Q. How many snowplows does the department own?
The department does not own any snowplows. Instead, the department
contracts with the 72 county highway departments to plow and provide
ice control on all state and US-numbered highways, and the
Interstate system. The county highway departments have 729 snowplows that operate on
the state highway system throughout the state.
Q. Why does the department contract with the county highway
departments for maintenance on state maintained highways?
The system was set up over 85 years ago. Legislative audits have shown that
this arrangement is not only cost effective but in the best interest
of the citizens of Wisconsin and the users of our state highway
Q. Why do we salt the roadways in the winter?
Salt is used to make the roadways safer during the winter. It lowers the freezing point of snow and
ice and keeps the snow "workable" so it is more easily
removed. Salt can
be used for anti-icing, de-icing, or melting. Anti-icing is a
technique where a
chloride is applied to the roadway prior to a storm to prevent the
snow/ice from bonding to the pavement. De-icing and melting is when
a chloride is applied after the storm has begun in order to break up
ice and snow pack or to melt glare/black ice.
Q. What are the limitations of road salt?
The minimum practical
application range for salt is a pavement temperature of 15-20°F
and above. While salt
will melt snow and ice down to a pavement temperature of -6°F,
it can melt over five times as much ice at 30°F
as at 20°F.
Thus the effectiveness of salt is sensitive to small differences in
pavement temperature. Counties will attempt to apply only the
amount required for temperature, time and use. Too little and the
roadway will refreeze, too much is a waste of money and
the pavement temperature drops below 15°F
the effectiveness of salt is decreased significantly. At these lower
temperatures, the county highway departments will typically cease
straight salt applications and begin adding other chemicals to
the salt such as calcium chloride or magnesium chloride that will
lower the freezing point even further.
conditions must also be considered when deciding on whether to apply salt or other de-icing agents. As the temperatures
drop and the snow becomes dryer, the wind can begin to blow the snow
across the pavement. If there is a chemical residue left on the
pavement from a previous salt application, blowing snow can be
attracted to the residue and stick to the pavement creating hazardous conditions that would
not have existed if no de-icing agents were previously applied. This is why counties are sometimes reluctant to apply salt or
chemicals when the pavement temperatures are below 15°F.
The effectiveness of salt can also be
affected by the type of pavement. For example, salt works better on
new asphaltic (blacktop) pavements than on tined concrete pavements.
The salt being used today typically includes other ice melting de-icing
agents to increase its effectiveness at lower
temperatures and to help it better adhere to the pavement. Adding other de-icing agents to the
salt also reduces the number of applications needed. WisDOT is always looking for new ways to reduce the
amount of chlorides needed to return the roadways to safe winter
Sometimes counties use sand and other abrasives at lower
temperatures to improve friction
on the roadway. Abrasives have no ice melting properties and thus
their use is limited.
Q. Why doesn't the department use more sand?
Our experience, and the body of research on the use of sand, indicate the benefits of abrasives
(sand) applied to roadways are very minimal. Abrasives are
easily displaced from the roadway by traffic and they have no ice melting properties.
There are also negative environmental consequences such as air
pollution and siltation of waterways.
Q. What is
the importance of pavement and subsurface temperatures? Why can't
you just use air temperatures?
The ability of deicing agent to melt snow and ice depends on the
temperature of the roadway and not the air temperature. During the fall the pavement is
often kept warmer than the surrounding air because of the warm soil.
During the spring the reverse may be true. The pavement temperatures
can be colder than the air because the soil is still frozen from the
low winter temperatures. The sun also has a strong influence on the
pavement temperatures. It can help heat the pavement and speed the
melting process. Air and pavement temperatures can often differ by
as much as 20 degrees Fahrenheit. For example, on a recent bitterly cold early winter day the air temperature was
and the pavement or surface temperature was 24°F,
primarily because the subsurface temperature had not yet dropped
Q. Am I allowed to pass a snowplow?
There are no state laws that prohibit you from passing a
snowplow. However, it is illegal (State Statute 346.915) to follow a
snowplow closer than 200 feet upon any highway having
the posted speed limit of more than 35 mph if the
snowplow is engaged in snow and ice removal. The majority of crashes
involving snowplows and vehicles happen when a snowplow is rear
ended or hit while being passed. Snowplows have wing plow blades that can
extend anywhere between 2 and 10 feet beyond the width of the truck.
