BLACK ICE = Deadly!
BLACK ICE On our Northwestern Ontario highways is blamed
for the loss of several lives and  for numerous accidents every winter.

Is this normal?  How much are we contributing to it?

Black ice has been a problem on highways for years. In warmer areas of the country it may be more of a common problem.  In Northwestern Ontario, with our much colder winter climate, it seems that this is now becoming a household word.

Over the past several years, the Ontario Ministry of Transportation (MTO) has moved on from applying salt and calcium chloride on snow or ice covered roads, to the present day thinking of 'presoaking' the roadway in advance of storms to help maintain a clear highway condition throughout the province.

Can 'presoaking' cause black ice? Is this partially why we hear of more black ice incidents? If so, is the MTO playing with lives trying to maintain a 'clear highway' policy?

What is black ice?
    Black ice is a thin formation of ice that occurs when water freezes on a road surface. Because it is so thin and clear, the dark underlying road surface easily shows through, lending to its common name.
    An excellent description of natural forming black ice on highways can be found at  Winter's Shadowy Danger:  Black Ice
    Black ice can naturally form at any temperature at or below freezing, but it is favoured to form when the road surface is between 25F and 32F (-4C and 0C).

So, what else can cause 'Black Ice'?
    Applying a de-icing substance that will melt ice or snow on the highway at temperatures below freezing!
    What happens: the deicing compound, salt (Sodium Chloride), magnesium, etc. is applied in a concentration  or mixture that will melt ice or snow on the highway at temperatures which may be much below the normal range of black ice formation. The compound works well, perhaps too well.
    Say the compound is mixed to melt down to -15F (-26C). Ok, the applied compound starts melting the packed snow or ice on the highway. But, if the temperature does not rise, or worse, falls, the compound   diluted by the melting action is now below its working temperature and may start to freeze!
    If left unattended, and more concentrated deicing agent is not immediately applied to strengthen the dilution back to a point where it again melts - guess what?  There may now be 'black ice' on the roadway!
    In the event the temperature falls and no precipitation occurs, the lower temperature may now be below the liquid point of the applied deicing agent, which would result in a thin layer of frozen or slippery 'deicing' compound that is now 'black ice'! - MAN MADE¹
    This can be a very dangerous condition because where there was packed snow or traces of ice and snow that was visible to the driver has now dissolved into a thin liquid film that refreezes and is not readily seen, and is unexpected at the low temperatures!

Ontario Government Objectives
Quote from MTO web site
"Maintaining safe, clean and liveable communities is a priority for the McGuinty government. We will continue to work to ensure Ontario's roads are safe for drivers in the winter and throughout the year."
    Over the past several years, MTO has tried various methods of deicing control, some very experimental, and possibly resulted in dangerous driving conditions due to the lack of knowledge and experience in early stages of testing!
    At one time, 'centre bare' was the objective with salt being applied to the centre of the highway to melt a strip wide enough so traffic going in either direction could have traction on one side of the vehicle even if the other side had snow packed conditions. Although refreezing of the area is possible, you would normally have some traction on the snow packed side, especially in lower temperatures. Applications of sand would also help.
    When temperatures got below the effective melting action of the salt application, the salt would remain on the roadway or would be blown off by traffic. Sand was usually applied, but it seems it was not applied until after the salt brine refroze resulting in most of the sand being blown off the highway also.
    Current thinking is preemptive deicing, which means the application of deicing materials at the start of a forecasted snowstorm. Because 'dry' salt does not stick to the road surface, it may be 'prewetted' with a brine solution to make it stick. This will form a brine solution under the falling snow being packed by traffic, which helps prevent the packed snow from sticking to the roadway. This also can be very dangerous and form ice if not closely monitored in changing conditions! ¹

Dangers as we see it
     Northwestern Ontario has hundreds of kilometers of highways, each kilometer totally different with constantly changing conditions with varying altitudes, topography, weather conditions including temperatures. Every kilometer can have a totally different requirement for deicing or snow removal.
     This is not an ideal area for 'experimental' highway deicing as it is impossible to constantly monitor every kilometer of highway and changing weather conditions and act accordingly and immediately over these distances to keep the highway surfaces ice free.
     If deicing applications have taken place over a maintenance area, it may be hours before subsequent action can be taken to either reinforce or take other action should the original deicing applications have icing occur. When looking at the possibility of fatal or serious accidents occurring between follow-up applications of deicing and traction materials, any experimentation with new methods should be tightly controlled to small areas of constant diligence.
    It has been noted that last year magnesium chloride solutions were tested on large areas along with other deicing agents during extremely cold weather.  Below 15 deg F ( - 10C) it is recommended that only traction material (i.e. sand or sand mixtures) be applied to the highways! ³
    It appears that ice control was attempted in Northwestern Ontario at much lower temperatures with deicing materials, which resulted in quite questionable road surfaces!

Yes, it is possible that in the efforts to keep and maintain a clear highway condition at all times, people are inadvertently being killed or maimed in accidents due to slippery conditions brought on by efforts to keep the highways ice and snow free!
 
Reference
¹Additionally, the authors note that if calcium chloride is used in anticipation of incoming weather, and it does not occur, one should pay close attention to the relative humidity. If indeed the humidity drops, and part of the moisture in the calcium chloride solution evaporates, the concentration of the solution will increase accordingly. If the humidity drops to a level where equilibrium with the saturated solution is reached, and the humidity continues to drop further for a longer period of time, (2 - 5 hours) a portion of the calcium chloride solution on the road is converted into a solid form, (hexahydrate - CaCl2 - 6 H20). This causes “ice to develop”.- “Calcium Chloride in Winter Road Maintenance: A Literature Study”, VTI Report 829, 1998 from the Swedish Road and Transport Research Institute.

²Some evidence suggest that anti-icing operations should not be conducted (using liquid, prewetted, or dry salt) when the pavement temperature is at or below about -9.5^oC (15^oF). Some highway agencies also believe that it is not practical to use salt below -9^oC (15^oF) for general snow and ice control operations, at least not without calcium chloride. This experience has convinced them that salt’s action is too slow at these lower temperatures. - U.S Department of Transportation Manual of Practice for an Effective Anti-icing Program

 ³In snow and ice control operations and particularly during anti-icing treatments, it is necessary to operate with brine solutions as close as possible to, but less than, the eutectic composition. The brine solution concentration will decrease as it is diluted with water from either the melting of snow/ice or falling rain/freezing rain. Consequently, it is important to monitor the dilution process so that the solution concentration does not decrease to a value which corresponds to a temperature in the freezing temperature range above the pavement temperature. When this occurs, a refreeze of the solution will take place. - U.S Department of Transportation Manual of Practice for an Effective Anti-icing Program