As you would expect, these are the most Frequently Asked Questions where British Roads are concerned. It started off as somewhere to put answers to questions I got asked a lot, and grew into this formidable document. It's now been adopted as the official FAQ for SABRE, the Society for All British and Irish Road Enthusiasts. If the answer you want's not in here, or if you think I've missed one out, you can either ask me or pose your question to the kindly folk of SABRE who are bound to know the answer.
The FAQ is updated irregularly and erratically. Contributors are listed in no particular order at the end of this page. This system is about as organised as the roads themselves.
Technical terms, jargon and other road-specific words can be found in CBRD's Dictionary, which provides a comprehensive resource defining words and phrases found in this FAQ and in the wider world of roads. Definitions of terms are not included in this document.
- 1 The Network
- 2 Classification and Numbering
- 2.1 How are the roads classified?
- 2.2 How are the roads numbered?
- 2.3 How are new roads allocated numbers?
- 2.4 What happens when a road crosses a zone boundary?
- 2.5 When were the roads classified, and who by?
- 2.6 What is a 'trunk road'?
- 2.7 What is a 'primary route'?
- 3 Signing and directions
- 3.1 Where can I find information on the road signing system?
- 3.2 Who puts up the signs?
- 3.3 Who designs the signs?
- 3.4 Colour coding on directional signs
- 3.5 Shapes of signs
- 3.6 Fonts used on signs
- 3.7 Old signs
- 3.8 Specific questions about signing and directions
- 4 Motorways
- 4.1 What is a motorway?
- 4.2 Old motorways
- 4.3 New motorways
- 4.4 Specific questions about the motorway network
- 4.4.1 Is the M25 numbered correctly?
- 4.4.2 What are the big masts at the M1/M6 junction?
- 4.4.3 What happened to the A40(M), M41, A102(M)?
- 4.4.4 What's so bad about Spaghetti Junction?
- 4.4.5 Where is the busiest section of motorway in Britain?
- 4.4.6 Where is the widest section of motorway in Britain?
- 4.4.7 Where is the narrowest section of motorway in Britain?
- 4.4.8 Where is the highest section of motorway in Britain?
- 4.4.9 Which counties don't have a motorway?
- 4.4.10 Why do some motorways start at junctions above 1?
- 4.4.11 Where does the M62 go at Manchester?
- 4.4.12 Why is Watford Gap so far from Watford?
- 4.4.13 What happened to M1 junction 3?
- 4.4.14 What's the secret "Works Exit" on the M4?
- 4.4.15 Why was the M50 seen as so important?
- 4.4.16 What happened to the M8 east of Glasgow?
- 4.4.17 Why are there two numbers, M74 and A74(M), for one motorway in Scotland?
- 4.4.18 Will the M6 ever be extended into Scotland?
- 4.4.19 Why does the M1 stop at Brent Cross (j1)?
- 4.4.20 What is the longest distance between motorway junctions?
- 4.4.21 What are the blue and yellow signs at the side of motorways?
- 4.4.22 Will the A1 north of Leeds become M1?
- 4.4.23 Why is there no M7?
- 4.4.24 What is the total mileage of the UK motorway network?
- 4.4.25 Which is the steepest hill on a UK motorway?
- 5 Other Roads
- 5.1 Specific questions about the non-motorway road network
- 5.1.1 What's so bad about the Hanger Lane Gyratory?
- 5.1.2 What's wrong with the A42?
- 5.1.3 Where was the original A42?
- 5.1.4 Why is part of the A30 called the A303?
- 5.1.5 What happened to the road numbers around Cambridge, and where did the A604 go?
- 5.1.6 Which is the shortest A or B road?
- 5.1.7 Where is the greatest vertical separation between two carriageways of the same road?
- 5.1.8 What are bar code signs for?
- 5.2 Central London
- 5.1 Specific questions about the non-motorway road network
- 6 Technical Terms
- 7 More Information
- 8 Contributors
1. The Network
1.1 Who owns and runs the roads?
This is a surprisingly difficult question. There is a simple answer and a complicated answer.
