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What’s driving the growth of smart motorways?

Reliable journeys are crucial for businesses to prosper – and making motorways smarter could boost traffic flow now and in the years to come.

Last updated: 27 Nov 2020 7 min read

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  • Today’s smart motorways use the hard shoulder to ease traffic congestion, while roadside data triggers speed limit revisions
  • The next phase would see vehicles connecting wirelessly with sensors that advise on optimum speed to aid traffic management
  • In the future, fully connected vehicles would link directly to a central system – which would have to be assessed regularly to prevent any security risks

It’s bound to get a driver’s blood boiling: red brake lights all the way to the horizon. And on England’s 4,436-mile-long Strategic Road Network (SRN), it’s a situation that’s getting worse. The latest Department for Transport (DfT) provisional figures estimate quarterly traffic levels on the SRN are 327.1bn vehicle miles (BVM) for July to September 2018, a rise on 325.7BVM for Q3 2017.

On top of this, journey time data comparing year ending September 2018 to year ending September 2017 shows that:

  • The average delay to SRN users has risen to 9.4 seconds per vehicle mile from 8.9.
  • The average speed on the SRN has fallen to 59mph from 59.5.
  • The proportion of SRN users who needed extra time to arrive at their destination is up to 69% from 67%.

Congestion is bad for business. According to transport analyst INRIX, the cost of congestion to UK drivers alone will amount to £62bn over the next decade.

So it’s in this context that the DfT has been increasingly turning to technology, as pressure mounts for cost-efficient ways to expand SRN capacity. One solution has been the development of smart motorways.

The road to intelligent transport

A smart motorway is an active traffic-management scheme that optimises highway capacity and minimises disruptions. It involves various road enhancements and technologies adopted since the first scheme on the M42 in 2006.

Sensors, previously in the road surface but increasingly in roadside radar systems, collect data such as vehicle speeds and flow rates, while a visual feed to monitor traffic comes from CCTV cameras. This is fed via the National Roads Telecommunications Services (NRTS) to seven regional control centres operated by Highways England (HE), where the data is assessed using an algorithm to determine if a lower speed limit would be better for road safety and traffic flow.

“Replacing the hard shoulder with a running lane increases the capacity of the motorway. So when you’ve got the same amount of traffic on a motorway with a higher capacity, you can generally expect the traffic to flow more freely”Tim Morton, director, Transport Planning Society

To alert drivers, variable message signs are activated, either manually by HE traffic operations staff or automatically. These reduced limits are legally enforceable thanks to the HADECS 3 speed cameras that can cover up to five lanes of traffic.

Optimising capacity isn’t just about controlling the traffic speed; it requires extra space too. The smart motorway alternative to road widening is to use the hard shoulder and either convert it for permanent traffic use (known as all-lane running or ALR), use it for peak-time traffic (dynamic hard shoulder running or DHS) or retain it for emergency use only (a controlled motorway).

To counteract no hard shoulder, emergency refuge areas (ERAs) are installed no further than 2.5km apart, while lanes can be closed by displaying red X signs above them. Despite recent public concern about the perceived risks of replacing hard shoulders with a traffic lane, HE is adamant about the safety of smart motorways. A spokeswoman says: “Evidence proves smart motorways are as safe as traditional motorways. Feedback from road users shows the majority feel confident driving on a smart motorway.”

Clearly, smart motorways are here to stay, with a number of schemes already in operation across England, and more in construction or planned for the future.

Benefits and drawbacks

Tim Morton, a director from the professional body for transport planners, the Transport Planning Society, acknowledges there are short-term business benefits. “Replacing the hard shoulder with a running lane increases the capacity of the motorway,” he explains. “So in the short term, when you’ve got the same amount of traffic on a motorway with a higher capacity, you can generally expect the traffic to flow more freely. That gives you shorter journey times and improved journey time variability. It should be a help for just-in-time deliveries and so on.”

But Morton also notes potential problems both now and in the future. One is the constraints on emergency services by ALR schemes with no hard shoulder: “In theory with all-lane running, the motorway controllers could close one lane to all traffic except emergency vehicles by just putting up red crosses. But if the motorway is completely blocked by a serious incident, then the traffic is just going to come to a standstill, and a tailback is rapidly going to build.”

On top of this, the positive outcome of smart motorways may affect long-term travel patterns and behaviours, which in turn may revive congestion problems. “The risk in the longer term is that peak period traffic will grow to fill the space available. If it does you get back to the same congested operating conditions that you had before the smart motorway was introduced, but with higher volumes of traffic, more pressure on connecting local road networks, and more emissions,” Morton says.

More to come

Ryan Hood, from the Transport Research Laboratory (TRL) and also vice-chairman of intelligent transport association ITS UK, sees the current smart motorway initiative as the first step to revolutionising transport. “Right now, I would say the focus is on what I would call smart motorway version one, which is a smart motorway, all-lane running, additional capacity, and roadside technology for active traffic management.”

The next step, which Hood calls “smart motorway 2.0”, would see vehicles directly communicating with roadside sensors that collect traffic data through the development of connected corridors. This is something TRL is researching along the A2/M2 corridor for the DfT, HE, TfL, Kent County Council and with UK Connected Intelligent Transport Environment (UK CITE) and Smart Mobility Living Lab: London. “The vision is to get to a naked road where there is no real visible infrastructure and all this stuff is done wirelessly,” he adds.

Such connected vehicles could benefit from several trials under way, including a system that would provide an in-car countdown and recommended speed to ensure drivers reach junctions when traffic lights are green, and probe vehicle data systems, which would provide vehicle counts and speeds to assist traffic-management operations. Meanwhile, developing machine-readable roads, as Hood describes them, along with future upgrades to advanced driver-assistance systems (ADAS), which are designed to reduce human error, would open up the possibilities of connected vehicles even more.

“When you combine those, the vehicle itself will undertake some of the functions that are currently undertaken by a smart motorway,” says Hood. The final step would be smart motorway 3.0 where fully connected autonomous vehicles make journey decisions. That, as Hood sees it, would be the holy grail of optimising traffic flows with the “whole system acting as a system and not independent drivers or agents”.

Continuous safety is vital

While building ever-greater connectivity into the highways network appears to be the future, Siraj Shaikh, professor of systems security at Coventry University’s Institute for Future Transport and Cities, stresses the importance of properly managing data-controlled transport.

“The more digital we make any system, the more potential there is for abuse or manipulation,” says Shaikh. “If you take into account some of the unique features of motorways, as opposed to any other cyber-physical system, they include this high-speed journey element. It may just take inducing a delay of three to four seconds, or manipulating the speed limit, and within a very short time, it could be a catastrophe. That is a risk we need to acknowledge.

“The response to that, of course, is that we need to be much better in our evaluations of those technologies that are involved. All computer systems go through updates. If that happens continuously, than the security risk around it has to be assessed continuously.”

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