Friday, 19 July 2019

Smart motorways, do they work?

The short answer, in my experience, no. That's not to say that I think “smart” or “managed” motorways are an inherently bad idea. The theory is sound and a study of a section of the M42 which was upgraded in 2006 showed that journey time savings of between 1 and 4 minutes could be achieved during rush hour. 1 minuted saved using variable speed limits alone and 4 minutes with variable speeds and opening of the hard shoulder. Highways England also say that “personal injury accidents reduced by more than half” and “where accidents did occur, severity was much lower overall with zero fatalities and fewer seriously injured”.

So if the data suggests that smart motorways can reduce journey times and make motorways safer, why do I think that they do not work in practice? The main factor which I believe means they do not work to their full potential is the human factor. But I also believe there are other issues which hinder drivers and the ability for smart motorways to smooth traffic flow effectively.

Smart motorways if you haven't driven on one already, are motorways which are designed to control traffic flow through the use of variable speed limits and increase capacity through the use of hard shoulder running. Gantries which are spaced at regular intervals and span the entire motorway width, provide drivers with information governing the speed limit and which lanes are open. An LED matrix mounted on the gantry above each lane indicates the speed drivers should stick to and whether or not the hard shoulder is open to traffic. Live CCTV and traffic information is fed back to a control room from where controllers can set the speed limits for individual gantries and open and close lanes as required. Controllers can also indicate that lanes other than the hard shoulder are closed in case of incidents or breakdowns.

The video below shows one of the UK's newest sections of smart motorway in action. The M6 between junction 16 for Crewe and junction 19 for Knutsford.




In many cases speed limits are enforced by speed cameras located on each gantry, although it is not clear if the speed cameras are always turned on, or if cameras are selectively turned off and on.  The issue of speed and enforcement brings me to my first complaint about smart motorways. Whilst I fully agree that in order to maintain a set speed, that enforcement is necessary, as many drivers would simply otherwise ignore the speed limit, I find that the speed limit drops are too steep. For example, I was travelling along the M6 through Birmingham and the gantries were displaying a speed limit of 60mph, then the speed limit changed to 40mph at the next gantry. The gantry had a sign indicating that there was a speed camera facing directly behind it, so drivers had to slow from 60mph to 40mph from the point of seeing the gantry to passing under the gantry itself. In most cases this caused drivers to apply the brakes in order to slow down to 40mph and avoid potential points and a fine.

Highways England argues that it should be possible to slow down without needing to apply the brakes. But I would argue that slowing from 60mph to 40mph from the point of seeing the gantry, to passing under the gantry is not always possible without applying the brakes, especially if travelling down hill. Forcing drivers to apply the brakes on a motorway is just about the worst thing you can do if want to smooth traffic flow. There is an excellent video which shows the impact braking can have on creating phantom traffic jams.


Forcing drivers to brake can cause the above phenomenon, which can, in turn, lead to drivers responding as shown in the video below, further interrupting traffic flow.


In my opinion, the simple solution is to graduate speed decreases, 60mph to 50mph at the next gantry and then the gantry after that 40mph, for example.

The problem with speed limits is something that the Highways England controllers have direct control over, however, there are human factors which come into play over which Highways England has little control.

One of the issues for the affective use of hard shoulder running is middle lane hogging drivers. They are drivers who refuse to change lane even if the left-most lane is clear. For the purposes of this explanation, I will use lane numbers, with lane 1 the leftmost and lane 4 rightmost lane. I have witnessed on multiple occasions drivers who are sat in the middle lane (lane 2) continue to sit in that lane, even after it is indicated that the hard shoulder is now open. This means drivers who were in lane 2 are now in lane 3, yet still do not move over to the left, despite lane 1 (hard shoulder) and lane 2 being clear. Sometimes gantries can direct drivers to keep in lane and not to change lane, but on the journeys that I witnessed middle lane or lane 3 hogging, no such directions were indicated.

In 2013 police were given the power to hand out on-the-spot fines of £100 and 3 penalty points, as middle lane hogging is classed as careless driving.