The simple answer is that the public own and run them. Roads exist for the use of the public and are maintained by various government bodies at public expense. Roads in Great Britain can be divided into two categories for this purpose: trunk roads and non-trunk roads. Trunk roads (see 2.6 What is a 'trunk road'?) are nationally important routes, which are maintained by the national highway authority of each country (for example, the Highways Agency in England). All other public roads are maintained by local authorities — usually a city or county council. Roads in Northern Ireland are all maintained by the Northern Ireland Roads Service.
The complex answer is that roads — or more properly public highways — cannot easily be said to be owned by anyone. Often the land on which they exist actually belongs to whoever owns the adjacent land, and theoretically, rather like a path across a field, the land is theirs even if the right of way is superimposed on top of it. If the right of way were ever to be removed, or the road were ever torn up, the land would revert to its historical owner. However, a public highway is extremely difficult to get rid of and for all practical purposes the land between its boundary fences is treated as though it is owned by the authority that maintains it.
Land for new roads that were built more recently (from the early 20th century), and did not evolve from ancient pathways and tracks, is bought from the landowner by compulsory purchase before construction begins, and is then owned, outright, by the Crown.
1.2 What are the roads like?
The British road network provides dense coverage of the whole country and is, by international standards, well developed and well maintained. It arguably has suffered from a lack of long-term planning and consistent investment.
Nearly all public roads were surfaced in the early part of the 20th century, and the country has a good coverage of purpose-built high speed roads, built from the 1950s onwards. New-build roads are subject to very high design standards. Older roads are generally well maintained and surfaced, but are rarely widened or re-aligned (particularly when compared to other countries in Western Europe) and often their courses have been unchanged for centuries.
1.3 How are the roads funded?
For trunk roads (see 2.6 What is a 'trunk road'?), Central Government pays 100% of the maintenance costs. For roads maintained by local authorities, Central Government will pay 50% of the costs for A-roads and 30% for B-roads, with the remaining cost of maintaining these (and the entire cost of maintaining unclassified roads) met by the local authority itself.
1.4 How safe are the roads?
The UK generally has very safe roads and, compared to other countries, is among the safest places in the world to travel by road.
Motorways are the safest type of road, accounting for only 3-6% of all those killed or injured while carrying a large proportion of all road traffic. In total about 2,500 people die in road accidents every year and another 26,000 are seriously injured.
In 2013 there were 1,770 deaths on the UK's roads, which corresponds to 28 deaths per million of population. By that measure, in Europe in 2013, only Sweden had fewer deaths.
2. Classification and Numbering
2.1 How are the roads classified?
Classification refers to the allocation of numbers to British roads. Numbers are allocated on a national basis and within Great Britain each number is unique (except in certain places where a number has been duplicated by mistake). Northern Ireland has its own system which exists entirely separately.
There are three tiers of classification in both GB and NI: motorways, A-roads and B-roads. Motorways are grade-separated expressways and have 1, 2 or 3-digit numbers prefixed with 'M' or suffixed '(M)'. A-roads are the other major routes; they vary from motorway-standard to narrow local roads, and have 1, 2, 3 or 4-digit numbers prefixed with 'A'. B-roads are local routes and have 3 or 4-digit numbers prefixed with 'B'.
2.2 How are the roads numbered?
2.2.1 How are A- and B- roads numbered?
Kinneir also designed a third typeface to complete the set, called "Transport Light", which was intended for use on internally lit signs. It was never adopted.
Not all signs use the Transport alphabets, usually as the result of a design mistake. North Yorkshire County Council sometimes use a generic Helvetica or Univers font (which looks very ugly indeed) and the Welsh Office used to have a fondness for Arial, though none of these imaginative substitutes are permitted.
3.6.2 What is the taller font used on motorway signs?
There is also a heavier version of the alphabet called "Motorway Temporary", used for black-on-yellow temporary motorway signs. It has not been adapted to include the word "Toll", though it is not clear why this is so. Motorway Permanent was, like the Transport alphabets, developed by Jock Kinneir. Some sources claim this was done by modifying an existing typeface called Commercial Grotesque, but this has been difficult to confirm.