This wing plow blade is often not seen because of the snow cloud being
kicked up by the snowplow. These wing plows can often weigh as much
as a compact car.
Q. Who determines when the snowplows are called out?
Under department policy, county highway departments determine
when and how to respond to a storm. The county patrol superintendent
is typically responsible for calling out the crews.
Q. Why is
it that I never seem to see a snowplow during a winter storm?
The department is responsible for snow removal on 11,612 centerline miles of
roadway (or 31,429 lane miles) and 4,887 bridges. Using 729 trucks, the average time to
complete a snow route is approximately 2½-3 hours, but some cycle
times can be
as long as four hours. Time is also needed to
load and reload the truck with de-icing materials. The number of lane miles, if
placed end to end, would circle the earth.
Q. Why does
the department have its own weather reporting stations?
WisDOT has 61 specialized weather reporting stations that collect
road surface information and atmospheric information that reflect
conditions on the roadway. The systems measure air and pavement
temperatures, relative humidity, wind speed and direction,
subsurface temperatures, depth of precipitation on the roadway, and
salt concentration. This information is used by weather
forecasters to develop county specific forecasts. It is also used by
county patrol superintendents to help determine the appropriate
response to a storm.
Why the difference in performance from storm to storm?
One of the biggest factors that determine county highway department performance is the
type of storm and range of temperatures. There are reportedly more than
combinations of winter storms that can hit Wisconsin during the
winter and each poses unique problems to snowplow operators. Storms with low
temperatures can be difficult because deicing agents become less
effective at the lower temperatures. Storms with high winds also are
a challenge because the snow quickly blows back onto the roadway
after the plows pass.
Q. Why are
you spraying water on the roadway on a perfectly clear day?
We are actually spraying a liquid salt solution on the roadway that
will help keep snow and ice from bonding to the pavement. Spraying a
salt solution on the roadway is similar to spraying a frying pan
with oil to keep food from sticking to the bottom of the pan. The
salt solution acts as a barrier so that the snow and ice won't form
a strong bond to the pavement. Studies show that under extremely
cold conditions ice frozen to concrete has a stronger bond than
concrete alone. In many locations we also spray the salt solution on
bridge decks the afternoon before a predicted frost. The early
application of the salt solution helps prevent frost from forming on
bridge decks throughout the night.
hours do the plows operate during a storm?
On higher volume roadways the plows usually operate 24 hours a day
when the conditions warrant. There are times, however when hours
need to be reduced to give operators the opportunity to rest. On lower volume
highways, roadways are usually plowed between 4 AM and 10 PM, when
conditions warrant. If weather
conditions are so severe that we are making no progress or it is
unsafe for them to operate, trucks may
be pulled off the road until conditions improve.
Q. Who is
responsible for the winter road condition report that I see on the Internet?
else can I get road condition information?
The Wisconsin State Patrol is responsible for providing
the winter road condition reports.
the typical size of trucks in the department's fleet?
The county highway departments have two basic categories of trucks used in winter
operations. A typical tandem tri-axle truck has a
capacity of 15 tons and the single axle truck has a capacity of 5
tons. Trucks are usually kept for about 15-20 years and then sold at
Q. Who is
responsible for plowing snow on a state highway in a city or town?
It could be WisDOT or the city. In many communities, agreements between WisDOT and the city
give the city full maintenance responsibility, including the removal
of snow and ice, on state highways passing through those
communities. These agreements can help reduce costs
to WisDOT and provide for better continuity of service.