U.S. patent number 3,593,262 [Application Number 04/783,598] was granted by the patent office on 1971-07-13 for a traffic control system for merge junctions.
This patent grant is currently assigned to Electric & Musical Industries Limited. Invention is credited to Rolf Edmund Spencer.
United States Patent |
3,593,262 |
Spencer |
July 13, 1971 |
A TRAFFIC CONTROL SYSTEM FOR MERGE JUNCTIONS
Abstract
In a traffic control system for a merge junction between first
and second vehicular paths there is provided means for detecting
movement of a vehicle along the second path towards the junction. A
first set of indicators are arranged in succession along a length
of the first path and in advance of the junction; the indicators
being so controlled by the detecting means as to direct the
creation of a moving gap in the traffic on the first path. The
moving gap is arranged to arrive at the merge junction
simultaneously with the merging vehicle so that said vehicle can
safely merge with the traffic on the first path.
Inventors: |
Spencer; Rolf Edmund (London,
EN) |
Assignee: |
Electric & Musical Industries
Limited (Middlesex, EN)
|
Family
ID: |
10478136 |
Appl.
No.: |
04/783,598 |
Filed: |
December 13, 1968 |
Foreign Application Priority Data
|
|
|
|
|
Dec 15, 1967 [GB] |
|
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57014/67 |
|
Current U.S.
Class: |
340/932;
340/907 |
Current CPC
Class: |
G08G
1/075 (20130101) |
Current International
Class: |
G08G
1/07 (20060101); G08g 001/08 () |
Field of
Search: |
;340/31,36,38 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Racing Light In Tunnel Etc." POPULAR SCIENCE MONTHLY March 1932
page 26, 340-41 .
"Ramp Control Key To Freeway Efficiency" THE AMERICAN CITY April
1969 page 138, 340-36 copies in search files, Group 230.
|
Primary Examiner: Cooper; William C.
Claims
I claim:
1. A traffic control system for a merge junction between first and
second vehicular paths including first detecting means for
detecting movement of a vehicle along the second path towards the
junction and a first set of indicators, arranged in succession
along a length of the first path, the indicators being so
controlled by the detecting means as to direct the creation of a
moving gap in the traffic on said first path, into which gap the
vehicle can merge at the junction.
2. A traffic control system according to claim 1 including a second
detecting means for detecting movement of a vehicle along said
first path and a second set of indicators being so controlled by
said second detecting means as to indicate the presence of the
vehicle on said first path.
3. A traffic control system according to claim 1 wherein said
indicators are so controlled by said first detecting means as to
cause said gap to move with substantially constant velocity and to
reach said junction at the same time as the joining vehicle.
4. A traffic control system according to claim 1 in which the
control of said first set of indicators by said first detecting
means is arranged to take account of different velocities of
vehicles on said two paths.
5. A traffic control system according to claim 1 in which the
control of said first set of indicators by said first detecting
means is arranged to take account of relative acceleration of
vehicles on said two paths.
6. A traffic control system according to claim 1 in which said
first detecting means comprises a plurality of vehicle detectors
arranged in succession along a length of the said second vehicular
path.
7. A traffic control system according to claim 6 wherein the
spacing between successive vehicle detectors is progressively
increased in accordance with a predetermined vehicle acceleration
characteristic.
8. A traffic control system according to claim 6 wherein said
vehicle detectors include inductive loops.
9. A traffic control system according to claim 1 wherein said
indicators comprise lamp units.
10. A traffic control system according to claim 9 wherein each lamp
unit includes two lamps of different colors.
11. A traffic control system according to claim 10 wherein the
first lamp of each lamp unit is of one color, the second lamp of
those lamp units nearer to the merge junction is of a second color,
and the second lamp of those lamp units further from the merge
junction is of a third color.
Description
In a traffic control system for a merge junction between first and
second vehicular paths there is provided means for detecting
movement of a vehicle along the second path towards the junction. A
first set of indicators are arranged in succession along a length
of the first path and in advance of the junction; the indicators
being so controlled by the detecting means as to direct the
creation of a moving gap in traffic on the first path. The moving
gap is arranged to arrive at the merge junction simultaneously with
the merging vehicle so that said vehicle can safely merge with the
traffic on the first path.
