Patent Publication Number: US-9428186-B2

Title: Exterior monitoring for vehicles

Description:
This application is a continuation of U.S. patent application Ser. No. 13/596,914 filed Aug. 28, 2012, now U.S. Pat. No. 8,965,677, which is a continuation-in-part (CIP) of U.S. patent application Ser. No. 11/874,749 filed Oct. 18, 2007, now U.S. Pat. No. 8,255,144, which is: 
     1. a CIP of U.S. patent application Ser. No. 11/461,619 filed Aug. 1, 2006, now U.S. Pat. No. 7,418,346, which claims priority under 35 U.S.C. §119(e) of U.S. provisional patent application Ser. No. 60/711,452 filed Aug. 25, 2005, and is:
         A) a CIP of U.S. patent application Ser. No. 10/822,445 filed Apr. 12, 2004, now U.S. Pat. No. 7,085,637, which is:
           1) a CIP of U.S. patent application Ser. No. 10/118,858 filed Apr. 9, 2002, now U.S. Pat. No. 6,720,920, and   2) a CIP of U.S. patent application Ser. No. 10/216,633 filed Aug. 9, 2002, now U.S. Pat. No. 6,768,944; and   
           B) a CIP of U.S. patent application Ser. No. 11/028,386 filed Jan. 3, 2005, now U.S. Pat. No. 7,110,880 which is a CIP of U.S. patent application Ser. No. 10/822,445 filed Apr. 12, 2004, now U.S. Pat. No. 7,085,637; and   C) a CIP of U.S. patent application Ser. No. 11/034,325 filed Jan. 12, 2005, now U.S. Pat. No. 7,202,776 which is a CIP of U.S. patent application Ser. No. 10/822,445 filed Apr. 12, 2004, now U.S. Pat. No. 7,085,637;       

     2. a CIP of U.S. patent application Ser. No. 11/464,385 filed Aug. 14, 2006, now U.S. Pat. No. 7,629,899, which claims priority under 35 U.S.C. §119(e) of U.S. provisional patent application Ser. No. 60/711,452 filed Aug. 25, 2005, and is a CIP of U.S. patent application Ser. No. 11/028,386 filed Jan. 3, 2005, now U.S. Pat. No. 7,110,880, and a CIP of U.S. patent application Ser. No. 11/034,325 filed Jan. 12, 2005, now U.S. Pat. No. 7,202,776; 
     3. a CIP of U.S. patent application Ser. No. 11/562,730 filed Nov. 22, 2006, now U.S. Pat. No. 7,295,925, which is a CIP of U.S. patent application Ser. No. 11/034,325 filed Jan. 12, 2005, now U.S. Pat. No. 7,202,776; 
     4. a CIP of U.S. patent application Ser. No. 11/681,817 filed Mar. 5, 2007, now U.S. Pat. No. 7,426,437, which is a CIP of U.S. patent application Ser. No.11/034,325 filed Jan. 12, 2005, now U.S. Pat. No. 7,202,776; and 
     5. a CIP of U.S. patent application Ser. No. 11/778,127 filed Jul. 16, 2007, now U.S. Pat. No. 7,912,645. 
    
    
     All of the above applications are incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The present invention relates generally to arrangements and methods for monitoring objects around a vehicle. 
     BACKGROUND OF THE INVENTION 
     A detailed discussion of background information is set forth in U.S. patent application Ser. Nos. 60/062,729 filed Oct. 22, 1997, now expired, Ser. No. 09/177,041 filed Oct. 22, 1998, now U.S. Pat. No. 6,370,475, 60/123,882 filed Mar. 11, 1999, now expired, Ser. No. 09/523,559 filed Mar. 10, 2000, now abandoned, Ser. No. 09/679,317 filed Oct. 4, 2000, now U.S. Pat. No. 6,405,132, Ser. No. 09/909,466 filed Jul. 19, 2001, now U.S. Pat. No. 6,526,352, Ser. No. 10/822,445, now U.S. Pat. No. 7,085,637, Ser. No. 11/028,386, now U.S. Pat. No. 7,110,880, and Ser. No. 11/034,325, now U.S. Pat. No. 7,202,776, all of which are incorporated by reference herein. 
     All of the patents, patent applications, technical papers and other references mentioned below and in the parent applications are incorporated by reference herein in their entirety. No admission is made that any or all of these references are prior art and indeed, it is contemplated that they may not be available as prior art when interpreting 35 U.S.C. §102 in consideration of the claims of the present application. 
     Definitions of terms used in the specification and claims are also found in the parent applications. 
     SUMMARY OF THE INVENTION 
     A vehicular arrangement for obtaining information about objects exterior to the vehicle in accordance with the invention includes several distance measuring systems fixed to the vehicle along the windshield, an edge or a side of the vehicle, each including a camera configured to obtain images of objects exterior of the vehicle and a processor that determines a distance between the vehicle and objects included in images obtained by the camera and a speed of the objects based on the successive distance determinations. A reactive system is arranged on the vehicle and coupled to the distance measuring systems, and considers both distance between the objects and the vehicle and the speed of the objects and reacts accordingly. A position of the distance measuring systems is selected to encompass an area in front of the vehicle, an area behind the vehicle and an area on each side of the vehicle in the fixed fields of view of the distance measuring systems. 
     The reactive system may include a system which limits the speed of the vehicle such that the speed of the vehicle can be limited in the presence of other objects or vehicles within a threshold distance from the vehicle, a warning system for providing a warning to a driver of the vehicle about the objects exterior of the vehicle, and/or be configured to access a map database containing information about vehicular travel lanes and consider the information when determining how to react to the presence of the object. In the latter case, the reactive system may be configured to, based on the map database, ignore objects on travel lanes where there is a physical barrier separating these travel lanes from the travel lane on which the vehicle is traveling, ignore stationary objects on a side of the travel lane and/or differentiate between stationary objects on a side of the travel lane and stationary objects in the travel lane. 
     A vehicle includes any of the configurations of the above arrangement with four distance measuring systems, one at each of the four corners of the vehicle, and which may be coupled to one or more common reactive systems. Two of the distance measuring systems may be arranged above headlights of the vehicle. Another vehicle includes four distance measuring systems, one at each of the four sides of the vehicle, and which are coupled to one or more common reactive systems. Yet another vehicle includes four distance measuring systems, one located on or near a roof of the vehicle, and which are coupled to one or more common reactive systems. 
     A method for operating a vehicle in consideration of objects exterior to the vehicle in accordance with the invention includes obtaining images of objects exterior of the vehicle by means of a camera of a plurality of distance measuring systems, each fixed to the vehicle along the windshield, an edge or a side of the vehicle, a position of the distance measuring systems encompassing an area in front of the vehicle, an area behind the vehicle and an area on each side of the vehicle in the fixed fields of view of the distance measuring systems, and determining using a processor, a distance between the vehicle and objects included in images obtained by the camera and a speed of the objects based on the successive distance determinations. The method also includes determining using the processor, whether an action must be undertaken to prevent contact between the object and the vehicle based on the objects and their distance from the vehicle, and if so undertaking an action to prevent contact between the vehicle and the object. 
     The step of undertaking an action may entail limiting the speed of the vehicle in the presence of other vehicles determined to be within a threshold distance from the vehicle, and/or providing a warning to a driver of the vehicle about the objects exterior of the vehicle. Determining whether an action must be undertaken to prevent contact between the object and the vehicle may entail accessing a map database containing information about vehicular travel lanes and considering the position of the object relative to a map in the map database, determining, based on the map database, whether there is a physical barrier separating travel lanes on which the objects are moving from the travel lane on which the vehicle is moving, in which case, the method entails precluding the action from being undertaken when it is determined, based on the map database, that there is a physical barrier separating these travel lanes from the travel lane on which the vehicle is moving, and/or determining, based on the map database, whether the object is a stationary object on a side of the travel lane, in which case, the method entails precluding the action from being undertaken when it is determined, based on the map database, that the object is a stationary object on a side of the travel lane. Determining whether an action must be undertaken to prevent contact between the object and the vehicle may additionally or alternatively entail configuring the system to differentiate, based on the map database, between stationary objects on a side of the travel lane and stationary objects in the travel lane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various hardware and software elements used to carry out the invention described herein are illustrated in the form of system diagrams, block diagrams, flow charts, and depictions of neural network algorithms and structures. Preferred embodiments are illustrated in the following figures: 
         FIG. 1  illustrates the GPS satellite system with the 24 satellites revolving around the earth. 
         FIG. 2  illustrates four GPS satellites transmitting position information to a vehicle and to a base station which in turn transmits the differential correction signal to the vehicle. 
         FIG. 3  illustrates a Wide Area Differential GPS or WADGPS system with four GPS satellites transmitting position information to a vehicle and to a base station which in turn transmits the differential correction signal to the vehicle. 
         FIG. 4  is a logic diagram showing the combination of the GPS system and an inertial navigation system. 
         FIG. 5  is a block diagram of the overall vehicle accident avoidance, warning, and control system and method of the present invention illustrating system sensors, radio transceivers, computers, displays, input/output devices and other key elements. 
         FIG. 5A  is a block diagram of a representative accident avoidance, warning and control system. 
         FIG. 6  is a block diagram of an image analysis computer of the type that can be used in the accident avoidance or identification system and method of this invention. 
         FIG. 7  illustrates a vehicle traveling on a roadway in a defined corridor. 
         FIG. 8  illustrates two adjacent vehicles traveling on a roadway and communicating with each other. 
         FIG. 9  is a schematic diagram illustrating a neural network of the type useful in the image analysis computer of  FIG. 5 . 
         FIG. 10  is a schematic diagram illustrating the structure of a node processing element in the neural network of  FIG. 9 . 
         FIG. 11  illustrates the use of a Precise Positioning System employing three micropower impulse radar transmitters, two or three radar reflectors or three RFID tags in a configuration to allow a vehicle to accurately determine its position. 
         FIG. 12 a    is a flow chart of the method in accordance with the invention for preventing run off the road accidents. 
         FIG. 12 b    is a flow chart of the method in accordance with the invention for preventing center (yellow) line crossing accidents. 
         FIG. 12 c    is a flow chart of the method in accordance with the invention for preventing stoplight running accidents. 
         FIG. 13  illustrates an intersection with stop signs on the lesser road where there is a potential for a front to side impact and a rear end impact. 
         FIG. 14  illustrates a blind intersection with stoplights where there is a potential for a front side to front side impact. 
         FIG. 15  illustrates an intersection where there is a potential for a front-to-front impact as a vehicle turns into oncoming traffic. 
         FIG. 16A  is a side view of a vehicle equipped with a road-mapping arrangement in accordance with the invention. 
         FIG. 16B  is a front perspective view of a vehicle equipped with the road-mapping arrangement in accordance with the invention. 
         FIG. 17  is a schematic perspective view of a data acquisition module in accordance with the invention. 
         FIG. 17A  is a schematic view of the data acquisition module in accordance with the invention. 
         FIG. 18  shows the view of a road from the video cameras in both of the data acquisition modules. 
         FIG. 19  shows a variety of roads and vehicles operating on those roads that are in communication with a vehicle that is passing through a Precise Positioning Station. 
         FIG. 20  is a schematic of the manner in which communications between a vehicle and a transmitter are conducted according to some embodiments of the invention. 
         FIGS. 21A and 21B  illustrate a preferred embodiment of a laser radar or camera system mounted at the four corners of a vehicle above the headlights and tail lights. 
         FIGS. 22A and 22B  illustrate the system of  FIGS. 21A and 21B  for vehicles on a roadway. 
         FIGS. 23A and 23B  illustrate an alternative mounting location for laser radar or camera units. 
         FIG. 24  is a schematic illustration of a typical laser radar device showing the scanning or pointing system with simplified optics. 
         FIG. 25  is a schematic showing a method for avoiding collisions in accordance with the invention. 
         FIG. 26  is a schematic of a multi-form communication system in accordance with the invention. 
         FIG. 27  is a schematic of a ubiquitous communication system in accordance with the invention. 
     
    
    
     DETAILED DISCUSSION OF PREFERRED EMBODIMENTS 
     1. Vehicle Collision Warning and Control 
     According to U.S. Pat. No. 5,506,584, the stated goals of the US DOT IVHS system are:
         improving the safety of surface transportation   increasing the capacity and operational efficiency of the surface transportation system   enhancing personal mobility and the convenience and comfort of the surface transportation system   reducing the environmental and energy impacts of the surface transportation system       

     The RtZF® (Road to Zero Fatalities®) system in accordance with the present invention satisfies all of these goals at a small fraction of the cost of prior art systems. The safety benefits have been discussed above. The capacity increase is achieved by confining vehicles to corridors where they are then permitted to travel at higher speeds. This can be achieved immediately where carrier phase DGPS is available or with the implementation of the highway-located precise location systems as shown in  FIG. 11 . An improvement is to add the capability for the speed of the vehicles to be set by the highway or highway control system. This is a simple additional few bytes of information that can be transmitted along with the road edge location map, thus, at very little initial cost. To account for the tolerances in vehicle speed control systems, the scanning laser radar, or other technology system, which monitors for the presence of vehicles without RtZF® is also usable as an adaptive cruise control system. Thus, if a faster moving vehicle approaches a slower moving vehicle, it will automatically slow down to keep a safe separation distance from the leading, slower moving vehicle. Although the system is not planned for platooning, that will be the automatic result in some cases. The maximum packing of vehicles is automatically obtained and thus the maximum vehicle flow rate is also achieved with a very simple system. 
     For the Intelligent Highway System (ITS) application, some provision is required to prevent unequipped vehicles from entering the restricted lanes. In most cases, a barrier will be required since if an errant vehicle did enter the controlled lane, a serious accident could result. Vehicles would be checked while traveling down the road or at a tollbooth, or similar station, that the RtZF® system was in operation without faults and with the latest updated map for the region. Only those vehicles with the RtZF® system in good working order would be permitted to enter. The speed on the restricted lanes would be set according to the weather conditions and fed to the vehicle information system automatically, as discussed above. Automatic tolling based on the time of day or percentage of highway lane capacity in use can also be easily implemented. 
     For ITS use, there needs to be a provision whereby a driver can signal an emergency, for example, by putting on the hazard lights. This would permit the vehicle to leave the roadway and enter the shoulder when the vehicle speed is below a certain level. Once the driver provides such a signal, the roadway information system, or the network of vehicle-based control systems, would then reduce the speed of all vehicles in the vicinity until the emergency has passed. This roadway information system need not be actually associated with the particular roadway and also need not require any roadway infrastructure. It is a term used here to represent the collective system as operated by the network of nearby vehicles and the inter-vehicle communication system. Eventually, the occurrence of such emergency situations will be eliminated by vehicle-based failure prediction systems such as described in U.S. Pat. No. 5,809,437. 
     Emergency situations will develop on intelligent highways. It is difficult to access the frequency or the results of such emergencies. The industry has learned from airbags that if a system is developed which saves many lives but causes a few deaths, the deaths will not be tolerated. The ITS system, therefore, must operate with a very high reliability, that is approaching “zero fatalities”™. Since the brains of the system will reside in each vehicle, which is under the control of individual owners, there will be malfunctions and the system must be able to adapt without causing accidents. An alternative is for the brains to reside on the network providing that the network connection is reliable. 
     Spacing of the vehicles is the first line of defense. Secondly, each vehicle with a RtZF® system has the ability to automatically communicate to all adjacent vehicles and thus immediately issue a warning when an emergency event is occurring. Finally, with the addition of a total vehicle diagnostic system, such as disclosed in U.S. Pat. No. 5,809,437, potential emergencies can be anticipated and thus eliminated with high reliability. 
     Although the application for ITS envisions a special highway lane and high speed travel, the potential exists in the invention to provide a lower measure of automatic guidance where the operator can turn control of the vehicle over to the RtZF® system for as long as the infrastructure is available. In this case, the vehicle would operate in normal lanes but would retain its position in the lane and avoid collisions until a decision requiring operator assistance is required. At that time, the operator would be notified and if he or she did not assume control of the vehicle, an orderly stopping of the vehicle, e.g., on the side of the road, would occur. 
