Smart Motorways

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In the last decade there have been huge changes on some of England's busiest motorways. Where once you could rely on three lanes and a hard shoulder, now there are countless new electronic signs, road markings and rules.

A section of Smart Motorway on the M25

These schemes have gone by various names in the past but now the Highways Agency refers to them all as "Smart Motorways". This page explains what they are.

What are Smart Motorways?

Any section of motorway that has been upgraded with new technology — electronic signs, intensive CCTV monitoring, enforcement cameras and so on — is now considered a "Smart Motorway", regardless of the different ways in which these schemes operate across the country. This work is done to help reduce congestion and keep traffic moving.

Congestion on the M25During the 1990s various countries around the world experimented with using improved technology to control traffic on motorways, either to increase the capacity of the road or to reduce the severity of congestion. In the UK this included trials of ramp metering (where traffic is sometimes held back on entrance sliproads) and variable speed limits.

In 2006 the Highways Agency began a trial of what it called "Active Traffic Management" on the M42 between junctions 3A and 7 east of Birmingham. This included ramp metering, variable speed limits and trials of hard shoulder running. This experiment was considered a success and, in various forms, Active Traffic Management was then installed on other congested motorways. Today it has all but replaced conventional motorway widening projects, and many of the proposals to widen motorways that were made in the late 1990s or early 2000s have now been carried out using ATM instead.

Each upgrade scheme incorporates slightly different elements of the Active Traffic Management concept, depending on traffic levels, the engineering standard of the road to which it is being applied and the sort of improvement that is being attempted. For example, in some locations hard shoulder running is not included because the road doesn't have continuous hard shoulders; in other places ramp metering is not included because the volume of traffic joining the motorway is not thought to be one of the causes of congestion there.

In 2013, the Highways Agency took the decision to use the new term "Smart Motorways" for all the different systems of control operating across England's motorway network. "Smart" is a term that is increasingly used to describe intelligent technology, like smartphones, which is probably why it was chosen as a name. It can also mean clever or fast, both of which are positive associations for these Highways Agency flagship projects. (In Scotland, similar schemes exist with similar technology, but Transport Scotland uses the name "Intelligent Transport System" to describe them.)

The word "smart" comes from the Old English word smeortan, which was used to describe something that caused sharp pain, and is related to the Greek word smerdnos meaning something terrible or dreadful. At times, those definitions can seem fairly appropriate too.

A rose by any other name...

There have been many names for the various control systems that have been installed on English motorways since the early 1990s. These are just a few of the terms you may have come across before.

  • Variable Speed Limits were introduced on the M25 in 1995.
  • Ramp Metering has been on use on the M6 in the West Midlands for about 20 years and was trialled in further locations nationwide in the early 2000s.
  • Active Traffic Management was the name of the pilot scheme operated on the M42 incorporating Variable Speed Limits, Ramp Metering and other new ideas.
  • Controlled Motorways was used for a short time to refer to ATM schemes and is still sometimes used in reference to areas where Variable Speed Limits operate.
  • Managed Motorways referred to ATM schemes for several years.
  • Smart Motorways was adopted in 2013 as the name for all ATM and variable speed limit schemes of any kind, so that every system that uses increased technology to improve traffic flow now operates under this name.

What might I see on a Smart Motorway?

Overhead control signals

On any type of Smart Motorway, the ability to relay information to motorists is vital, and this is almost always done using overhead signals mounted on gantries spanning the road. These are often very frequent.

Overhead signal gantry

Overhead signals showing lane allocationsThere are, broadly, two types of signal: small signals mounted individually over each traffic lane (and often over the hard shoulder), and larger signals capable of displaying complex graphics and multiple lines of text, usually mounted over the hard shoulder or verge.

Signals over each lane can be used to indicate whether lanes are open or closed and to indicate speed limits. Digital speed cameras may be mounted behind them.

Large signal panels display information that applies to the whole road, such as written indications that the hard shoulder is open, or about delays further ahead, or even graphical signs indicating the arrangement of lanes at a junction.

Roadside control signals

On a few Smart Motorway schemes, usually on longer lengths of rural motorway where there are fewer junctions, signals positioned by the roadside may be used instead of frequent overhead gantries. These take the form of large panels, capable of displaying complex messages and graphics, and indicate lane allocations, written instructions or variable speed limits.

