1286251 Inter-vehicle signalling and control EMI Ltd 23 Sept 1969 [25 July 1968] 35436/68 Heading H4D [Also in Division G4] System.-In an inter-vehicle signalling system, e.g. for PSVs on highspeed highways incorporating radio transponders for inter-vehicle detection, it is shown that safe headway is given by H = P + QV + RV<SP>2</SP> where H is headway, V is speed of following vehicle in fps, and P, Q, R are constants dependent on vehicle length, brake reaction delay and brake retardation respectively; specifically, H = 40 + 1À5V + 0À05V<SP>2</SP> for typical PSVs. Early warning of a stationary or decelerating leading vehicle is given by signals from its transponder indicating braking or speed below a critical value to a following vehicle. In Fig. 1, a bus station 1 is situated adjacent to a highway 2 on sections 3, 4, 5 of a layby, with optional entry and exit roads 6, 7 to the highway. Coded magnets 8, 10, 11, 13, 15, 16, 18 as described in Specification 1,231,794 are placed as shown on the highway, the layby sections, the station and the exit road. On the open highway all vehicles emit interrogating signals comprising binary coded pulses to which vehicle responders reply. The driver of a vehicle entering the Fig. 1 layout sets a right or left steering bias to continue along highway 2, or to enter section 3, according to whether magnets 8 have null effect or cause the interrogator to operate alternately on the highway 2 and section 3 codes. A vehicle calling at station 1 traverses magnets 10 which cause the interrogator to operate solely on the section 3 code and the responder to react only to such code, while a fixed responder at station 1 reacts to interrogation to halt the vehicle at station 1. In presence of road 7, entry to section 4 is permissible only on application of right steering bias before leaving section 3. On leaving station 1, traversal of magnets 11 sets the interrogator to operate only on codes for sections 4, 5, and the responder to react to the code of section 4 and (unless the vehicle is leaving the system at point 12) to a highway ghost code, controlling the merging with the highway traffic as described in Specification 1,231,794. The vehicle traverses coded magnets 13 causing the interrogator to operate on the highway code and the responder to react to the codes of the highway and of section 5, after which the vehicle traverses coded magnets 15, causing the responder to react to the highway code only, and then enters the highway 2. A vehicle by-passing the station 1 traverses coded magnets 16, which cause the interrogator to operate alternately on the highway code and the highway ghost code to display warning of vehicles in sections 4, 5, while as described in Specification 1,231,794 a driver warned of less than minimum headway with respect to a second vehicle in section 4 by responses in the ghost code may override the warning and overtake, but must conform to a highway responder signal and fall behind when the second vehicle is on section 5. A vehicle entering at point 17 under traffic signal control has its transponder switched on by magnet 11, and on leaving at point 12 has it switched off by magnet 18. Structure.-Fig. 3 shows an interrogatorresponder vehicle system utilizing a magnetron TX 20 switchable at 21 to front and rear interrogator and responder antennµ 22, 23. Interrogating pulses from generator 24 are jittered from unit 25 so that I-R signals from different vehicles are incoherent, and energize an oscillator fed coded pulse train generator 26 giving spaced groups of seven pulses at recurrent intervals (Fig. 2a). In each group a reference pulse is followed by three binary code position modulated pulses to denote the interrogator under code control 40, while the remaining three pulses respectively determine the nearest vehicles on the same track which are running, braking, and stationary. The output of 26 is also applied over OR gate 28 to the transmitter modulator 29. Receiving front and rear antennµ 32, 33 are respectively connected over coupler 34 muted by modulator 29, and also directly, to respective receivers 35, 37 and amplifiers 36, 38; and the latter energize radar code sensor 39 comparing the received code of 2nd, 3rd and 4th pulses with the responder code derived from code control 40, to pass the 5th, 6th and 7th pulses at its three outputs, on equality. OR/AND logic 42, 43, 44, 45 operates switch 21 to pulse transmitter 20 after a variable delay at unit 46, thus ensuring distinction between reflection returns and responder returns; the delay being compensated by equivalent delay in the interrogator ranging circuit; and being reduced by a control input where the vehicle is moving slowly or is stationary so as to give earlier warning to an interrogating vehicle. Vehicle data