Feeling the benefit of driving on a ‘green wave’

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You know that feeling when you drive towards a green light and it turns red a few metres before you get there? Frustrating, isn’t it. Think also about the extra fuel you use accelerating to ‘beat’ the light or waste when you slam on the brakes – it’s, well …. a waste!

In our towns and city centres, this scenario seems to be the norm rather than the exception. However, imagine if when you got a green light you could cruise along and know all the lights will turn green as you arrive.

Whilst some councils have implemented this scenario on a small-scale, these ‘green waves’ have the potential to become a widespread reality.

Current logic

The reason for the current situation is the way our traffic signals are optimised. Minimising delay is the ultimate goal with traffic jams (congestion) to be avoided at all costs. At the moment, current thinking is that if vehicles stop at every light on their journey, but sit in less traffic, that is good. The rationale behind this is based on average speed models, which assume that reducing journey time uses less fuel, because it calculates that average speed multiplied by engine running time equals petrol consumption. However, this is not actually the case.

Working with Aardvark EM Limited, Hydrock is looking at things differently.

Applying a new logic

The National Planning Policy Framework notes that sustainability has three strands – social, economic and environmental. Whilst queuing and delay remain key considerations in how we manage our roads, other factors can carry equal or greater weight – including air quality.

Take a 4km journey in a 1384kg vehicle (the EU average), moving through seven sets of traffic lights. If the car stops at every light and waits for 10 seconds it will use 2.3kWh of energy (the equivalent of 23 hours of watching TV).

If that same car drove the trip without stopping and starting it would use around 1.25 kWh – nearly half the energy. If it doesn’t have to stop on the journey, the car could sit at the first set of traffic lights for ten minutes, engine running, and still consume the same energy as the car stopping and starting.

This huge energy difference is achieved because idling vehicle fuel consumption is a fraction of consumption during acceleration, and lower than consumption when cruising.

Could a rethink of our approach to traffic lights, focusing on eliminating wasteful stops and starts, be in order?

Modelling a new approach

Hydrock is working with Aardvark and a local university to prepare a city-wide detailed (microsimulation) model. Our VISSIM microsimulation modelling tools can simulate individual vehicles down to each gear change, and even model aggression profiles of drivers.

Our work will test the operation of the highway network as it currently is, as well as networks which are optimised in the interests of queuing / delay (the standard approach) and air quality.

Changing behaviours

‘Green waves’ require some compromise. As a driver, you are likely to sit at a light for a bit longer, whilst others are ‘getting all the green lights’.

But, think of it as rolling all your stationary time for a journey into one, so overall journey times are not dramatically affected. Ten minutes is an extreme example, but provided people know why they are waiting, once that first red light turns green, they would not have to stop – as long as they stick to the speed limit. It’s a bit like taking a plane – arrive, wait and then go.

Knock-on benefits

The energy saving potential is huge. As well as this, non-exhaust emissions, which are particles from the wear and tear of car tyres, brakes, engines and the roads we drive on, would be slashed. These are estimated by the National Atmospheric Emissions Inventory (NAEI) to contribute to over half of all Particulate Matter emissions in the country.

Reducing these would also reduce vehicle and road wear and tear, meaning lower car servicing bills on top of the fuel savings and less road maintenance.

This research project is just one example of how Hydrock and its partners are engaging with the opportunities and challenges of future transport across disciplines that include air quality, noise, carbon accounting, transport planning, transport modelling, and transport policy.

For more information please contact Blaise Kelly, Air Quality, or James McKechnie, Director, Transportation.