It's tricky when the temperature in the air starts to fluctuate up and down around 0 degrees. One day it's cloudy with rain and the next day clearing.
When it clears up, the temperature drops rapidly at the ground, ice forms in patches or all over the road and it becomes glassy.
Bridges and valleys
Typical places where it freezes quickly are bridges and valleys. When the temperature drops in the evening, bridges cool down from both above and below. The moisture in the air can turn into frost on the bridge and the risk of slipperiness is therefore high.
A treacherous type of slippery road occurs when, after a cold period, rain falls on roads that have become "frozen" and it quickly freezes to icy conditions.
When it has been cold for a while, frost has formed in the ground, which acts as a cooling element. The insidious thing about icy conditions is that it can be above zero degrees in the air, which means that you do not think about the fact that there may be ice on the road.
Ice on a dark road surface can also be difficult to see and you can be surprised. That is why icy conditions are also called black slippery conditions.
When freezing rain hits the ground, the droplet instantly freezes, as there are plenty of freezer kernels on the ground. Therefore, it easily becomes very slippery in connection with freezing rain and cold roads.
Frost slipperiness in autumn
Frost slipperiness is also common in the autumn when we have clear and cold nights. It is formed on snow-free roads when the moisture in the air freezes on the road surface.
A variation on frost slipperiness is when there is fog and the fog droplets freeze on the road at sub-zero temperatures.
Then we also have slippery snow that is simply due to snowfall that settles on cold roads. This, in combination with wind, creates snow drifts, but it is more of a winter phenomenon.