     For all cases where vehicle steering control is assumed by the RtZF® system, an algorithm for controlling the steering should be developed using neural networks or neural fuzzy systems. This is especially true for the emergency cases discussed herein where it is well known that operators frequently take the wrong actions and at the least, they are slow to react. Algorithms developed by other non-pattern recognition techniques do not, in general, have the requisite generality or complexity and are also likely to make the wrong decisions (although the use of such systems is not precluded in the invention). When the throttle and breaking functions are also handled by the system, an algorithm based on neural networks or neural fuzzy systems is even more important. 
     For the ITS, the driver will enter his or her destination so that the vehicle knows ahead of time where to exit. Alternately, if the driver wishes to exit, he merely turns on his turn signal, which tells the system and other vehicles that he or she is about to exit the controlled lane. 
     Neural networks have been mentioned above and since they can play an important role in various aspects of the invention, a brief discussion is now presented here.  FIG. 9  is a schematic diagram illustrating a neural network of the type useful in image analysis. Data representing features from the images from the CMOS cameras  60  are input to the neural network circuit  63 , and the neural network circuit  63  is then trained on this data (see  FIG. 6 ). More specifically, the neural network circuit  63  adds up the feature data from the CMOS cameras  60  with each data point multiplied by an associated weight according to the conventional neural network process to determine the correlation function. 
     In this embodiment,  141  data points are appropriately interconnected at  25  connecting points of layer  1 , and each data point is mutually correlated through the neural network training and weight determination process. In some implementations, each of the connecting points of the layer  1  has an appropriate threshold value, and if the sum of measured data exceeds the threshold value, each of the connecting points will output a signal to the connecting points of layer  2 . In other cases, an output value or signal will always be outputted to layer  2  without thresholding. 
     The connecting points of the layer  2  comprises  20  points, and the  25  connecting points of the layer  1  are appropriately interconnected as the connecting points of the layer  2 . Similarly, each data value is mutually correlated through the training process and weight determination as described above and in neural network texts. Each of the  20  connecting points of the layer  2  can also have an appropriate threshold value, if thresholding is used, and if the sum of measured data exceeds the threshold value, each of the connecting points will output a signal to the connecting points of layer  3 . 
     The connecting points of the layer  3  comprises  3  points in this example, and the connecting points of the layer  2  are interconnected at the connecting points of the layer  3  so that each data is mutually correlated as described above. 
     The value of each connecting point is determined by multiplying weight coefficients and summing up the results in sequence, and the aforementioned training process is to determine a weight coefficient Wj so that the value (ai) is a previously determined output.
 
 ai=ΣWj·Xj ( j= 1 to  N ) +W   0  
 
     wherein Wj is the weight coefficient,
         Xj is the data   N is the number of samples and   W 0  is bias weight associated with each node.       

     Based on this result of the training, the neural network circuit  63  generates the weights and the bias weights for the coefficients of the correlation function or the algorithm. 
     At the time the neural network circuit  63  has learned from a suitable number of patterns of the training data, the result of the training is tested by the test data. In the case where the rate of correct answers of the object identification unit based on this test data is unsatisfactory, the neural network circuit  63  is further trained and the test is repeated. Typically, about 200,000 feature patterns are used to train the neural network  63  and determine all of the weights. A similar number is then used for the validation of the developed network. In this simple example chosen, only three outputs are illustrated. These can represent another vehicle, a truck and a pole or tree. This might be suitable for an early blind spot detector design. The number of outputs depends on the number of classes of objects that are desired. However, too many outputs can result in an overly complex neural network and then other techniques such as modular neural networks can be used to simplify the process. When a human looks at a tree, for example, he or she might think “what kind of tree is that?” but not “what kind of tiger is that”. The human mind operates with modular or combination neural networks where the object to be identified is first determined to belong to a general class and then to a subclass etc. Object recognition neural networks can frequently make use of this principle with a significant simplification resulting. 
     In the above example, the image was first subjected to a feature extraction process and the feature data was input to the neural network. In other cases, especially as processing power continues to advance, the entire image is input to the neural network for processing. This generally requires a larger neural network. Alternate approaches use data representing the difference between two frames and the input data to the neural network. This is especially useful when a moving object of interest is in an image containing stationary scenery that is of no interest. This technique can be used even when everything is moving by using the relative speed as a filter to remove unwanted pixel data. Any variations are possible and will now be obvious to those skilled in the art. Alternately, this image can be filtered based on range, which will also significantly reduce the number of pixels to be analyzed. 
     In another implementation, the scenes are differenced based on illumination. If infrared illumination is used, for example, the illumination can be turned on and off and images taken and then differenced. If the illumination is known only to illuminate an object of interest then such an object can be extracted from the background by this technique. A particularly useful method is to turn the illumination on and off for alternate scan lines in the image. Adjacent scan lines can then be differenced and the resulting image sent to the neural network system for identification. 
     The neural network can be implemented as an algorithm on a general-purpose microprocessor or on a dedicated parallel processing DSP, neural network ASIC or other dedicated parallel or serial processor. The processing speed is generally considerably faster when parallel processors are used and this can also permit the input of the entire image for analysis rather than using feature data. A combination of feature and pixel data can also be used. 
     Neural networks have certain known potential problem areas that various researchers have attempted to eliminate. For example, if data representing an object that is totally different from those objects present in the training data is input to the neural network, an unexpected result can occur which, in some cases, can cause a system failure. To solve this and other neural network problems, researchers have resorted to adding in some other computational intelligence principles such as fuzzy logic resulting in a neural-fuzzy system, for example. As the RtZF® system evolves, such refinements will be implemented to improve the accuracy of the system. Thus, although pure neural networks are currently being applied to the problem, hybrid neural networks such as modular, combination, ensemble and fuzzy neural networks will undoubtedly evolve. 
     A typical neural network processing element known to those skilled in the art is shown in  FIG. 10  where input vectors, (X 1 , X 2 , . . . , Xn) are connected via weighing elements  120  (W 1 , W 2 , . . . , Wn) to a summing node  130 . The output of node  130  is passed through a nonlinear processing element  140 , typically a sigmoid function, to produce an output signal, Y. Offset or bias inputs  125  can be added to the inputs through weighting circuit  128 . The output signal from summing node  130  is passed through the nonlinear element  140  which has the effect of compressing or limiting the magnitude of the output Y. 
     Neural networks used in the accident avoidance system of this invention are trained to recognize roadway hazards including automobiles, trucks, animals and pedestrians. Training involves providing known inputs to the network resulting in desired output responses. The weights are automatically adjusted based on error signal measurements until the desired outputs are generated. Various learning algorithms may be applied with the back propagation algorithm with the Delta Bar rule as a particularly successful method. 
     2. Accurate Navigation 
     2.1 GPS 
       FIG. 1  shows the current GPS satellite system associated with the earth and including 24 satellites  2 , each satellite revolving in a specific orbital path  4  around the earth. By means of such a GPS satellite system, the position of any object can be determined with varying degrees of precision as discussed herein. A similar system will appear when the European Galileo system is launched perhaps doubling the number of satellites. 
     2.2 DGPS, WAAS, LAAS and Pseudolites 
       FIG. 2  shows an arrangement of four satellites  2  designated SV 1 , SV 2 , SV 3  and SV 4  of the GPS satellite system shown in  FIG. 1  transmitting position information to receiver means of a base station  20 , such as an antenna  22 , which in turn transmits a differential correction signal via transmitter means associated with that base station, such as a second antenna  16 , to a vehicle  18 . 
     Additional details relating to  FIGS. 1 and 2  can be found in U.S. Pat. No. 5,606,506. 
       FIG. 3  shows an arrangement of four satellites  2  designated SV 1 , SV 2 , SV 3  and SV 4  of the GPS satellite system as in  FIG. 2  transmitting position information to receivers of base stations  20  and  21 , such as an antenna  22 , which in turn transmit a differential correction signal via transmitters associated with that base stations, such as a second antenna  16 , to a geocentric or low earth orbiting (LEO) satellite  30  which in turn transmits the differential correction signals to vehicle  18 . In this case, one or more of the base stations  20 , 21  receives and performs a mathematical analysis on all of the signals received from a number of base stations that cover the area under consideration and forms a mathematical model of the errors in the GPS signals over the entire area. For the continental U.S. or CONUS, for example, a group of 13 or more base stations are operated by OMNISTAR® that are distributed around the country. By considering data from the entire group of such stations, the errors in the GPS signals for the entire area can be estimated resulting in a position accuracy of about 3 cm over the entire area. The corrections are then uploaded to the geocentric or low earth orbiting satellite  30 , or communicated to the Internet, for retransmission to vehicles on the roadways. In this way, such vehicles are able to determine their absolute position to within about 3 centimeters. This is known as Wide Area Differential GPS or WADGPS. The wide area corrections can be further corrected when there are additional local stations that are not part of the WADGPS system. 
     It is important to note that future GPS and Galileo satellite systems plan for the transmission of multiple frequencies for civilian use. Like a lens, the ionosphere diffracts different frequencies by different amounts and thus the time of arrival of a particular frequency will depend on the value of that frequency. This fact can be used to determine the amount that each frequency is diffracted and thus the delay or error introduced by the ionosphere. Thus with more than one frequency being emitted by a particular satellite, the equivalent of the DGPS corrections can be determined be each receiver and there is no longer a need for DGPS, WADGPS, WAAS, LAAS and similar systems. 
     The WAAS system is another example of WADGPS for use with airplanes. The U.S. Government estimates that the accuracy of the WAAS system is about 1 meter in three dimensions. Since the largest error is in the vertical direction, the horizontal error is much less. 
     3. Maps and Mapping 
     3.1 Maps 
     All information regarding the road, both temporary and permanent, should be part of the map database, including speed limits, presence of guard rails, width of each lane, width of the highway, width of the shoulder, character of the land beyond the roadway, existence of poles or trees and other roadside objects, exactly where the precise position location apparatus is located, etc. The speed limit associated with particular locations on the maps should be coded in such a way that the speed limit can depend upon the time of day and the weather conditions. In other words, the speed limit is a variable that will change from time to time depending on conditions. It is contemplated that there will be a display for various map information which will always be in view for the passenger and for the driver at least when the vehicle is operating under automatic control. Additional user information can thus also be displayed such as traffic conditions, weather conditions, advertisements, locations of restaurants and gas stations, etc. 
     A map showing the location of road and lane boundaries can be easily generated using a specially equipped survey vehicle that has the most accurate position measurement system available. In some cases, it might be necessary to set up one or more temporary local DGPS base stations in order to permit the survey vehicle to know its position within a few centimeters. However, with the improvements in GPS accuracy from multiple frequencies and from more accurate DGPS systems, accurate mapping can now be done without requiring carrier phase DGPS. The vehicle would drive down the roadway while operators, using specially designed equipment, sight the road edges and lanes. This would probably best be done with laser pointers and cameras. Transducers associated with the pointing apparatus record the angle of the apparatus and then by triangulation determine the distance of the road edge or lane marking from the survey vehicle. Since the vehicle&#39;s position would be accurately known, the boundaries and lane markings can be accurately determined. It is anticipated that the mapping activity would take place continuously such that all roads in a particular state would be periodically remapped in order to record any changes which were missed by other monitoring systems and to improve the reliability of the maps by minimizing the chance for human error. Any roadway changes that were discovered would trigger an investigation as to why they were not recorded earlier thus adding feedback to the mapping part of the process. 
     The above-described method depends on human skill and attention and thus is likely to result in many errors. A preferred approach is to carefully photograph the edge of the road and use the laser pointers to determine the location of the road lines relative to the pointers and to determine the slope of the roadway through triangulation. In this case, several laser pointers would be used emanating from above, below and/or to the sides of the camera. The reduction of the data is then done later using equipment that can automatically pick out the lane markings and the reflected spots from the laser pointers. One aid to the mapping process is to place chemicals in the line paint that could be identified by the computer software when the camera output is digitized. This may require the illumination of the area being photographed by an infrared or ultraviolet light, for example. 
     In some cases where the roadway is straight, the survey vehicle could travel at moderate speed while obtaining the boundary and lane location information. In other cases, where the road in turning rapidly, more readings would be required per mile and the survey vehicle would need to travel more slowly. In any case, the required road information can be acquired semi-automatically with the survey vehicle traveling at a moderate speed. Thus, the mapping of a particular road would not require significant time or resources. It is contemplated that a few such survey vehicles could map all of the interstate highways in the U.S. in less than one year. Eventually, it is contemplated that between 50 and 100 such vehicles using photogramity techniques would continuously map and remap the Unites States. 
     3.2 Mapping 
     An important part of some embodiments of the invention is the digital map that contains relevant information relating to the road on which the vehicle is traveling. The digital map usually includes the location of the edge of the road, the edge of the shoulder, the elevation and surface shape of the road, the character of the land beyond the road, trees, poles, guard rails, signs, lane markers, speed limits, etc. as discussed elsewhere herein. Additionally, it can contain the signature as discussed above. This data or information is acquired in a unique manner for use in the invention and the method for acquiring the information and its conversion to a map database that can be accessed by the vehicle system is part of this invention. The acquisition of the data for the maps will now be discussed. It must be appreciated though that the method for acquiring the data and forming the digital map can also be used in other inventions. 
     With reference to  FIGS. 16A, 16B, 17 and 17A , a mapping vehicle  200  is used and obtains its location from GPS satellites and its corrections from the local differential stations. Such a system is capable of providing the 2 cm accuracy desired for the map database. Typically, at least two GPS receivers  226  are mounted on the mapping vehicle  200 . Each GPS receiver  226  is contained within or arranged in connection with a respective data acquisition module  202 , which data acquisition modules  202  also contain a GPS antenna  204 , an accurate inertial measurement unit (IMU)  206 , a forward-looking video camera  208 , a downward and outward looking linear array camera  210  and a scanning laser radar  212 . The relative position of these components in  FIG. 17  is not intended to limit the invention. 
     A processor including a printed circuit board  224  is coupled to the GPS receivers  226 , the IMUs  206 , the video cameras  208 , the linear cameras  210  and the scanning laser radars  212 (see  FIG. 17A ). The processor  224  receives information regarding the position of the vehicle from the GPS receivers  226 , and optionally the IMUs  206 , and the information about the road from both linear cameras  210  or from both laser radars  212 , or from all of the linear cameras  210  and laser radars  212 , and forms the road map database. Information about the road can also come from one or both of the video cameras  208  and be incorporated into the map database. 
     An alternate preferred approach uses a series of 4-6 cameras looking forward, backward, and one, two or more on each side. In this configuration, the linear cameras and scanning laser radars can be omitted and all relevant information comes from the IMU and GPS with differential corrections. The scene may be illuminated with general illumination which can be in the IR part of the spectrum. In some cases, laser pointers or another form of structured light is also used primarily to permit later analysis of various elevation changes, especially at the side of the roadway. The resulting data is analyzed using photogramity techniques to obtain a fully digital map. 
     The map database can be of any desired structure or architecture. Preferred examples of the database structure are of the type discussed in U.S. Pat. No. 6,144,338 (Davies) and U.S. Pat. No. 6,247,019 (Davies). 
     The data acquisition modules  202  are essentially identical and each can mount to the vehicle roof on an extension assembly  214  which extends forward of the front bumper. Extension assembly  214  can include a mounting bracket  216  from the roof of the vehicle  200  forward to each data acquisition module  210 , a mounting bracket  218  extending from the front bumper upward to each data acquisition module  202  and a cross mounting bracket  220  extending between the data acquisition modules  202  for support. Since all of the data acquisition equipment is co-located, its precise location is accurately determined by the IMU, the mounting location on the vehicle and the differential GPS system. 
     The forward-looking video cameras  208  can provide views of the road as shown in  FIG. 18 . These cameras  208  permit the database team to observe the general environment of the road and to highlight any anomalies. They also permit the reading of traffic signs and other informational displays all of which can be incorporated into the database. The cameras  208  can be ordinary color video cameras, high-speed video cameras, wide angle or telescopic cameras, black and white video cameras, infrared cameras, etc. or combinations thereof. In some cases, special filters are used to accentuate certain features. For example, it has been found that lane markers frequently are more readily observable at particular frequencies, such as infrared. In such cases, filters can be used in front of the camera lens or elsewhere in the optical path to block unwanted frequencies and pass desirable frequencies. Polarizing lenses have also been found to be useful in many cases. Natural illumination can be used in the mapping process, but for some particular cases, particularly in tunnels, artificial illumination can also be used in the form of a floodlight or spotlight that can be at any appropriate frequency of the ultraviolet, visual and infrared portions of the electromagnetic spectrum or across many frequencies. Laser scanners can also be used for some particular cases when it is desirable to illuminate some part of the scene with a bright spot. In some cases, a scanning laser rangemeter can be used in conjunction with the forward-looking cameras  204  to determine the distance to particular objects in the camera view. Other geometries of the mapping vehicle are not excluded from this general description of one simplified arrangement. 
