Developments in signal head lens technology

Heads and tails Leading manufacturers of traffic signal systems discuss developments in signal head technology as well as some of the legacy issues which affect future deployments

Long after the much talked-about cooperative infrastructure systems of the future are in place, the traffic signal will remain a valid and indeed necessary part of intersection management, not least because there will continue to be a need to take account of that remaining but dwindling number of unequipped vehicles on the roads and the safety of pedestrians and cyclists, for whom two-way connectivity is more problematic.

The signals themselves continue to evolve. LED-based optics continue their march to ubiquity, although that journey is far from over and indeed just how far things have progressed is a matter of debate. John Chipperfield, COO of 129 Swarco Futurit's Traffic Management Division, feels that North America has made the most progress.

"There is an installed base of about 70 per cent," he says, "compared to about 30 per cent in Europe - and this is heavily concentrated in Western, mainland Europe. Central and Eastern Europe are now beginning to catch up, as is the UK after a very slow start."

5852 PeekTraffic Netherlands  Martin de Vries, by contrast, considers LEDs to already be the de facto standard for both traffic signals and Variable Message Signs (VMS).

2194 Dambach's Mannfred Rosskopf, meanwhile, puts the number of new installations in Germany at more than 90 per cent, with the shift from traditional incandescent bulbs on the existing installed base running at 10-20 per cent per year. There remain obstacles to progress, however - Keith Manston, Head of Product Management at 678 Siemens Traffic Controls: "Existing controller technology isn't always suitable for driving and monitoring LED bulbs. The very large base of installed controller equipment is having some impact on LED take-up. Siemens has addressed this by offering retrofit solutions which allow upgrading at significantly lower cost than all-new equipment."

The carbon savings over traditional bulbs, he notes, are of the order of 75 per cent.

Pushing on, there are other refinements. The use of Fresnel or programmed visibility lenses to focus light output is another development, although once again there are differing views of their effectiveness. Peek's de Vries feels that they fail to bring significant extra functionality. Others are more positive. Manston: "Many LED signals, including Siemens Central Light Source signals, already use Fresnel lenses. What we would term 'Narrow Field of View' signals are also widely used in pedestrian equipment. For traffic signals this is often achieved using cowls but it is perceivable that this could be superseded by the greater use of lens technology."

The use of lens technology allows the use of fewer LEDs and thus power savings.

"This means that the optics are returning to those that were commonplace for bulb-type technology, instead of the large, 200+ arrays which were commonplace in early LED applications," says 525 Telent's Paul Smith. "They are however being designed to ensure that a large proportion of the LED light is aimed in the appropriate direction. Required power is therefore reduced."

Chipperfield and Rosskopf both pick up on this trend.

Chipperfield: "Aiming the light where it is really needed reduces the power consumption which also results in longer LED lifetimes and higher environmental benefits. Current work is focused on determining the reliability of single LED light source solutions or whether multiple LEDs offer better product lifetimes and availability."

We can expect near-term reductions in the number of LEDs in a signal head and thus power consumption, says Rosskopf: "The six LEDs operating at 7W which is typical today will reduce down to one or two 3W LEDs. This will eventually lead, in the medium term, to further integration of the existing electronics into the signals together with the switching and monitoring electronics."

Although colour-changing LEDs are in use in some locations, including China, there appears to be agreement among manufacturers that they are perhaps less appropriate - at least at present - for use in traffic signals than in, say, VMS. There are common concerns over adequately addressing the needs of road users who suffer from colour blindness (a condition which affects about 10 per cent of the male population) and Canada, for example, has used shape in conjunction with colour to try and overcome this. Nevertheless, there is also the fact that the three-aspect signal strategy (that is, both colour and light position) in common use today would be compromised.

The decreasing power needs of future LED solutions are the primary advance which signal manufacturers allude to when asked to comment on environmental developments. Swarco Futurit, for example, has just completed development of its new Futura range which was designed to take green principles into account in both production and use. In 2008, this picked up an award from the Austrian Federal Ministry of Transport for efficiency in climate protection. Telent's Smith sees progression from a 'cheapest is best' philosophy to one which takes more account of whole-life costs, something which he sees already being reflected in tender evaluations and procurement processes.

Over at Siemens, Manston says that the introduction of lower power products that also require less maintenance and so fewer miles driven is the big push at the moment - "but it's difficult to see how this can really progress at the moment as there are no real processes in place which would enable a purchaser to make clear decisions based on the total carbon footprint of a product."

