On Estonia’s roads across the frozen sea you may drive below 25km/h or over 40km/h, but never in between. And never wear a seat belt

While most roads have an upper speed limit, and some have a lower speed limit, there are some unusual roads in Estonia with a middle limit. You can only drive at less than 25km/h or more than 40km/h. Anything in between could be extremely dangerous.

The speed limits apply on Estonia’s seasonal ice roads laid out across the frozen sea. For most of the year these routes are traversed by ferries. While the ice is normally thick enough to support vehicles, there is a particular danger between 25 and 40km/h, because the motion of the car can produce a wave in the ice resembling the bow wave of a ship. Carry on for too long in this speed range, and the wave becomes powerful enough to crack the ice, with disastrous consequences.

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Other special safety rules are a mandatory separation of 250m between vehicles, and a prohibition on wearing seat belts. You may need to get out of the car quickly.

Unofficial ice roads are extremely hazardous and there are accidents every year. But the authorised ice roads safely provide what Visit Estonia calls “unforgettable driving experiences,” so long as you avoid that dangerous band of resonant speeds.