     The video camera system can be used by itself with appropriate software as is currently being done by Lamda Tech International Inc. of Waukesha, Wis., to obtain the location of salient features of a road. However, such a method to obtain accurate maps is highly labor intensive and therefore expensive. The cameras and associated equipment in the present invention are therefore primarily used to supplement the linear camera and laser radar data acquisition systems to be described now. This however is one approach with a preferred alternate approach using four, six or more cameras as described above. 
     In this approach, the mapping vehicle data acquisition modules will typically contain both a linear camera and a scanning laser radar, however, for some applications one or the other may be omitted. 
     The linear camera  210  is a device that typically contains a linear CCD, CMOS or other light sensitive array of, for example, four thousand pixels. An appropriate lens provides a field of view to this camera that typically extends from approximately the center of the vehicle out to the horizon. This camera records a one-dimensional picture covering the entire road starting with approximately the center of the lane and extending out to the horizon. This linear array camera  210  therefore covers slightly more than 90 degrees. Typically, this camera operates using natural illumination and produces effectively a continuous picture of the road since it obtains a linear picture, or column of pixels, for typically every one-inch of motion of the vehicle. Thus, a complete two-dimensional panoramic view of the road traveled by the mapping vehicle is obtained. Since there are two such linear camera units, a 180 degree view is obtained. This camera will typically record in full color thus permitting the map database team to have a complete view of the road looking perpendicular from the vehicle. The view is recorded in a substantially vertical plane. This camera will not be able to read text on traffic signs, thus the need for the forward-looking cameras  208 . Automated software can be used with the images obtained from these cameras  208 ,  210  to locate the edge of the road, lane markers, the character of land around and including the road and all areas that an errant vehicle may encounter. The full color view allows the characterization of the land to be accomplished automatically with minimal human involvement. 
     The scanning laser radar  212  is typically designed to cover a 90 degree or less scan thus permitting a rotating mirror to acquire at least four such scans per revolution. The scanning laser radar  212  can be coordinated or synchronized with the linear camera  210  so that each covers the same field of view with the exception that the camera  210  typically will cover more than 90 degrees. Scanning laser radar  212  can be designed to cover more or less than 90 degrees as desired for a particular installation. The scanning laser radar  212  can operate in any appropriate frequency from above ultraviolet to the terahertz. Typically, it will operate in the eye-safe portion of the infrared spectrum for safety reasons. The scanning laser radar  212  can operate either as a pulse-modulated or a tone-modulated laser as is known in the art. If operating in the tone-modulated regime, the laser light will be typically modulated with three or more frequencies in order to eliminate distance ambiguities. Noise or code modulated radar can also be used. 
     For each scan, the laser radar  212  provides the distance from the scanner to the ground for up to several thousand points in a vertical plane extending from approximately the center of the lane out to near the horizon. This device therefore provides precise distances and elevations to all parts of the road and its environment. The precise location of signs that were observed with the forward-looking cameras  204 , for example, can now be easily and automatically retrieved. The scanning laser radar therefore provides the highest level of mapping automation. 
     Scanning laser radars have been used extensively for mapping purposes from airplanes and in particular from helicopters where they have been used to map portions of railway lines in the US. Use of the scanning laser radar system for mapping roadways where the radar is mounted onto a vehicle that is driving the road is believed to be novel to the current assignee. 
     Ideally, all of the above-described systems are present on the mapping vehicle. Although there is considerable redundancy between the linear camera and the scanning laser radar, the laser radar operates at one optical frequency and therefore does not permit the automatic characterization of the roadway and its environment. 
     As with the forward-looking cameras, it is frequently desirable to use filters and polarizing lenses for both the scanning laser radar and the linear camera. In particular, reflections from the sun can degrade the laser radar system unless appropriate filters are used to block all frequencies except frequency chosen for the laser radar. 
     Laser radars are frequently also referred to as ladars and lidars. All such devices that permit ranging to be accomplished from a scanning system, including radar, are considered equivalent for the purposes of this invention. 
     4. Precise Positioning 
     Another important aid as part of some of the inventions disclosed herein is to provide markers along the side(s) of roadways which can be either visual, passive or active transponders, reflectors, or a variety of other technologies including objects that are indigenous to or near the roadway, which have the property that as a vehicle passes the marker it can determine the identity of the marker and from a database it can determine the exact location of the marker. The term “marker” is meant in the most general sense. The signature determined by a continuous scan of the environment, for example, would be a marker if it is relatively invariant over time such as, for example, buildings in a city. Basically, there is a lot of invariant information in the environment surrounding a vehicle as it travels down a road toward its destination. From time to time, a view of this invariant landscape or information may be obstructed but it is unlikely that all of it will be during the travel of a mile, for example. Thus, a vehicle should be able to match the signature sensed with the expected one in the map database and thereby obtain a precise location fix. This signature can be obtained through the use of radar or laser radar technologies as reported elsewhere herein. If laser radar is used, then an IR frequency can be chosen in the eyesafe part of the spectrum. This will permit higher transmitted power to be used which, especially when used with range gating, will permit the penetration of a substantial distance through fog, rain or snow. See in particular Section 5 below and for example, Wang Yanli, Chen Zhe, “Scene matching navigation based on multisensor image fusion” SPIE Vol. 5286 p. 788-793, 2003 and more recently “Backing up GNSS with laser radar &amp; INS, RAIM in the city, antenna phase wind-up”, Inside GNDD July/August 2007. 
     For the case of specific markers placed on the infrastructure, if three or more of such markers are placed along a side of the roadway, a passing vehicle can determine its exact location by triangulation. Note that even with two such markers using radar with distance measuring capability, the precise position of a vehicle can be determined as discussed below in reference to the Precise Positioning System. In fact, if the vehicle is only able to observe a single radar or lidar reflector and take many readings as the reflector is passed, it can determine quite accurately its position based on the minimum distance reading that is obtained during the vehicle&#39;s motion past the reflector. Although it may be impractical to initially place such markers along all roadways, it would be reasonable to place them in particularly congested areas or places where it is known that a view of one or more of the GPS satellites is blocked. A variation of this concept will be discussed below. 
     Although initially it is preferred to use the GPS navigational satellites as the base technology, the invention is not limited thereby and contemplates using all methods by which the location of the vehicle can be accurately determined relative to the earth surface. The location of the roadway boundaries and the location of other vehicles relative to the earth surface are also to be determined and all relevant information used in a control system to substantially reduce and eventually eliminate vehicle accidents. Only time and continued system development will determine the mix of technologies that provide the most cost effective solution. All forms of information and methods of communication to and between vehicles are contemplated including direct communication with stationary and moving satellites, communication with fixed earth-based stations using infrared, optical, terahertz, radar, radio and other segments of the electromagnetic spectrum, direct or indirect communication with the internet and inter-vehicle communication. Some additional examples follow: 
     A pseudo-GPS can be delivered from cell phone stations, in place of or in addition to satellites. In fact, the precise location of a cell phone tower need not initially be known. If it monitors the GPS satellites over a sufficiently long time period, the location can be determined as the calculated location statistically converges to the exact location. Thus, every cell phone tower could become an accurate DGPS base station for very little cost. DGPS corrections can be communicated to a vehicle via FM radio via a sub-carrier frequency for example. An infrared or radar transmitter along the highway can transmit road boundary location information. A CD-ROM, DVD or other portable mass storage can be used at the beginning of a controlled highway to provide road boundary information to the vehicle. Finally, it is contemplated that eventually a satellite will broadcast periodically, perhaps every five minutes, a table of dates covering the entire CONUS that provides the latest update date of each map segment. If a particular vehicle does not have the latest information for a particular region where it is operating, it will be able to use its cell phone or other communication system to retrieve such road maps perhaps through the Internet or from an adjacent vehicle. Emergency information would also be handled in a similar manner so that if a tree fell across the highway, for example, all nearby vehicles would be notified. 
     To implement map updating, a signal may be directed by the infrared or radar transmitter to the area covered by a segment of the map relating to the latest update information for that segment in a form receivable by a transmitter on vehicles passing through the area. A processor on the vehicle receives the signals, analyzes it and determines whether its map includes the latest updated map information for the segment in which the vehicle is presently located. If not, an update for the vehicle&#39;s map information is downloaded via the transmitter. This embodiment is particularly advantageous when the transmitter is arranged before a section of road and thus provides vehicles entering the road and in range of the transmitter with the map data they will subsequently need. 
     The transmitter which transmits information to the vehicle, whether map information or other information, may be movable and thus would be particularly useful for roads undergoing construction, subject to closure or blockage in view of construction or other factors, or for which map data is not yet available. In this case, the movable, temporary transmitter would be able to provide map data for the affected section of road to vehicles in range of the transmitter. As the transmitter is moved along the roadway, the information transmitted can be changed. 
     One of the possible problems with the RtZF® system described herein is operation in areas of large cities such as lower Manhattan. In such locations, unless there are a plurality of local pseudolites or precise position location system installations or the environment signature system is invoked such as with adaptive associative memories as described above, the signals from the GPS satellites can be significantly blocked. Also, there is frequently a severe multipath problem in cities. A solution is to use the LORAN system as a backup for such locations. The accuracy of LORAN can be comparable to DGPS. Use of multiple roadway-located Precise Positioning Systems would be a better solution or a complementary solution. Additionally, some location improvement can result from application of the SnapTrack system as described in U.S. Pat. No. 5,874,914 and other patents to Krasner of SnapTrack. 
     The use of geo-synchronous satellites as a substitute for earth bound base stations in a DGPS system, with carrier phase enhancements for sub-meter accuracies, is also a likely improvement to the RtZF® system that can have a significant effect in urban areas. 
     It is expected, especially initially, that there will be many holes in the DGPS or GPS and their various implementations that will leave the vehicle without an accurate means of determining its location. The inertial navigation system described above will help in filling these holes but its accuracy is limited to a time period significantly less than about an hour and a distance of less than about 50 miles before it needs correcting. That may not be sufficient to cover the period between DGPS availability. It is therefore contemplated that the RtZF® system will also make use of low cost systems located along the roadways that permit a vehicle to accurately determine its location. 
     Such a position-determination assistance system would include a plurality of transmitters placed on or alongside a road, with signals from the transmitters being directed to an area in the path of a traveling vehicle to enable the vehicle to determine its position using the transmitted signals and information about the position of the transmitters. Positional information about the transmitters either being previously provided to the vehicle&#39;s processor, e.g., from a map database, or along with the transmission. The transmitters may be a group of a linked MIR, IR or RF transmitters which direct signals to a common area through which vehicles pass. Alternatively, the transmitters may be a group of a plurality of RFID devices, in which case, one or more interrogators are arranged on the vehicle to cause the RFID devices to direct signals in response to an interrogation signal from the interrogator. 
     One example of such a system would be to use a group of three Micropower Impulse Radar (MIR) units such as developed by Lawrence Livermore Laboratory. 
     A MIR operates on very low power and periodically transmits a very short spread spectrum radar pulse. The estimated cost of a MIR is less than $10 even in small quantities. If three such MIR transmitters,  151 ,  152  and  153 , as shown in  FIG. 11 , are placed along the highway and triggered simultaneously or with a known delay, and if a vehicle has an appropriate receiver system, the time of arrival of the pulses can be determined and thus the location of the vehicle relative to the transmitters determined. The exact location of the point where all three pulses arrive simultaneously would be the point that is equidistant from the three transmitters  151 ,  152 ,  153  and would be located on the map information. Only three devices are required since only two dimensions need to be determined and it is assumed that the vehicle in on the road and thus the vertical position is known, otherwise four MIRs would be required. Thus, it would not even be necessary to have the signals contain identification information since the vehicle would not be so far off in its position determination system to confuse different locations. By this method, the vehicle would know exactly where it was whenever it approached and passed such a triple-MIR installation. The MIR triad PPS or equivalent could also have a GPS receiver and thereby determine its exact location over time as described above for cell phone towers. After the location has been determined, the GPS receiver can be removed. In this case, the MIR triad PPS or equivalent could be placed at will and they could transmit their exact location to the passing vehicles. An alternate method would be to leave the GPS receiver with the PPS time of arrival of the GPS data from each satellite so that the passing vehicles that do not go sufficiently close to the PPS can still get an exact location fix. A similar system using RFID tags is discussed below. 
     Several such readings and position determinations can be made with one approach to the MIR installation, the vehicle need not wait until they all arrive simultaneously. Also the system can be designed so that the signals never arrive at the same time and still provide the same accuracy as long as there is a sufficiently accurate clock on board the vehicle. One way at looking at  FIG. 11  is that transmitters  151  and  152  fix the lateral position of the vehicle while transmitters  151  and  153  fix the location of the vehicle longitudinally. The three transmitters  151 , 152 , 153  need not be along the edges on one lane but could span multiple lanes and they need not be at ground level but could be placed sufficiently in the air so that passing trucks would not block the path of the radiation from an automobile. Particularly in congested areas, it might be desirable to code the pulses and to provide more than three transmitters to further protect against signal blockage or multipath. 
     The power requirements for the MIR transmitters are sufficiently low that a simple photoelectric cell array can provide sufficient power for most if not all CONUS locations. With this exact location information, the vehicle can become its own DGPS station and can determine the corrections necessary for the GPS. It can also determine the integer ambiguity problem and thereby know the exact number of wave lengths between the vehicle and the satellites or between the vehicle and the MIR or similar station. These calculations can be done on vehicle if there is a connection to a network, for example. This would be particularly efficient as the network, once it had made the calculations for one vehicle, would have a good idea of the result for another nearby vehicle and for other vehicles passing the same spot at a different time. This network can be an ad-hoc or mesh network or the internet using WiMAX, for example. Alternately, the information can be broadcast from the vehicle. 
     MIR is one of several technologies that can be used to provide precise location determination. Others include the use of an RFID tag that is designed in cooperation with its interrogator to provide a distance to the tag measurement. Such as RFID can be either an active device with an internal battery or solar charger or a passive device obtaining its power from an RF interrogation signal to charge a capacitor or a SAW-based tag operating without power. An alternate and preferred system uses radar or other reflectors where the time of flight can be measured, as disclosed elsewhere herein. 
     Once a vehicle passes a Precise Positioning Station (PPS) such as the MIR triad described above, the vehicle can communicate this information to surrounding vehicles. If the separation distance between two communicating vehicles can also be determined by the time-of-flight or equivalent method, then the vehicle that has just passed the triad can, in effect, become a satellite equivalent or moving pseudolite. That is, the vehicle sends (such as by reflection so as not to introduce a time delay) its GPS data from the satellite and the receiving vehicle then gets the same message from two sources and the time difference is the time of flight. Finally, if many vehicles are communicating their positions to many other vehicles along with an accuracy of position assessment, each vehicle can use this information along with the calculated separation distances to improve the accuracy of its position determination. In this manner, as the number of such vehicles increases, the accuracy of the entire system increases until an extremely accurate positioning system for all vehicles results. Such a system, since it combines many sources of position information, is tolerant of the failure of any one or even several such sources. Thus, the RtZF® system becomes analogous to the Internet in that it cannot be shut down and the goal of perfection is approached. Some of the problems associated with this concept will be discussed below. 
       FIG. 11  shows the implementation of the invention using the Precise Positioning System (PPS)  151 ,  152 ,  153 , in which a pair of vehicles  18 ,  26  are traveling on a roadway each in a defined corridor delineated by lines  14  and each is equipped with a system in accordance with the invention and in particular, each is equipped with PPS receivers. Four versions of the PPS system will now be described. This invention is not limited to these examples but they will serve to illustrate the principals involved. 
