This week our self-confessed transport nerd, Laurie Winkless, visited TfL’s traffic control centre and tells us more about the intricate traffic systems that run our capital.
It’s happened to all of us. You’re stuck in horrible city-centre traffic jam. Everyone in the car is cranky, and the traffic light only seems to turn green for a millisecond. Edging forward slowly, you wonder, “Surely it can’t be that hard to manage traffic flow?”
Well, the maths behind traffic lights tells a very different story! In fact, switching traffic lights in a large complex network (like a city) is what’s called a computationally intractable problem. This means that it’s not something that we can solve, just by throwing money and computing power at it. All we can hope to do is find a compromise that keeps traffic flowing as much of the time as possible.
On my recent visit to Transport for London’s traffic control centre, I learned about the many tools available to those managing our roads. One is called SCOOT (Split Cycle Offset Optimization Technique) and it uses magnetic sensors in the road called inductive loops, to monitor the flow of traffic at each traffic junction. Glynn Barton, who runs TfL’s SCOOT system, told me that this data is monitored 24 hours a day, 365 days a year, from 4200 traffic lights in the capital. This is then fed back to the TfL “core”, where it is analysed, in real-time, by a combination of computers and experienced traffic engineers. Where areas of high congestion are identified, engineers can intervene to change the switching pattern of the traffic lights, giving vehicles longer to get through the lights where needed.
Figure 1:SCOOT can detect when a cyclist enters a junction
But TfL have recently taken SCOOT to a whole new level. Successful trials using a combination of radar systems and thermal cameras, have shown that it is possible to detect the presence of pedestrians and cyclists at key junctions throughout the city. When the sensors detect large volumes of pedestrians waiting to cross, the timing of the traffic lights will automatically update, to give them longer to cross. For cyclists, longer-term, this will mean that if there are lots of you at a particular junction, the traffic signal timings will be adjusted, to give you an official ‘head-start’.
So, it’s good to know that improvements are constantly being made to the system. To be honest, I was completely staggered by the sheer volume of incredible engineering and mathematics hidden in traffic control! There are even ambitions to develop a system that ‘learns’ – where measured data can be put back into the computer model to make it ever-more accurate. It’s important to remember that these systems won’t ever be perfect (blame maths for that), but to know that there’s so much going on behind the scenes will definitely give me pause for thought when I next try to cross at a junction.
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