De-icing of roads
Salt keeps roads safe in winter time. Using salt as a de-icing agent carries numerous advantages: it is abundant and easy to store, it is budget-friendly and has a low environmental impact when used properly. This makes salt the most widely used de-icing agent in Europe and throughout the world.
The saltwater created by applying salt on snowy and icy roads has a lower freezing temperature than the surrounding ice or snow. De-icing salt is usually used at temperatures as low as -15°C but it works best when spread before ice has formed.
Winter services using de-icing salt have improved substantially in recent years due to economic and ecological requirements. The employment of new technologies such as: damp (pre-wetted) salt technology, infrared and EDP-controlled spreading methods, networked road condition diagnosis, improved weather information and optimised operational planning helped in reducing the quantity of used salt and in limiting the salt spreading areas.
Snow clearing priority is given to high-capacity roads and hazardous sections and snow removal down to the pavement is eliminated when this is a responsible choice. Depending on weather conditions, only 5 to a maximum of 40 grammes of salt are now spread per square meter.
Road salt and its impact on environment
Road salt used to be held the sole responsible for the poor condition of roadside vegetation but we now know that this allegation is groundless. There are numerous factors of stress for the roadside tress including soil condition, constriction of the root zone, lack of water, nutrients and oxygen, contamination, mechanical damage to the roots, trunk and branches or air pollution in the form of gases and dust just to name a few.
Salinisation of the soil by de-icing salt is also considered a stress factor for the surrounding vegetation. However, a study conducted for several years on roadside trees in Hanover showed that most of the de-icing salt was carried into the sewer system and into the flowing bodies of rain or meltwater, therefore not reaching the root zone of plants.
By planning and following codes of good practice, winter maintenance professionals make sure that salt is used sensibly and selectively. The guiding principle for winter services is “as much as necessary, but as little as possible”.
Salt vs grit
For a long time, grit was seen as the ecological alternative to de-icing salt. But grit performs poorly when it comes to traffic safety. Blunting agents actually have no effect on slippery frost and black ice. Accident analyses prove this point clearly.
In terms of quantities, grit also comes off worse because ten to twenty times more grit than de-icing salt must be spread to achieve the same effect. It takes only 300 to 500 vehicles to drive over the grit for it to be thrown off the carriageway. The purchasing, transport, storage and spreading costs are therefore higher. Moreover, compaction (which generates dust), complex recycling or disposal as special waste are all costly procedures.