Discussion about street lighting, road signs, traffic signals - and all other street furniture - goes here.
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Are there any isolated traffic light installations, with detection on the side roads only in the UK, and if so, how common are they?
They're pretty common in the US, where they're known as "semi-actuated" signals, as opposed to "fully-actuated" signals which have detection on all approaches, as it significantly reduces maintenance costs, but at the expense of a fixed main road green. They also can be useful in coordinated networks (fixed-time UTC in the UK), because it allows unused side road time to be transferred to the main road, but as far as I know, the closest to that you'll ever get in the UK are UTC demand-dependent stages.
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- Location: Liverpool, UK
It's reasonably common in some areas where sites run UTC fixed time, SCOOT or CLF full time and so the VA loops are only generally providing the demand for demand dependent stages, or perhaps a gap-out, though I'm not sure how common the latter is in most areas. If the site fell onto VA for whatever reason, the main road would just be a permanent demand and extend to max, but areas that are that reliant on UTC/SCOOT will likely have a CLF fall back in the first instance anyway.
I'm also aware of sites where the main road is just so busy that it runs permanent demands and extensions on the main road, so there's no detection other than for right turn pockets and adjoining roads.