Wednesday, 18 July 2018

Scoot, the computer that keeps traffic flowing

QUEUES of vehicles on Remenham Hill, Reading Road and Greys Road are a familiar sight

QUEUES of vehicles on Remenham Hill, Reading Road and Greys Road are a familiar sight to drivers in Henley.

But while some see the tailbacks as a problem to be solved, Oxfordshire County Council says they are a vital way of tackling pollution and protecting pedestrians.

In fact, the highways authority deliberately arranges the traffic so that it builds up at the town’s entrances and flows smoothly in the centre.

It achieves this using a computer system that measures how busy the roads are and automatically adjusts the timing of the traffic lights.

This is known as Split-Cycle Offset Optimisation Technique, or Scoot.

The signals at four of the busiest spots in Henley are connected by fibre-optic cables to a central hub at the council’s offices in Oxford.

These four are the junction of Reading Road and Station Road, the Duke Street and Greys Road crossroads, the Hart Street and Market Place crossroads and the west side of Henley bridge.

Sensors are buried beneath the tarmac at each location which record vehicles as they pass.

When there is little traffic, Scoot cycles the signals more rapidly so drivers don’t have to wait long for them to change.

If a light is green but traffic is stationary, the system knows congestion is building up and takes steps to remedy it.

It switches the lights less frequently because each cycle stops the flow for a few seconds, reducing its efficiency.

When one road at a junction is more congested than another, it gets a bigger share of “green time” to clear the backlog.

Scoot makes all its decisions in real time, with a delay of two seconds between a change in road conditions and action being taken.

The council says this does not make journeys longer but simply moves existing queues out of residential and shopping areas.

As a result, exhaust fumes disperse more easily instead of getting trapped between the buildings that line Henley’s streets.

The town’s average annual nitrogen dioxide level is 62.4 micrograms per cubic metre compared with the 40mcm objective set by Air Quality England.

Pollution in Duke Street, Bell Street and Reading Road, the worst affected areas, is said to be comparable to that in London. This has been a problem for more than a decade but the council says it would be even worse without Scoot.

It says the system also makes Henley safer for shoppers as drivers don’t get too close together at junctions, meaning pedestrians don’t have to weave around cars when crossing the road and motorists do not lose patience and drive rashly.

Tim Atkinson, the council’s traffic control systems manager, who oversees Scoot, says: “A complaint we often hear is, ’why am I waiting so long on Remenham Hill or Reading Road when the town centre is totally clear?’

“But Henley’s streets can only physically accommodate so much traffic. It is a very old market town and it is stuck with the infrastructure it has; we cannot build new road lanes or allocate bus lanes. Any major changes would involve demolishing buildings and that would be unacceptable given the town’s historic character.

“We want to make Henley a better and safer town to live and work in so that it is as economically viable as possible.

“The idea with Scoot is that overall journey times should not be any longer. You just spend your queuing time up on the hill, not in the town - it’s exactly what the system is meant to do.

“It may seem counter-intuitive and I can see why people struggle to get it because they don’t have the overview of the situation that we have.

“When people complain to us about queues outside the town, that’s actually good feedback as we know the system is working.”

Mr Atkinson says that when traffic is exceptionally heavy Scoot actually speeds up journeys. This was put to the test during the floods early last year, when Sonning Bridge was closed and traffic in Henley increased significantly.

To check the system wasn’t making things worse, the council turned it off for a day and congestion across the town doubled.

Mr Atkinson says: “We know we haven’t throttled traffic too much because if we even release it a bit, motorists still get trapped in the system and spend more time queuing in the town than they would on its approaches.”

Scoot was introduced in 2006 as part of the council’s integrated transport strategy for Henley. Before that, the lights at Hart Street and Henley Bridge had basic monitoring systems but these were not centrally controlled.

There were no signals in Greys Road or Reading Road and the latter had a mini-roundabout instead of a box junction.

Mr Atkinson’s team of eight operators can see the system working on a wall of giant screens that show the colour of every traffic signal at any given moment.

There are CCTV cameras at Reading Road and Henley Bridge, which are said to be the most significant areas for problems. If traffic slows in those locations, the operators can see what has caused it and take action.

Mr Atkinson says: “There’s nothing better than being able to see what’s happening with your own eyes. The system can show patterns of congestion but the cameras give you a better idea of what’s causing it.

“The screens mean it takes very little effort to keep an eye on things - it’s an instant health check. We can just look up to see if anything is wrong.”

Most of the time Scoot is left to its own devices but there are times when it must be overridden.

When a road is closed, for example, it thinks traffic is at a standstill when in fact there is none. The operators must tell it to ignore that spot or it will assume there is heavy congestion and act accordingly.

Scoot must also be managed during Henley Royal Regatta, when there are large volumes of pedestrians at Henley bridge.

A highways officer is present at all times and periodically turns the lights red in all directions so the crowds can cross.

Back in Oxford, operators can see the knock-on effects and adjust the other signals.

To help them, temporary CCTV cameras are set up on Fair Mile and on the eastern side of Henley bridge.

Mr Atkinson says: “The controllers know exactly how the wider network is being affected. We used to have stewards across Henley during regatta week but this is as good as having a dozen people out there.”

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