
• The use of new technology allows ODOT to determine advisory speeds for curves with greater certainty; current speeds were set using the analog tools that have now been replaced with GPS-aided digital tools;
• Vehicles, road design and pavements have advanced, with newer vehicles able to corner with increased speeds, while maintaining a comfortable ride. Oregon’s roads have also benefited in the past several decades from improved design and advanced pavements, creating safer, smoother roads.

Current advisory speeds were set by investigators using the ‘ball bank’ indicator method, which involved driving curves multiple times to calculate how far to the right or left a ball suspended in liquid traveled in its arc. The variability inherent in the method, and irregularities in road surfaces, contributed to setting inconsistent and conservative advisory speeds, which is why so many drivers are comfortable going faster than the posted advisory speeds. In addition, roadway crews would sometimes reduce speeds even further on curves where other problems occurred. ODOT now employs GPS technology that allows an engineer to drive a curve fewer times and provides more consistent and reliable results. Special software processes the data after each trip, so engineers can set the correct advisory speed.

Now ODOT are using a dashboard-mounted Curve Advisory Reporting System (CARS) from Rieker Inc, which combines a software package with GPS integrated accelerometer technology to deliver a completely portable system, that meets new Federal Highway Administration (FHWA) guidelines on how to determine safe curve speed. It allows the operator to drive as many miles of road in a day as needed, even stop and go rush hour traffic. They can then review and analyze individual curve data anytime on any computer. There is no need for multiple passes, constant speeds, or manual data input, making the job safer, faster, and better value.

ODOT says most curve advisory speeds will increase by 5-10mph, although some will increase by even more. ODOT crews and contractors have already started replacing or removing signs across the state with the program due to continue through 2019. All public roads in Oregon that see volumes of more than 1,000 vehicles a day are subject to the new FHWA requirements. ODOT is lending GPS curve analysis equipment to local jurisdictions to assist in the process of updating the speed advisory on local and county roads.

“It is going to be very important to watch and follow the new advisories,” said Eric Leaming (above), an ODOT traffic devices engineer involved in the curve analysis program. “Before, advisory speeds were very conservative and inconsistent. 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.”

For a video explaining the system click here.

May 10, 2016

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