     Vehicle  18  contains two receivers  160 , 161  for the micropower impulse radar (MIR) implementation of the invention. MIR or ultrawideband (UWB) transmitter devices are placed at locations  151 ,  152  and  153  respectively. They are linked together with a control wire, not shown, or by a wireless connection such that each device transmits a short radar or RF pulse at a precise timing relative to the others. These pulses can be sent simultaneously or at a precise known delay. Vehicle  18  knows from its map database the existence and location of the three MIR transmitters. The transmitters  151 , 152  and  153  can either transmit a coded pulse or non-coded pulse. In the case of the coded pulse, the vehicle PPS system will be able to verify that the three transmitters  151 ,  152 ,  153  are in fact the ones that appear on the map database. Since the vehicle will know reasonably accurately its location and it is unlikely that other PPS transmitters will be nearby or within range, the coded pulse may not be necessary. Two receivers  160  and  161  are illustrated on vehicle  18 . For the MIR implementation, only a single receiver is necessary since the position of the vehicle will be uniquely determined by the time of arrival of the three MIR pulses. A second receiver can be used for redundancy and also to permit the vehicle to determine the angular position of the MIR transmitters as a further check on the system accuracy. This can be done since the relative time of arrival of a pulse from one of the transmitters  151 ,  152 ,  153  can be used to determine the distance to each transmitter and by geometry its angular position relative to the vehicle  18 . If the pulses are coded, then the direction to the MIR transmitters  151 ,  152 ,  153  will also be determinable. 
     The micropower impulse radar units require battery power or another power mechanism to operate. Since they may be joined together with a wire in order to positively control the timing of the three pulses, a single battery can be used to power all three units. This battery can also be coupled with a solar panel to permit maintenance free operation of the system. Since the MIR transmitters use very small amounts of power, they can operate for many years on a single battery. 
     Although the MIR systems are relatively inexpensive, on the order of ten dollars each, the installation cost of the system will be significantly higher than the RFID and radar reflector solutions discussed next. The MIR system is also significantly more complex than the RFID system; however, its accuracy can be checked by each vehicle that uses the system. Tying the MIR system to a GPS receiver and using the accurate clock on the GPS satellites as the trigger for the sending of the radar pulses can add additional advantages and complexity. This will permit vehicles passing by to additionally accurately set their clocks to be in synchronization with the GPS clocks. Since the MIR system will know its precise location, all errors in the GPS signals can be automatically corrected and in that case, the MIR system becomes a differential GPS base station. For most implementations, this added complexity is not necessary since the vehicle themselves will be receiving GPS signals and they will also know precisely their location from the triad of MIR transmitters  151 ,  152 ,  153 . 
     A considerably simpler alternate approach to the MIR system described above utilizes reflective RFID tags. These tags, when interrogated by an interrogator type of receiver  160 ,  161 , reflect or retransmit after a known delay a modified RF signal with the modification being the identification of the tag. Such tags are described in many patents and books on RFID technology and can be produced for substantially less than one dollar each. The implementation of the RFID system would involve the accurate placement of these tags on known objects on or in connection with infrastructure. These objects could be spots on the highway, posts, signs, sides of buildings, poles, in highway reflectors or structures that are dedicated specifically for this purpose. In fact, any structure that is rigid and unlikely to change position can be used for mounting RFID tags. In downtown Manhattan, building sides, street lights, stoplights, or other existing structures are ideal locations for such tags. A vehicle  18  approaching a triad of such RFID tags represented by  151 ,  152 ,  153  would transmit an interrogation pulse from interrogator  160  and/or  161 . The pulse would reflect off of, or be retransmitted by, each tag within range and the signal would be received by the same interrogator(s)  160 ,  161  or other devices on the vehicle. Once again, a single interrogator is sufficient. It is important to note that the range to RFID tags is severely limited unless a source of power is provided. It is very difficult to provide enough power from RF radiation from the interrogator for distances much greater than a few feet. For longer distances, a power source should be provided which can be a battery, connection to a power line, solar power, energy harvested from the environment via vibration, for example, unless the RFID is based on SAW technology. For SAW technology, reading ranges may be somewhat extended. Greater distances can be achieved using reflectors or reflecting antennas. 
     Electronic circuitry, not shown, associated with the interrogator  160  and/or  161  would determine the precise distance from the vehicle to the RFID tag  151 ,  152 ,  153  based on the round trip time of flight and any retransmission delay in the RFID. This will provide the precise distance to the three RFID tags  151 ,  152 ,  153 . Once again, a second interrogator  161  can also be used, in which case, it could be a receiver only and would provide redundancy information to the main interrogator  160  and also provide a second measure of the distance to each RFID tag. Based on the displacement of the two receivers  160 ,  161 , the angular location of each RFID tag relative into the vehicle can be determined providing further redundant information as to the position of the vehicle relative to the tags. 
     Using the PPS system, a vehicle can precisely determine its location within about two centimeters relative to the MIR, RFID tags or radar and reflectors and since the precise location of these devices has previously been recorded on the map database, the vehicle will be able to determine its precise location on the surface of the earth. With this information, the vehicle will thereafter be able to use the carrier wave phase to maintain its precise knowledge of its location, as discussed above, until the locks on the satellites are lost. This prediction of phase relies on the vehicle system being able to predict the phase of the signal from a given satellite that is reaching a fixed location such as the location that the vehicle was in when it was able to determine its position precisely. This requires an accurate knowledge on the satellite orbits and an accurate clock. Given this information, the vehicle system should be able to determine the phase of a satellite signal at the fixed location and at its new location and, by comparing the phase from such a calculation from each satellite, it should be able to precisely determine its position relative to the fixed location. Errors due to changes in the ionosphere and the vehicle clock accuracy will gradually degrade the accuracy of these calculations. The vehicle  18  can broadcast this information to vehicle  26 , for example, permitting a vehicle that has not passed through the PPS triad to also greatly improve the accuracy with which it knows its position. Each vehicle that has recently passed through a PPS triad now becomes a differential GPS station for as long as the satellite locks are maintained assuming a perfect clock on-board the vehicle and a stable ionosphere. Therefore, through inter-vehicle communications, all vehicles in the vicinity can also significantly improve their knowledge of their position accuracy resulting in a system which is extremely redundant and therefore highly reliable and consistent with the “Road to Zero Fatalities”™ process. Once this system is operational, it is expected that the U.S. government and other governments will launch additional GPS type satellites, each with more civilian readable frequencies, or other similar satellite systems, further strengthening the system and adding further redundancy eventually resulting in a highly interconnected system that approaches 100% reliability and, like the Internet, cannot be shut down. 
     As the system evolves, the problems associated with urban canyons, tunnels, and other obstructions to satellite view will be solved by the placement of large numbers of PPS stations, or other devices providing similar location information. 
       FIG. 19  shows a variety of roads and vehicles operating on those roads that are in communication with a vehicle that is passing through a Precise Positioning Station (PPS). The communication system used is based on noise modulated spread spectrum technologies such as described in papers by Lukin et al. listed in the parent &#39;445 application. Determination of the presence of any of the PPS devices enables the vehicle to know its approximate location which is sufficient for navigation purposes when the GPS signals are blocked, unreliable or otherwise not useable or the vehicle does not have a GPS receiver. 
       FIG. 20  shows a schematic of the operation of a communication and/or information transmission system and method in accordance with the invention. Transmitters are provided, for example at fixed locations and/or in vehicles or other moving objects, and data about each transmitter, such as its location and an identification marker, is generated at  240 . The location of the transmitter is preferably its GPS coordinates as determined, for example, by a GPS-based position determining system (although other position determining systems can alternatively or additionally be used). The data may include, when the transmitter is a moving vehicle, the velocity, speed, the direction of travel, the estimated travel path and the destination of the vehicle. The data is encoded at  242  using coding techniques such as those described above, e.g., phase modulation of distance or time between code transmissions, phase or amplitude modulation of the code sequences themselves, changes of the polarity of the entire code sequence or the individual code segments, or bandwidth modulation of the code sequence. The coded data is transmitted at  244  using, e.g., noise or pseudo-noise radar. 
     Instead of data about each transmitter being generated at  240 , general data for transmission could also be generated such as road condition information or traffic information. 
     A vehicle  246  includes an antenna  248  coupled to a control module, control unit, processor or computer  250 . The antenna, which can be an imager,  248  receives transmissions (waves or wireless signals) including transmissions  252  when in range of the transmitters. The processor  250  analyzes the transmissions  252 . Such analysis may include a determination as to whether any transmissions are from transmitters within a pre-determined area relative to the vehicle, whether any transmissions are from transmitters situated within a pre-determined distance from the vehicle, whether any transmissions are from transmitters traveling in a direction toward the vehicle&#39;s current position, whether any transmissions are from transmitters traveling in a direction toward the vehicle&#39;s projected position based on its current position and velocity, the angle between the transmitter and the vehicle, and any combinations of such determinations. In general, the initial analysis may be any position-based filtering, location-based filtering, and/or motion-based filtering. Other analyses could be whether any transmissions are from particular transmitters which might be dedicated to the transmission of road conditions data, traffic data, map data and the like. Once the processor  250  ascertains a particular transmission from a transmitter of interest (for operation of the vehicle, or for any other pre-determined purpose), it extracts the information coded in the transmission, but preferably does not extract information coded in transmission from transmitters which are not of interest, e.g., those from transmitters situated at a location outside of the pre-determined area. It knows the code because the code is provided by the transmission, i.e., the initial part of the transmission  252   a  contains data on the location of the transmitter and the code is based on the location of the transmitter. As such, once the initial part of the transmission  252   a  is received and the location of the transmitter extracted, the code for the remainder of the transmission  252   b  can be obtained. 
     In this manner, the extraction of information from radio frequency wave transmission may be limited based on a threshold determination (a filter of sorts) as to whether the transmission is of potential interest, e.g., to the operation of the vehicle based on its position, location and/or motion. To enable this threshold determination from the analysis of the waves or filtering of information, the initial part of the transmission  252   a  can be provided with positional or location information about the transmitter and information necessitated by the information transferring arrangement (communication protocol data) and the remainder of the transmission  252   b  provided with additional information of potential interest for operation of the vehicle. The information contained in initial part of each transmission (or set of waves) is extracted to determine whether the information in the final part of the transmission is of interest. If not, the information in the final part of the transmission is not extracted. This reduces processing time and avoids the unnecessary extraction of mostly if not totally irrelevant information. An information filter is therefore provided. 
     Generating the transmission based on a code derived from the position of the transmitter, and thus the vehicle or infrastructure in which or to which it is fixed, provides significant advantages as discussed above. The code required for spread spectrum, UWB or other communication systems is thus determined according to the position of the transmitter, and can be accomplished in several different ways, some of which are disclosed elsewhere herein. However, use of coded transmissions is not required in all embodiments of the information transferring method and arrangement. 
     Further, the antenna  248  serves as a transmitter for transmitting signals generated by the processor  250 . The processor  248  is constructed or programmed to generate transmissions or noise signals based on its location, determined by a position determining device  254  in any known manner including those disclosed herein, and encode information about the vehicle in the signals. The information may be an identification marker, the type of vehicle, its direction, its velocity or speed, its proposed course, its occupancy, etc. The processor  248  can encode the information in the signals in a variety of methods as disclosed above in the same manner that the data about the transmitter is encoded. Thus, the processor  248  not only interprets the signals and extracts information, it also is designed to generate appropriate noise or otherwise coded signals which are then sent from the antenna  248 . 
     5. Radar and Laser Radar Detection and Identification of Objects External to the Vehicle 
     5.1 Sensing of non-RtZF® equipped objects 
     Vehicles with the RtZF® system in accordance with the invention ideally should also be able to detect those vehicles that do not have the system as well as pedestrians, animals, bicyclists, and other hazards that may cross the path of the equipped vehicle. 
     Systems based on radar have suffered from the problem of being able to sufficiently resolve the images which are returned to be able to identify the other vehicles, bridges, etc. except when they are close to the host vehicle. One method used for adaptive cruise control systems is to ignore everything that is not moving. This, of course, leads to accidents if this were used with the instant invention. The problem stems from the resolution achievable with radar unless the antenna is made very large or the object is close. Since this is impractical for use with automobiles, only minimal collision avoidance can be obtained using radar. 
     Optical systems can provide the proper resolution but may require illumination with a bright light or laser. If the laser is in the optical range, there is a danger of causing eye damage to pedestrians or vehicle operators. At a minimum, it will be distracting and annoying to other vehicle operators. A laser operating in the infrared part of the electromagnetic spectrum avoids the eye danger problem, provided the frequency is sufficiently far from the visible, and, since it will not be seen, it will not be annoying. If the IR light is sufficiently intense to provide effective illumination for the host vehicle, it might be a source of blinding light for the system of another vehicle. Therefore a method of synchronization may be required. This could take the form of an Ethernet protocol, for example, where when one vehicle detects a transmission from another then it backs off and transmits at a random time later. The receiving electronics would then only be active when the return signal is expected. Transmission can also be synchronized based on the GPS time and a scheme whereby two nearby vehicles would transmit at different times. Since the transmission duration can be very short, since the intensity of the IR can be high if it is in the eye-safe range, many adjacent vehicles can transmit each fraction of a second without interfering with each other, 
     Another problem arises when multiple vehicles are present that transmit infrared at the same time if there is a desire to obtain distance information from the scene. In this case, each vehicle needs to be able to recognize its transmission and not be fooled by transmissions from another vehicle. This can be accomplished, as discussed above, through the modulation scheme. Several such schemes would suffice with a pseudo-noise or code modulation as a preferred method for the present invention. This can also be accomplished if each vehicle accurately knows its position and controls its time of transmission according to an algorithm that time multiplexes transmissions based on the geographical location of the vehicle. Thus, if multiple vehicles are sensed in a given geographical area, they each can control their transmissions based on a common algorithm that uses the GPS coordinates of the vehicle to set the time slot for transmission so as to minimize interference between transmissions from different vehicles. Other multiplexing methods can also be used such as FDMA, CDMA or TDMA, any of which can be based on the geographical location of the vehicles. 
     Infrared and terahertz also have sufficient resolution so that pattern recognition technologies can be employed to recognize various objects, such as vehicles, in the reflected image as discussed above. infrared has another advantage from the object recognition perspective. All objects radiate and reflect infrared. The hot engine or tires of a moving vehicle in particular are recognizable signals. Thus, if the area around a vehicle is observed with both passive and active infrared, more information can be obtained than from radar, for example. Infrared is less attenuated by fog than optical frequencies, although it is not as good as radar. Infrared is also attenuated by snow but at the proper frequencies it has about five times the range of human sight. Terahertz under some situations has an effective range of as much as several hundred times that of human sight. Note, as with radar, Infrared and terahertz can be modulated with noise, pseudonoise, or other distinctive signal to permit the separation of various reflected signals from different transmitting vehicles. 
     5.2 Laser and Terahertz Radar scanning system 
     Referring to  FIG. 25 , a digital map  116  can be provided and when the vehicle&#39;s position is determined  118 , e.g., by a GPS-based system, the digital map can be used to define the field  122  that the laser or terahertz radar scanner  102  will interrogate. 
     Note, when the term scanner is used herein, it is not meant to imply that the beam is so narrow as to require a back and forth motion (a scan) in order to completely illuminate an object of interest. To the contrary, inventions herein are not limited to a particular beam diameter other than that required for eye safety. Also a scanner may be limited to an angular motion that just covers a vehicle located 100 meters, for example, from the transmitting vehicle, which may involve no angular motion of the scanner at all, or to an angular motion that covers 90 or more degrees of the space surrounding the transmitting vehicle. Through the use of high-powered lasers and appropriate optics, an eye safe laser beam can be created that is 5 cm in diameter, for example, with a divergence angle less than one degree. Such an infrared spotlight requires very little angular motion to illuminate a vehicle at 100 meters, for example. 
     Generally herein, when laser radar, or lidar, is used it will also mean a system based on terahertz where appropriate. The laser radar or lidar scanner will return information as to distance to an object in the scanned field, e.g., laser beam reflections will be indicative of presence of object in path of laser beam  104  and from these reflections, information such as the distance between the vehicle and the object can be obtained. This will cover all objects that are on or adjacent to the highway. The laser pulse can be a pixel that is two centimeters or 1 meter in diameter at 50 meters, for example and that pixel diameter can be controlled by the appropriate optical system that can include adaptive optics and liquid lenses (such as described in “Liquid lens promises cheap gadget optics”, NewScientist.com news service, Mar. 8, 2004). 
