[account42]

Increasing accuracy is a wild understatement. Dead reckoning with mobile phone hardware won't give you a usable result for long. Maybe your experiences are from tunnels with dedicated beacons to tell the phone where you are.

[kube-system]

Most vehicular tunnels aren't too terribly long, if you're stuck in one in traffic, yeah dead reckoning drifts quite a bit. But if you're driving through one for a minute or two, it's sufficient.

On a side note I've personally had bad experience with beacons in train tunnels telling me I'm miles away from where I'm actually at.