For those of us living around or travelling near Southampton, we’re currently dealing with closures, roadworks, and traffic jams as the M27 and M271 are upgraded to become ‘smart motorways’. Works started at the beginning of 2019 on the M27 between junctions 4 and 11, and are expected to continue until early 2021 – well over two years of traffic nightmares.

Motorways and roads used heavily are all receiving similar treatment in an attempt to decongest the UK’s roads and help traffic flow smoother. Large parts of the M25 have already undergone the work to upgrade them with many more miles of motorway in the process of being upgraded also.

The economic cost of the M27 ‘upgrades’ is £224 million. That’s assuming it stays within budget and doesn’t include the costs of delays to the thousands of people that will inevitably be delayed during the construction period. According to Highways England, the £224 million will be used to:

  • Permanently convert the hard shoulder to create a fourth lane and change junction slip roads to accommodate this
  • Install new CCTV cameras and electronic information signs and signals on gantries – these will show variable mandatory speed limits and manage traffic flow and incidents
  • Create emergency refuge areas throughout the length of the scheme
  • Harden the central reserve and install a reinforced barrier to improve safety

There is also the environmental impact to consider. The air quality around the M27 will only be made worse and carbon emissions will certainly increase with a greater number of cars on the road using the M27.

And what do we get at the end of all this? A few electronic signs that supposedly improve the flow of traffic and cameras that keep us to a variable speed limit as well as an additional lane for us to sit in when congestion inevitably gets no better. So why are Highways England upgrading the M27?

Why Upgrade?

The M27 is an important motorway connecting parts of the south of England together as well as providing a link to the M3 that runs between Southampton and London. Ensuring a high-quality road system is important for cars travelling along the south coast and accessing London and the many cities located north of Southampton.


Sections of the M27 are regularly congested


According to Highways England, who is overseeing the project, there are five aims.

  • Reduce congestion and smooth the flow of traffic by turning the hard shoulder into a permanent running lane
  • Improve journey time reliability on the strategic road network
  • Support the economy and facilitate economic growth by providing increased capacity on the motorway
  • Continue to deliver a high level of safety performance on the network using smart motorway techniques
  • Minimise environmental impacts of the scheme and where possible allow for enhancements to be made to the environment

It all sounds positive and beneficial in many ways, but will it be successful?

New Lanes Don’t Work

Short term: Possibly

Long term: Highly unlikely

It would seem to make sense that having an additional lane on a motorway would have a positive impact in reducing traffic jams and the time that’s taken to travel along a particular stretch of road. However, there is plenty of evidence to suggest that doing so makes absolutely no difference at all.

Take the Katy Freeway in Houston as an example. It spans 26 lanes at it’s widest making it one of the widest in the USA. The project to expand it to that size cost $2.8billion and the work took place between 2008 and 2011. Surely expanding a freeway to 26 lanes would solve any traffic problems? No. In fact, exactly the opposite happened.


Even after expansion, Katy Freeway was even more congested!


Research carried out between 2011 and 2014 found that during the morning rush hour, time spent in traffic increased by 30%. In the evening rush hour, commuting times increased by 55%. So not only did the expansion not work, but it actually made things much, much worse.

This phenomenon that has puzzled city and transport planners, as well as policymakers, for years is called ‘induced traffic’ or ‘induced demand’ (which will be used for the purpose of this article). In a recent report by WSP and RAND Europe, commissioned by the Department for Transport, induced demand was defined as ‘the increment in new vehicle traffic that would not have occurred without the improvement of the network capacity‘.

That same report was unable to come to any concrete conclusion on the impact of induced demand but did recognise that there were a number of case studies that backed the creation of induced demand with the expansion of motorways. The report also commented on the importance of accounting for induced demand during the appraisal process of any project going forward.

So was there any consideration of induced demand in the M27? Unfortunately not. After searching through a number of documents relating to the M27 expansion project, there is no consideration of induced demand in any of the documents made available online suggesting that it’s something that hasn’t been considered by Highways England or the parliamentary group that would have given the green light for the project.

But that’s no surprise. A 2012 study that looked into traffic forecasts that ignored induced demand found that there was a considerably lower cost-benefit ratio when induced demand was accounted for.

What About The Environment?

In the same way that we shouldn’t be considering a third runway at Heathrow, we must stop looking at smart motorways or motorway expansion as the solution to our roads getting busier. We need to be reducing the number of cars on the road, not making space for more.

In much the same way that ignoring the induced demand from road expansion increases the cost-benefit ration, ignoring the induced demand that comes from the expansion of roads overinflates the environmental benefits. The environmental assessment carried out for the M27 project suggested that expanding the M27 would adversely affect air quality with the increase of cars on the M27 but benefit air quality with a reduction in congestion.

The reality is that induced demand will increase the number of cars on the road and have very little impact in reducing the congestion on the M27. So air quality will likely only be adversely affected.

What Should We Be Doing Instead?

Policymakers can easily sell road expansion and lane additions to commuters as a solution to traffic issues that blight many UK roads. However, as shown here, they aren’t solving the problem at all – it could even make things worse. The easiest way to reduce traffic is to reduce the number of cars on the road. To do that, those commuting by car need to have good quality and cost-effective alternatives in the form of public transport.

But rather than invest in public transport and offer companies subsidies for running better and cheaper services that encourage more to use public transport (for example), hundreds of millions of pounds are being wasted on projects like the M27 ‘smart motorway’ to find solutions to congestion problem that will very likely be made worse.

So, drivers of the M27, things may be bad now with the roadworks to implement the expansion, but things could be just as bad when the work is completed and the motorway is reopened in 2021.


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