Patent Publication Number: US-8125750-B2

Title: Street furniture safety device

Description:
DESCRIPTION OF INVENTION 
     The invention relates to a safety device for street furniture and in particular to an isolation system for use in street furniture which include an electrical supply, such as for examples a traffic signal (commonly referred to as a traffic light), street light, or illuminated sign. 
     Many installations of street furniture which include an electrical supply are located very close to the roadway, and thus are vulnerable to being collided with by vehicles. When such a collision occurs the street furniture itself represents a danger to the vehicles and its occupants, in that it might remain in place as a rigid structure ensuring that the vehicle suffers very significant damage or it might fall onto the vehicle. Recently laws or new practices have been introduced in many territories which require or advise that, at least in some circumstances such as on roads with a speed limit of 50 mph or higher, the street furniture collapses in some predetermined manner in order to minimise the physical danger the street furniture represents. 
     In addition the electrical supply itself can represent a danger to the people involved in such an accident, or those who arrive to assist those involved, or those who subsequently arrive to repair the street furniture. If the electrical supply remains connected to the damaged street furniture then live electrical wires may be open to the elements and to being touched by such people, thus leading to risk of electric shocks being inflicted on those people, and to sparks igniting spilt fuel or chemicals. 
     In some territories there are now also requirements to disconnect the electrical supply to the street furniture in the event of damage to it, and in general such safety cut-off systems are being included in new installations and in some cases in refurbishment of existing installations. In the United Kingdom at present the only system available to implement this requirement includes an in-line socket and connector which are held under tension and are designed to part company when the street furniture is badly damaged, thus disconnecting the electrical supply to the street furniture within the street furniture itself. However, this has two distinct disadvantages. First, plugs and sockets used in this way tend to be unreliable, and second they only work to disconnect the electrical supply in certain kinds of accidents and then only within the street furniture installation itself. This means that a live feed still exists to the base of the street furniture and this still represents a risk of electrical shock in some circumstances, in particular to those people who come to repair the street furniture. 
     It is an aim of the present invention to provide an alternative electrical isolation system for use in street furniture. 
     According to a first aspect of the present invention there is provided an electrical isolation system as set out in claim  1 . Further features of the electrical isolation system according to the invention are set out in dependent claims  2  to  10 . 
     According to a second aspect of the present invention there is provided a method of providing electrical isolation as set out in claim  11 . Further features of the method according to the invention are set out in dependent claims  12  to  15 . 
     According to a third aspect of the present invention there is provided street furniture having an electrical supply to working electrical components and including an electrical isolation system according to the first aspect of the invention and/or which operates in accordance with the method of the second aspect of the invention. 
    
    
     
       An example of the present invention will now be described, by way of example only, with reference to the drawings in which: 
         FIG. 1  is a schematic plan view of a cross-roads junction with traffic signals incorporating the electrical safety isolation system according to the invention; 
         FIG. 2  is a side view of part of the junction of  FIG. 1  showing a traffic signal, a termination cabinet and a control cabinet; 
         FIG. 3  is a schematic view of the electrical safety isolation system. 
     
    
    
     Referring first to  FIGS. 1 and 2 , a simple cross-roads junction having traffic signal control is illustrated in two different views. There are four traffic signals  10 , one at each road entry to the junction, located close to the roadway  12  and thus vulnerable to being collided with by vehicles. The traffic signal control for the junction includes a termination cabinet  14  and a control cabinet  16  (as in the prior art, for normal control of the traffic signal installation at the junction, and thus which will not be described further here), located at a greater distance from the road way than the traffic signals  10  are, and in this example back off the pedestrian pavement  18  in a grassed area  19 . It should be understood that a single cabinet may be provided in place of the two described here. 
     Referring now also to  FIG. 3 , a schematic view of the traffic signal control for the junction is illustrated. In each traffic signal  10  are working components  20  of the traffic signal, as in the prior art and thus which will not be described further here, and an impact sensor  22 , such as an accelerometer although any suitable kind may be used. The working components  20  of the traffic signal  10  have an electrical feed  24  and the impact sensor  22  has an applied voltage via line  26 . The impact sensor  22  is, in this case, a switch which is normally closed but which when triggered is open. 
     In the termination cabinet  14  are a monitoring unit  30  and a plurality of isolators  32 , in this case four, one for each traffic signal  10 . The applied voltage lines  26  to the impact sensors  22  of each traffic signal  10  are connected to the monitoring unit  30 . The electrical feed  24  to the working components  20  of each traffic signal  10  are each connected to an isolator  32  which is controlled by the monitoring unit  30 . Each isolator  32 , typically an MCCB (multi-pole circuit breaker) although any other suitable type may be used, receives an electrical feed  34  from the control cabinet  16 . 
     The monitoring unit  30  includes visual indicators (not shown) for the supply of power to each traffic signal  10  and for the activation of each impact sensor  22 , although these could be omitted. Preferably the monitoring unit  30  also includes visual indicators for the status of other features of the traffic signals  10 , such as to indicate failure of a bulb, or a software problem within the controls of the junction in the control cabinet  16 . The monitoring unit  30  is also provided with additional contacts  36 ,  38  for integration into a telemetry system if provided, such that any failures noticed by the monitoring unit  30 , or a complete power failure at the junction, can automatically be reported to a remote control room, but these can be omitted if not required. 
     The electrical isolation system operates as follows. When an impact sensor  22  is activated, the switch opens (effectively sending a signal) and the monitoring unit  30  identifies that it has gone open circuit. In response the monitoring unit  30  disconnects the voltage to the sensor  22  via electrical feed  26  and lights the respective visual indicator. In addition the monitoring unit  30  provides a constant latched output to the respective isolator  32  resulting in disconnection of the electrical supply to the working components  20  of the respective traffic signal  10  via the supply  24 , and the relevant visual indicator is activated to show the disconnection. This disconnection occurs rapidly after activation of the impact sensor  22 , (e.g. within 400 milliseconds) although any time period which meets the relevant regulations (if any) can of course be provided for. 
     The latched output to the respective isolator  32  prevents inappropriate re-energising of the supply to the working components  20  of the respective traffic signal  10 . There is a reset switch (not shown) on the monitoring unit  30  for each feed to an impact sensor  22 . However, even if the reset switch is activated the monitoring unit  30  maintains the latched output to the isolator  32  until it receives a further signal, in this case a return voltage via line  26 , indicating that the sensor  22  has been reset or replaced. Receipt of such signal also switches off the visual indicators for activation of the sensor  22  and disconnection of the electrical feed  24 . 
     Hence, when an impact is sensed the electrical supply to a traffic signal  10  is cut off quickly at a remote location and cannot be reconnected until such time as the impact sensor  22  has been reset or replaced. Thus, the electrical isolation system of the invention provides a significant improvement on safety when compared with the prior art. 
     Alternative forms of impact sensor, such as those which actively send a signal, may of course be used in place of the switch described above. In addition alternative forms of electrical isolator may be employed. 
     When used in this specification and claims, the terms “comprises” and “comprising” and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components. 
     The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.