Together with the usual networks of urban traffic lights or the typical road signs, other systems are becoming known and finding complementary or supportive utility in assisting the general traveller, said systems being global positioning by satellite communications, such as GPS, and also telephone systems, such as Inmarsat or Iridium, etc., or others for mobile telephony, such as GSM, AMPS, etc., together with those for paging, such as Pager.
There are also broadcast radio systems, such as RDS (Radio Data System) or DRB (Digital Radio Broadcasting). Others are based on computer operating systems arising from Microsoft Windows, such as AutoPC.
Insofar as the technologies employed for vehicle identification are concerned, widespread deployment already exists of AVI (Automatic Vehicle Identification) and RFID (Radio-frequency Identification), which mainly find use in motorway electronic toll collection when the vehicles pass a determined point like, for example, the payment booths. These advances in technology have seen their accuracy and reliability greatly enhanced and their cost of implementation or deployment reduced considerably, for which reason new uses are becoming feasible. This technology is used in the present invention as part of its principal components, which have to be suitably adapted to adjust to its objectives.
Finally mention has to be made of the existence of police radar detecting devices, which have had their functions extended to become Safety Warning System (SWS) devices, similar to those described in the present invention.
Based on the previously existing device for radar detection, these incorporate detectors of traffic hazard signals. In this case the transmitters broadcast radio waves on the same frequency-as the police radar, so that the receivers only incorporate a memory to translate the code transmitted into one of 60 possible warning signals.
The transmitters can be mobile, being incorporated in emergency vehicles, such as police cars, fire trucks, ambulances, etc., or in fixed locations at traffic danger points, such as intersections, bridges, etc. But in no case are the transmitters designed to form a radio beacon network, in which the information they transmit cannot be modified remotely or incorporate geographical or topographical data, information for tourists, first aid, services, identification and black box facilities, etc., being capable only of serving as a warning mechanism.
The technical: characteristics of these radio transmitters are as follows:                Power: 50 mW, rated value.        Working frequency: 24.1 GHz (the same frequency band as the police radar in North America).        Transmitted power density: 1 mW/cm2 on the side incorporating the antenna (comparable with the density in police radar equipment).        Voltage: between +10 and +16 VDC (connectable to the vehicle emergency light circuit).        Transmission pattern: Bidirectional, beam of 23° in horizontal plane and aligned along the longitudinal axis of the vehicle.        Message transmission: any one of the 64 pre-established for SWS. The transmitter selects automatically between two types of message: one if the transmitter is located in a moving vehicle (e.g. alarm of emergency vehicle in motion), and another if it is stopped (e.g. accident alarm).        Electronic characteristics: digital signal processing, high density, surface-mount technology, non-erasable memory.        Admissible temperature range: operational, between −30° C. and 65° C.; off, between −40° C. and +85° C.        Impact and vibration: withstands an impact of 10 G in half-sinusoidal wave lasting for 11 ms, and vibration of 1.4 G in sinusoid at between 10 and 60 Hz, in all cases parallel to the vertical axis, with no resulting permanent damage.        Weather resistance: Designed for mounting externally on vehicles or for installation at fixed outdoor sites.        