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Slippery roads

Ice on the roads develops as a result of cold and wet conditions.

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Swiss federal authoritiesSwiss federal authorities

These warnings apply primarily to the road conditions, whilst differentiating between the following hazards:

  • Slippery conditions due to packed snow: Snow that has frozen solid on the roads (up to 4 cm thick)
  • Black ice: Wet roads which subsequently freeze over as a result of clear skies at night
  • Icy roads: Cold or cooled precipitation (freezing rain/drizzle/fog precipitation) that falls onto a road sur-face with a temperature below 0 degrees, thus freezing solid instantly
  • Rime ice: High levels of moisture that freezes on supercooled road

Hazard level 5 (very severe hazard)

Widespread ice formation on roads over a sustained period is a rare occurrence in Switzerland.

Danger levels 4 (severe danger)

Possible impacts
  • Sudden, acute danger of skidding
  • Road and air travel brought to a standstill
  • Disruption to rail travel
  • Falling branches or trees as a result of their ice load
Interruption of electricity supply and/or telephone network
Description of measurement and prognostic values Freezing rain: over 2 mm (total precipitation volume freezing on the ground)

Hazard category 3 (significant hazard)

Possible impacts

  • Sudden, acute danger of skidding
  • Icy roads to the extent of being impassable
  • Disruption to road and air travel
  • Breaking branches as a result of their ice load

Description of measurement and prognostic values

Freezing rain: up to 2 mm (total precipitation volume freezing on the ground)

Hazard category 2 (moderate hazard)

Possible impacts

Risk of skidding

Description of measurement and prognostic values

  • Packed snow (less than 4 cm, road temperature of < 0 degrees)
  • Black ice (wet roads that have frozen over)
  • Icy roads (freezing rain)
  • Rime ice

Recommendations for action

Recommendations during slippery roads

Notes

Warnings of slippery conditions are issued up to 800 m above sea level on the northern side of the Alps and up to 1600 m above sea level on the southern side of the Alps.