VaneWhy Your Speedometer App Shows 0 on a Train
A train carriage is a metal box, often with coated windows, running through cuttings and tunnels. That is about the hardest place there is for a phone's GPS. A few habits make the difference between 0 and a steady reading.
Updated 1 October 2026
Why trains are hard for GPS
- The carriage is metal. A steel or aluminium body blocks satellite signals almost completely. What reaches the phone comes through the windows.
- Many windows are coated. Modern trains often use heat-reflective window glass with a thin metallic layer, which also weakens radio signals. Some railways now treat windows so phone signals get through, which can help GPS too.
- Half the sky is the other side of the train. From one window you see satellites on one side only. Fewer satellites, all in one direction, means poorer positions.
- Railways run through cuttings and tunnels, where even the window view is blocked.
So the phone often has either no fix or a weak one. Apps differ in what they do then. Some show 0 or freeze, and some show the poor fix's jumpy speed. Few say plainly that the signal is weak.
How to get a steady reading
- Sit at a window, ideally on the side facing the open sky, away from buildings and platforms.
- Hold the phone flat against the glass, or rest it on the window ledge. A few centimetres closer can be the difference between a fix and none.
- Give it a minute after boarding or leaving a tunnel. The first fix through a window takes longer than outdoors.
- Upper deck, end of the carriage, or a vestibule window sometimes sees more sky.
- Get a fix before you board, on the platform, so the phone has fresh satellite data.
Reading the numbers
Once there is a fix, the speed itself is good. Satellite receivers measure speed from the Doppler shift of the signals, which works the same at 300 km/h as at 30 (see how GPS measures speed). What suffers through a window is the position: it can be tens of metres off, so a map may show you beside the line, and distance worked out from positions comes out too long.
| Train | Typical top speed |
|---|---|
| Regional and commuter | 100 to 160 km/h · 60 to 100 mph |
| Intercity | 160 to 200 km/h · 100 to 125 mph |
| High-speed lines | 250 to 320 km/h · 155 to 200 mph |
Typical service speeds; individual lines and trains vary.
In tunnels
No signal reaches a tunnel, so there is no satellite speed until the train comes out. A phone has no connection to the train's wheels, and its motion sensors cannot hold an accurate speed for long on their own. The honest display is "no reading" until the sky is back. See why GPS stops in tunnels.
Sources
- US Government, GPS accuracy: signal blockage and reflections as causes of degraded accuracy.
- ESA Navipedia, GNSS basic observables (Doppler measurement).
Common questions
Why does my speedometer app show 0 on a train?
The carriage's metal body and often its coated windows block most satellite signals, so the phone either has no fix or only a poor one. Many apps then show 0 or freeze. Sitting at a window and holding the phone against the glass usually brings the reading back.
Does GPS work on high-speed trains?
Yes. GPS measures speed from the Doppler shift of the satellite signals and has no trouble at 300 km/h. The problem on trains is reception through the carriage, not the speed.
Why does the train speed jump around?
With only a few satellites visible through one window, positions are poor and reflections from the train and buildings add noise. Speed from the receiver's Doppler measurement is steadier than speed worked out from positions, so apps that use it read more smoothly.