GPS in Tunnels and Underpasses: What to Expect
Why location updates can pause in tunnels and why the displayed speed may freeze or change abruptly after exit.
Tunnels, covered car parks and some underpasses block much of the sky, so a phone may lose satellite-derived location. The browser can retain the last known position while waiting for a fresh fix. A frozen speed value is not proof that the phone is still travelling at that speed; it may simply be stale.
A stale value is different from a current value
The location response includes a timestamp, but not every interface displays it. If updates stop, the last number may remain on screen unless the page explicitly marks it as old. A good tracker should make the status understandable and avoid implying that an old reading is live.
After exiting the tunnel
The device may need time to reacquire satellites and reconcile a new position. The first few points can be noisy as the estimate stabilizes. A sudden jump in trip distance may result from the gap between the last point before the tunnel and the first point after it, not from the actual route being a straight line.
Do not use the display for driving decisions
Keep attention on the road and use the vehicle's approved instruments. Never handle a phone while driving to restart a tracker. If you need to review the session, stop in a safe location first.
How to interpret a gap
A continuous-looking line does not guarantee continuous measurements. Some systems connect points across a gap for display purposes. When evaluating distance, note that the missing section is estimated or under-recorded, and do not treat it as a precise measurement.
Frequently asked questions
Why does speed freeze in a tunnel?
The device may not be receiving fresh location updates.
Can GPS fill in the tunnel route exactly?
No. The route during a signal gap cannot be reconstructed exactly from the missing GPS points alone.
Technical references
These references explain the underlying browser and positioning concepts. They do not imply endorsement of this website.