     The scanner should scan the entire road at such a speed that motion of the car can be considered insignificant. Alternately, a separate aiming system that operates at a much lower speed, but at a speed to permit compensation for the car angle changes, may be provided. Such an aiming system is also necessary due to the fact that the road curves up and down. Therefore two scanning methods, one a slow, but for large angle motion and the other fast but for small angles may be required. The large angular system requires a motor drive while the small angular system can be accomplished through the use of an acoustic wave system, such as Lithium Niobate (LiNbO 3 ), which is used to drive a crystal which has a large refractive index such as Tellurium dioxide. Other acoustic optical systems can also be used as scanners. 
     For these systems, frequently some means is needed to stabilize the image and to isolate it from vehicle vibrations. Several such stabilization systems have been used in the past and would be applicable here including a gyroscopic system that basically isolates the imaging system from such vibrations and keeps it properly pointed, a piezoelectric system that performs similarly, or the process can be accomplished in software where the image is collected regardless of the vibration but where the image covers a wider field of view then is necessary and software is used to select the region of interest. 
     Alternately, two systems can be used, a radar system for interrogating large areas and a laser radar for imaging smaller areas. Either or both systems can be range gated and noise or pseudonoise modulated. 
     The laser radar scanner can be set up in conjunction with a range gate  106  so that once it finds an object, the range can be narrowed so that only that object and other objects at the same range, 65 to 75 feet for example, are allowed to pass to the receiver. In this way, an image of a vehicle can be separated from the rest of the scene for identification by pattern recognition software  108 . Once the image of the particular object has been captured , the range gate is broadened, to about 20 to 500 feet for example, and the process repeated for another object. In this manner, all objects in the field of interest to the vehicle can be separated and individually imaged and identified. Alternately, a scheme based on velocity can be used to separate a part of one object from the background or from other objects. The field of interest, of course, is the field where all objects with which the vehicle can potentially collide reside. Particular known and mapped features on the highway can be used as aids to the scanning system so that the pitch and perhaps roll angles of the vehicle can be taken into account. 
     Once the identity of the object is known, the potential for a collision between the vehicle and that object and/or consequences of a potential collision with that object are assessed, e.g., by a control module, control unit or processor  112 . If collision is deemed likely, countermeasures are effected  114 , e.g., activation of a driver alert system and/or activation of a vehicle control system to alter the travel of the vehicle (as discussed elsewhere herein). 
     Range gates can be achieved as high speed shutters by a number of devices such as liquid crystals, garnet films, Kerr and Pockel cells or as preferred herein as described in patents and patent applications of 3DV Systems Ltd., Yokneam, Israel including U.S. Pat. Nos. 6,327,073, 6,483,094, US2002/0185590, WO98/39790, WO97/01111, WO97/01112 and WO97/01113. 
     Prior to the time that all vehicles are equipped with the RtZF® system described above, roadways will consist of a mix of vehicles. In this period, it will not be possible to totally eliminate accidents. It will be possible to minimize the probability of having an accident however, if a laser radar system similar to that described in U.S. Pat. No. 5,529,138 with some significant modifications is used, or those described more recently in various patents and patent applications of Ford Global Technologies such as U.S. Pat. Nos. 6,690,017 and 6,730,913, and U.S. Pat. Appl. Publ. Nos. 2003/0034462, 2003/0155513 and 2003/0036881. It is correctly perceived by Shaw that the dimensions of a radar beam are too large to permit distinguishing various objects which may be on the roadway in the path of the instant vehicle. Laser radar provides the necessary resolution that is not provided by radar. Laser radar as used in the present invention however would acquire significantly more data than anticipated by Shaw. Sufficient data in fact would be attained to permit the acquisition of a three-dimensional image of all objects in the field of view. The X and Y dimensions of such objects would, of course, be determined knowing the angular orientation of the laser radar beam. The longitudinal or Z dimension can be obtained by such methods as time-of-flight of the laser beam to a particular point on the object and reflected back to the detector, by phase methods or by range gating. All such methods are described elsewhere herein and in patents listed above. 
     At least two methods are available for resolving the longitudinal dimension for each of the pixels in the image. In one method, a laser radar pulse having a pulse width of one to ten nanoseconds, for example, can be transmitted toward the area of interest and as soon as the reflection is received and the time-of-flight determined, a new pulse would be sent at a slightly different angular orientation. The laser, therefore, would be acting as a scanner covering the field of interest. A single detector could then be used, if the pixel is sufficiently small, since it would know which pixel was being illuminated. The distance to the reflection point could be determined by time-of-flight thus giving the longitudinal distance to all points in view on the object. 
     Alternately, the entire area of interest can be illuminated and an image focused on a CCD or CMOS array. By checking the time-of-flight to each pixel, one at a time, the distance to that point on the vehicle would be determined. A variation of this would be to use a garnet crystal as a pixel shutter and only a single detector. In this case, the garnet crystal would permit the illumination to pass through one pixel at a time through to a detector. A preferred method, however, for this invention is to use range gating as described elsewhere herein. 
     Other methods of associating a distance to a particular reflection point, of course, can now be performed by those skilled in the art including variations of the above ideas using a pixel mixing device (such as described in Schwarte, R. “A New Powerful Sensory Tool in Automotive Safety Systems Based on PMD-Technology”, S-TEC GmbH Proceedings of the AMAA 2000) or variations in pixel illumination and shutter open time to determine distance through comparison of range gated received reflected light. In the laser scanning cases, the total power required from the laser is significantly less than in the area illumination design. However, the ability to correctly change the direction of the laser beam in a sufficiently short period of time complicates the scanning design. The system can work approximately as follows: The entire area in front of the instant vehicle, perhaps as much as a full 180 degree arc in the horizontal plane can be scanned for objects using either radar or laser radar. Once one or more objects had been located, the scanning range can be severely limited to basically cover that particular object and some surrounding space using laser radar. Based on the range to that object, a range gate can be used to eliminate all background and perhaps interference from other objects. In this manner, a very clear picture or image of the object of interest can be obtained as well as its location and, through the use of a neural network, combination neural network or optical correlation or other pattern recognition system, the identity of the object can be ascertained as to whether it is a sign, a truck, an animal, a person, an automobile or other object. The identification of the object will permit an estimate to be made of the object&#39;s mass and thus the severity of any potential collision. 
     Once a pending collision is identified, this information can be made available to the driver and if the driver ceases to heed the warning, control of the vehicle could be taken from him or her by the system. The actual usurpation of vehicle control, however, is unlikely initially since there are many situations on the highway where the potential for a collision cannot be accurately ascertained. Consequently, this system can be thought of as an interim solution until all vehicles have the RtZF® system described above. 
     To use the laser radar in a scanning mode requires some mechanism for changing the direction of the emitted pulses of light. One acoustic-optic method of using an ultrasonic wave to change the diffraction angle of a Tellurium dioxide crystal is disclosed elsewhere herein. This can also be done in a variety of other ways such as through the use of a spinning multifaceted mirror, such as is common with laser scanners and printers. This mirror would control the horizontal scanning, for example, with the vertical scanning controlled though a stepping motor or the angles of the different facets of the mirror can be different to slightly alter the direction of the scan, or by other methods known in the art. Alternately, one or more piezoelectric materials can be used to cause the laser radar transmitter to rotate about a pivot point. A rotating laser system, such as described in Shaw is the least desirable of the available methods due to the difficulty in obtaining a good electrical connection between the laser and the vehicle while the laser is spinning at a very high angular velocity. Another promising technology is to use MEMS mirrors to deflect the laser beam in one or two dimensions. A newer product is the Digital Light Processor (DLP) from Texas Instruments which contains up to several million MEMS minors which can be rotated through an angle of up to 12 degrees. Although intended for displays, this device can be used to control the direction(s) of beams from a laser illuminator. The plus or minus 12 degree limitation can be expanded through optics but in itself, it is probably sufficient. See US published patent application No. 20050278098 for more details. 
     Although the system described above is intended for collision avoidance or at least the notification of a potential collision, when the roadway is populated by vehicles having the RtZF® system and vehicles which do not, its use is still desirable after all vehicles are properly equipped. It can be used to search for animals or other objects which may be on or crossing the highway, a box dropping off of a truck for example, a person crossing the road who is not paying attention to traffic. Motorcycles, bicycles, and other non-RtZF® equipped vehicles can also be monitored. 
     One significant problem with some previous collision avoidance systems which use radar or laser radar systems to predict impacts with vehicles, is the inability to know whether the vehicle that is being interrogated is located on the highway or is off the road. In at least one system of the present invention, the location of the road at any distance ahead of the vehicle would be known precisely from the sub-meter accuracy maps, so that the scanning system can ignore, for example, all vehicles on lanes where there is a physical barrier separating the lanes from the lane on which the subject vehicle is traveling. This, of course, is a common situation on super highways. Similarly, a parked vehicle on the side of the road would not be confused with a stopped vehicle that is in the lane of travel of the subject vehicle when the road is curving. This permits the subject invention to be used for automatic cruise control. In contrast with radar systems, it does not require that vehicles in the path of the subject vehicle be moving, so that high speed impacts into stalled traffic can be avoided. 
     If a system with a broader beam to illuminate a larger area on the road in front of the subject vehicle is used, with the subsequent focusing of this image onto a CCD or CMOS array, this has an advantage of permitting a comparison of the passive infrared signal and the reflection of the laser radar active infrared. Metal objects, for example appear cold to passive infrared. This permits another parameter to be used to differentiate metallic objects from non-metallic objects such as foliage or animals such as deer. The breadth of the beam can be controlled and thereby a particular object can be accurately illuminated. With this system, the speed with which the beam steering is accomplished can be much slower. Both systems can be combined into the maximum amount of information to be available to the system. 
     Through the use of range gating, objects can be relatively isolated from the environment surrounding it other than for the section of highway which is at the same distance. For many cases, a properly trained neural network or other pattern recognition system can use this data and identify the objects. An alternate approach is to use the Fourier transform of the scene as input to the neural network or other pattern recognition system. The advantages of this latter approach are that the particular location of the vehicle in the image is not critical for identification. Note that the Fourier transform can be accomplished optically and optically compared with stored transforms using a garnet crystal or garnet films, for example, as disclosed in U.S. Pat. No. 5,473,466. 
     At such time, when the system can take control of the vehicle, it will be possible to have much higher speed travel. In such cases all vehicles on the controlled roadway will need to have the RtZF® or similar system as described above. Fourier transforms of the objects of interest can be done optically though the use of a diffraction system. The Fourier transform of the scene can then be compared with the library of the Fourier transforms of all potential objects and, through a system used in military target recognition, multiple objects can be recognized and the system then focused onto one object at a time to determine the degree of threat that it poses. 
     Of particular importance is the use of a high powered eye-safe laser radar such as a 30 to 100 watt laser diode in an expanded beam form to penetrate fog, rain and snow through the use of range gating. If a several centimeter diameter beam is projected from the vehicle in the form of pulses of from 1 to 10 nanoseconds long, for example, and the reflected radiation is blocked except that from the region of interest, an image can still be captured even though it cannot be seen by the human eye. This technique significantly expands the interrogation range of the system and, when coupled with the other imaging advantages of laser radar, offers a competitive system to radar and may in fact render the automotive use or radar unnecessary. One method is to use the techniques described in the patents to 3DV listed above. In one case, for example, if the vehicle wishes to interrogate an area 250 feet ahead, a 10 nanosecond square wave signal can be used to control the shutter which is used both for transmission and reception and where the off period can be 480 nanoseconds. This can be repeated until sufficient energy has been accumulated to provide for a good image. In this connection, a high dynamic range camera may be used such as that manufactured by IMS chips of Stuttgart, Germany as mentioned above. Such a camera is now available with a dynamic range of 160 db. According to IMS, the imager can be doped to significantly increase its sensitivity to IR, 
     These advantages are also enhanced when the laser radar system described herein is used along with the other features of the RtZF® system such as accurate maps and accurate location determination. The forward-looking laser radar system can thus concentrate its attention to the known position of the roadway ahead rather than on areas where there can be no hazardous obstacles or threatening vehicles. 
     5.3 Blind Spot Detection 
     The RtZF® system of this invention also can eliminate the need for blind spot detectors such as discussed in U.S. Pat. No. 5,530,447. Alternately, if a subset of the complete RtZF® system is implemented, as is expected in the initial period, the RtZF® system can be made compatible with the blind spot detector described in the &#39;447 patent. 
     One preferred implementation for blind spot monitoring as well as for monitoring other areas near the vehicle is the use of range-gated laser radar using a high power laser diode and appropriate optics to expand the laser beam to the point where the transmitted infrared energy per square millimeter is below eye safety limits. Such a system is described above 
     5.4 Anticipatory Sensing-Smart Airbags, Evolution of the System 
     A key to anticipating accidents is to be able to recognize and categorize objects that are about to impact a vehicle as well as their relative velocity. As set forth herein and in the current assignee&#39;s patents and patent applications , this can best be done using a pattern recognition system such as a neural network, combination neural network, optical correlation system, sensor fusion and related technologies. The data for such a neural network can be derived from a camera image but such an image can be overwhelmed by reflected light from the sun. In fact, lighting variations in general plague camera-based images resulting in false classifications or even no classification. Additionally, camera-based systems are defeated by poor visibility conditions and, additionally, have interference problems when multiple vehicles have the same system which may require a synchronization taking time away from the critical anticipatory sensing function. 
     To solve these problems, imaging systems based on millimeter wave radar, laser radar (lidar) and more recently terahertz radar can be used. All three systems generally work for anticipatory sensors since the objects are near the vehicle where even infrared scanning laser radar in a non-range gated mode has sufficient range in fog. Millimeter wave radar is expensive and to obtain precise images a narrow beam is required resulting in large scanning antennas. Laser radar systems are less expensive and since the beams are formed using optic technology they are smaller and easier to manipulate. 
     When computational power is limited, it is desirable to determine the minimum number of pixels that are required to identify an approaching object with sufficient accuracy to make the decision to take evasive action or to deploy a passive restraint such as an airbag. In one military study for anti-tank missiles, it was found that a total of 25 pixels are all that is required to identify a tank on a battlefield. For optical occupant detection within a vehicle, thousands of pixels are typically used. Experiments indicate that by limiting the number of horizontal scans to three to five, with on the order of 100 to 300 pixels per scan that sufficient information is available to find an object near to the vehicle and in most cases to identify the object. Once the object has been located then the scan can be confined to the position of the object and the number of pixels available for analysis substantially increases. There are obviously many algorithms that can be developed and applied to this problem and it is therefore left to those skilled in the art. At least one invention is based on the fact that a reasonable number of pixels can be obtained from the reflections of electromagnetic energy from an object to render each of the proposed systems practical for locating, identifying and determining the relative velocity of an object in the vicinity of a vehicle that poses a threat to impact the vehicle so that evasive action can be taken or a passive restraint deployed. See the discussion in section 5.5 below for a preferred implementation. 
     The RtZF® system is also capable of enhancing other vehicle safety systems. In particular, by knowing the location and velocity of other vehicles, for those cases where an accident cannot be avoided, the RtZF® system will in general be able to anticipate a crash and assessment the crash severity using, for example, neural network technology. Even with a limited implementation of the RtZF® system, a significant improvement in smart airbag technology results when used in conjunction with a collision avoidance system such as described in Shaw (U.S. Pat. Nos. 5,314,037 and 5,529,138) and a neural network anticipatory sensing algorithm such as disclosed in U.S. Pat. No. 6,343,810 . A further enhancement would be to code a vehicle-to-vehicle communication signal from RtZF® system-equipped vehicles with information that includes the size and approximate weight of the vehicle. Then, if an accident is inevitable, the severity can also be accurately anticipated and the smart airbag tailored to the pending event. Information on the type, size and mass of a vehicle can also be implemented as an RFID tag and made part of the license plate. The type can indicate a vehicle having privileges such as an ambulance, fire truck or police vehicle. 
     Developments by Mobileye include a method for obtaining the distance to an object and thus the relative velocity. Although this technique has many limitations, it may be useful in some implementations of one or more of the current inventions. 