Theoretically speaking if all drivers are were driving at the same speed, as indicated by the gantry, then middle lane hogging should not be a real issue, although still against the law. However I have witnessed drivers in lanes 2 and 3 of 4 sitting at 50-60mph when there were no speed restrictions in place. There were also HGVs in lane 2 who were unsure of the rules or simply refusing to use the hard shoulder despite it being open to traffic.

The situation as described above becomes a problem when faster-moving traffic travelling in lane 1 wishes to pass slower-moving traffic sat in lanes 2 and 3. In order not to undertake, the driver would be forced to cross 3 lanes of traffic and then back again. Changing lanes if done properly should not be inherently risky, but add in slower moving traffic and speeding traffic, then moving across 3 lanes can increase the level of risk.

In my opinion, if the police are unable to clamp down on middle lane hogging, then the government should clarify the rules on undertaking. If there are vehicles in lanes 2 and 3 travelling below the indicated speed limit despite lane 1 being clear, then it leaves drivers who do wish to obey the law but wish to travel at the speed limit with a dilemma. Do they cross 3 lanes of traffic, or pass vehicles on the left which despite having plenty of opportunity have not moved over. In Germany it is common for drivers to flash their headlights whilst travelling on the Autobahn, which means the driver behind wishes you to move over. Flashing your headlights at a car in front in the UK would probably be seen as an aggressive act, or the driver in front may think you are trying to warn them that something is wrong, so probably best avoided. But personally, I do think it would be a perfectly reasonable way of indicating that perhaps a driver should move over to the left.

Undertaking isn't strictly illegal, however it can be considered as careless driving and as such drivers caught undertaking can receive penalty points and a fine. However the Highway Code (Clause 268) states: “In congested conditions, where adjacent lanes of traffic are moving at similar speeds, traffic in left-hand lanes may sometimes be moving faster than traffic to the right. In these conditions you may keep up with the traffic in your lane even if this means passing traffic in the lane to your right. Do not weave in and out of lanes to overtake.” So while it is not advisable to undertake there are certain situations when it is permissible.

Middle lane hogging mostly becomes and issue when traffic is flowing freely, undertaking on the other hand can have negative impacts during periods of congestion. I have come across situations where the hard shoulder was suddenly opened to traffic which was travelling slowly or at a standstill. In this instance a small number of cars would enter the hard should and then get up to speed (what ever the speed restriction was at the time) straight away, undertaking drivers at a much high speed than those in lane 2, this would make it difficult for other vehicles to safely move over to the hard shoulder. In this instance the hard shoulder is being used by only a relatively small number of vehicles.

The situation is made more complex by lane drops, this is when a section of hard shoulder which is open to traffic is strictly for vehicles leaving at the next junction. Drivers who may not have seen the matrix message saying that the hard shoulder is exit only, can be forced to leave the motorway, or come to standstill in an otherwise clear lane whilst they wait for an opening to get back onto to motorway. There are also those who use the circumstances to deliberately undertake slow-moving traffic and then just before the junction exit force their way back onto the motorway.

Highways England say that studies show that smart motorways do cut congestion and reduce accidents, but from my experience I don't think that the system is being used to its full potential. One issue is eduction, a large number of motorists have yet to experience driving on a smart motorway and would perhaps not fully understanding how they work. So currently we have a mix of experienced and inexperienced drivers, complicated by drivers who even on normal motorways refuse to move over to the left-most lane and aggressive drivers who use whichever lane is free to make as much headway as possible, as quickly as possible.

It took me a few trips over the M6 through Birmingham to know to look out for matrix notices which say if the hard shoulder is to be used for exiting the motorway only and to look as far ahead to next gantry as possible in order to slow down if necessary. But I do believe there are changes Highways England could do make, such as graduating speed decreases and there should be a widespread campaign to inform motorists of how to drive on smart motorways.

The theory of controlling speeds during periods of congestion is sound, but the human element sometimes means that theory doesn't always work out completely as intended. And then there is the adage that by increasing capacity on the roads you just created more congestion down the line.


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