While Motorway appears bigger than other lettering, the width of each character is the same as the corresponding character in Transport.
3.6.3 What other countries use the font?
Both the "Transport" alphabets (see 3.6.1 What font is used?) and "Motorway Permanent" (see 3.6.2 What is the taller font used on motorway signs?) have been appropriated for use by other countries. You can see Transport on non-motorway signs in Spain (in a modified form even heavier than Transport Heavy), all road signs in Iceland and Ireland (both using only Transport Heavy), and some signs in Italy (which also uses a condensed version — the two often appear on the same sign and together look quite unpleasant). Malaysia seems to have adopted Transport in recent years.
Egypt and China both use Transport on road signs for the English translations of place names and instructions, and Greece sometimes uses a Worboys-reminiscent signage system complete with Transport font, but doesn't remain loyal to one particular typeface.
Ireland and Portugal also use the "Motorway Permanent" alphabet, Ireland on motorways and Portugal on all roads.
3.7 Old signs
3.7.1 What did the old-style signs look like?
The road today has four lanes in each direction following extensive reconstruction in the early 1990s, and is utterly unrecognisable from its original form.
The first long-distance section of motorway was the first part of the M1, which was opened from Aldenham (close to present-day J5) to Rugby (J18), a distance of about 60 miles (100km), in 1959. It included the spurs M10 and M45, which opened at the same time and were designed to distribute the traffic at each end as it returned to the existing road network. There are features in the Photo Gallery showing the road under construction and today.
CBRD has an article about the development and construction of the Preston Bypass.
4.2.2 How do old motorways differ from new ones?
In many ways they remain unchanged. Design standards regarding the hard shoulder, width of lanes and overhead clearance through bridges were settled in the earliest days of motorway design and are no different today.
Improvements have been made over the years, however; in the late 1960s continuous central crash barriers were included in the specification, and were retrofitted onto existing roads. From the early 1970s electronic message signs and emergency telephones were added as standard and retrofitted too. Since the early 1960s, requirements for the maximum curvature of the road and for maintaining clear forward visibility have improved.
4.2.3 Where can I see examples of old motorways?
The oldest, with intact sections worth seeing, are the M50 spur from the M5 to Ross-on-Wye, which includes some very tight junctions and missing hard shoulders, and the incredibly quiet M45.
4.3 New Motorways
4.3.1 Will there be any new motorways?
Yes, but today construction of new sections of motorway almost exclusively takes the form of short links and improvements, and it is unlikely that entirely new motorway corridors will be developed in the forseeable future. New high-speed roads tend to be built as A-road "expressways" in preference to motorways, owing to their less demanding design standards and lower cost of construction.
CBRD's Road Schemes pages provide a constantly updated listing of current construction projects.
4.3.2 What did the "New Deal for Trunk Roads" mean?
The "New Deal" was part of the former Labour Government's ten year transport strategy which was started when they gained office in 1997. In terms of road transport, the government effectively wiped the slate of the previous government's road-building plans, jacked up fuel prices and put in place measures to ensure that only major bottlenecks in the road system would ever get attention. It resulted in final cancellation of the M65 across the Pennines, among other schemes. The ten-year transport plan was eventually abandoned, and road construction has increased in pace, though not greatly.
4.3.3 What was the last big motorway project?
The M40 was the last long-distance route on a new line to be constructed. Originally the M40 had run from London to Oxford along the line of the A40, but in the late 1980s traffic on the M1/M6 route from London to Birmingham had become unbearable and a single motorway link between Britain's two largest cities was at last agreed to. The M40 was extended north from Oxford to connect with the M42 south-east bypass near Birmingham. The route was completed in 1991. Nothing on a similar scale has been contemplated since.
4.3.4 What were the most recent motorways to be built?
Some of the most recent projects to be completed were the A1(M) between Dishforth and Leeming in April 2012, the M80 between Stepps and Haggs in November 2011, and the M74 into the centre of Glasgow in June 2011.
Before the start of work on the M6 Toll, there were no motorways under construction for the first time since work started on the M6 Preston Bypass in 1956. The M6 Toll itself opened in late 2003. Prior to this was the opening of the missing link in the M60 Manchester Orbital in 2000; before that, the M1 extension connecting to the A1 in 1999; before that the M65 Preston to Blackburn section in 1997.