     A further recent development is reported in U.S. patent application publication No. 20030154010, as well as other patents and patent publications assigned to Ford Global Technologies including Ser. Nos. 06/452,535, 06/480,144, 06/498,972, 06/650,983, 06/568,754, 06/628,227, 06/650,984, 06/728,617, 06/757,611, 06/775,605, 06/801,843, 06/819,991, 20030060980, 20030060956, 20030100982, 20030154011, 20040019420, 20040093141, 20040107033, 20040111200, and 20040117091. In the disclosures herein, emphasis has been placed on identifying a potentially threatening object and once identified, the properties of the object such as its size and mass can be determined. An inferior system can be developed as described in U.S. patent application publication No. 20030154010 where only the size is determined. In inventions described herein, the size is inherently determined during the process of imaging the object and identifying it. Also, the Ford patent publications mention the combined use of a radar or a lidar and a camera system. Combined use of radar and a camera is anticipated herein and disclosed in the current assignee&#39;s patents. 
     Another recent development by the U.S. Air Force uses a high powered infrared laser operating at wavelengths greater than 1.5 microns and a focal plane array as is reported in “Three-Dimensional Imaging” in AFRL Technology Horizons, April 2004. Such a system is probably too expensive at this time for automotive applications. This development illustrates the fact that it is not necessary to limit the lidar to the near infrared part of the spectrum and in fact, the further that the wavelength is away from the visible spectrum, the higher the power permitted to be transmitted. Also, nothing prevents the use of multiple frequencies as another method of providing isolation from transmissions from vehicles in the vicinity. As mentioned above for timing transmissions, the GPS system can also be used to control the frequency of transmission thus using frequency as a method to prevent interference. The use of polarizing filters to transmit polarized infrared is another method to provide isolation between different vehicles with the same or similar systems. The polarization angle can be a function of the GPS location of the vehicle. 
     It is an express intention of some of the inventions herein to provide a system that can be used both in daytime and at night. Other systems are intended solely for night vision such as those disclosed in U.S. Pat. Nos. 6,730,913, 6,690,017 and 6,725,139. Use of the direction of travel as a method of determining when to transmit infrared radiation, as disclosed in these and other Ford Global patents and patent applications, can be useful but it fails to solve the problem of the transmissions from two vehicles traveling in the same vicinity and direction from receiving reflections from each others&#39; transmissions. If the directional approach is used, then some other method is required such as coding the pulses, for example. 
     U.S. Pat. Nos. 6,730,913 and 6,774,367 are representative of a series of patents awarded to Ford Global Technologies as discussed above. These patents describe range gating as disclosed in the current assignee&#39;s earlier patents. An intent is to supplement the headlights with a night vision system for illuminating objects on the roadway in the path of the vehicle but are not seen by the driver and displaying these objects in a heads-up display. No attempt is made to locate the eyes of the driver and therefore the display cannot place the objects where they would normally be located in the driver&#39;s field of view as disclosed in the current assignee&#39;s patents. Experiments have shown that without this feature, a night vision system is of little value and may even distract the driver to where his or her ability to operate the motor vehicle is degraded. Other differences in the &#39;913 and &#39;367 system include an attempt to compensate for falloff in illumination due to distance, neglecting a similar and potentially more serious falloff due to scattering due to fog etc. In at least one of the inventions disclosed herein, no attempt is made to achieve this compensation in a systematic manner but rather the exposure is adjusted so that a sufficiently bright image is achieved to permit object identification regardless of the cause of the attenuation. Furthermore, in at least one embodiment, a high dynamic range camera is used which automatically compensates for much of the attenuation and thus permits the minimum exposure requirements for achieving an adequate image. In at least one of the inventions disclosed herein, the system is used both at night and in the daytime for locating and identifying objects and, in some cases, initiating an alarm or even taking control of the vehicle to avoid accidents. None of these objects are disclosed in the &#39;913 or &#39;367 patents and related patents. Additionally, US20030155513, also part of this series of Ford Global patents and applications, describes increasing the illumination intensity based on distance to the desired field of view. In at least one of the inventions disclosed herein, the illumination intensity is limited by eye safety considerations rather than distance to the object of interest. If sufficient illumination is not available on one pulse, additional pulses are provided until sufficient illumination to achieve an adequate exposure is achieved. 
     If the laser beam diverges, then the amount of radiation per square centimeter illuminating a surface will be a function of the distance of that surface from the transmitter. If that distance can be measured, then the transmitted power can be increased while keeping the radiation per square centimeter below the eye safe limits. Using this technique, the amount of radiated power can be greatly increased thus enhancing the range of the system in daylight and in bad weather. A lower power pulse would precede a high power pulse transmitted in a given direction and the distance measured to a reflective object would be measured and the transmitted power adjusted appropriately. If a human begins to intersect the path of transmission, the distance to the human would be measured before he or she could put his or her eye into the transmission path and the power can be reduced to remain within the safety standards. 
     It is also important to point out that the inventions disclosed herein that use lidar (laser radar or ladar) can be used in a scanning mode when the area to be covered is larger that the beam diameter or in a pointing mode when the beam diameter is sufficient to illuminate the target of interest, or a combination thereof. 
     It can be seen from the above discussion that the RtZF® system will evolve to solve many safety, vehicle control and ITS problems. Even such technologies as steering and drive by wire will be enhanced by the RtZF® system in accordance with invention since it will automatically adjust for failures in these systems and prevent accidents. 
     5.5 A Preferred Implementation 
       FIGS. 21A and 21B  illustrate a preferred embodiment of a laser radar or camera based system having components mounted at the four corners of a vehicle above the headlights and tail lights, i.e., fixed to the vehicle&#39;s frame. Although hereinafter laser radar is used, there is also an equivalent optical imager based system that can also be used. Laser radar units or assemblies  260  and  261  have a scan angle of approximately 150 degrees; however, for some applications a larger or smaller scanning angle can of course be used. The divergence angle for the beam for one application can be one degree or less when it is desired to illuminate an object at a considerable distance from the vehicle such as from less than fifty meters to 200 meters or more. In other cases, where objects are to be illuminated that are closer to the vehicle, a larger divergence angle can be used. Generally, it is desirable to have a field of illumination (FOI) approximately equal to the field of view (FOV) of the camera or other optical receiver.  FIGS. 22A and 22B  illustrate the system of  FIGS. 21A and 21B  for vehicles on a roadway. Note that the divergence angle in the horizontal plane and vertical plane are not necessarily equal. 
       FIGS. 23A and 23B  illustrate an alternative mounting location for laser radar units on or near the roof of a vehicle. They can be either inside or outside of the vehicle compartment. The particular design of the laser radar assemblies  262  and  263  are similar to those used in  FIGS. 21A, 21B, 22A and 22B . Although not shown, other geometries are of course possible such as having the laser radar assemblies mounted on or near the roof for the rear assemblies and above the headlights for the frontal assemblies or vice versa. Also, although assemblies mounted on the corners of the vehicle are illustrated, in some cases it may be desirable to mount laser radar assemblies in the center of the front, back and sides of the vehicle or a combination or center and corner-mounted laser radar assemblies can be used. 
       FIG. 24  is a schematic illustration of a typical laser radar assembly showing the scanning or pointing system with simplified optics for illustration only. In an actual design, the optics will typically include multiple lenses. Also, the focal point will typically not be outside of the laser radar assembly. In this non-limiting example, a common optical system  267  is used to control a laser light  265  and an imager or camera  266 . The laser source transmits, usually eye-safe infrared, light through its optical sub-system  271  which collimates the radiation. The collimated radiation is then reflected off mirror  273  to mirror  274  which reflects the radiation to the desired direction through lens system  267 . The direction of the beam can be controlled by a motor  272  which can rotate both mirror  274  and optical system  267  to achieve the desired scanning or pointing angle for scanning designs. A preferred approach is to use a non-scanning approach. The radiation leaves the optical system  267  and illuminates the desired object or target  276 . The radiation reflected from object  276  can pass back through lens  267 , reflect off mirror  274  pass through semitransparent minor  273  through optic subsystem  268  and onto optical sensitive surface  266 . Many other configurations are possible. The transmission of the radiation is controlled by optical shutter  270  via controller  275 . Similarly, the light that reaches the imager  266  is controlled by controller  275  and optical shutter  269 . These optical shutters  269 ,  270  can be liquid crystal devices, Kerr or Pockel cells, garnet films, other spatial light monitors or, preferably, high speed optical shutters such as described in patents and patent applications of the 3DV Systems Ltd., of Yokneam, Israel, as set forth above or equivalent. Since much of the technology used in this invention related to the camera and shutter system is disclosed in the 3DV patents and patent applications, it will not be repeated here, by is incorporated by reference herein. 
     In some embodiments, it may be important to assure that the lens through which the laser radar radiation passes is clean. As a minimum, a diagnostic system is required to inform the RtZF® or other system that the lens are soiled and therefore the laser radar system can not be relied upon. Additionally, in some applications, means are provided to clean one or more of the lens or to remove the soiled surface. In the latter case, a roll of thin film can be provided which, upon the detection of a spoiled lens, rolls up a portion of the film and thereby provides a new clean surface. When the roll is used up it can be replaced. Other systems provide one or more cleaning methods such as a small wiper or the laser radar unit can move the lens into a cleaning station. Many other methods are of course possible and the invention here is basically concerned with ascertaining that the lens is clean and if not informing the system of this fact and, in some cases, cleaning or removing the soiled surface. The lens can also be coated with a coating that resists soiling as disclosed in U.S. Pat. Nos. 7,136,494, 6,991,339 and 6,193,378. 
     Note that although laser radar and radar have been discussed separately, in some implementations, it is desirable to use both a radar system and a laser radar system. Such a case can be where the laser radar system is not capable to achieve sufficient range in adverse weather whereas the radar has the requisite range but insufficient resolution. The radar unit can provide a warning that a potentially dangerous situation exists and thus the vehicle speed should be reduced until the laser radar device and obtain an image with sufficient resolution to permit an assessment of the extent of the danger and determine whether appropriate actions should be undertaken. 
     6. Infrastructure-to-Vehicle Communication 
     6.1 General 
     In order to eliminate fatalities on roads and mitigate congestion, it is critical that vehicles communicate with each other. The type of communication can take at least two forms, that which is time critical such when two vehicles are about to collide and that which can have some delay such as information that the road is icy 2 miles ahead. Time critical communication is discussed above. This section will concentrate on the not time-critical communication which can also include information from a vehicle that passed through an area an hour prior to the subject vehicle or information derived from a server that may not be near the vehicle. Thus, this second type of communications can involve an entity that is not a vehicle such as a network server. In many cases, such a server will be required such as when a vehicle transmits a picture of an accident that needs to be interpreted before it can be added as a temporary update to a map of the area. 
     Referring to  FIG. 26  to explain this multi-form of communications, a method for transmitting information to a host vehicle traveling on a road using two different types or ways of communications in accordance with the invention includes generating information from one or more sources thereof to be wirelessly transmitted to an information receiving system resident on the host vehicle during travel of the vehicle  280 . The sources may be other vehicles on the road(s) on which the vehicle is traveling or about to or expected to travel, or infrastructure facilities, e.g., stations or transmitters. Thus, the information may be about one or more roads on which the host vehicle will travel in the future from other vehicles which traveled the road prior to the host vehicle. 
     The information is then prioritized to distinguish between high priority, time-critical information of immediate relevance to operation of the vehicle and low priority, non-time-critical information of non-immediate relevance to the operation of the host vehicle  282 . This prioritization may be performed by the information receiving system resident on the vehicle, e.g., based on an initial transmission from each source, or at a data storage facility separate and apart from the host vehicle at which the information is being gathered. The prioritization may be performed based on the current position of the host vehicle, the location of the source and/or identity of the source. Some sources can always be considered high priority sources, e.g., vehicles within a pre-determined range and in an expected path of travel of the host vehicle. 
     In particular when prioritization is performed by the information receiving system resident on the vehicle, it can be performed using the method described above with reference to  FIG. 20  to prioritize the received information in the form of waves or signals, i.e., filter transmissions from transmitters. That is, any transmission from a particular transmitter deemed to be a transmission of interest (based on decoding of the initial part of the transmission  252   a ) may be considered high priority information whereas any transmission from a transmitter not deemed to contain information of interest (based on decoding of the initial part of the transmission  252   a ), is considered low priority information. 
     High priority information  284 , such as information from vehicles in close proximity to the host vehicle and information potentially useful or necessary for collision avoidance, is preferably transmitted directly from the source  286 . This ensures that the host vehicle will immediately have information necessary for it to continue safe operation of the vehicle, e.g., by avoiding collisions with other proximate vehicles or infrastructure. 
     Low priority information  288 , or any other information not deemed high priority, is gathered at the data storage facility  290  and directed therefrom to the host vehicle using the ubiquitous network described below, e.g., the Internet  292 . 
     6.2 Summary 
       FIG. 27  shows a schematic of the flow of data. Information to be wirelessly transmitted, preferably via a ubiquitous network, to an information receiving system resident on the “host” vehicle  294  during travel of the vehicle  294  is generated by one or more information sources which include “probe” vehicles  294 , traffic cameras  296  and road sensors  298 . The probe vehicles  294  provide information about one or more roads on which the host vehicle will travel or is expected to travel at some time in the future, the difference being if the road the vehicle expects to travel on is congested, the driver of the host vehicle can take an alternative route. Other sources of information include data channels with weather information, i.e., meteorological reports, and traffic information such as that provided by highway, bridge and tunnel operators and municipalities. It is important to note that the host vehicle can also be a probe vehicle, in that information it obtains can be used for transmission to vehicles behind it on the same path, and that a probe vehicle can be a host vehicle in that information it receives was obtained by vehicle in front of it on the same path. As such,  FIG. 27  shows element  294  designated as vehicles. 
     This information is sent from the various sources, preferably over a ubiquitous network, and is gathered in a central data storage, monitoring and/or processing facility  300 , e.g., a network server or mainframe computer, which may entail directing the information sources to respond to inquiries for information from the data facility or programming the information sources to automatically provide the information at set times. The probe vehicles  294  can also continually provide information limited only by the components of the transmission unit thereon. The data facility  300  can also be programmed to automatically access data channels on a regular basis to obtain current information about roads and weather. Although the data facility  300  gathers a large amount of information, not all of the information will be directed to the vehicle  294 , i.e., only potential relevant information will be considered for each vehicle  294  in communication with the data facility  300 . Thus, different subsets of the total available information will be generated for each host vehicle  294 . 
     The data facility  300  includes software and hardware components which enables it to prioritize the information to distinguish between high priority, time-critical information of immediate relevance to operation of the host vehicle  294  and low priority, non-time-critical information of non-immediate relevance to the operation of the host vehicle  294 . It can thus be programmed to control and communicate with the information receiving system to cause it to receive and process high priority information before low priority information, the transmission of both of which are directed by the data facility  300 . Prioritization can be established based on the current position of the host vehicle  294 . 
     Data facility  300  can be programmed to maintain a map of roads resident in host vehicles by transmitting map updates necessary for the maps to be current, the map updates being generated based on the gathered information. If a temporary map update is created based on a change in the operability or functionality of a road, e.g., based on a traffic accident, the data facility  300  is programmed to continuously monitor the change to determine when the use of the road reverts to a state preceding the change. When this happens, notification of this reversion is transmitted to the host vehicle, e.g., via another map update. 
     Data facility  300  communicates with traffic control devices  302  via the ubiquitous network of transceivers. It can thus analyze vehicular traffic and control the traffic control devices based on the vehicular traffic, e.g., regulate the pattern of green lights to optimize traffic, eliminate traffic jams and expedite emergency response vehicles. 
     Data facility  300  also communicates with an emergency response facility  304  to direct aid to a host vehicle when necessary or to the site of an accident as determined by the information gathered from the sources thereof. 
     Data facility  300  also communications with Internet content providers  306  to allow the occupants of host vehicles to request Internet content over the ubiquitous network. 
     It should be understood that the transmission of information between vehicles is one exemplifying use of the invention which also encompasses generating information from other types of mobile units, transmitting the information to a common monitoring station, generating at the monitoring station an update for, e.g., a map, based on the transmitted information, and then transmitting the update to each of the mobile units. 