This invention relates to a traffic control system for a merge
junction between first and second vehicular paths.
One difficulty associated with the control of road traffic is that
encountered when traffic enters a main road from a side road. It
has been proposed to detect a gap of a predetermined minimum length
in the traffic stream on the main road while the gap is at some
distance from the merge point, and to release a vehicle waiting on
the side road at such a time that the released vehicle should reach
the merge point at the same time as the gap in the main stream.
This system has the disadvantage that vehicles in the side road may
have to wait for a considerable time before a gap appears in the
mainstream and the further disadvantage that it depends on there
being no significant change in the length and velocity of the gap
between the point of detection and the merge point. If, as may
often occur in practice, significant changes do take place, the
vehicle reaching the merge point may find that the gap has already
passed, has not yet arrived, or has been closed, and a dangerous
situation is created.
It is an object of the present invention to provide a traffic
control system for merge junctions in which the above-mentioned
problems are overcome.
According to the invention there is provided a traffic control
system for a merge junction between first and second vehicular
paths including first detecting means for detecting movement of a
vehicle along the second path towards the junction and a first set
of indicators, arranged in succession along a length of the first
path, the indicators being so controlled by the detecting means as
to direct the creation of a moving gap in the traffic on said first
path, into which gap the vehicle can merge at the junction.
The present invention is intended for systems in which vehicles are
driven only by disciplined drivers and it overcomes the above
mentioned difficulties by commanding and maintaining a moving gap
in the main traffic stream while causing the minimum disturbance to
the main traffic stream. Preferably a number of lamps are spaced
along the main road and a gap to be made is denoted by lighting a
group of adjacent lamps. The gap length is determined by the
interval between lamps and the number of lamps in a group. Groups
of lamps are illuminated in sequence in response to the movement of
a vehicle on the side road so as to produce a moving group of
lights, and the position and velocity of the group is so related to
the position and acceleration of the vehicle on the side road that
the moving group of lamps reaches the merge point at the same time
as the vehicle. It is the duty of drivers in the main stream to
keep behind or in front of the illuminated group of lamps. As the
merging vehicle is not required stop at the merge point, its
velocity at this point may be close to that of the main traffic
stream and there is consequently no need for the vehicles behind
the gap to slow down or stop while the merge is being effected.
Some slowing down will, of course, be necessary when a gap has to
be introduced into the main stream, but as only a gradual slowing
down is necessary, disturbance of traffic flow is minimized.
In order that the invention may be clearly understood and readily
carried into effect it will now be described with reference to the
accompanying drawings, in which:
FIG. 1 (which comprises FIGS. 1a to 1d) is a block diagram of a
system for controlling traffic at a merge point in accordance with
the invention,
FIG. 2 (which 2a FIGS. 2a to 2c) of a typical traffic layout using
the invention, and
FIG. 3 shows in more detail one of the lamp units used in the
invention.
Referring first to FIG. 2, this shows part of a traffic layout, a
complex one being chosen to illustrate the capabilities of the
invention. A down lane DL handles traffic moving from left to
right. At point A a bypass lane leads to a coach station denoted by
platform 1. Beyond platform 1 an outlet lane branches from the
bypass lane at point B and the bypass lane rejoins the main down
lane at point C. Similarly an up lane UL is bypassed between points
D and F, a feeder lane joining the bypass at point E and a coach
station, denoted by platform 2, being provided between points E and
F. As shown in the drawing, a deceleration lane is provided between
point A and platform 1 to avoid the necessity for vehicles which
intend to stop at platform 1 to slow down unduly before point A. It
has been found that to bring a fully laden coach travelling at 30
m.p.h. to a halt, taking into account the limits imposed on
deceleration by passenger comfort considerations, a deceleration
lane of 250 feet is adequate. As has already been mentioned, in
order to minimize disturbance of the main stream, a vehicle
intending to merge should, ideally, have reached the same speed as
the main traffic stream by the time the vehicle reaches the merge
point. In practice, however, this may not be possible. If the main
traffic stream is travelling at high speed, either a very long
acceleration lane would be required between platform 1 and merge
point C, or a higher rate of acceleration than that dictated by
passenger comfort would be required. In the present example,
therefore, a compromise is made by providing an acceleration lane
of 550 feet. This will allow a fully laden coach to accelerate
smoothly to 30 m.p.h. by the time it reaches merge point C. A
number of detector devices V1 to V20 are located along the
acceleration lane. Each device may, for example, take the form of
an inductive loop buried in the road and connected to a vehicle
detector unit, as shown in FIG. 1, the detector unit producing an
output each time a vehicle passes over the loop to which it is
connected. Such loops and detector units are well known and will
not be described in detail. Suitable dimensions for the loop are 6
feet long by 4 feet wide, buried to a depth of 2 inches.
