Tuesday, January 28, 2014

Road Plowing Science

Cleaning roads in winter is determined by weather conditions, so the Wisconsin DOT uses its own weather information stations to inform plow operators. 
Salt is primarily used to make plowing easier, but its effectiveness declines below 15 degrees.  In low temperatures, common salt may be mixed with sand, calcium chloride or magnesium chloride to enhance effectiveness and provide additional traction. Highway crews sometimes do "anti-icing" – spraying bridge decks, curves, hills and other known trouble spots with a salt solution - to prevent snow or ice from bonding to the pavement.
Most counties pre-wet salt just before applying it to roadways. Pre-wetted salt adheres better to pavement, starts the melting process faster, and can save money by reducing overall salt usage about 25-percent compared to dry salt. Pre-wetting using a salt brine or similar liquid can also help salt work better at lower temperatures.
During sub-zero temperatures common this winter, the only practical snow removal technique is plowing.
"Plowing is still the work-horse when it comes to removing snow and ice from Wisconsin highways," says WisDOT Winter Maintenance Engineer Mike Sproul. "Salt accelerates melting, but most importantly, salt keeps snow and ice workable so it can be removed by plowing."  County highway departments do most of the work, under contract to WisDOT.
60 weather information stations along the state highway system continually gather and transmit information on air and pavement temperatures, relative humidity, wind speed and direction, depth of precipitation on the roadway, and even salt concentrations. The comprehensive data helps highway departments know how and when to treat specific highways.
Many county snowplows are equipped with Automatic Vehicle Locators. The AVL systems use global positioning technology and help county highway superintendents locate plows and determine the de-icing materials to apply.

All motorists can check road conditions using the 511 Travel Information System, a colored-coded map of current driving conditions everywhere in the state.  Sproul reminds drivers that state law requires staying 200 foot behind a working snowplow.