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15 years ago, sat nav systems built into cars would sometimes be fitted with a rate gyro and get a wheel speed signal from the car - to make them work better in tunnels and other areas with poor GPS signals.

(Of course, that one area of superior performance couldn't make up for the awful GUIs, the awful resistive touchscreens, the $100 map updates, and suchlike)

I can't see inside Maps, but it does look like they use accellerometer data or just assumptions to continue animating your position on the map. Assumption being for example that you will follow the route through the tunnel at your current average speed. Close and good enough for most tunnels I suppose.

Apple maps does this.