A"green wave"comprises a road provided with a number of traffic lights, which traffic lights are attuned to each other in such a manner that if a driver of a vehicle maintains a recommended speed as indicated on signs, he will only encounter green lights along that route and will not have to stop for a red light, therefore. To that end, the driver must adjust, i. e. increase or decrease, his speed, if necessary, from the moment he enters the route in question in order to ensure that the recommended speed has been realised, at least on average, upon arrival at the next traffic light.

The object of the invention is to provide a system that can help the driver maintain the recommended speed along a route To that end, the system comprises a position determining device, an electronic database containing position data that represent the starting point and the end point of at least one route and speed data linked thereto, which represent the desired upper limit and/or lower limit of the average speed of the vehicle along that route, position comparing means capable of determining whether the vehicle is present within said route, speed determining means capable of determining, if the vehicle is present within said route, a representative of the average speed of the vehicle from the moment the

vehicle has entered the route according to the position comparing means, speed comparing means capable of determining to what extent the average speed determined in this manner deviates from the desired lower limit or upper limit of the average speed, and signalling means capable of delivering a control signal to increase or decrease the speed of the vehicle, as the case may be, in dependence thereon.

In relation to a"green wave", the term route is to be understood to mean a road section between the beginning of a green wave and the first traffic lights, or between two successive traffic lights in a green wave. In general, the term route as used within the framework of the invention comprises a road section between two successive positions along a road, between which an average speed is to be maintained.

The position determining device may be a GPS device or a LORAN device, for example.

In a first preferred embodiment, the database is present in the vehicle'. The database may be loaded with current data at regular intervals. In a second preferred embodiment, the database is present at a fixed position outside the vehicle, wherein the system furthermore comprises wireless communication means by which a wireless data link can be maintained between the database and the vehicle. Said communication means may be GSM or RDS, for example.

In a simple embodiment, the system only determines whether the speed of the vehicle falls outside the desired speed range and the only signalling that takes place is to increase

or decrease the speed. In a more advanced embodiment, the system determines by how much the speed deviates from the lower limit and/or the upper limit, and the control signal preferably comprises a calculated recommended speed that is to be maintained on the remaining part of the route in order to realise an average speed, calculated over the entire route, above or at the desired lower limit or below or at the desired upper limit.

The control signal may be an audio signal and/or a visual signal. Furthermore, the control system may be transmitted to a cruise control device, in which case the calculated recommended speed is automatically set by the cruise control device. Preferably, the latter only takes place if the calculated recommended speed is lower than the actual speed of the vehicle.

Furthermore, the signalling means preferably indicate the distance from the vehicle to the end point of the route. This enables to driver to estimate how much time he has left to adapt his speed.

The database is preferably stored in electronic memory means, and preferably the position comparing means, the speed determining means and the speed comparing means are at least partially formed by at least one central processing unit, which is connected to memory means and which can be loaded with an instruction set for that purpose.

The invention will now be explained in more detail with reference to an embodiment which is schematically illustrated in the figure.

According to the figure, a system for controlling the speed of a vehicle 1 along a route comprises a central processing unit 2, which is connected to signalling means 3, a GPS position determining device 4, a memory 5 and a speedometer 6.

The memory 5 is loaded with a database that contains position data representing the starting point and the end point of at least one route. Said starting point and end point may be the positions of two successive traffic lights in a green wave, for example. Furthermore, said positions may be the starting point and the end point of routes along which speed checks are frequently carried out. The database is furthermore contains speed data linked to each route, which represent the desired upper limit and/or lower limit of the vehicle 1 along that route.

The central processing unit 2 is loaded with an algorithm for comparing the position that is supplied by the GPS device 4 at short intervals with the database in the memory 5 so as to determine whether the vehicle 1 is present within a particular section.

If the vehicle 1 is present within said section, the average speed of the vehicle 1 can be determined by means of the speedometer 6 from the moment the vehicle 1 has entered the section in question.

The central processing unit 2 is furthermore loaded with a speed comparing algorithm for determining to what extent the calculated average speed deviates from the desired lower limit or upper limit of the average speed associated with the

section in question.

In that case the display 3 can display a control or warning signal in dependence thereon, telling the driver to increase or decrease the speed of the vehicle 1, as the case may be, in order to ensure that an average speed that remains within the desired limits has been realised at the end of the section. The warning signal, which may also be an audio signal, may be a simple warning signal or a signal that provides exact information about the recommended speed to be maintained on the remaining part of the route.

Preferably, the driver will be able to set, using a control panel, whether the calculated recommended speed is the highest possible speed at which the average speed will equal the desired upper limit or the lowest possible speed at which the average speed will equal at the desired lower limit, or a value therebetween.

If required, the system can easily be arranged such that it can provide the driver with additional information, such as the average speed at which he has driven along the route until that moment, his maximum speed along the route in question, the total length of the route, the distance yet to be covered along that roue, the direction in which the vehicle is driving, etc. Advantageously, the device may also be at least partially integrated with a road information system, because the system has many components in common therewith, as well as with a cruise control device so as to effect speed adjustments at least partially automatically.