Random thoughts, poems, jottings, and as it says, musings. About anything and everything!
Tuesday, 26 July 2016
Lighting the Way
Readers of this blog may have noticed that the lights at the junction at the bottom end of Mont Millais have been replaced, and also those at First Tower junction. Each traffic light set is a combination of control unit and lights themselves, run from the programs in the control box.
These upgrades replace the junction control box, which has been in place with the lights themselves, for around 17 years. As might be imagined, the technology has advanced considerably over that time.
In fact the 17 year old systems were the first with printed circuits; they replaced transistorised traffic lights controllers, which were prone to need re-soldering as the transistor joints became brittle and broke off over time!
Before that Jersey actually had traffic lights with controllers using valves, large cumbersome electronic devices the size of small light bulbs, which tended to break down, and were also used in the old TV sets of the 1960s. Older people may remember how long it took for the TV to warm up because valve technology was rather inefficient.
But let us go back to 1999, 17 years ago, and the time of the controllers and lights being replaced, and look at the kind of everyday technology. In 1999, only around 2% of homes had a DVD player and the main technology was VCR players. Flatscreen technology was only just beginning to come in for TVs, most of which had bulky Cathode Ray tubes. Mobile phones were in existence, but the first full internet service on mobile phones was introduced only in Japan that year. There were no smart phones or iPads or iPhones.
As can be imagined, parts for the 17 year old system are now difficult to come by, as the manufacturer has long since stopped making any spares! There are still some older systems deployed in Jersey, and the components of the systems being replaced will be stored and used as spares. Every opportunity to make savings has been made.
In terms of technology, the light systems from 17 years ago each had a transformer in the traffic light head, taking the voltage down from 240 volts to around 48 volts. As might be expected, water invariably got into the systems, and with that amount of power, transformer boxes broke down.
The new systems have one transformer inside the controller box, and the current is already reduced when it goes to the lights, so there is no need for transformers there, and less chance for anything to go wrong.
The lights themselves have been replaced. The new technology uses LED systems for lighting, rather than the older halogen bulbs. The result again is increased reliability, as well as less cost. The halogen lights would be replaced either annually or when they broke down, and about 20% of them broke down before the annual change. The newer LED systems are far more reliable, and also use around 1/3 of the power, which over a year, is a considerable saving.
The upgrade of traffic lights at the junction at the bottom end of Mont Millais uses the new ST950 Intersection controller. This traffic controller is the brains of the unit and changes the traffic lights based on timed settings, and feedback from devices detecting traffic flow.
Reduced power and cabling costs, and highly reliable lamp monitoring of very low power LED traffic and pedestrian signals, makes the ST950 the new benchmark for intersection control. It also allows for non-UK use because Jersey does not have the UK style "red-amber before green" phase but just goes from Red to Green.
There is also increased electrical safety for members of the public in the event of damage to the signal installation and personnel working on or around the intersection.
Often the most frequently damaged components within a traffic controller are the output drive switches, which are particularly vulnerable to cable faults and short circuits. The ST950 ELV design incorporates an active short circuit protection system on all lamp outputs, ensuring that even under direct short circuit conditions, the outputs are protected from damage.
The ST950 is used in conjunction with Siemens extra low voltage (48v), single light source LED traffic signals.. As anyone passing the junction will be able to see, the signal is extremely clear and easy to see in all weather and lighting conditions.
The signals at Mont Millais work on "max sets" which apply at different times of the day (am peak, pm peak, school peak, evening etc). These max timings are set to best allow for the varying traffic and pedestrian demands, and are brought in or removed by the controller time clock. For reasons of traffic safety, all significant timing and program changes are carried out on site, where the engineer can see the effect of the changes.
If you have ever wondered how the lights change, as well as the sets, there is a careful balance worked out to also allow pedestrians to cross, as all of these new junctions have pedestrian lights as well.
There is a problem of ever increasing traffic congestion, as people commute to most of their daily activities. Traffic-actuated signals have been created to alleviate this problem by efficiently managing traffic flow. The system is capable of detecting live traffic data and assigning the appropriate light cycle (for instance, turning on green lights at a desired time).
This is done by a number of additional systems in Jersey which feed information back to the traffic controller so that it can intelligently change lights particularly at times that are not as busy. These are called “actuation detectors” because a vehicle or a pedestrian activates them, either by vehicle detection devices or pedestrian push buttons.
Vehicle-actuated control uses information obtained from detectors within the intersection, to alter one or more aspects of the signal timing. These
• Can reduce delay (if properly timed).
• Are adaptable to short-term fluctuations in traffic flow.
• Usually increase capacity (by continually reapportioning green time).
• Provide continuous operation under low volume conditions.
• Especially effective at multiple phase intersections.
Jersey engineers use the following methods:
Vehicle actuated detection. Here junctions have a small device which looks like a camera on top of the traffic light. This detects any vehicle moving at more than 4 mph. These are not cameras but actually microwave radar detectors.
Another method of detecting traffic is by induction loops. When a vehicle drives over the loop, the traffic controller detector senses the change in electromagnetic field caused by the introduction of metal (from the vehicle) over the loop. This starts a countdown for the light to turn green.
The local traffic controller unit will automatically:
• Process these outputs,
• Compare processed detector information with some preset control
parameter or parameters, and
• Make a decision on intersection phasing and timing.
There is also a very clever system called Microprocessor Optimised Vehicle Actuation (MOVA). This maintains the optimum green stage, cycle time and control strategy to accommodate prevailing conditions to minimise queuing at traffic signal junctions…achieving significant improvement in performance.
It uses vehicle detectors cut into the road surface to monitor vehicles on the immediate approaches to signal controlled junctions to determine green times in real time.
As an example, consider approaching a junction at night. You are the only vehicle. The lights do not go through a full time of the peak cycle for all the other junction users, but change to green as you approach, so that you don’t have to wait.
It also creates more green time for congested approaches, at the expense of those uncongested, maximising control effectiveness. So if three lanes approaching lights are busy, and a fourth is largely empty, that will get less green time.
Also where more than one junction is situated too close to be considered as isolated, there are ways in which two or more junctions can be linked by the use of MOVA control. At First Tower, two such traffic light systems are linked together. Mova also maintains historic data for each lane so it can use previous flows to guide how it behaves, rather like having its own “memory”.
The changes in technology in traffic control are improving all the time to help resolve the increased problems of traffic congestion. Whereas in the past, simple traffic lights were adequate, today’s local traffic engineers have to use all the means in their toolkit, both in assessing traffic flow, programming traffic controllers, putting in detectors, and improving the technology. At the same time, the newer systems also are more reliable and energy efficient.
Easing traffic also cuts the time an individual car spends during a normal commute, reducing fuel consumption. To continue to ease the problem of traffic congestion, engineers need to make a continued effort to improve roads and signal systems.
It is clear that in Jersey, we have at the Department of Infrastructure, traffic engineers keeping up to date with the latest improvements and techniques to keep Jersey’s traffic flowing.