A visit to traffic control centre (TCC)

(This follows on a bit from this post about a traffic junction)

One of the fun things about being a councillor, is that it’s entirely legitimate to ask people to explain things to you. It’s very helpful to develop a specialism and to work on your knowledge in that area.

By and large, officers of the Council are very happy to meet with councillors and explain how things work. There are, of course, limits: people need to do their job, and can’t respond to every whim. And it would be completely inappropriate, for example,  to job-shadow a social worker into a family in difficult.

In the seven years or so I’ve been elected, I’ve concentrated on transport, the environment and planning sorts of issues, and so I serve on committees that focus on that, and I’ve tried to learn about how these things work on a practical level as well as a policy level.

Part of that, a few years ago was to ask for a SCOOT briefing. SCOOT (Split Cycle Offset Optimisation Technique) is a computer program that runs traffic lights, and having read a bit about it on the internet, I wanted to know how it works in practice in Nottingham. I emailed the relevant council employee and in response I got an invitation to the Traffic Control Centre to see it in action. This was, in fact, the first time I had even heard there was a TCC!

(NB what follows is my understanding, and my recollection of a briefing I had two years ago – please let me know if I have something wrong.)

My visit was ever so slightly disappointing. The staff were great, the visit was really interesting, and my knowledge of how hard the Council works to keep traffic moving in our city was really deepened.

But in my mind, I’d built up SCOOT as some sort of semi-sentient, all-seeing computer system that controlled every traffic light in the city. It’s not actually like that. SCOOT is used sparingly on just a few junctions. Most traffic lights are pure and simple timers – 20 seconds on one phase, 20 seconds on the next, green man phase if someone pushes the button. Some of them just do that all day, some of them have programs that take account of variations throughout the day – eg peak flow of traffic into the city and out of it again; giving priority to major routes over minor ones. Even this is pretty unsophisticated – it’s just time based. From 8-10 it runs Program A, 10-4, Program B etc.

The phasing is planned so that are deliberate sweet spots – if you time it right you should get repeated green lights – and so that they don’t encourage people to speed to get through the phases. But this is less and less possible these days because of sheer pressure of traffic. There is so much traffic on the roads that systems that were installed decades ago and haven’t changed all that much since can’t really cope.

A second type of lights is used in more remote places, usually where there is a main road and a lightly-trafficked road. Detectors in the road spot traffic and only change phase when there is demand. These are called MOVA – micro-processor optimised vehicle actuation.

And SCOOT is reserved for relatively few places where there are a series of complicated junctions with lots of different sets of lights and multiple entrances and exits and cars using the junctions in lots of different ways. These are referred to as “SCOOT regions”.

You can often tell the difference between SCOOT and other road junctions by the shape of the car detectors buried in the road. SCOOT ones are usually square, the other sort are chevron shaped across the carriageway.

In Nottingham, SCOOT is in use on the Queen’s Road near the Clifton Flyover; in Sherwood right the way through the main shopping district from Haydn Road to Edwards Lane; and in various places on the ring road, including the junctions around St Leo’s church.

In all these places, fundamentally what the computer system is doing is counting the cars in each lane, working out where they are planning to go, and changing the lights to let them do it. It counts them into the region and counts them out again. It knows how much road space there is so changes the lights wherever it can to stop too many vehicles queuing. It can plan ahead, make predictions, make changes automatically to take account of changing conditions, and let the operators know if something unusual is going on. It also takes constant readings of the numbers of cars, which means there is a huge dataset to analyse for future improvements.

The system is computer controlled, with a computer at the roadside, and a phoneline link to the main computer in TCC. If the line goes down, the system continues in failsafe mode but is less aware.

One final SCOOT fact: The Queens Road region has different priorities weekdays / weekends. In the week, it’s all about getting traffic into and out of the city.  At the weekend, it switches priority to helping traffic get in and out of the Riverside Retail park.

Some other TCC facts

  • TCC has a fab website with realtime information about road transport in the city. Check it before leaving for work: www.itsnottingham.info
  • TCC is mostly an operator and a huge bank of CCTV screens. Most of the feeds are also available on the website above.
  • If necessary, TCC staff can take direct control of most of the traffic lights and get important vehicles through quickly. This is useful for getting blue light response vehicles through the city, and when I visited, they were proud of how quickly they’d got the Prime Minister from one side of town to the railway station.
  • When an incident occurs, TCC turn off the live feed of the CCTV cameras to stop gawkers

One final point: it’s sometimes tempting to think, as a councillor, that after having a brief you fully understand something. It’s rarely the case.  The officers are dumbing it down to a level where you can understand it.  But they’re the trained people, often with decades of experience and training. If you think you’ve got a good understanding of SCOOT, pop over to this website and see how far through it you get before you lose the plot.

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