circuits comprise a braking sensor 47 coupled to the brake gear or an accelerometer, a speedometer transmitter 48, a road magnet sensor 49, a reverse motion sensorindicator 55 and a steering bias indicator circuit 50. The sensor 49 reads out a pulse train to a road code discriminator 51, whose output energizes code control circuit 40 and display 52. Braking sensor 47 enables AND gate 43 to pass the 6th pulse of a code group on brake application, and transmitter 48 delivers pulses to detector 56 at a speed rate which, if the pulse interval exceeds a preset value, enables AND gate 44 to pass the 7th pulse of a code group; and also pulses a discriminator 57 to apply a speed analog signal to function generators 58, 59 generating H 1 = P + QV + RV<SP>2</SP> and H 2 = P + QV + 2À3 RV<SP>2</SP> for minimum headway allowable for normal retardation, and allowable for acceptable retardation, respectively. Pump circuit 60 initially excited by a predetermined level signal from code discriminator 51 is pulsed from transmitter 48 to progressively reduce a control signal as the vehicle progresses, in dependence on road speed and distance travelled, and analog gate 6 responsive thereto and controlled from code circuit 40 when the latter is coding a highway " ghost " regulates the delay 46 to increase with increasing control signal, so that a vehicle leaving station 1 appears when interrogated by a highway vehicle to be closer than it actually is; the law of variation of the delay being matched to expected vehicle performance. Operation.-Each group of 7 interrogation pulses produces up to three responder pulses (Fig. 2b) under control of logic 42 to 45 enabled by amplified output of receiver 37. Pulse A in response to the 5th interrogation pulse is derived from transmitter 20 through delay element 46, B in response to sensor 39 when vehicle is braking, and C in response to sensor 39 when vehicle speed is low, so that a following vehicle receives any of the three pulses, detected at receiver 35, amplified, and applied to an analyser 53. The detected responder pulses (Fig. 2c) comprise e.g., three pulses A<SP>1</SP>, A<SP>11</SP>, A<SP>111</SP> due to three leading vehicles, pulse B<SP>1</SP> due to a braking leading vehicle producing pulse A<SP>11</SP> and pulse C<SP>1</SP> due to a stationary vehicle producing pulse A<SP>111</SP>. The pulses are gated at 62 under control of coded train generator 26 to a ramp generator 63 triggered by pulses from 26 timed as A, B, C (Fig. 2b) to generate a linearly increasing signal D (Fig. 2d) until arrival of pulse A<SP>1</SP>, after which a level signal E is generated until trigger pulse B, when a linearly decreasing signal F is generated until arrival of pulse B<SP>1</SP>. Thereafter the level is held for a fixed delay of 15 Ás and then reset to zero until arrival of trigger pulse C when a linearly increasing signal is generated until arrival of pulse C<SP>1</SP>, when the level is held for 15 Ás. The ramp length corresponds to the range of the stationary vehicle, and the output is applied to comparators 64, 65, 66. Then 64 is triggered from generator 26 3 Ás after start of ramp F to compare level G with zero, and if the level is below zero a vehicle other than the nearest is braking; if it is zero the nearest vehicle is braking. The output is stored in bi-stable 67 for display at 52, while a further bi-stable 68 connected to ramp generator 63 indicates on display that the nearest vehicle is stationary. OR gate 69 connected to two of the three outputs of coded train generator 26 (Fig. 2e) which are delayed 15 Ás from those applied to ramp generator 63 and gates 62, resets the ramp levels to zero. The analog signals from 58, 59 representing H 1 and H 2 the minimum and the stationary vehicle headways are summed at 71, 72 with the output of a velocity dependent function generator to produce initial values of staircase generators 74, 75 producing N steps under control of pulse generator 76 enabled by code train generator 26 over gate 77 to start 3 Ás after the earliest time of response to the 5th and 7th pulses. The staircase waveforms starting from headway voltages H 1 , H 2 by steps dependent on vehicle speed are compared at 65, 66 with ramp levels E, K (Fig. 2d) and the first comparator to indicate excess is selected at 78 to reset ring counter store 79, so that the stored digit positionally denotes the smaller margin over the minimum headways appropriate to the nearest moving and stationary vehicles. The store 79 and bistables 67, 68 are resettable by pulses from control 40, after plural interrogations, and the output at reset is transferred to display 52 indicating allowable headway by a lamp code. Fault detection and standby equipment substitution are provided as described in Specification 1,213,630.