You’ve seen them out there, watching your every move.

As you get closer, they’ll let you know if you’re breaking the law.

They’re called “speed trailers” or radar signs and they flash just how fast you are driving and whether you’re over the speed limit or under.

A reader asked the newspaper to find out more information about them.

Who has them

The city of Alexandria owns one speed trailer and Douglas County also owns one through the Douglas County Safe Communities Coalition, according to City Engineer Tim Schoonhoven.

Also, the Minnesota Department of Transportation has a number of speed trailers that they move around throughout the state.

The city-owned speed trailer is primarily operated by the police department, Schoonhoven explained.

“They often decide where and when to use it but sometimes, when we have a specific request, citizen complaint, or if we are doing a study of a specific area, the city’s highway committee will request it be deployed,” Schoonhoven said.

The amount of time that it stays at any one location varies but generally a week or two is common. It only takes about 5 minutes to set the trailer up and 5 minutes to take it down.

The cost

The cost of a speed trailer varies widely depending on features, such as its size. They can cost $7,000 or $8,000 on the low end and up to $25,000 to $30,000.

The city’s is a mid-range model that costs around $15,000.

“They have a variety of purposes and uses, depending on these features,” Schoonhoven said.

The low-end models only display speed while the more advanced models can record data and include software that will generate reports, he added.

Some have solar panels so that they can run for several days on the same battery.

A recent purchase

In June 2018, the city purchased a Stalker MC 360 speed and message trailer for $15,498.

In recommending the purchase, Alexandria Police Chief Rick Wyffels said the trailer will serve several purposes – reducing speed in neighborhoods, collecting data on the number of vehicles traveling in certain areas and their speeds, traffic studies and to help investigate complaints about potentially dangerous streets.

The trailer has a three-by-six-foot message board and is used for directing traffic at events such as the Alexandria Technical and Community College graduation, Vikingland Band Festival, Party in the Street and Art in the Park. The trailer can also be used in areas that will be closed because of upcoming construction.

The benefits

Alexandria Police Captain Scott Kent said the trailers are a great tool for collecting data.

“The benefit is mostly educational,” he said. “People will have concerns about speeding and traffic in their neighborhoods and the (speed trailers) will be able to collect the data about the number of cars and average speeds.”

The public’s perception of speeding can be influenced by a variety of factors, Kent said. If a street is narrow and there are no yield or stop signs for several blocks, it can appear that traffic is flying along at ridiculous speeds.

Kent added that most times, the data from the trailer shows that vehicles are not speeding and it’s helpful to share that data with neighborhoods that are concerned. He said the data from the trailer, collected at all times of the day and night, is more accurate than having officers sitting at an intersection for a few hours at a time. It also saves time and money because officers don’t have to be in the area around the clock to monitor speeds.

The trailers also serve as a calming tool because drivers see the trailers and reduce their speed.

“It creates some short-term awareness,” Kent said.

Stalker in action

The Stalker MC 360 was used this past summer at the intersection of Eighth Avenue and Lake Street in Alexandria to gauge the speed of northbound and southbound traffic.

The device generated a report containing detailed information such as average speed, maximum speed and minimum speed during a four-day period, July 8-11.

It turned out that drivers are actually traveling much slower than the posted 30 miles per hour limit in the residential area.

A total of 1,072 vehicles passed through the intersection and an overwhelming majority of drivers, 99.8 percent, were traveling below the speed limit.

The average speed was 17.8 mph. The maximum speed was 32 mph.

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To submit a You Asked question, email Ross Evavold at revavold@echopress.com.