As indicated in the drawings, the spacing between the vehicle
detector loops progressively increases with distance from platform
1. This, as will be explained more fully in due course, it to take
account of the acceleration characteristics of vehicles leaving the
platform. Associated with the vehicle detector units are lamp units
L1 to L20 etc., spaced along the main down lane. Each lamp unit
contains two lamps, one green and the other amber, in the case of
units L1 to L15, and one green and the other red in the case of
units L16 to L20. Further vehicle detector loops V21 to V24 are
spaced along the main lane following the merge point.
Four vehicle detector loops V25 to V28 are spaced along the main
lane prior to the merge point and are associated with lamp units
L22 to L25 spaced along the acceleration lane. The lamp units are
so placed that the lamps are visible only to drivers in the
appropriate lane. They may for example, be mounted on the crash
barrier at the side of the lane and at such an angle that the lamps
are not visible to drivers in the adjacent lane. As shown in FIG.
1, each vehicle detector unit, apart from D21 to D24, is connected
via a 2-gate to a bistable circuit. The latter controls two lamp
drivers which switch two lamps in the lamp unit. In FIG. 1,
corresponding units have, as far as possible, been given the same
reference numeral. Thus the output from vehicle detector unit D1 is
applied via the 2-gate G1 to set the bistable B1 to the 1-state.
When in this state, B1 energizes lamp driver 1A which switches on
the A (amber) lamp of lamp unit L1. The reset input of each
bistable is connected to the output of the vehicle detector unit
five places to its right i.e., the reset input of B1 is connected
to D6, B2 to D7 etc. Each bistable reset input is also connected to
the vehicle detector units six and seven places to the right, i.e.,
to D7 and D8 in the case of B1. These additional connections are
shown as broken lines to indicate that they are effective only so
far as the reset inputs are concerned. For example, the broken
lines joining the output terminals of D6, D7 and D8 indicate that
the outputs of all these units are connected to the reset input of
B1, but that there is no connection between the output of any of
D6, D7 or D8 and the set input of the bistable associated with the
other two vehicle detector units. Each bistable, when in its reset
or 0 condition, energizes its associated lamp driver e.g. 1G, which
switches on its lamp G, (green).
The apparatus described so far operates in the following manner.
All bistables B1 to B20 are initially in the reset condition and
consequently all the green lamps are on. Assume a stationary
vehicle at platform 1 begins to move. When it crosses vehicle
detector loop V1, vehicle detector unit D1 produces an output which
sets bistable B1. Lamp driver 1A is therefore energized and lamp
driver 1 G is deenergized, switching on the A (amber) lamp of unit
L1 and switching off the G (green) lamp. Similarly as the vehicle
crosses vehicle detector loops V2 to V5, the G lamps of units L2 to
L5 will be switched off and the A lamps switched on. The first five
lamps on the main lane are therefore now at amber, and the
remainder at green. When the vehicle crosses loop V6, the output
from D6 causes lamp unit L6 to change from green to amber. The
output of D6 also resets bistable B1 causing lamp unit L1 to revert
to green. If, for some reason, B1 should fail to be reset by D6, it
will subsequently be reset by D7 or D8. This multiple reset, which
applies to all the bistables, is a safety precaution. Thus as the
vehicle proceeds along the acceleration lane, a group of five
successive amber lights will move along the main lane. If drivers
in the main lane respond so as to keep behind or in front of the
moving amber lights, a moving gap is created in the traffic stream.