4.3.5 Where will the next new motorways open?
The completion of the M8 between junctions 6 and 8 and the upgrade of the A1 to motorway between Leeming and Barton are both due to open in 2017.
4.4 Specific questions about the motorway network
4.4.1 Is the M25 numbered correctly?
This is often asked because the M25 does not follow the A25 or because it passes through motorway zones 1, 2, 3 and 4 (see 2.2.2 How are motorways numbered?). The answer is yes, its number is valid, because its start point is south of the Dartford Tunnel in the motorway 2-zone.
4.4.2 What are the big masts at the M1/M6 junction?
These are a famous landmark and known to interfere with some car radios. They are thought to be high-power transmitters for submarines, which are apparently still used to send out high powered transmissions to date. Rugby used to be the location of the National Physical Laboratory, which was responsible for broadcasting the correct time signal, used by some clocks and VCRs. This is now done elsewhere. Other sites of masts, such as on the M1 close to Daventry and the M5/M42 junction are BBC transmitters.
Unfortunately, this question is no longer as relevant as it once was — the landmark masts at Rugby, visible from the M1 and M6, and erected in 1929, were demolished by BT on the weekend of June 21st, 2004. Only a handful of masts are still standing.
4.4.3 What happened to the A40(M)/M41/A102(M)?
These three were motorways in central London, sections of motorway that were the first stages of a vast motorway plan for London that were built before the plan was axed. They are otherwise known as Westway (A40(M)), the West Cross Route (M41) and the Blackwall Tunnel Approach Roads (A102(M)). They were downgraded to A-roads in 2000 when the Greater London Authority took control of all roads within its boundaries, with the exception of the M1, M3, M4 and M11 which remain property of the Highways Agency. Transport for London (TfL) now maintains these roads.
A full history of the Ringway plans is in CBRD's Articles section.
4.4.4 What's so bad about Spaghetti Junction?
It is the most complex junction on the motorway network, joining the M6, A38 and A38(M) at Gravelly Hill in Birmingham. The whole thing looks like a confusing tangle from the air — from where it is usually photographed — but on the ground it is very well signposted and it is hard to go wrong. There is, really, nothing wrong with Spaghetti Junction.
4.4.5 Where is the busiest section of motorway in Britain?
Most reports suggest the M25 between the A30 and the Heathrow Spur, junctions 13 to 14. However in 2005 a close contender was the M60 north of Manchester between junctions 16 and 17.
4.4.6 Where is the widest section of motorway in Britain?
The Guinness Book of World Records lists the M61 at Linnyshaw Moss, Greater Manchester (close to the M60 interchange), which has 17 separate traffic lanes side by side, spread across several parallel carriageways. However, a look on the ground makes it clear that there are 18 lanes parallel for a very short while (aerial photographs confirm this).
The image above shows part of the junction complex at Linnyshaw Moss, though there are further multi-lane carriageways out of view to both sides.
CBRD has a photo gallery of Linnyshaw Moss.
4.4.7 Where is the narrowest section of motorway in Britain?
The A601(M) which is single-carriageway between the M6 roundabout and Over Kellet (where it ends on a B-road). The A6144(M) was also a contender, being entirely single-carriageway, but was downgraded in May 2006 and is no longer a motorway. It was built to a substantially higher standard than the A601(M)'s southern section.
4.4.8 Where is the highest section of motorway in Britain?
The very highest point is the "M62 Summit" (as signposted in both directions at the location), well over 350m above sea level. The exact point is the overbridge across the A672 at junction 22, in the wilds of Saddleworth Moor.
4.4.9 Which counties don't have a motorway?
Owain Vaughan compiled this list of traditional counties:
Isle of Wight
4.4.10 Why do some motorways start at junctions above 1?
In every case this is simply because the motorway was proposed to be extended further and the plan was never carried out, usually because this involved taking it deep into a city which proved problematic. Some examples of motorways that do this include the M23 (starting at J7 outside London) and the M11 (starting at J4 on the A406 North Circular Road, London).