All too often, the capabilities of legacy analogue devices used for a variety of applications such as data gathering or enforcement has led to a multiplicity of systems being deployed on roads worldwide. Digitisation has allowed the development of systems which offer multiple capabilities but all too often technical development has outstripped legislative progress. Looking slightly further ahead, therefore, the mounting of other technologies such as video monitoring in the signal head would appear to have some merit. Swarco Futurit's Chipperfield notes the 'Christmas tree' effect often encountered at pedestrian crossings but also adds that video devices often need to be aimed and focused differently to traffic signals in order to be effective.

"There is a need for standardised mounting points and interfaces," he continues. "Also, traffic signal heads are moulded using complex and expensive tooling which cannot easily be modified to accommodate a wide range of different fixings."

Maintenance and restricted fields of vision are issues for Manston, meanwhile Rosskopf sees the development of more reliable cameras with better algorithms and sensor fusion substituting for inductive loops in more and more applications. He also foresees new 3D technologies such as laser being used in special cases.

Telent is involved in a consortium which is being supported by the UK's Technology Strategy Board and which is looking at '3rd Generation Road Side Equipment (3GRSE). Other members include 43 Efkon UK, 539 CitySync and 491 TRL. This relates to the use of vehicle signature, image processing and Automatic Number Plate Recognition (ANPR) technologies mounted in the signal head to allow Time-Distance-Place (TDP) road-pricing schemes to be deployed. The theory behind the work is that potentially many existing structures within a traffic management system can be used as a base for TDP charging as they already offer mounting possibilities, cabling, power and communications. The deployment of charging systems can therefore be integrated with traffic control and made less expensive. The list of potential upgrades which 3GRSE is intended to make possible is impressive and includes: microwave (CEN TC 278) tolling and vehicle identification at 5.8GHz; active, wireless communications; ANPR; satellite location; smart card services; and use of the CALM protocol to provide interoperable services.

Progress towards the deployment of cooperative infrastructure goes on. At Peek, says de Vries, and based on the company's involvement in Europe's current research efforts, there are very clear opinions on the role of cooperative intersection controllers.

"In the short- to medium-term, we see applications emerging which provide driving assistance in-vehicle on the one hand and improved traffic management capabilities on the other. In the longer term, cooperative systems may have a more direct influence on operation of the vehicle and/or the controller. However, this will take many years to come about."

Manston finds it difficult to conceive of a time when cooperative systems fully replace traffic signals.

"The safety challenges are enormous and require 100 per cent implementation within all vehicles of the signaling technology. Then it must be guaranteed that it's working - not easy to do. It is possible that advanced warning of signal changes could be communicated to the vehicle but I'm not convinced that the cost-benefit case for this has yet been made - who pays for it?"

Rosskopf sees significant opportunities but also some challenges. There are major safety and traffic management gains to be had, however infrastructure financing, legislation on (for example) active driving intervention, and harmonised information content all have to be addressed.

"Nevertheless," he adds, "the steps towards the basic technology can be taken in a short space of time as interfaces to Internet Protocol communications are already in place in some existing traffic controllers. Also with the definition of the frequency band for the 802.11p standard, the first wireless controllers will be available and integrated in the very near future."

With all this information flowing to and from the traffic controller, it might seem that bandwidth could become an issue. The solution, unsurprisingly, is to ringfence the applications delivered via the intersection. In reality, that means excluding from the intersection many of the comfort/mobility applications which cooperative infrastructure will enable and delivering them via other means.

Smith: "Historically, the 'safety integrity' of the intersection has resided in the traffic controller and this is unlikely to change. This ringfenced low-level functionality ensures that no matter what is asked of the controller it will not break intrinsic, basic safety constraints. Bandwidth availability to the street corner has grown at a rapid rate and is generally delivered via technology and applications which are intended for the greater deployment of high-speed easy-access communications for myriad uses."

In some respects, bandwidth will always be an issue as the list of possible applications will continue to grow, says Chipperfield. "Fortunately, evolving technology generally manages to find innovative and faster solutions."

Where serial data control is used, the delineation between safety (for the heads) and other data is rigorously maintained, says Manston. "Whilst it isn't impossible to mix safety-critical and non safety-critical data on the same communications channels, it is easier to make a safety case if you don't."