As the gap is controlled by the movement of the vehicle in the
acceleration lane, this ensures that the gap will reach the merge
point at the same time as the vehicle. It will be appreciated that
if the vehicle detector loops in the acceleration lane were equally
spaced, the series of amber lights would move slowly initially as
the vehicle accelerated from rest. Drivers in the main lane would
in these circumstances be suddenly confronted by a slowly moving
series of amber lights and would be forced to brake sharply. To
avoid this, the spacing of the vehicle detector loops is
progressively increased in accordance with the acceleration
characteristics of a typical vehicle so that the loops are crossed
at a substantially constant rate, say one per second. It will also
be appreciated that in the time taken by a vehicle to travel the
550 feet of the acceleration lane, a vehicle travelling at a
constant speed along the main lane will travel a much greater
distance. For this reason the lamps begin 950 feet from the merge
point. This is the distance which a vehicle travelling at 30
m.p.h., i.e., the speed at which vehicles are expected to merge,
will travel while a vehicle in the acceleration lane is
accelerating from rest at platform 1 to 30 m.p.h. at the merge
point. The amber lights moving along the main lane can therefore be
said to represent the translated position of a vehicle on the
acceleration lane. It has been mentioned that the object of the
series of amber lights is to create a moving gap in the main
traffic stream. However a driver confronted with a series of amber
lights need not reduce speed to remain behind them. He has the
option of maintaining or increasing speed to pass them. There must
come a point, however, at which the moving lights cannot be safely
passed before they reach the merge point. To indicate this the lamp
units immediately preceding the merge point, namely units L16 to
L20, contain red lamps in place of amber lamps. The presence of one
or more red lamps therefore indicates to a driver that the group of
lamps must not be overtaken. Consequently when a vehicle on the
acceleration lane crosses vehicle detector loop V20, lamps L16 to
L20 will be red and there will therefore be a gap of 200 feet in
the main traffic stream. As the vehicle will be slightly ahead of
red lamp L20, the driver will not be confused by the red lamp. The
driver of the vehicle immediately behind the series of red lamps
will now see five red lamps with the merged vehicle alongside the
furthermost one, L20. As he is still required to remain behind the
lamps, this ensures a headway of approximately160 feet between the
vehicles. As the merged vehicle crosses vehicle detector loops V21
to V24 in the main lane the lamp units L16 to L20 are successively
restored to green by the resetting of bistables B16 to B20 and the
second driver then maintains a suitable headway by visual
means.
Vehicle detector loops V25 to V28 in the main lane and
corresponding lamp units L22 to L25 in the acceleration lane
provide an additional safety measure. If there is a slowly moving
or stationary vehicle in the main lane approaching the merge point,
it could be overtaken by the moving series of red lamps. The
vehicle would then be in the "gap," and the driver might be unable
to get out of it before it reached the merge point. However, as the
slowly moving vehicle crosses vehicle detector loops V25 to V28,
the corresponding lamp units L22 to L25 in the acceleration lane
are changed to red to warn the vehicle in the acceleration lane of
the danger. The driver of the merging vehicle can then reduce his
speed so as to remain behind the red lights. This slowing down will
result in a slowing down of the moving lights, and consequently the
traffic, in the main lane, so that when the vehicle does reach the
merge point a gap will be present. Lamps L22 to L25 are
subsequently restored to green by the crossing of vehicle detector
loops V21 to V24 by the main lane vehicle.
In the preceding description, it has been assumed that a vehicle
leaving platform 1 intends to merge. If, however, the vehicle
intends to proceed to the outlet lane, there is clearly no need to
create a gap in the main lane traffic. At platform 1, a steering
bias detector SBD is provided to detect whether the driver of a
vehicle proposes to turn left on to the outlet lane or right on to
the main lane. The driver may indicate this in one of several ways.
For example, the vehicle may be provided with two inductive
signalling loops, connected to the traffic indicator light circuits
of the vehicles and a pair of sensing loops provided on the ground.
