Mark Fischenich: Ask Us: PSST, MnDOT cutting number of posts on highway signs

·4 min read

Jul. 17—Q: Ask It Guy, could you please find out why the signs on Highway 60 going to Lake Crystal are being changed, from two posts to one post? Are they going to stay up in the ice and snow and wind? Thank you.

A: This question was heartening to Scott Thompson of the Minnesota Department of Transportation.

"Just as this traffic engineer was starting to question whether the signs that are so carefully curated for installation along the state's highways were even read by users, someone has observed that they're being installed differently!" Thompson said. "But then the reader referred to 'Ask Us Guy' as 'Ask It Guy.' I'm not sure what that does for my crisis of faith."

But the reader is correct about MnDOT cutting many of its sign posts by 50%.

"For more than 50 years, MnDOT had traditionally installed nearly every one of its signs on at least two U-channel posts (the post name deriving from the shape of the post's cross section)," Thompson said. "Bigger signs were installed on up to four U-channel posts, and some signs even used U-channel knee braces to ensure a sign could stand the tortures of its 15-year life on the prairie."

At first glance, a person might think there's only one consideration when deciding how many posts are used to hold up a highway sign: What's the minimum number required to keep the sign from blowing over?

But highway safety folks also have to think about the impact, literally, of anything that's placed along the roadways. That's even more true when federal crashworthiness standards are in play, which is the case for any stretch of road that's part of the National Highway System — interstates, U.S. highways and other critical routes such as Highway 60 between Mankato and Iowa.

"The MnDOT U-channel sign designs passed crashworthiness muster in the 1970s, and were grandfathered in under the crash testing requirements of the 1990s," Thompson said. "However, significantly more stringent requirements were released in 2016, which require omni-directional crashworthiness."

So, previously, a sign had to be installed so it wasn't overly hazardous if a driver left the roadway and hit the posts head-on. Under the new rules, which went into effect on National Highway System projects starting in 2020, the crashworthiness of the posts also has to be considered if they're hit from behind by a wrong-way driver or hit from the side.

"The increased focus on crashworthiness goes hand in hand with the federal government's and Minnesota's Toward Zero Deaths campaigns to reduce the number of fatalities on our roadways," he said.

MnDOT could have submitted its traditional U-channel design for crash testing to see if it met the new federal standards, but that testing costs hundreds of thousands of dollars and there was serious skepticism about the odds of the old design passing the new requirements.

So instead, MnDOT decided to switch to an alternate approach that had already passed the new testing standards — perforated steel square tube, or PSST, posts. To avoid confusion, MnDOT also elected to use PSST on new sign installations on all state highways, even if they aren't part of the National Highway System.

"Aside from being a more safe sign structure system, PSST also allows for significantly reduced labor when repairing signs that are damaged by snow removal or mowing operations, or more commonly, errant vehicles," Thompson said.

As for the number of posts, crews have always based that decision on calculations in a MnDOT "windloading chart," which specifies how many would be needed to withstand 90 mph wind gusts based on the sign's size and the foundation available at a particular installation site.

"To the question of whether PSST posts will stay up during the ice, snow and wind we experience, the math says yes," Thompson said, adding that the agency will be watching to see if adjustments are needed to the windloading chart.

Ask Us Guy knows that many readers — after already being forced to say goodbye to clock radios, incandescent lightbulbs and DVD players — are feeling a little melancholy about the end of the U-channel sign posts. After all, they were part of our lives for half a century.

Thompson offered some consolation. MnDOT signs have a useful life of up to 15 years, so those U-channel posts installed just before the new standards went into effect could remain along state highways until as late as 2034.

Even after that, folks feeling nostalgic for a good old-fashioned sign post will probably still be able to find them along city streets and county and township roads, according to Thompson: "While PSST is the apparent wave of the future, people will still see U-channel for many years to come."

Contact Ask Us — or Ask It, if you prefer — at The Free Press, 418 S. Second St., Mankato, MN 56001. Call Mark Fischenich at 344-6321 or email your question to; put Ask Us in the subject line.