Patent GB-827654-A (GB)
Title: Highway traffic control system
IPC: G08G1/09
Filed: 1956-02-08
Abstract: 827,654. Road signals for controlling traffic; electric measuring systems. BARTELINK, E. H. b. Feb. 8, 1956 [Feb. 8, 1955], No.3996/56. Classes 40 (1) and 118 (2). [Also in Groups XIX, XXXVI, XL (b) and XL (c)] A traffic control system comprises means 11 for measuring the number of vehicles in a predetermined section of highway, means 12 for measuring the visibility in such section, illumination measuring means 14, means 13 for measuring the adhesion between the wheels of a vehicle and the surface of said section, and means 15 for measuring the speed of the slowest vehicle in said section, together with computing means 23 . . . 28 and 47 connected to all said measuring means and controlled thereby for computing the maximum safe speed under the measured conditions. The value of the maximum safe speed thus determined by the computer is displayed on a number of indicators 49, 50 ... 51, spaced along the section. Other parameters affecting the maximum safe speed, such as the time of day, may be fed in by apparatus 16. The output of each sensing unit 11 to 16 is applied to computer input units 23 to 28, respectively. These have manual controls 29-34 which may modify the outputs or substitute therefor, and also have indicators 35-40 showing the values of the parameters being transmitted to the cornputer 47. Excess speed apparatus 53 receives inputs from the maximum safe speed computer 47 and from speed measuring apparatus 54 (or 15) and gives an alarm if a vehicle exceeds the computed maximum safe speed (see Groups XIX). In order to economize on the number of data transmission links required two or more -parameters may be combined in a partial computer, such as 55, and transmitted to one computer input unit; the dotted lines show the alternative connections in this case. The sensing units 11-16 each provide a voltage output which is a function of the quantity measured, and the respective computer input units 23-28 translate these voltages into mechanical rotations of their output shafts by means of amplifiers and servo systems (see Group XXXVI). These shafts rotate cams in the main computer 47 (see Group XXXVI) to move sliders on potentiometers, the potentials of which are amplified and combined to produce an output indicative of the maximum safe speed. The traffic density measuring apparatus 11 is shown in schematic detail in Fig. 2 and comprises vehicle-operated contacts 65, 66, 67 at the beginning of the road section and contacts 68, 69, 70 at the end, the traffic being divided into three lanes by means of flexible or other known separators 61-64. Closure of these contacts impulse electrical stepping mechanisms 77-79 and 80-82 respectively. The output shaft rotations of the three counters in each set are added by differentials, as shown, and the resultant two rotations (representing the number of vehicles entering the section and the number leaving) are fed to a subtracting differential 96 the output shaft of which moves a slider 98 on a potentiometer 99 by means of a cam 101. By suitable choice of the cam 101 and the winding 99 the output voltage may represent the input voltage from battery 102 or a source 103 multiplied by a function of the number of cars, e.g. the reciprocal, and thus provide a measure of the average spacing between cars. The cam 105 and potentiometer 107 are merely an alternative arrangement giving an inverse voltage. Instead of the contacts 65-70 the vehicles may interrupt a light beam (Fig. 3, not shown) for counting purposes (see Group XL (b)). The visibility measuring apparatus 12 comprises a series of lamps spaced at increasing distances from a photo-electric cell as in Fig. 4 (not shown) and these are energized in sequence while a potentiometer is stepped in synchronism until the cell is not sufficiently excited (see Group XL (b)). The voltage output is then a measure of the visibility. The illumination sensing unit 14 may be a conventional light measuring device giving a voltage output dependent upon light intensity. The adhesion measuring apparatus 13 comprises a box-like structure 180 (Fig. 5) pivoted at 183 and supported on two wheels 181, 182, the first of which is driven to run on the road surface under test and rotate the structure 180 against the action of a spring 187 (Fig. 7) until slipping occurs when the amount of rotation of the device is automatically recorded and the drive disconnected. The device is operated at intervals determined by a timing motor 192. This periodically closes contacts 194 to release pawl 241 such that the slider 244 on potentiometer 245 reverts to zero, and then closes contacts 204 to energize the drive motor 191 and relay 195. Relay 195 holds itself and motor 191 energized and also energizes the magnetic clutch 198 to couple a shaft 199 to the output of a differential 207 which is connected between wheels 181 and 182. Motor 191 drives the wheel 181 through gearing and a differential 218 the output shaft of which is locked by the pawl 208 engaging gear 209. As the structure 180 rotates, wheel 182 follows the motion of drive wheel 181 exactly and there is no output from differential 207. A cam 236 moves slider 244 along potentiometer 245 to provide a voltage at terminals 247, 248 which is a function of the rotation of the device. When wheel 181 slips on the road surface differential 207 immediately rotates shaft 199 and contacts 205 are closed. Relay 202 is thereby energized to open the circuit of drive motor 191 and relay 195. It also releases pawl 208 from gear 209 which frees differential 218 and allows the whole device 180 to return to its starting position under action of spring 187. The magnetic clutch 198 is released and contacts 203 opened. Although cam 236 reverts to its zero position the slider 244 is retained by pawl 241, and a voltage indicative of the adhesion between wheel 181 and the road remains on terminals 247, 248 until the timing motor 192 closes contacts 194 and recommences the cycle. The means 15 for measuring the speed of the slowest vehicle comprises a Doppler radar system (see Group XL (c)) in which the beat frequencies derived from moving vehicles are analysed by a series of filters (Fig. 8, not shown) and a stepping potentiometer is automatically set to a position depending upon the lowest frequency so as to provide a voltage output proportional to the slowest speed. It is shown that the maximum safe speed depends upon a function of visibility, illumination, speed of slowest vehicle, and road adhesion, unless the average spacing between vehicles becomes smaller than the effective visibility; then the maximum safe speed should be determined simply by the traffic density and road adhesion. The computer 47 arranged to switch automatically from a combination of visibility, illumination and slowest speed to traffic density according to which produces the lowest voltage; the road-adhesion parameter is fed in subsequently in either case (see Group XXXVI). Facility is provided for direct control of indicators 49-51 by a manually operated potentiometer.