There are applications which require very precise tracking. An example is the GPS-supported calculation of motorway tolls or exact logging of the trace of vehicles on racing courses (e.g. Formula 1 trainings).

Precise DGPS tracking makes it possible to ascertain whether or not a vehicle is travelling along a toll road.
As a result, the system can determine if the vehicle is on a motorway as opposed or on a nearby country road.

DGPS works as follows:

The positioning calculation is the result of cooperation between two receivers, not one (as with GPS). One of these receivers is roving (e.g., in the vehicle), and the other is at a fixed reference point. The location of the reference receiver is therefore very accurately known. Given the fundamentals of satellite technology, even if the fixed receiver is a few hundred kilometres away from the roving receiver, the timing of the GPS satellites will have virtually the same errors.
Using its known position, the fixed reference calculates the timing errors of the GPS satellites and transmits them to the roving receivers. This 'differential' process allows for very precise calculation of the positions of the roving receivers.

DGPS reference stations are normally operated by large institutions also in charge of broadcasting correction signals. In Germany there is a long wave station (122.5KHz), known as 'ALF', which broadcasts continously DGPS signals. Another nationwide signal is broadcast by the ARD (Consortium of the Statutory Broadcast Institutions of the Federal Republic of Germany) via shortwave radio.

The correction factor of DGPS can be calculated immediately or at a later time. The status reports of all ENAiKOON VTUs include a time stamp which allows to correct the GPS position of a vehicle at any given time.