You are flying at 100 km/h, enter a tunnel, and the speed test drops to 0. Is the tool broken? No — this is exactly how GPS physics works.
GPS times radio signals from satellites 20,000 km above Earth. Those signals cannot pass through rock or concrete. Inside a tunnel your phone hears nothing, so speed reads zero.
Underground metro sections, ghats and deep cuttings all block GPS; the reading returns on open sections.
Within 2–10 seconds of exiting, the phone re-locks and live speed resumes. The max-speed stat keeps your earlier record.
No — it proves honesty. Zero only in tunnels with correct speeds outside means GPS works perfectly.
Why does speed show 0 in tunnels but the train is moving?
GPS radio signals cannot penetrate rock or concrete.
How long after a tunnel does speed return?
Usually 2–10 seconds after exiting.
Does this happen in the Konkan Railway tunnels?
Yes — test on open coastal stretches instead.
Will a tunnel ruin my max speed record?
No — the max stat preserves your highest reading.