Lengths of motorway equipped with roadside signals instead of overhead signals are a little less versatile because there are fewer signals available and each signal can only display one message at a time. That makes it impossible to convey information about the hard shoulder, speed limits and lane closures at the same time.

Variable speed limits

Users of the M25 have been familiar with Variable Speed Limits since the mid-1990s. Unlike advisory speed limits that can be shown on electronic signals on normal motorways, variable speed limits are mandatory, and appear on overhead or roadside signals with a red circle, resembling a normal speed limit sign.

VSL on the M20. Click to enlarge
A sign advising of Variable Speed Limits on approach to the M20. Click to enlarge

Variable speed limits are a feature of all Smart Motorway schemes. They are used to reduce congestion by reducing the speed limit in order to prevent stop-start traffic jams. By slowing traffic they also increase the capacity of the road, because slower vehicles travel more closely together, making better use of the available road space.

All variable speed limits are enforced by digital speed cameras mounted over every traffic lane.

Part time hard shoulder running

Part time hard shoulder running (from an original by David Dixon). Click to enlarge

Many Smart Motorways incorporate hard shoulder running, which enables the hard shoulder to be opened to traffic as an extra lane when the road is particularly busy. This provides an instant increase in capacity and helps to keep everybody moving rather than suffer congestion caused by the volume of traffic.

The earliest trials of hard shoulder running opened it to traffic between junctions simply for use as an extended exit lane, so traffic leaving at the next junction would be directed to use the hard shoulder (like in the picture to the left), which would then turn into the sliproad.

In most cases, the installation of extra signalling and rotating panels on fixed blue direction signs now permit hard shoulder running to continue through junctions as well, if needed. In these locations, the hard shoulder is marked as a normal traffic lane from a point before the exit sliproad to a point after the entry sliproad. Signals and signs then indicate whether the hard shoulder is open and which traffic should use it — either only those exiting, or all traffic.

If the hard shoulder is not open to traffic, signals clearly indicate this, and traffic entering or leaving at the junction simply moves across the hard shoulder as though it was an empty traffic lane.

All lane running

Some sections of motorway now operate All Lane Running (ALR), which is a rather euphemistic term that actually means the hard shoulder has been converted into a permanent running lane.

ALR on the M25. Click to enlarge
Something missing? All Lane Running on the M25, J5-6. Click to enlarge

This tends to happen on sections of motorways that are so busy — and so frequently overloaded or congested — that hard shoulder running would be necessary for most or all of the day. In these circumstances it's considered simpler and easier to just use the hard shoulder as an extra lane all the time and avoid the need to make such heavy use of the electronic signalling.

ALR is, arguably, a way of widening a motorway without having to actually widen it, and instead just settling for an increase in width at the expense of the standard of the road.

Emergency refuges

Emergency refuge area. Click to enlarge

Any Smart Motorway scheme that involves some element of hard shoulder running will have emergency refuges installed. These take the form of long, wide lay-bys at the back of the hard shoulder, equipped with emergency telephones and CCTV. In the event that a vehicle breaks down or needs to make an emergency stop, it can use an emergency refuge to get off the road.

The Highways Agency encourages the use of the refuges even if the hard shoulder is not in use as they get vehicles further away from live traffic lanes.

On the original Active Traffic Management trial scheme, emergency refuges were installed every 500m (550 yards), but that standard has been progressively relaxed to reduce the cost of Smart Motorway schemes and now on some sections of road (such as the M6 in the West Midlands, parts of which are elevated on a viaduct) the refuges can be spaced more than twice that distance apart.

Ramp metering

Where the volume of traffic joining the motorway causes serious problems, ramp metering can be used to smooth out the number of vehicles joining from a sliproad. Traffic lights placed on the sliproad change from red to green and back every few seconds, allowing a steady trickle of vehicles through and avoiding platoons of traffic attempting to merge all at once.

Ramp metering improves flow on the mainline of the motorway but can add to the congestion experienced by traffic trying to join. It has been tried in many places on the motorway network but in many of those locations has been switched off again as it was not found to be suitable. It is also often attacked by regular users of the motorway as being simply a way of moving congestion off the motorway and on to the local road network.