     7. The RtZF® System 
     7.1 Road Departure 
       FIG. 4  is a logic diagram of the system  50  in accordance with the invention showing the combination  40  of the GPS and DGPS processing systems  42  and an inertial reference unit (IRU) or inertial navigation system (INS) or Inertial Measurement Unit (IMU)  44 . The GPS system includes a unit for processing the received information from the satellites  2  of the GPS satellite system, the information from the satellites  30  of the DGPS system and data from the inertial reference unit  44 . The inertial reference unit  44  contains accelerometers and laser or MEMS gyroscopes. 
     The system shown in  FIG. 4  is a minimal RtZF® system that can be used to prevent road departure, lane crossing and intersection accidents, which together account for more than about 50% of the fatal accidents in the U.S. 
     Map database  48  works in conjunction with a navigation system  46  to provide a warning to the driver when he or she is about to run off the road, cross a center (yellow) line, run a stop sign, or run a red stoplight. The map database  48  contains a map of the roadway to an accuracy of 2 cm (1σ), i.e., data on the edges of the lanes of the roadway and the edges of the roadway, and the location of all stop signs and stoplights and other traffic control devices such as other types of road signs. Another sensor, not shown, provides input to the vehicle indicating that an approaching stoplight is red, yellow or green. Navigation system  46  is coupled to the GPS and DGPS processing system  42 . For this simple system, the driver is warned if any of the above events is detected by a driver warning system  45  coupled to the navigation system  46 . The driver warning system  45  can be an alarm, light, buzzer or other audible noise, or, preferably, a simulated rumble strip for yellow line and “running off of road” situations and a combined light and alarm for the stop sign and stoplight infractions. 
     7.2 Accident Avoidance 
       FIG. 5  is a block diagram of the more advanced accident avoidance system of this invention and method of the present invention illustrating system sensors, transceivers, computers, displays, input and output devices and other key elements. 
     As illustrated in  FIG. 5 , the vehicle accident avoidance system is implemented using a variety of microprocessors and electronic circuits  100  to interconnect and route various signals between and among the illustrated subsystems. GPS receiver  52  is used to receive GPS radio signals as illustrated in  FIG. 1 . DGPS receiver  54  receives the differential correction signals from one or more base stations either directly or via a geocentric stationary or LEO satellite, an earth-based station or other means. Inter-vehicle communication subsystem  56  is used to transmit and receive information between various nearby vehicles. This communication will in general take place via broadband or ultra-broadband communication techniques, or on dedicated frequency radio channels, or in a preferred mode, noise communication system as described above. This communication may be implemented using multiple access communication methods including frequency division multiple access (FDMA), time division multiple access (TDMA), or code division multiple access (CDMA), or noise communication system, in a manner to permit simultaneous communication with and between vehicles. Other forms of communication between vehicles are possible such as through the Internet. This communication may include such information as the precise location of a vehicle, the latest received signals from the GPS satellites in view, other road condition information, emergency signals, hazard warnings, vehicle velocity and intended path, and any other information which is useful to improve the safety of the vehicle road system. 
     Infrastructure communication system  58  permits bi-directional communication between the host vehicle and the infrastructure and includes such information transfer as updates to the digital maps, weather information, road condition information, hazard information, congestion information, temporary signs and warnings, and any other information which can improve the safety of the vehicle highway system. 
     Cameras  60  are used generally for interrogating environment nearby the host vehicle for such functions as blind spot monitoring, backup warnings, anticipatory crash sensing, visibility determination, lane following, and any other visual information which is desirable for improving the safety of the vehicle highway system. Generally, the cameras will be sensitive to infrared and/or visible light, however, in some cases a passive infrared camera will the used to detect the presence of animate bodies such as deer or people on the roadway in front of the vehicle. Frequently, infrared or visible illumination will be provided by the host vehicle. In the preferred system, high brightness eye-safe IR will be used. 
     Radar  62  is primarily used to scan an environment close to and further from the vehicle than the range of the cameras and to provide an initial warning of potential obstacles in the path of the vehicle. The radar  62  can also be used when conditions of a reduced visibility are present to provide advance warning to the vehicle of obstacles hidden by rain, fog, snow etc. Pulsed, continuous wave, noise or micropower impulse radar systems can be used as appropriate. Also, Doppler radar principles can be used to determine the object to host vehicle relative velocity. 
     Laser or terahertz radar  64  is primarily used to illuminate potential hazardous objects in the path of the vehicle. Since the vehicle will be operating on accurate mapped roads, the precise location of objects discovered by the radar or camera systems can be determined using range gating and scanning laser radar as described above or by phase techniques. 
     The driver warning system  66  provides visual and/or audible warning messages to the driver or others that a hazard exists. In addition to activating a warning system within the vehicle, this system can activate sound and/or light systems to warn other people, animals, or vehicles of a pending hazardous condition. In such cases, the warning system could activate the vehicle headlights, tail lights, horn and/or the vehicle-to-vehicle, Internet or infrastructure communication system to inform other vehicles, a traffic control station or other base station. This system will be important during the early stages of implementation of RtZF®, however as more and more vehicles are equipped with the system, there will be less need to warn the driver or others of potential problems. 
     Map database subsystem  68 , which could reside on an external memory module, will contain all of the map information such as road edges up to 2 cm accuracy, the locations of stop signs, stoplights, lane markers etc. as described above. The fundamental map data can be organized on read-only magnetic or optical memory with a read/write associated memory for storing map update information. Alternatively, the map information can be stored on rewritable media that can be updated with information from the infrastructure communication subsystem  58 . This updating can take place while the vehicle is being operated or, alternatively, while the vehicle is parked in a garage or on the street. 
     Three servos are provided for controlling the vehicle during the later stages of implementation of the RtZF® product and include a brake servo  70 , a steering servo  72 , and a throttle servo  74 . The vehicle can be controlled using deterministic, fuzzy logic, neural network or, preferably, neural-fuzzy algorithms. 
     As a check on the inertial system, a velocity sensor  76  based on a wheel speed sensor, or ground speed monitoring system using lasers, radar or ultrasonics, for example, can be provided for the system. A radar velocity meter is a device which transmits a noise modulated radar pulse toward the ground at an angle to the vertical and measures the Doppler velocity of the returned signal to provide an accurate measure of the vehicle velocity relative to the ground. Another radar device can be designed which measures the displacement of the vehicle. Other modulation techniques and other radar systems can be used to achieve similar results. Other systems are preferably used for this purpose such as the GPS/DGPS or precise position systems. 
     The inertial navigation system (INS), sometimes called the inertial reference unit or IRU, comprises one or more accelerometers  78  and one or more gyroscopes  80 . Usually, three accelerometers would be required to provide the vehicle acceleration in the latitude, longitude and vertical directions and three gyroscopes would be required to provide the angular rate about the pitch, yaw and roll axes. In general, a gyroscope would measure the angular rate or angular velocity. Angular acceleration may be obtained by differentiating the angular rate. 
     A gyroscope  80 , as used herein in the IRU, includes all kinds of gyroscopes such as MEMS-based gyroscopes, fiber optic gyroscopes (FOG) and accelerometer-based gyroscopes. 
     Accelerometer-based gyroscopes encompass a situation where two accelerometers are placed apart and the difference in the acceleration is used to determine angular acceleration and a situation where an accelerometer is placed on a vibrating structure and the Coriolis effect is used to obtain the angular velocity. 
     The possibility of an accelerometer-based gyroscope  80  in the IRU is made possible by construction of a suitable gyroscope by Interstate Electronics Corporation (IEC). IEC manufactures IMUs in volume based on μSCIRAS (micro-machined Silicon Coriolis Inertial Rate and Acceleration Sensor) accelerometers. Detailed information about this device can be found at the IEC website at iechome.com. 
     An accelerometer  78 , as used herein in the IRU, includes conventional piezoelectric-based accelerometers, MEMS-based accelerometers (such as made by Analog Devices) and the type as described in U.S. Pat. No. 6,182,509. 
     Display subsystem  82  includes an appropriate display driver and either a heads-up or other display system for providing system information to the vehicle operator. Display subsystem  82  may include multiple displays for a single occupant or for multiple occupants, e.g., directed toward multiple seating positions in the vehicle. One type of display may be a display made from organic light emitting diodes (OLEDs). Such a display can be sandwiched between the layers of glass that make up the windshield and does not require a projection system. 
     The information being displayed on the display can be in the form of non-critical information such as the location of the vehicle on a map, as selected by the vehicle operator and/or it can include warning or other emergency messages provided by the vehicle subsystems or from communication with other vehicles or the infrastructure. An emergency message that the road has been washed out ahead, for example, would be an example of such a message. 
     Generally, the display will make use of icons when the position of the host vehicle relative to obstacles or other vehicles is displayed. Occasionally, as the image can be displayed especially when the object cannot be identified. Icons can be selected which are representative of the transmitters from which wireless signals are received. 
     A general memory unit  84  which can comprise read-only memory or random access memory or any combination thereof, is shown. This memory module, which can be either located at one place or distributed throughout the system, supplies the information storage capability for the system. 
     For advanced RtZF® systems containing the precise positioning capability, subsystem  86  provides the capability of sending and receiving information to infrastructure-based precise positioning tags or devices which may be based on noise or micropower impulse radar technology, IR lasers, radar or IR reflector (e.g. corner cube or dihedral) or RFIR technology or equivalent. Once again the PPS system can also be based on a signature analysis using the adaptive associative memory technology or equivalent. 
     In some locations where weather conditions can deteriorate and degrade road surface conditions, various infrastructure-based sensors can be placed either in or adjacent to the road surface. Subsystem  88  is designed to interrogate and obtained information from such road-based systems. An example of such a system would be an RFID tag containing a temperature sensor. This device may be battery-powered or, preferably, would receive its power from energy harvesting (e.g., solar energy, vibratory energy), the vehicle-mounted interrogator, or other host vehicle-mounted source, as the vehicle passes nearby the device. In this manner, the vehicle can obtain the temperature of the road surface and receive advanced warning when the temperature is approaching conditions which could cause icing of the roadway, for example. An RFID based on a surface acoustic wave (SAW) device is one preferred example of such a sensor, see U.S. Pat. No. 6,662,642. An infrared sensor on the vehicle can also be used to determine the road temperature and the existence of ice or snow. 
     For some implementations of the RtZF® system, stoplights will be fitted with transmitters which will broadcast a signal when the light is red. Such a system could make use of the vehicle noise communication system as described above. This signal can be then received by a vehicle that is approaching the stoplight provided that vehicle has the proper sensor as shown as  92 . Alternatively, a camera can be aimed in the direction of stoplights and, since the existence of the stoplight will be known by the system, as it will have been recorded on the map, the vehicle will know when to look for a stoplight and determine the color of the light. 
     An alternative idea is for the vehicle to broadcast a signal to the stoplight if, via a camera or other means, it determines that the light is red. If there are no vehicles coming from the other direction, the light can change permitting the vehicle to proceed without stopping. Similarly, if the stoplight has a camera, it can look in all directions and control the light color depending on the number of vehicles approaching from each direction. A system of phasing vehicles can also be devised whereby the speed of approaching vehicles is controlled so that they interleave through the intersection and the stoplight may not be necessary. 
     Although atomic clocks are probably too expensive to the deployed on automobiles, nevertheless there has been significant advances recently in the accuracy of clocks to the extent that it is now feasible to place a reasonably accurate clock as a subsystem  94  to this system. Since the clock can be recalibrated from each DGPS transmission, the clock drift can be accurately measured and used to predict the precise time even though the clock by itself may be incapable of doing so. To the extent that the vehicle contains an accurate time source, the satellites in view requirement can temporarily drop from 4 to 3. An accurate clock also facilitates the carrier phase DGPS implementations of the system as discussed above. Additionally, as long as a vehicle knows approximately where it is on the roadway, it will know its altitude from the map and thus one less satellite is necessary. 
     Power is supplied to the system as shown by power subsystem  96 . Certain operator controls are also permitted as illustrated in subsystem  98 . 
     The control processor or central processor and circuit board subsystem  100  to which all of the above components  52 - 98  are coupled, performs such functions as GPS ranging, DGPS corrections, image analysis, radar analysis, laser radar scanning control and analysis of received information, warning message generation, map communication, vehicle control, inertial navigation system calibrations and control, display control, precise positioning calculations, road condition predictions, and all other functions needed for the system to operate according to design. 
     A display could be provided for generating and displaying warning messages which is visible to the driver and/or passengers of the vehicle. The warning could also be in the form of an audible tone, a simulated rumble strip and light and other similar ways to attract the attention of the driver and/or passengers. Although vibration systems have been proposed by others, the inventors have found that a pure noise rumble strip is preferred and is simpler and less costly to implement, 
     Vehicle control also encompasses control over the vehicle to prevent accidents. By considering information from the map database  48 , from the navigation system  46 , and the position of the vehicle obtained via GPS, DGPS and PPS systems, a determination can be made whether the vehicle is about to run off the road, cross a yellow line and run a stop sign, as well as the existence or foreseen occurrence of other potential crash situations. The color of an approaching stoplight can also be factored in the vehicle control as can information from the vehicle to vehicle, vehicle to infrastructure and around vehicle radar, visual or IR monitoring systems. 
       FIG. 5A  shows a selected reduced embodiment of the accident avoidance system shown in  FIG. 5 . The system includes an inertial reference unit including a plurality of accelerometers and gyroscopes, namely accelerometers  78 A, preferably three of any type disclosed above, and gyroscopes  80 A, preferably three of any type disclosed above. An accurate clock  94 A is provided to obtain a time base or time reference. This system will accurately determine the motion (displacement, acceleration and/or velocity) of the vehicle in 6 degrees of freedom (3 displacements (longitudinal, lateral and vertical)) via the accelerometers  78 A and three rotations (pitch, yaw and roll) via the gyroscopes  80 A. As such, along with a time base from clock  94 A, the processor  100 A can determine that there was an accident and precisely what type of accident it was in terms of the motion of the vehicle (frontal, side, rear and rollover). This system is different from a crash sensor in that this system can reside in the passenger compartment of the vehicle where it is protected from actually being in the accident crush and/or crash zones and thus it does not have to forecast the accident severity. It knows the resulting vehicle motion and therefore exactly what the accident was and what the injury potential is. A typical crash sensor can get destroyed or at least rotated during the crash and thus will not determine the real severity of the accident. 
     Processor  100 A is coupled to the inertial reference unit and also is capable of performing the functions of vehicle control, such as via control of the brake system  70 A, steering system  72 A and throttle system  74 A, crash sensing, rollover sensing, cassis control sensing, navigation functions and accident prevention as discussed herein. 
     Preferably, a Kalman filter is used to optimize the data from the inertial reference unit as well as other input sources of data, signals or information. Also, a neural network, fuzzy logic or neural-fuzzy system could be used to reduce the data obtained from the various sensors to a manageable and optimal set. The actual manner in which a Kalman filter can be constructed and used in the invention would be left to one skilled in the art. Note that in the system of the inventions disclosed herein, the extensive calibration process carried on by other suppliers of inertial sensors is not required since the system periodically corrects the errors in the sensors and revises the calibration equation. This in some cases can reduce the manufacturing cost on the IMU by a factor of ten. 
     Further, the information from the accelerometers  78 A and gyroscopes  80 A in conjunction with the time base or reference is transmittable via the communication system  56 A, 58 A to other vehicles, possibly for the purpose of enabling other vehicles to avoid accidents with the host vehicle, and/or to infrastructure. 
     One particularly useful function would be for the processor to send data from, or data derived from, the accelerometers and gyroscopes relating to a crash, i.e., indicative of the severity of the accident with the potential for injury to occupants, to a monitoring location for the dispatch of emergency response personnel, i.e., an EMS facility or fire station. Other telematics functions could also be provided. 
     7.3 Exterior Surveillance System 
       FIG. 6  is a block diagram of the host vehicle exterior surveillance system. Cameras  60  are primarily intended for observing the immediate environment of the vehicle. They are used for recognizing objects that could be most threatening to the vehicle, i.e., closest to the vehicle. These objects include vehicles or other objects that are in the vehicle blind spot, objects or vehicles that are about to impact the host vehicle from any direction, and objects either in front of or behind the host vehicle which the host vehicle is about to impact. These functions are normally called blind spot monitoring and collision anticipatory sensors. 
