[0001] The invention relates to a traffic flow unit for installation at a road surface for
controlling the flow of road traffic.
[0002] In some car parking areas or on factory sites or in other areas where it is desired
to control road traffic flow it is known to provide a traffic flow unit in the road
surface for this purpose. A traffic flow control unit incorporates a plate which is
movable, normally by pivoting action, between a retracted position where it is flush
with the road surface and a deployed position where it projects sufficiently from
the surface to prevent flow of traffic.
[0003] Typically such a flow plate is used in a situation where traffic flow is always allowed
in one direction and is always to be prevented in the opposite direction. The flow
plate can then be a simple pivoting member which retracts by pivoting when engaged
by wheels of a road vehicle in one direction but incorporates a stop to prevent rotation
in the reverse direction whereby it prevents traffic flow. Of course this prevention
is not necessarily absolute but the plate should project sufficiently to act as a
very strong deterrent and generally to inflict damage on a vehicle which does endeavour
to pass in the reverse direction.
[0004] One problem with traffic flow control units incorporating flow plates is that traffic
can pass over them quickly in the direction in which traffic flow is permitted. This
can result in very noisy operation and a high degree of wear and tear on the mechanism.
[0005] An object of the invention is to provide a traffic flow control unit in which this
disadvantage is overcome or reduced.
[0006] The invention is concerned particularly with a traffic flow control unit for installation
at a road surface comprising: a fixed body, a barrier member pivotally mounted to
the body and pivotal between a deployed position where it projects upward and acts
as a barrier to prevent traffic flow and a retracted position where it allows traffic
to pass. According to the invention such a traffic flow control unit is characterised
in that the body projects above the road surface such as to provide a speed bump with
a speed control entry ramp at its entry side and the barrier member at its exit side.
[0007] The provision of a speed bump in connection with the flow control unit slows traffic
down and thus acts as a deterrent to fast traffic flow over the unit.
[0008] Preferably the barrier member when retracted forms an exit ramp from the speed control
bump. This allows a good height of barrier to be presented to prevent traffic flow
from the exit side whereas the height of the barrier above the speed bump as encountered
by a vehicle from the entry side is much less and facilitates retraction of the barrier
by engagement by a vehicle wheel.
[0009] The shape or inclination of the entry and exit ramps may be such that the entry ramp
provides a harsher disturbance to vehicle suspension than is provided by the exit
ramp. Typically, the entry ramp has a convex contour and the exit ramp is a straight
inclined ramp. The height of the speed bump above the road surface should preferably
be at least 60 mm and more typically is between 70 mm and 80 mm. This provides sufficient
height for an effective speed bump.
[0010] The barrier member may be biased towards its deployed position, held against further
movement in one direction by a stop and freely pivotable in the opposite direction
against the bias by contact from a vehicle wheel. It may be biased by its own weight.
[0011] The barrier member may be wedge shaped such that in its deployed position it provides
an inclined face from the entry side and a vertical or near vertical face from the
exit side.
[0012] There may be means for locking the barrier member in its retracted position.
[0013] An embodiment of the invention will now be described by way of example only with
reference to the accompanying drawings in which:
Figure 1 is a perspective view of two traffic flow control units of the invention,
also illustrating a vehicle wheel passing over one of the units; and
Figure 2 is a side elevation of one traffic flow control unit, with parts broken away,
in particular showing details of its installation.
[0014] The main body 11 of a traffic flow control unit is a fabricated steel structure.
The structure incorporates a base plate 12, side plates 13 and a top plate 14. A recess
15 below the level of the base plate 12 is defined by further vertical plates 16 and
17 and a horizontal plate 18. A secondary base plate 19 continues the line of the
base plate 12 on the opposite side of the recess 15. The left hand section of the
assembly as shown in Figure 2 is its entry side, in the form of a conventional speed
bump, with the steel body 11 carrying a rubber or similar block 21 which acts as a
ramp at the left hand side of the bump. The entry side speed bump contour is convex,
following normal practice, to provide a harsh disturbance to vehicle suspension.
[0015] Towards its right hand end, the assembly incorporates two barrier members 22 and
23 which are freely pivotal about a transverse pivot pin 24 carried in two opposite
side members 13 and also carried in a further central vertical support plate 25. To
provide a long life to the pivot, the pin 24 is of stainless steel and a bronze or
similar bush is provided for running on the pivot. The operative upper part of each
barrier member 23 as shown in Figure 1 is generally wedge shaped with a steep near
vertical surface 26 presented to flow of traffic from the right and a less steep angled
surface 27 presented to flow of traffic from the left. The barrier member also incorporates
a heavy lower section as shown which tends to cause it to pivot under its own weight
into the deployed position shown for member 22 in Figure 1. The lower part of the
barrier member as shown is housed within the recess 15 below the level of the roadway.
[0016] When traffic approaches from the right that is the exit side, it meets the steep
high wall 26 and if a vehicle is driven against this wall of the unit, retraction
of the barrier member is prevented by engagement of the lower part of the member against
a stop formed by vertical wall 17 of the recess 15. Thus traffic flow is prevented
unless a driver takes very drastic action which is likely to damage the vehicle. The
surface 26 incorporates red reflectors 28 to warn approaching traffic and may be painted
in a prominent colour or otherwise have surface features to warn a vehicle driver.
A rubber buffer 29 on the vertical plate 17 acts to silence and cushion movement of
the barrier member into the near vertical position.