4.4.11 Where does the M62 go at Manchester?
Until 2000, the M62 was a single length of motorway running from Liverpool, around the north of Manchester, and across the Pennines to Leeds and Hull. When Manchester's Ring Road was completed, its northern section was routed along the M62. The whole thing was given the number M60, including the section of M62 that formed part of it.
The M62 is now signposted along that section as (M62), the equivalent of saying "towards the M62". That section is now numbered M60, meaning the M62 now exists in two distinct parts.
4.4.12 Why is Watford Gap so far from Watford?
Watford Gap on the M1 was the first service area in Britain to open and is extremely well known. But Watford is a Hertfordshire town within the M25, and Watford Gap is some fifty miles north of London. The answer is surprisingly simple: the services are named for the tiny village of Watford, on the B5385 just outside Daventry. Watford Gap is a low pass through the Northampton uplands, used by the Roman Road 'Watling Street' (now A5), the Grand Union Canal, the railway, and now the M1.
4.4.13 What happened to M1 junction 3?
The section of M1 from J5 to the A406 North Circular Road was built over several years in the 1960s. It was constructed from junction 4 to 2 with the overpasses provided to add junction 3 when the Scratchwood Link to the A1 had been built. The link road was cancelled in the end, leaving a redundant junction.
Today, Scratchwood services (officially renamed some years ago to "London Gateway") occupies the site, and the incomplete roundabout has now become a set of sliproads for the approach to the services.
4.4.14 What's the secret "Works Exit" on the M4?
West of junction 13 on the eastbound carriageway of the M4, there are a set of sliproads signposted "Works Access Only". The signs have red borders, implying a military exit. It is a back entrance to RAF Welford, a Second World War airfield and now an RAF/USAF military installment mainly used for storing munitions. The M4 entrance allows easier access for the large vehicles used to carry the munitions.
Some rumours also claim that it was here that the nuclear weapons were stored instead of Greenham Common, though this cannot be confirmed. Conventional munitions from here were used during the Gulf War.
4.4.15 Why was the M50 built before the M5?
This question arises because of the odd sequence of events that saw the M50 built. It is a spur to the M5, less important than the main route, but it was built before the M5 itself was. Even today it seems quieter than most other motorways, so the question of why it exists and was prioritised over the M5 is often raised.
The reason it exists is as part of a larger scheme to connect the Midlands to South Wales: the A40 and A449 are high standard roads from Ross to Newport. The M50 is built differently because, rather than being an upgrade of an existing road, it had to take a new line to meet the M5. Since it would only carry traffic to and from a motorway, it also was a motorway.
It seems most likely that it was built first so that it would already be ready for service when the M5 was opened, rather than having the M5 open first and then have South Wales traffic diverted along local roads or through Gloucester for several years until the spur was complete.
4.4.16 What happened to the M8 east of Glasgow?
It was simply never built, meaning the road between the A73 and M73 (junction 6 to 8) is the A8, built to dual carriageway standard and with grade-separated junctions but no motorway restrictions. An upgrade is now under way and the M8 will be completed in 2017.
4.4.17 Why are there two numbers, M74 and A74(M), for one motorway in Scotland?
The Glasgow to Carlisle motorway replaces the A74, and was largely built in the 1990s. The northern section, from junction 1 to 13, is the M74, large sections of which were in place from the 1960s onwards. The southern section, a direct continuation of the route, is numbered A74(M). The simple explanation far for this is that the northern part was built as a straightforward new motorway and designated M74, while the southern section was upgraded from the original road in a series of short sections over a long period and those sections were given the temporary number A74(M). As the sections were joined up the temporary number was retained instead of being replaced. It's possible that the temporary number survives because there was an intention to renumber the whole thing M6: see 4.4.18 Will the M6 ever be extended into Scotland?
4.4.18 Will the M6 ever be extended into Scotland?
In 2006, the M6 was extended northwards from its original terminus at Carlisle to run a further six miles north to reach the Scottish border. This meant that there was continuous motorway between England and Scotland for the first time.
