Patent GB-1257413-A (GB)
IPC: G06G7/76
Filed: 1970-03-06
Abstract: 1,257,413. Simulating traffic flow. COMPAGNIE GENERALE D'AUTOMATISME. 6 March, 1970 [6 March, 1969], No. 10839/70. Heading G4G. Flow of traffic on a system of one-way traffic paths is represented, for each stage of a path, by a capacitor the value of which represents the traffic capacity of the stage, the voltage on which represents the traffic concentration-i.e. the ratio of the number of vehicles in the stage to the total vehicle capacity of the stage-and the current flowing between successive capacitors,- such that the path is simulated by the ladder line of Fig. 2. The B ij  are charge transfer circuits having transfer characteristics appropriate to the assumed traffic flow law, and arranged to satisfy the general requirements that the movement of charge must be unidirectional, and that charge withdrawn from aparticular capacitor must correspond to the charge inserted into the capacitor immediately following it, and that both saturation, and the relief of saturation, of a capacitor mustoccur first in the final capacitor of the stage, and thereafter in successive immediately preceding capacitors. For a linear flow law; for which where q = flow of vehicles over stage, k = vehicle concentration in the stage, k s  = saturation concentration of the stage, U = mean speed of vehicles in the stage and U max  is a constant, the charge transfer circuits B ij  may each be as shown in Fig. 4, where 10 is a voltage-to-frequency converter providing a frequency a ij  being a constant, which is applied to a trigger 11 to provide -output pulses of frequency f i  and duration # i . The pulses are applied to a subtracting circuit 12 which also receives a constant voltage V s  corresponding tok s , such that the mean current I ij  injected into capacitor C j  is analogous to (1). In order to ensure that capacitor C i  is discharged according to the same law, a second voltage-to-frequency converter 20 providing a frequency f j  = a ji (V s -V j ) is connected to capacitor C j , and supplies a second trigger 21 generating pulses of duration # j  at frequency f j . These pulses are applied to the AND gate 22, whereby the mean discharge current I ji  of capacitor C i  is  the circuit parameters being adjusted to make a ij /R j  = a ji /R i , and hence I ij  = I ji . In a further embodiment, Fig. 6 (not shown), and Fig. 7, applicable to the case of a traffic flow law which, over the range of interest, may be considered to be hyperbolic i.e.  where b is a constant, the charge transfer circuits B ij  are each formed of two sections, one of which (Fig. 6, not shown) permits the passage of charge from capacitor C i  to capacitor C j  via a path the conductance of which is governed by a transistor, the transistor being cyclically switched on and cut off by signals from a circuit section; Fig. 7, which ensures that the duration of the conducting, periods is such that the mean transfer current is appropriate to the hyperbolic flow law. As shown in Fig. 7, signal (V s -V j ) from subtracting circuit S is applied to the integrator 30 to produce a sawtooth voltage having a slope (V s -V j ) the sawtooth voltage and the signal (0À5V s  + V i ) from adding circuit A D  being applied to the comparator C p , which provides an output to the pulse operator P when the two inputs attain equality. The output of pulse generator P both switches a transistor in the circuit path between two successive capacitors, to permit charge transfer therebetween, and also switches on transistor T D  to discharge the integrator capacitor C D .