Alternatively, if the vehicle employs an automatic guidance system
of the kind in which a mechanical pin mounted under the vehicle
follows a slot in the road, the driver would be required to set the
pin to follow either the left- or right-hand side of the slot, and
the position of the pin could be detected, for example
magnetically, to indicate the direction in which the vehicle
intends to turn. When the steering bias detector detects a left
turn, a signal is applied to a 1-gate G29 and to the set input of a
normally reset bistable B29. Setting B29 removes an input from each
of gates G1 to G20 so preventing bistables B1 to B20 from being set
when the vehicle crosses the vehicle detector loops V1 to V20. The
lamps L1 to L20 in the main lane therefore remain green. The output
of gate G29 is applied to one input of a 2-gate G24, the other
input being derived from the reset output of a bistable B22. The
output of G22 is applied to the reset input of a bistable B21 which
controls two lamp drivers 21R and 21G. When B21 is reset, driver
21G is energized to switch on the green lamp of lamp unit L21. The
latter is located at the departure point of platform 1. It can
therefore be seen that a driver cannot receive permission to
proceed, as indicated by the green lamp, until his proposed turning
direction has been detected. When the vehicle crosses the first
vehicle detector loop V1, the output of vehicle detector unit D1
resets bistables B21 and B22. The departure lamp unit L21 is
therefore changed to red to prevent another vehicle from leaving.
When the vehicle crosses V15, the output from D15 resets bistable
B22. Bistable B21 remains in the set condition and the departure
lamp remains red until another vehicle indicates its proposed
turning direction. Once a vehicle has indicated that it will turn
left, it must be prevented from entering the main lane, as no gap
will be provided for it. The set output of bistable B29 is
therefore applied via gates G25 to G28 to set bistables B25 to B28
so switching lamp units L22 to L25 at the end of the acceleration
lane to red. This warns the driver not to proceed any further. When
the vehicle enters the outlet lane it crosses a vehicle detector
loop V29 so producing an output from detector unit D29 which resets
bistables B29. The resetting of B29 restores one input to gates G1
to G20 and also energizes a pulse generator PG whose output is
applied via gates G30, G31 and G32 to reset B25 to B28, restoring
lamp units L22 to L25 to green. It will be noted that although the
latter would normally be restored to green by vehicles crossing V21
to V24, this is prevented in this situation by gates G21 to G23
which are inhibited when B29 is in the set condition. It will be
appreciated that if there is no outlet lane, or if it is located
near the platform, the steering bias detector and bistable B29 may
be dispensed with.
The apparatus shown in FIG. 1 is for the control of traffic in the
down lane. The apparatus for control of traffic in the up lane will
be identical and need not be described. When the traffic layout is
symmetrical as in FIG. 2, some lamp units in the down lane are in
the same positions as lamp units in the up lane, and in such cases
the two lamp units may be mounted in the same housing as shown in
FIG. 2, and in more detail in FIG. 3. With the exception of the
vehicle detector loops, lamps and steering bias detector, all the
equipment may be housed in a common cabinet which may, for
convenience, be located at the platform. As shown in FIG. 1, the
main power supply is connected to a power supply unit PS1 which
produces the DC required by the electronic units. Means may be
provided to detect a fall in the DC supply and to switch over to
the standby power supply PS2. The lamps are connected to the AC
supply by the lamp drivers which may comprise solid state AC
switches such as triacs. Failure of the main supply will therefore
result in the extinguishing of all lamps. It is for this reason
that it is preferred to employ green lamps to indicate a clear
condition rather than simply the absence of amber or red lamps. The
absence of lamps will warn drivers that the control system is not
operating and that they should proceed with caution.
Although the invention has been described with reference to merging
vehicles leaving a station, it is clearly applicable to any
situation in which it is desired to merge vehicles from a side road
with a main traffic stream.
Many alternatives to the particular types of vehicle detectors,
indicating lamps and logic circuits described will be obvious to
those skilled in the art, and the invention is in no way limited to
the particular apparatus described.
* * * * *