City streets could be runway-clear, but the price would be high

  • Article by: BILL MCAULIFFE , Star Tribune
  • Updated: March 6, 2014 - 5:11 AM

Airport benefits from costly ice-busting chemical, fewer miles to keep free of snow and less traffic to deal with.

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Jeff Mattson, an airside operations duty manager at Minneapolis-St. Paul International Airport, demonstrated how the airport uses specially equipped cars to measure runway traction against federal standards.

Photo: JIM GEHRZ ‘ • jgehrz@startribune.com,

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If a pilot can land a 300-ton jetliner traveling 170 miles per hour on a strip of pavement at the Twin Cities airport without slipping, why is it that cars weighing 2 tons have been spinning and sliding through metro-area intersections for much of the winter?

The answer is complicated, involving traffic patterns, timing and, of course, money.

“We could provide the same level of service the airport does, but we’d go broke,” said Minneapolis street maintenance supervisor Mike Kennedy.

The airport uses plows, sweepers and blowers when snow falls, as well as an ice-busting chemical that costs about $15,000 for each pass. Kennedy said it would cost $455,000 to coat 1,000 miles of city streets once with the chemical, potassium acetate.

Sodium chloride (aka rock salt) remains the chief de-icing tool for street and highway departments, in part because it’s so cheap. But it can’t be used at the airport because it corrodes airplane bodies and parts. Cars, obviously, don’t qualify for the same protection.

Crews at Minneapolis-St. Paul International Airport are also able to rotate incoming and outgoing planes among four runways during a snowstorm, allowing ground crews to attack pavement when it’s free of traffic — a far different task than clearing a metro freeway during a rush hour. Plows and sweepers and chemical sprayers are followed by specially equipped cars that measure traction on the runway against FAA minimum requirements.

While metro streets and highways have been plagued with packed snow and stubborn ice since December, causing thousands of traffic accidents, the airport has not suspended traffic on its runways once this winter.

On Wednesday, as ice on Twin Cities streets began transforming into spring slush, MSP’s runways were dry and clear, as they had been for most of the time since a 9.9-inch snowfall ended Feb. 21.

MSP has less than 6 miles of runways — though they’re about as wide as 10 highway lanes — compared with 1,100 miles of streets in Minneapolis alone. And the airport has more snow- and ice-removal devices than the entire city of Atlanta, according to assistant MSP operations director Paul Sichko. The airport handles about 1,150 flights per day. Interstate 35W at Diamond Lake Road in Minneapolis alone carries 172,000 cars per day.

Those numbers inspire envy and defensiveness among road people at other public agencies.

“They don’t have the traffic we do,” Minnesota Department of Transportation spokesman Kevin Gutknecht said. “They clear it off much more frequently when we do. They don’t let ice form. Snow doesn’t get compacted.”

Sichko agreed that it’s not a fair fight.

“I know MnDOT has much more pavement to maintain than we do,” he said, adding that local agencies don’t have the luxury of temporarily keeping traffic off roads. Traffic compresses slush and snow, causing ice to form and to bond to pavement.

The un-chlorides

Potassium acetate, used on the airport runways, can melt ice in conditions down to about 22 degrees, Sichko said, so it’s not much better at melting than sodium chloride.

And like rock salt, it can also be harmful to aquatic life, said Brooke Asleson, metro watershed project manager for the Minnesota Pollution Control Agency.

In laboratory conditions, with controlled concentrations and distribution, rock salt can melt ice at 6 below zero, Kennedy said. But on the streets, it works down to about 15 above, he said.

Minneapolis, St. Paul and MnDOT also use magnesium chloride and calcium chloride, which work differently from rock salt and can — again, in the lab — melt ice to 25 below. In real life, 5 degrees is more like it, Kennedy said. The magnesium chloride is often mixed with molasses to help it stick to pavement better. St. Paul street maintenance engineer Matt Morreim said in rural areas the substance has been blamed for luring wildlife onto the roads.

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  • A wheel is dropped from the car’s trunk to calculate the coefficient of friction, the key measurement of snow-clearing effectiveness. Here’s another: The airport has not suspended runway traffic once this winter.

  • This Saab is one in the fleet used at Minneapolis-St. Paul International Airport to measure runway traction after plowing.

  • Jeff Mattson, an airside operations duty manager at the airport, demonstrated how one of the Saab automobiles is used to measure friction

  • Runway vs. roads

    MSP

    Runways: 6 miles

    Flights per day: 1,150

    Ice buster: Potassium acetate, $4 a gallon

    MPLS.

    Streets: 1,100 miles

    Cars per day: 19,800 alone on Lyndale Avenue S., at W. Lake Street

    Ice buster: Good old rock salt, $59 per ton

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