Motorways are used by huge volumes of long-distance traffic, and on any particular part of the road there will be thousands of drivers who are completely unfamiliar with the area they are passing through. That's fine most of the time (in fact, it's exactly what motorways are supposed to do) — but what happens when the motorway is suddenly closed?
Emergency Diversion Routes exist for that very reason: with no knowledge of the local area, a motorist can find their way back on to the motorway at the next junction. They are ready to use almost straight away, and across the country, there's a diversion route to allow for the closure of absolutely any stretch of motorway.
The existence of Emergency Diversion Routes also answers the common question: what's the point of those unexplained symbols stuck on to road signs?
What are these strange symbols?
Emergency Diversion Routes are signposted using black symbols on a yellow patch.
There are four shapes — square, triangle, circle and diamond — but each can be shown filled or in outline, making eight distinct symbols. Close to motorway junctions, and on roads near to or following the line of a motorway, they are commonly placed on direction signs, either manufactured as part of the sign or added later on a vinyl patch.
How does a diversion work?
If a motorway is closed — let's say because of an accident — then the police and traffic officers will close the road at the previous junction and force traffic to leave the motorway. Every motorway exit is equipped with a trigger sign, which is normally covered up (most are hinged and folded up when not in use) but which is uncovered when the diversion becomes active. This instructs motorists to follow a particular symbol in order to rejoin the motorway at the next junction.
From that point onwards, the Emergency Diversion Route is signposted using the symbols above, and as they are stuck on to existing road signs and visible even when not in use, the diversion can be followed immediately: only the trigger sign has to be uncovered and the rest is already in place.
Diversion routes are carefully chosen to follow roads of a suitable standard and width to carry all motorway traffic, so they tend to follow A-roads and may make detours to avoid low bridges or other obstructions.
Each diversion route will lead traffic to the next motorway junction, where it can rejoin the motorway. Many re-entry points have another folding sign, as the last one in the chain, which will show the way to re-join the motorway in its normal state. These final signs can be uncovered, like trigger signs, to indicate that traffic should follow the next EDR symbol to a later motorway junction, in case the motorway isn't open at that point. In this way Emergency Diversion Routes can be daisy-chained together to form longer diversions if the motorway is closed for more than one junction.
When will I see them?
If the motorway is open, you won't see very much at all. In normal circumstances, the Emergency Diversion Routes will appear as:
- Blank or folded-away signs near exits from the motorway;
- Black symbols on yellow patches applied to road signs near motorways.
When a motorway closure happens, you will see:
- Police or Traffic Officers directing traffic off the motorway at a sliproad.
- A yellow sign at the road closure, telling you to follow a specific symbol to rejoin the motorway.
- Direction signs will use that symbol to indicate a route to follow.
- The symbols will end at the point you take a sliproad to rejoin your original route.
The Emergency Diversion Route system in England underwent some investment and renewal in 2010 and 2011, following a long period in which it had not been maintained properly, and as well as the symbols now being much more conspicuous than they were previously, diversion routes are increasingly referred to in traffic reports when a motorway is closed. Traffic reports on the radio will refer to a diversion following, for example, a solid circle or a hollow diamond.
What other symbols are used?
Certain parts of the road network have signposted diversion routes that use their own symbols, usually because the diversion routes are lengthy and would interfere with normal Emergency Diversion Routes if they used one of the symbols above.
The Severn Bridge and Second Severn Crossing have a system of diversion routes for use when the bridges are closed in high winds or other adverse weather. A stylised pictogram of a suspension bridge is used to direct traffic via the M50 in the event that the bridges are closed.
In London, Transport for London have established diversion routes for the closure of river crossings, using a black cross symbol to direct traffic to an alternative route. They are used not just for road closures, but also for vehicles that are prohibited from certain crossings.
The black cross is used most widely for the Blackwall Tunnel, and this diversion route (which directs traffic over the Dartford Crossing instead) has signs and symbols in place as far away as the A1(M) in Cambridgeshire. It is used elsewhere too, including one very short diversion (comprising just one sign after the trigger) to avoid the Strand Underpass in Westminster.
Finally, the A27 Southwick Hills Tunnel near Worthing is unusual in having colourful diversion symbols: a red diamond for eastbound traffic and a blue circle for westbound traffic. The two symbols are used to route through traffic when the tunnel is closed, but are used at other times by traffic prohibited from using the tunnels.