     As discussed above, the cameras  60  can use naturally occurring visible or infrared radiation (particularly eye-safe IR), or other parts of the electromagnetic spectrum including terahertz and x-rays, or they may be supplemented with sources of visible or infrared illumination from the host vehicle. Note that there generally is little naturally occurring terahertz radiation other than the amount that occurs in black body radiation from all sources. The cameras  60  used are preferably high dynamic range cameras that have a dynamic range exceeding 60 db and preferably exceeding 100 db. Such commercially available cameras include those manufactured by the Photobit Corporation in California and the IMS Chips Company in Stuttgart Germany. Alternately, various other means exist for increasing the effective dynamic range through shutter control or illumination control using a Kerr or Pokel cell, modulated illumination, external pixel integration etc. 
     These cameras are based on CMOS technology and can have the important property that pixels are independently addressable. Thus, the control processor may decide which pixels are to be read at a particular time. This permits the system to concentrate on certain objects of interest and thereby make more effective use of the available bandwidth. 
     Video processor printed circuit boards or feature extractor  61  can be located adjacent and coupled to the cameras  60  so as to reduce the information transferred to the control processor. The video processor boards or feature extractor  61  can also perform the function of feature extraction so that all values of all pixels do not need to be sent to the neural network for identification processing. The feature extraction includes such tasks as determining the edges of objects in the scene and, in particular, comparing and subtracting one scene from another to eliminate unimportant background images and to concentrate on those objects which had been illuminated with infrared or terahertz radiation, for example, from the host vehicle. By these and other techniques, the amount of information to be transferred to the neural network is substantially reduced. 
     The neural network  63  receives the feature data extracted from the camera images by the video processor feature extractor  61  and uses this data to determine the identification of the object in the image. The neural network  63  has been previously trained on a library of images that can involve as many as one million such images. Fortunately, the images seen from one vehicle are substantially the same as those seen from another vehicle and thus the neural network  63  in general does not need to be trained for each type of host vehicle. 
     As the number of image types increases, modular or combination neural networks can be used to simplify the system. 
     Although the neural network  63  has in particular been described, other pattern recognition techniques are also applicable. One such technique uses the Fourier transform of the image and utilizes either optical correlation techniques or a neural network trained on the Fourier transforms of the images rather than on the image itself. In one case, the optical correlation is accomplished purely optically wherein the Fourier transform of the image is accomplished using diffraction techniques and projected onto a display, such as a garnet crystal display, while a library of the object Fourier transforms is also displayed on the display. By comparing the total light passing through the display, an optical correlation can be obtained very rapidly. Although such a technique has been applied to scene scanning by military helicopters, it has previously not been used in automotive applications. 
     The laser radar system  64  is typically used in conjunction with a scanner  65 . The scanner  65  typically includes two oscillating mirrors, or a MEMS mirror capable of oscillating in two dimensions, which cause the laser light to scan the two dimensional angular field. Alternately, the scanner can be a solid-state device utilizing a crystal having a high index of refraction which is driven by an ultrasonic vibrator as discussed above or rotating mirrors. The ultrasonic vibrator establishes elastic waves in the crystal which diffracts and changes the direction of the laser light. Another method is to use the DLP technology from Texas Instruments. This technology allows more than 1 million MEMS minors to control the direction of the laser light. 
     The laser beam can be frequency, amplitude, time, code or noise modulated so that the distance to the object reflecting the light can be determined. The laser light strikes an object and is reflected back where it can be guided onto a pin diode, or other high speed photo detector. Since the direction of laser light is known, the angular location of the reflected object is also known and since the laser light is modulated the distance to the reflected point can be determined. By varying modulation frequency of the laser light, or through noise or code modulation, the distance can be very precisely measured. 
     Alternatively, the time-of-flight of a short burst of laser light can be measured providing a direct reading of the distance to the object that reflected the light. By either technique, a three-dimensional map can be made of the surface of the reflecting object. Objects within a certain range of the host vehicle can be easily separated out using the range information. This can be done electronically using a technique called range gating, or it can be accomplished mathematically based on the range data. By this technique, an image of an object can be easily separated from other objects based on distance from the host vehicle. 
     Since the vehicle knows its position accurately and in particular it knows the lane on which it is driving, a determination can be made of the location of any reflective object and in particular whether or not the reflective object is on the same lane as the host vehicle. This fact can be determined since the host vehicle has a map and the reflective object can be virtually placed on that map to determine its location on the roadway, for example. 
     The laser radar system will generally operate in the near-infrared part of the electromagnetic spectrum and preferably in the eye-safe part. The laser beam will be of relatively high intensity compared to the surrounding radiation and thus even in conditions of fog, snow, and heavy rain, the penetration of the laser beam and its reflection will permit somewhat greater distance observations than the human driver can perceive. Under the RtZF® plan, it is recommended that the speed of the host vehicle be limited such that vehicle can come to a complete stop in one half or less of the visibility distance. This will permit the laser radar system to observe and identify threatening objects that are beyond the visibility distance, apply the brakes to the vehicle if necessary causing the vehicle to stop prior to an impact, providing an added degree of safety to the host vehicle. 
     Radar system  62  is mainly provided to supplement laser radar system. It is particularly useful for low visibility situations where the penetration of the laser radar system is limited. The radar system, which is most probably a noise or pseudonoise modulated continuous wave radar, can also be used to provide a crude map of objects surrounding the vehicle. The most common use for automotive radar systems is for adaptive cruise control systems where the radar monitors the distance and, in some cases, the velocity of the vehicle immediately in front of the host vehicle. The radar system  62  is controlled by the control processor  100 . 
     Display system  82  was discussed previously and can be either a heads up or other appropriate display. 
     Control processor  100  can be attached to a vehicle special or general purpose bus  110  for transferring other information to and from the control processor to other vehicle subsystems. 
     In interrogating other vehicles on the roadway, a positive identification of the vehicle and thus its expected properties such as its size and mass can sometimes be accomplished by laser vibrometry. By this method, a reflected electromagnetic wave can be modulated based on the vibration that the vehicle is undergoing. Since this vibration is caused at least partially by the engine, and each class of engine has a different vibration signature, this information can be used to identify the engine type and thus the vehicle. This technique is similar to one used to identify enemy military vehicles by the U.S. military. It is also used to identify ships at sea using hydrophones. In the present case, a laser beam is directed at the vehicle of interest and the returned reflected beam is analyzed such as with a Fourier transform to determine the frequency makeup of the beam. This can then be related to a vehicle to identify its type either through the use of a look-up table or neural network or other appropriate method. This information can then be used as information in connection with an anticipatory sensor as it would permit a more accurate estimation of the mass of a potentially impacting vehicle. 
     Once the vehicle knows where it is located, this information can be displayed on a heads-up display and if an occupant sensor has determined the location of the eyes of the driver, the road edges, for example, and other pertinent information from the map database can be displayed exactly where they would be seen by the driver. For the case of driving in dense fog or on a snow covered road, the driver will be able to see the road edges perhaps exactly or even better than the real view, in some cases. Additionally, other information gleaned by the exterior monitoring system can show the operator the presence of other vehicles and whether they represent a threat to the host vehicle (see for example “Seeing the road ahead”, GPS World Nov. 1, 2003, which describes a system incorporating many of the current assignee&#39;s ideas described herein). 
     7.4 Corridors 
       FIG. 7  shows an implementation of the invention in which a vehicle  18  is traveling on a roadway in a defined corridor in the direction X. Each corridor is defined by lines  14 . If the vehicle is traveling in one corridor and strays in the direction Y so that it moves along the line  22 , e.g., the driver is falling asleep, the system on board the vehicle in accordance with the invention will activate a warning. More specifically, the system continually detects the position of the vehicle, such as by means of the GPS, DGPS and/or PPS, and has the locations of the lines  14  defining the corridor recorded in its map database. Upon an intersection of the position of the vehicle and one of the lines  14  as determined by a processor, the system may be designed to sound an alarm to alert the driver to the deviation or possibly even correct the steering of the vehicle to return the vehicle to within the corridor defined by lines  14 . 
       FIG. 8  shows an implementation of the invention in which a pair of vehicles  18 ,  26  is traveling on a roadway each in a defined corridor defined by lines  14  and each is equipped with a system in accordance with the invention. The system in each vehicle  18 ,  26  will receive data informing it of the position of the other vehicle and prevent accidents from occurring, e.g., if vehicle  18  moves in the direction of arrow  20 . This can be accomplished via direct wireless broadband communication or any of the other communication methods described above, or through another path such as via the Internet or through a base station, wherein each vehicle transmits its best estimate of its absolute location on the earth along with an estimate of the accuracy of this location. If one vehicle has recently passed a precise positioning station, for example, then it will know its position very accurately to within a few centimeters. Each vehicle can also send the latest satellite messages, or a portion thereof or data derived therefrom, that it received, permitting each vehicle to precisely determine its relative location to the other since the errors in the signals will be the same for both vehicles. To the extent that both vehicles are near each other, even the carrier phase ambiguity can be determined and each vehicle will know its position relative to the other to within better than a few centimeters. As more and more vehicles become part of the community and communicate their information to each other, each vehicle can even more accurately determine its absolute position and especially if one vehicle knows its position very accurately, if it recently passed a PPS for example, then all vehicles will know their position with approximately the same accuracy and that accuracy will be able to be maintained for as long as a vehicle keeps its lock on the satellites in view. If that lock is lost temporarily, the INS system will fill in the gaps and, depending on the accuracy of that system, the approximate 2 centimeter accuracy can be maintained even if the satellite lock is lost for up to approximately five minutes. 
     A five minute loss of satellite lock is unlikely except in tunnels or in locations where buildings or geological features interfere with the signals. In the building case, the problem can be eliminated through the placement of PPS stations, or through environmental signature analysis, and the same would be true for the geological obstruction case except in remote areas where ultra precise positioning accuracy is probably not required. In the case of tunnels, for example, the cost of adding PPS stations is insignificant compared with the cost of building and maintaining the tunnel. 
     7.5 Vehicle Control 
       FIG. 12 a    is a flow chart of the method in accordance with the invention. The absolute position of the vehicle is determined at  130 , e.g., using a GPS, DGPS, PPS system, and compared to the edges of the roadway at  134 , which is obtained from a memory unit  132 . Based on the comparison at  134 , it is determined whether the absolute position of the vehicle is approaching close to or intersects an edge of the roadway at  136 . If not, then the position of the vehicle is again obtained, e.g., at a set time interval thereafter, and the process continues. If yes, an alarm and/or warning system will be activated and/or the system will take control of the vehicle (at  140 ) to guide it to a shoulder of the roadway or other safe location. 
       FIG. 12 b    is another flow chart of the method in accordance with the invention similar to  FIG. 12 a   . Again the absolute position of the vehicle is determined at  130 , e.g., using a GPS, DGPS, PPS system, and compared to the location of a roadway yellow line at  142  (or possibly another line which indicates an edge of a lane of a roadway), which is obtained from a memory unit  132 . Based on the comparison at  144 , it is determined whether the absolute position of the vehicle is approaching close to or intersects the yellow line  144 . If not, then the position of the vehicle is again obtained, e.g., at a set time interval thereafter, and the process continues. If yes, an alarm will sound and/or the system will take control of the vehicle (at  146 ) to control the steering or guide it to a shoulder of the roadway or other safe location. 
       FIG. 12 c    is another flow chart of the method in accordance with the invention similar to  FIG. 12 a   . Again the absolute position of the vehicle is determined at  130 , e.g., using a GPS, DGPS, PPS system, and compared to the location of a roadway stoplight at  150 , which is obtained from a memory unit  132 . Based on the comparison at  150 , it is determined whether the absolute position of the vehicle is approaching close to a stoplight. If not, then the position of the vehicle is again obtained, e.g., at a set interval thereafter, and the process continues. If yes, a sensor determines whether the stoplight is red (e.g., a camera, transmission from stoplight) and if so, an alarm will sound and/or the system will take control of the vehicle (at  154 ) to control the brakes or guide it to a shoulder of the roadway or other safe location. A similar flow chart can be now drawn by those skilled in the art for other conditions such as stop signs, vehicle speed control, collision avoidance etc. 
     7.6 Intersection Collision Avoidance 
       FIG. 13  illustrates an intersection of a major road  170  with a lesser road  172 . The road  170  has the right of way and stop signs  174  have been placed to control the traffic on the lesser road  172 . Vehicles  18  and  26  are proceeding on road  172  and vehicle  25  is proceeding on road  170 . A very common accident is caused when vehicle  18  ignores the stop sign  174  and proceeds into the intersection where it is struck on the side by vehicle  25  or strikes vehicle  25  on the side. 
     Using the teachings of this invention, vehicle  18  will know of the existence of the stop sign and if the operator attempts to proceed without stopping, the system will sound a warning and if that warning is not heeded, the system will automatically bring the vehicle  18  to a stop, preventing it from intruding into the intersection. 
     Another common accident is where vehicle  18  does in fact stop but then proceeds forward without noticing vehicle  25  thereby causing an accident. Since in the fully deployed RtZF® system, vehicle  18  will know through the vehicle-to-vehicle communication the existence and location of vehicle  25  and can calculate its velocity, the system can once again take control of vehicle  18  if a warning is not heeded and prevent vehicle  18  from proceeding into the intersection and thereby prevent the accident. 
     In the event that the vehicle  25  is not equipped with the RtZF® system, vehicle  18  will still sense the presence of vehicle  25  through the laser radar, radar and camera systems. Once again, when the position and velocity of vehicle  25  is sensed, appropriate action can be taken by the system in vehicle  18  to eliminate the accident. 
     In another scenario where vehicle  18  properly stops at the stop sign, but vehicle  26  proceeds without observing the presence of the stopped vehicle  18 , the laser radar, radar and camera systems will all operate to warn the driver of vehicle  26  and if that warning is not heeded, the system in vehicle  26  will automatically stop the vehicle  26  prior to its impacting vehicle  18 . Thus, in the scenarios described above the “Road to Zero Fatalities”® system and method of this invention will prevent common intersection accidents from occurring. 
       FIG. 14  is a view of an intersection where traffic is controlled by stoplights  180 . If the vehicle  18  does not respond in time to a red stoplight, the system as described above will issue a warning and if not heeded, the system will take control of the vehicle  18  to prevent it from entering the intersection and colliding with vehicle  25 . In this case, the stoplight  180  will emit a signal indicating its color, such as by way of the communication system, and/or vehicle  18  will have a camera mounted such that it can observe the color of the stoplight. There are of course other information transfer methods such as through the Internet. In this case, buildings  182  obstruct the view from vehicle  18  to vehicle  25  thus an accident can still be prevented even when the operators are not able to visually see the threatening vehicle. If both vehicles have the RtZF® system they will be communicating and their presence and relative positions will be known to both vehicles. 
       FIG. 15  illustrates the case where vehicle  18  is about to execute a left-hand turn into the path of vehicle  25 . This accident will be prevented if both cars have the RtZF® system since the locations and velocities of both vehicles  18 ,  25  will be known to each other. If vehicle  25  is not equipped and vehicle  18  is, then the camera, radar, and laser radar subsystems will operate to prevent vehicle  18  from turning into the path of vehicle  25 . Once again common intersection accidents are prevented by this invention. 
     The systems described above can be augmented by infrastructure-based sensing and warning systems. Camera, laser or terahertz radar or radar subsystems such as placed on the vehicle can also be placed at intersections to warn the oncoming traffic if a collision is likely to occur. Additionally, simple sensors that sense the signals emitted by oncoming vehicles, including radar, thermal radiation, etc., can be used to operate warning systems that notify oncoming traffic of potentially dangerous situations. Thus, many of the teachings of this invention can be applied to infrastructure-based installations in addition to the vehicle-resident systems. 
     While the invention has been illustrated and described in detail in the drawings and the foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. 
     This application is one in a series of applications covering safety and other systems for vehicles and other uses. The disclosure herein goes beyond that needed to support the claims of the particular invention that is claimed herein. This is not to be construed that the inventors are thereby releasing the unclaimed disclosure and subject matter into the public domain. Rather, it is intended that patent applications have been or will be filed to cover all of the subject matter disclosed above.