Catenary lighting parallel with and located in the centre of dual carriageways has a number of advantages and disadvantages over conventional lighting, and these can be summarised as follows. There are likely to be more advantages and disadvantages than listed.
Advantages:
* Very even distribution of light on the road surface
* Low glare
* Efficient use of light produced (no wasted backspill)
* Reduced visual intrusion of the scheme
* Lighting can span crossroads without a break
* Highly reduced numbers of service connections
Disadvantages:
* High upfront capital cost
* Requires tall and heavy duty columns
* Maintenance issues due to adverse weather and ageing
* Crash damaged columns cannot easily be fixed
At the end of the day, the relatively high cost and difficulty of maintenance killed off the idea of using catenary lighting. But is it time to think again?
Some catenary lighting that still exists on the A30 and A4 in West London consists of Phosco P415 twin-135W SOX lanterns, with five lanterns per span. These lanterns can also be fitted with 180W SOX lamps. Anybody who has picked up a 135/180W leak transformer will know how heavy these are, so imagine 10 per span, plus the weight of the lanterns themselves. No wonder the columns had to be so heavy duty. But times have changed, and the majority of councils and contractors fit new lanterns with electronic control gear, which is considerably lighter in weight. That would cause reduced stresses on column and lantern fixings, and columns wouldn't need to be so heavy duty. Furthermore, if a CosmoPolis catenary lantern were designed it could be a tiny lantern. Some of us have seen how tiny a WRTL 2Tone is, and they can handle 140W CosmoPolis lamps. Smaller size means reduced windage, and again, reduced structural issues.
Then there is the matter of cost of installation. Columns that aren't so heavy duty means the cost of installing catenary lighting would be reduced compared with in the old days. But the biggest cost when it comes to installing street lighting nowadays is the charge that the electricity company requests for every service connection. Five years ago this stood at £1000 per lighting column, and it has risen significantly since then. The catenary lighting on the A30 and A4 is fed by a supply from every other column, but when you look at the spacings between columns it is clear to see how much money could be saved when it came to service transfers. When it comes to the capital cost of installing street lighting, the fewer columns the better, and catenary lighting takes this to another level.
Just a rough calculation based on the A30 catenary lighting compared with an adjacent section of conventional columns. A length of five catenary lighting spans (six columns) equates to about nine conventional columns (or 18 if located in the verges). Five catenary spans would require service connections to three columns, so let's call that £3000. Nine conventional columns, that's £9000. Over the five catenary spans, with four 150W SON lanterns per span, that's 20x 150W, which is 3kW. Conventional lighting requires 18x 250W SON lanterns, which is 4.5kW. Oops, somebody's car has left the road. 44% less chance of hitting a catenary lighting column... except in the event of hitting such a column, it would be more problematic. Catenary lighting columns aren't crash friendly and are designed to stay upright, and how do you replace a catenary lighting column easily?
Food for thought.
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