Use a similar idea called ISOTrack for deliveries. Satellite tracking so the vehicle shows an ETA on screen. However this system is only as good as road conditions and vehicle reliability hold good, or the driver is not taking a legal break which can be within the catchment of the store and therefore the vehicle seems to be "on the doorstep" and yet not there. Vehicle breakdowns and road incidents also influence these systems and can make the data misleading. Can't tell you how often I have stood waiting for a vehicle which should be at the store but can be up to half an hour or more away.

As a guide this kind of system is a useful tool but not infallible.

Have to agree that the tube station signs do seem a poor waste of money as surely they could be like the old flap info panels on main line railways and announce the nigh on arrival of a train even if they don't do the more central tube station announcers list of next few trains.