Board considers report on setting speed limits

Setting speed limits that are based on the speed motorists already travel results in good compliance, minimized crash rates and less severe crashes when they occur, explained Thad Peterson, 1st Lt. with the Michigan Department of State Police Traffic Services Section.

Peterson shared his expertise in determining appropriate speed limits with the Idaho Transportation Board Wednesday (Jan. 18) during its monthly business meeting in Boise.

Speed limits should be set based on the 85th percentile: the speed at which 85 percent of drivers are traveling or below, Peterson emphasized. Realistic speed limits allow the safest, most efficient traffic flow.

Peterson also talked about Michigan’s experience with construction zone speed limits. When all of the work zones were posted at speeds of 45 miles per hour, a higher crash rate resulted. There were fewer crashes when work zones were posted at “60 miles per hour except when workers were present.” Most of the crashes in Michigan occur before drivers reach the work zone, when traffic backs up because of the lower speed limit, Peterson said.

The public’s perception is that a higher speed limit will make the roadways less safe because actual travel speeds will increase. Similarly, the perception is that a lower speed limit will make the roadway safer because the public falsely thinks actual speeds will decrease.

In reality, travel speeds generally don’t change just because there is a different number on the sign, Peterson said. However, if motorists believe the roadway is less safe, that may enhance safety by causing users to reduce risk-taking behavior.

Other board discussion

Annual Aeronautics report
The Division of Aeronautics presented its annual report to the board during the meeting at Headquarters. In addition to comments from the Aeronautics Advisory Board, ITD staff members summarized the division’s activities of the past year.

The report also included highlights of the division’s partnerships with other organizations in 2011. The Garden Valley airstrip has a new restroom/shower facility (photo at right), thanks to extensive teamwork. The Idaho Aviation Foundation contributed $29,000 and the division added $18,000 for the facility. More than 700 volunteer hours were recorded on the project.

The Stanley Airport also was paved with the help of District 4 workers and material. The $44,700 project resulted in the first paved state airport.

The airport volunteer program continues to be a successful way for the aviation industry, groups and individuals to contribute to Idaho’s popular airport network. Volunteers assisted with activities such as mowing, painting, rodent control, replacing windsocks, repairing fences and cleaning restrooms.

Volunteers dedicated approximately 1,300 hours of labor at the state’s 31 airports in 2011.

ITD staff members also reported that a 2010 Airport System Plan concluded that Idaho’s aviation industry generates $2.1 billion in economic activity and supports tens of thousands of jobs.

In 2011, there were 34 aviation accidents with 14 fatalities in Idaho.

Scope redefinition of five bridge projects
The board approved scope changes for five bridge projects. That will more efficiently use funding by repairing and rehabilitating multiple structures within a region under a single contract. The changes will reduce mobilization, advertising and bidding costs while addressing the most critical needs of bridges in a more timely manner. Four of the projects were re-scoped for the same cost.

The work on an Interstate 90 interchange in District 1 was downgraded, resulting in minor repairs to be scheduled on an additional seven structures.

In District 3, the I-84, Mayfield Road project was re-scoped to allow the rehabilitation of seven more decks. Funding for the expanded project is being supplemented from savings.

The other three projects being re-scoped are in District 4, resulting in repairs on 20 additional structures.

Published 1-27-2012