Traffic lights on motorways

There was a bit of a stir when Highways England announced an "innovative pilot project" to install traffic lights on a motorway sliproad. Why are they doing that? And how much of this is new at all?

The front-page headline in the Times was "Traffic lights on motorway sliproads to cut congestion". The Independent reported that "one of Britain’s busiest motorways is set to be fitted with traffic lights in a bid to ease congestion", while Auto Express announced that traffic lights are to be "introduced for the first time on UK motorways". They're referring to work that's about to start at Croft Interchange near Warrington, the junction of the M6 and M62.

We'll look at whether this really is the first time traffic lights have been introduced on UK motorways in a moment. But first, we should probably ask why you'd want to do such a thing in the first place.

Why would you put traffic lights on a motorway?

Ask anyone what is the point of a motorway and they'll tell you the answer. It's obvious. Motorways let large volumes of traffic move uninterrupted at high speed over long distances. Unlike ordinary roads, there's no roundabouts, no Give Way lines, no other traffic crossing your path, no access points to private property, no zebra crossings, no combine harvesters, no diving, no splashing, no heavy petting... and no traffic lights.

So it sometimes seems a bit odd that, worldwide, traffic lights do get installed on sliproads leading to motorways. It's called ramp metering. The name should tell you it's an American term (what they call a ramp we call a sliproad) because it was first tried in the US, and the point of it is to manage the rate at which traffic joins the motorway. If too many vehicles try to merge all at the same time, it can slow down the mainline of the motorway, causing waves of brake lights and stop-start jams - a problem that often affects motorways in the rush hour on the approach to towns and cities.

Ramp metering involves a set of traffic lights at the end of the sliproad, just before it merges with the motorway, which are activated in heavy traffic and cycle rapidly between red and green to allow one or two vehicles to proceed in each lane at a time, creating a steady trickle onto the motorway that will not disrupt the flow. In some advanced schemes, sensors watch for queues at the entrance to the sliproad and can let traffic join more quickly if the queue risks blocking up the junction, and can even link nearby junctions so that some can allow more traffic through than others to even out delays.

What Highways England are talking about is a new scheme to install ramp metering signals on the sliproad that allows traffic from the northbound M6 to join the eastbound M62.

So, let's get this straight. Are these going to be the first traffic lights used for ramp metering?

No, these are not the first traffic lights used for ramp metering

Far from it. Thanks to a major trial scheme in 2007, ramp metering signals have proliferated across the North West, particularly on sliproads approaching the often-jammed M60, but also on the M6 and M62, at a total of 30 sites. Motorists around Warrington who are regular motorway drivers will probably be well used to seeing them.

But the use of traffic lights on motorway sliproads in the UK goes back much further than that.

OK, yes, that's an edge case and a bit of an anomaly. How about the M27/M271 junction, described above, or the M62/A627(M) junction, or the M4/A308(M)/A404(M) junction? Not only do they have ramp metering, they also have roundabouts entirely under motorway regulations and controlled by traffic signals. To get from one motorway to another, you don't just negotiate ramp metering signals, you negotiate actual traffic signals as well. You'll find traffic lights at Wadworth Interchange to get between the A1(M) and M18 too, and you'll even find yourself confronted with a red light in certain directions at the junction of the M1 and M62.

So, fine. There's nothing unusual about traffic light controlled junctions on motorways. At least things haven't got too silly. At least this doesn't involve putting traffic lights on the mainline of motorways.

Actually we already have traffic lights on the mainline of motorways

Have you tried to follow the M60 clockwise around Manchester? At junction 18, Simister Island, staying on the clockwise M60 means negotiating a roundabout and passing through three sets of traffic lights. Three. At one junction. To stay on the same motorway.

So is the idea of traffic lights on motorways a new thing?

Not really, no

In fact not at all. But nobody in the media is going to look at the question in that much detail, and most members of the public won't care about splitting hairs, so Highways England's announcement that it's the first time traffic lights have been deployed on a "motorway link road" serves its purpose to get the scheme a remarkable amount of publicity - including the front page of the Times - and that surely was the point.

Will it work? Well, we will see.