Enforcement cameras

Speed cameras. Click to enlarge

Digital speed cameras mounted on some overhead signal gantries are linked to the variable speed limit system, and their trigger speed will change when the speed limit changes.

When the speed limit is reduced, the cameras will not change until a short time after the signs have changed, so there is no need to brake if a signal changes right in front of you. Only after a grace period will the camera begin to enforce the new limit.

When the speed limit is increased, the cameras change immediately so that motorists speeding up are not penalised for accelerating towards the new higher limit.

In free-flowing traffic, where there is no speed limit indicated on electronic signs, the National Speed Limit of 70mph applies and the cameras will normally only trigger at speeds some way above 70.

How do they work?

Movement of traffic is the whole purpose of Smart Motorways, so it's vital that the speed and volume of traffic is monitored all the time, in every lane. This is done using one of the least noticeable parts of the system: inductive loops embedded in each lane at regular intervals. These are used all over the road network — commonly to detect vehicles approaching traffic signals so that they change to green. Here they can be used to count the number of vehicles passing along each lane and also to gauge the overall speed of traffic.

A system of CCTV cameras along the length of the road is also capable of identifying vehicles in traffic lanes and estimating their speed, giving an accurate measure of whether each individual lane is moving and how fast.

CCTV camera. Click to enlarge

The loops and cameras feed their data into a central computer system that keeps track of how many vehicles are on the motorway and where they are. When traffic becomes heavy and flow starts to break down, the system will automatically adjust speed limits in an effort to keep it moving.

Not everything about the system is automated, though: supervision is needed to manage the use of the hard shoulder and to spot any problems as they happen, such as vehicles broken down and unable to get out of the way of traffic. The blanket CCTV coverage allows every inch of tarmac to be monitored.

The CCTV cameras, and the actions of the automated computer controller, are fed into a control centre where Highways Agency staff continually monitor what's happening and can intervene or override the automatic system. They can also communicate with Highways Agency Traffic Officers on the ground and direct them towards incidents.

Why do they take so long to install?

Compared to many road maintenance or upgrade schemes, Smart Motorway schemes can be relatively quick: the Highways Agency claims it can progress a Smart Motorway upgrade to construction in two years, compared to ten years for a traditional widening project. So if the road isn't physically being widened, why do the roadworks sometimes drag on for a year or — sometimes — two?

The minimum requirement is a communications upgrade: this involves running new communication cables down the verges of the motorway (and sometimes down the central reservation too) which supply power to the new electronic equipment and connect it all to the control centre. This job is usually clearly visible while it's happening because all the new cabling is installed in bright purple plastic piping which is often strung along the sides of the carriageway while it's being fitted. This work, in itself, is not too disruptive.

Smart Motorway roadworks
The central barrier being replaced as part of a Smart Motorway scheme

Almost all Smart Motorway schemes will also require the installation of signal gantries — which at a minimum will require a closure of the motorway to lift the overhead beams into place. The construction of supports and foundations often involves lane closures and other roadworks that affect traffic. Depending on their location and the work needed to make space for them, Emergency Refuge Areas can also require considerable work and disruption.

If hard shoulder running will feature, it's usually the case that there needs to be work to strengthen the hard shoulder so that it can carry a full traffic load. In many places the hard shoulder was originally built on a shallower foundation than the main carriageway, and stripping the surface away to reconstruct its foundation can mean months of lane closures and traffic restrictions.

Some Smart Motorway schemes have taken years to install — far longer than the work above could explain. This is where the installation of the Smart Motorway infrastructure has happened when the motorway was already due for major maintenance work. In these cases, the Smart Motorway scheme might be combined with full-depth carriageway reconstruction, in which the whole road surface and road bed of the entire motorway is stripped away to its foundation and rebuilt again. This work can take years. Very often, Smart Motorways also come with the removal of the existing central reservation and its replacement with new drainage channels and continuous concrete barrier.

Where will I find Smart Motorways?

Smart Motorway signMany of England's busiest motorways are now operated as Smart Motorways, and the technology is now also found in Wales and Scotland.

This list is not exhaustive. Work to install new Smart Motorways is going on all the time.

Photograph of part-time hard shoulder running on the M42 taken from an original by David Dixon and used under the Creative Commons Attribution-ShareAlike 2.0 Generic licence.

With thanks to Toby Speight for information on this page.