[0017] When a vehicle approaches from the left, that is the entry side, one feature which
the driver sees is the up-ramp as provided in a conventional speed bump and this naturally
causes the driver to slow to a speed of the order of 8 Kph. Once the wheels have ridden
up onto the speed ramp, they engage the inclined surface of the barrier member 27.
As they bear against it, they cause the barrier member to pivot as indicated by arrow
31 until the engaged barrier member reaches the generally horizontal retracted position
shown for member 23 in Figure 2. In this position, the inclined surface 27 acts as
an exit ramp with a straight inclined surface, allowing the vehicle to pass easily.
After passage of a front wheel over a barrier member, the barrier member pivots up
again to the near vertical position shown for plate 22. It can do this between passage
of front and rear wheels so a rear wheel following a front wheel again pivots the
barrier member down for passage of that rear wheel before the barrier member moves
up again to its deployed position. Cushioning corresponding to the rubber block 29
is provided on the under surface of plate 14 to limit noise as the barrier member
22 or 23 is pivoted to its retracted position.
[0018] In order to install the traffic flow control unit in a roadway, some excavation is
required and the whole assembly is then set in concrete. Lines 30 in Figure 2 illustrate
typical limits for excavation. A projection 32 and a welded on angle section 33 help
to anchor the unit firmly in position. A drainage connection 34 leads from the recess
15 to a drainage channel 35 so that rain water can be drained away from the recess.
The excavation may be filled in two stages with wire ties connecting the two stages
together.
[0019] In practice, a series of traffic flow control units are arranged side by side across
all or most of the width of a roadway over which it is desired to control passage
of traffic. Two such units are shown side by side in Figure 1 which also shows a vehicle
traversing the row of units from left to right and in such a position where it has
already engaged the inclined surface of a barrier member in its deployed position
and swung it over to its retracted position where it acts as the exit ramp from the
speed bump.
[0020] In most applications a simple pivotal action is all that is required of each barrier
member. However, if traffic flow from exit to entry is to be allowed on some ' occasions,
means may be provided for locking the barrier members in the retracted position. The
barrier members may then be swung over manually and locked in position. Alternatively,
means could be provided for powering the barrier members down to the retracted position.
The unit could then be controlled by a security guard. For example it may be set to
allow flow of traffic from left to right without any controls while passing from right
to left is under the control of security personnel.
[0021] By combining a traffic flow control unit with a speed bump, a deterrent is provided
against fast driving over the control unit which would generate excessive noise and
wear. Also, it allows a relatively high barrier member to prevent traffic flow in
one direction whilst there is only a low projection for engagement by the vehicle
for its passage in the opposite direction. The overall height of the barrier member
22 above the road surface should be limited to about 100 mm to ensure that it does
not damage a vehicle as the front wheels run down the ramp so that the vehicle straddles
the unit. Where low ground clearance cars cross the unit regularly it could be useful
to reduce the height to 85 mm.
[0022] The speed bump itself should have a height of at least 60 mm, otherwise it would
not be very effective as a speed bump and preferably its height should be 70 to 80
mm.
[0023] By having a convex entry ramp for an effective speed bump and a straight inclined
exit ramp which causes a less harsh disturbance to the vehicle suspension, the risk
of grounding the vehicle on the barrier members is reduced while effective speed bump
performance is retained.
1. A traffic flow control unit for installation at a road surface comprising: a fixed
body (11), a barrier member (22 or 23) pivotally mounted (at 24) to the body and pivotal
between a deployed position (22-Fig 2) where it projects upward and acts as a barrier
to prevent traffic flow and a retracted position (23-Fig 2) where it allows traffic
to pass, characterised in that the body (11) projects above the road surface such
as to provide a speed bump with a speed control entry ramp (21) at its entry side
and the barrier member at its exit side.
2. A traffic flow control unit according to Claim 1 characterised in that the barrier
member when retracted (23-Fig 2) forms an exit ramp from the speed control bump.
3. A traffic flow control unit according to Claim 2 characterised in that the shape or
inclination of the entry and exit ramps are such that the entry ramp (21) provides
a harsher disturbance to vehicle suspension than is provided by the exit ramp (27).
4. A traffic flow control unit according to Claim 3 characterised in that the entry ramp
(21) has a convex contour and the exit ramp (27) is a straight inclined ramp.
5. A traffic flow control unit according to any one of the preceding claims characterised
in that the height of the speed bump above the road surface is at least 60 mm.
6. A traffic flow control unit according to any one of the preceding claims characterised
in that the barrier member is biased towards its deployed position, is held against
further movement in one direction by a stop (17) and is freely pivotable in the opposite
direction against the bias by contact from a vehicle wheel.
7. A traffic flow control unit according to Claim 6 characterised in that the barrier
member is biased towards its deployed position by its own weight.
8. A traffic flow control unit according to any one of the preceding claims characterised
in that the barrier member is wedged shaped (26-27) such that in its deployed position
it provides an inclined face (27) from the entry side and a vertical or near vertical
face (26) from the exit side.
9. A traffic flow control unit according to any one of the preceding claims characterised
by further means for locking the barrier member in its retracted position.
10. A traffic flow control unit according to any one of the preceding claims characterised
in that the body incorporates a recess (15) intended for installation below road surface
level to allow part of the barrier member (22) to lie below road surface level when
the barrier member is in its deployed position.