Interesting point. Modern units and maps are 'tunnel aware'. The unit does still lose the satellite signal, but it uses a form of 'dead reckoning' to track the supposed progress thru a known tunnel based on the reported speed. It works fine for relatively short tunnels where traffic is flowing normally, but if there's a slowdown or you exceed the speed limit [bad idea!] your actual and assumed exit will not coincide.

If the tunnel is new and not shown on the map then the unit reports the loss of signal the same as when your car is in an underground carpark.


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