The need for speed (limits)

A speed limit on Crook County’s dirt roads is not a number that can be arbitrarily set.

The county commissioners have encountered requests to regulate driver speeds in recent months and so opted to invite a specialist to walk them through the process.

Austin Woody of the Wyoming Tech Transfer Center, part of the University of Wyoming College of Engineering and Applied Science, was already familiar to the commission for his work in completing a speed study on Barlow Canyon Rd.

Woody provided a detailed description of the process, explaining that the goal of each speed study his department performs is to determine the maximum safe speed on a particular road during favorable weather conditions and visibility.

This is done, he said, by documenting road and traffic conditions to come to a legally substantiated decision. One, he said, that is realistic, consistent, enforceable and able to be adjudicated.

There are statutory standards for common situations, he said. For example, the speed limit in a school zone is 20 mph while in an urban or residential area it’s 30 mph and on an unpaved county road it’s 55 mph.

But the county does not have to follow these precisely and can set limits within a range around the standard, allowing “local autonomy” to address specific situations where the standard might not fit the needs of a particular road.

Speed studies are generally needed, Woody said, if there is low compliance with the speed limit, a change in road conditions or traffic, a lot of accidents on the road, complaints from drivers or no speed limit to begin with.

A speed study gathers information on a number of different elements. The average daily traffic and truck traffic forms the basis, alongside the “free flow” traffic speed – the speed at which the average driver will navigate the straight part of a road when unimpeded by bends, corners and obstacles.

Roadway alignment and visibility are also incorporated, along with a horizontal curve ball bank measurement, the number of intersections and access points, roadside conditions and uses and WYDOT’s crash history for the road.

A minimum of 48 hours of data is used for a crash study, Woody said, but a full week is preferable in order to capture weekly patterns and the difference between week and weekend traffic. Automatic counters are left on the road, gathering traffic counts, speeds and time stamps.

In the end, the study is looking for the “85th percentile”. In other words, the speed that 85% of vehicles are traveling at or below.

While there may be factors that warrant a speed limit lower than this, the posted speed limit should never be below the 50th percentile or the lower limit of the 10mph range at which the largest percentage of vehicles are traveling.

“The idea here is that we’re going to limit the number of people we have to pull over,” he said.

The study also includes sign mapping, both to identify where signage might be useful and to evaluate the condition of current signs, which could be in bad condition or out of date.

Once all of this is complete, said Woody, the report is stamped by a professional engineer and provides a 10 mph range of acceptable suggested speeds for the road. This is presented to the commission for a decision, which allows for localized knowledge, preference and decision making.

A speed study was performed earlier this year for Barlow Canyon Rd after landowner Dave Wolfskill expressed concern about the speed of vehicles on the portion of road that travels through his property. He asked for a reduction to 30 mph for the safety of himself and his family when crossing the road.

As a gravel road, the statutory default is 55 mph.

Woody found that, while average speed on either side of the property is 41.2 mph to the south and 38.9 mph to the north, drivers are only traveling at an average of 19.6 mph through the Wolfskill property.

Conditions at that point are naturally regulating speed, he said, telling the commission that his recommendation would be for signage giving advance warning with an advisory speed, which is not enforceable.