Why does ice form on a road surface?

Caution – Black ice

At www.saltgritsupply.co.uk we are looking at the hazard of road ice itself and what sorts of weather conditions, we, as a society, can look out for. Then we can send for Kentcare’s team to grit our car parks or roadways.
  • Snow
    Snowflakes may be delicate and beautiful – but when they form together they turn to ice and our roads into potential death traps.In fact, statistically, the most accidents happen during very minor snowfall events, rather than during big snowstorms when awareness and preparation levels are greater. Snow on already cold roadways typically becomes more dangerous as more traffic travels on it. This is due to the heat from tires melting the solid water, but the cold road surface re-freezing and compacting the water into a thin sheet of ice.
  • Freezing Rain and Freezing Drizzle
    While snow is the most common cause of road icing, it is freezing rain and freezing drizzle that create the most treacherous and fearsome type of winter hazard, referred to as ‘black ice’. Freezing rain/drizzle happens when raindrops in a warm air higher layer  (in the middle levels of the atmosphere) falls through a layer of subfreezing air closer to the surface. When the raindrops hit the ground, they freeze on contact – creating a smooth, solid glaze that covers everything on the ground.
This type of icy layer is the most slick of all precipitation types – creating nearly zero friction conditions with vehicle tires. Correcting a skid on black ice can be nearly impossible, as the vehicle tires will have close to zero traction. Loss of control on these surfaces can occur even at slow speeds.
road ice
Ice on this road, compressed and melted by tires and re-frozen by the road surface temperature
Despite it being a clear thin layer of frozen water, ‘Black ice’ is so named because it appears dark, just like a wet pavement surface. It is important to remember that ‘black ice’ will only appear ‘black’ on darker pavement surfaces such as tarmac or asphalt. ‘Black ice’ on concrete pavement can appear gray or tan, for instance (the same color as the pavement surface).

Other conditions to look out for…

  • Residual rainwater and/or groundwater
    Previously-fallen rainwater can freeze onto roadways after surface temperatures drop below freezing. Runoff can drip or flow along any slope, covering lower roads with a sheet of ice.
    frosty lawn
  • Frost
    Although rare, pure frost has been documented to cover roads and bridges even during clear, calm weather. Bridges can be a concern because when they have a cold or freezing surface temperature they will take longer to warm due to lack of contact witth the warm earth below.

So there we have it, this is what to look for…

Please click the links for :

information on how salt melts ice 

Kentcare’s winter gritting services