What Are Those Weird White Stripes You See on the Road in Winter?

Have you ever noticed a mysterious streak of white lines on the road right before a winter storm is set to arrive and wondered how they got there? They are not figments of your imagination. In fact, they were purposely applied to the road for a very good reason: your safety.

It’s all part of a method known as anti-icing, which is intended to make roads safer to drive on during harsh winter weather. Typically with this technique, a liquid chemical such as magnesium chloride is used to lower the freezing point of water. (Salt brine solutions made of sodium chloride and water or calcium chloride and water are also popular.) Once the substance has been applied to a path or roadway, it helps prevent snow and ice from forming a strong bond to the pavement below, making it safer for drivers to navigate [PDF]. 

According to the Minnesota Stormwater Manual, anti-icing is “like frying eggs: grease the pan and the eggs come out easily with no mess to clean up. Like greasing the frying pan, the purpose of anti-icing is to keep snow from sticking to the pavement.”

That said, the key to any successful anti-icing regimen is to do it at the right time. Incidentally, that’s usually just before any type of rain, sleet, or snowflakes start to fall. It’s a sharp, proactive contrast to de-icing, which is like the inverse of anti-icing (even though the terms do sound similar).

When it comes to de-icing, it’s all about breaking down a bond after it's been formed between snow and/or ice and the pavement. This method is more reactive than proactive, and is a pretty common winter maintenance strategy. Usually it involves applying pre-wetted rock salt [PDF] to roadways after a storm to break down the bond between the snow and the pavement. When you spot snow plows barreling down some wintry terrain, chances are you might even get to see this de-icing technique in real life.

While de-icing is the more widespread method employed on our roads, experts claim it’s actually more expensive than anti-icing. Comparatively, anti-icing is seen as more affordable because it can be done during normal working hours and in non-inclement weather—reducing the need for staffers to work overtime. It also makes post-storm cleanups faster, as the treatment can last for several days at a time. Even if a blizzard doesn’t start right away, you will probably still be covered over the next few days. It also helps prevent snow and ice from sticking to streets to begin with.

Anti-icing advocates also claim that this method is safer for the environment, as fewer chemicals are used and there’s less of a buildup of silt, as well as less of a harmful runoff into stormwater systems and the like. However, the brine solutions used for anti-icing may not always be good news for your car, as those salt crystals often end up in a vehicle’s undercarriage, where they can be corrosive and lead to rust.

To better avoid this, experts say you should wash your car regularly throughout the winter months, paying special attention to the undercarriage (which you may want to clean every 10 days or so) to prevent buildup and overall corrosion.

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