When the M74/A74(M) upgrade was carried out in the 1980s and 90s, it appears to have been the intention that the whole route would become part of the M6 once they were linked together. Some signs have A74(M) on overlay panels which, when removed, reveal "M6".
When asked if there were plans to change the number to M6 in Scottish Parliament a couple of years ago, the Minister in charge of transport replied that there were no plans to change any Scottish trunk road numbers at the time of writing. This doesn't answer if they will be changed in the future, of course. The short answer is that the renumbering was once definite but nobody is now in any rush to do it.
4.4.19 Why does the M1 stop at Brent Cross (J1)?
Approaching the southern terminus of the M1 at Brent Cross, traffic is diverted down to the roundabout on what looks like a sliproad, with the main carriageway continuing ahead, completely empty. The A406 North Circular flyover is two levels up, with room for the M1 to pass between it and the roundabout.
The original plan was for it to continue following the Midland Mainline railway further into London, to terminate on the northern section of Ringway 1. None of this was ever completed. CBRD has details on the Ringway plans in the Articles section.
4.4.20 What is the longest distance between motorway junctions?
The longest distance is westbound on the M26 from junction 2A. The next interchange is with the M25, but exiting there is not possible in this direction. The next exit from the motorway is some 18 miles later at M25 junction 6. Signs on the M26 warn of this.
A close runner-up is the M11 southbound from junction 10. Junction 9 is limited access, leaving a 17 mile non-stop journey to junction 8.
4.4.21 What are the blue and yellow signs at the side of motorways?
Since the mid-2000s, small blue rectangular signs have been installed at intervals along the side of English motorways and trunk routes bearing three lines of numbers and letters (pictured right on the M6). These are called Driver Location Signs and are location markers. More information is available in CBRD's Driver Location Signs article.
4.4.22 Will the A1 north of Leeds become the M1?
This question arises because the A1 between Leeds and Darlington was progressively converted to a motorway, and at Hook Moor where the A1 and M1 merge, the M1 takes priority. The short answer is that this numbering change is unlikely. The idea was officially floated, and even mentioned in the Commons by then-Chancellor George Osborne, but the idea does not appear to have been pursued by Highways England since then. A numbering change on this scale is likely to cause confusion and inconvenience a large number of businesses located near the route.
4.4.23 Why is there no M7?
In Scotland, motorways take their number from the A-road they replace. There is no M7 because there has never been a need to replace the A7 with a motorway.
There was an idea in the 1990s to build a new toll road linking Edinburgh and the A74(M), approximately parallel to the A702, and it was suggested that this could take the M7 number. These plans have since been cancelled.
4.4.24 What is the total mileage of the UK motorway network?
The Department for Transport's "Road lengths in Great Britain: 2013" claims the total mileage of motorway is 3,640 km or 2,262 miles.
4.4.25 Which is the steepest hill on a UK motorway?
The current favourite is the Northern Ireland M2 climbing away from Belfast between junctions 2 and 4. It reaches a gradient of 1 in 15 at one point (the recommended maximum is 1 in 25). The only uncertainty is that no figures are available for the gradient of the M90 between Kinross and Perth, which is the only route with the potential to beat this incline. Niall Wallace has attempted to survey it using Ordnance Survey maps and has arrived at the figure of 1 in 10 between the Bridge of Earn and the top of the hill. That's very steep indeed!
Wesley Johnston has full details at the Northern Ireland Roads Site.
5. Other Roads
5.1 Specific questions about the non-motorway road network
5.1.1 What's so bad about the Hanger Lane Gyratory?
Otherwise known as "Malfunction Junction", the Hanger Lane Gyratory is the interchange where London's North Circular Road (A406) crosses Western Avenue (A40). It was rebuilt in its current form in the 1970s to eliminate the flat signalised junction that preceded it. Essentially, it is a simple roundabout interchange but it is seriously restricted for space and its capacity is not adequate for the situation. It regularly backs up in all directions which is quite an achievement to say that the A40 doesn't even touch the roundabout itself.
5.1.2 What's wrong with the A42's number?
For complex historical reasons best explained in 5.1.3 Where was the original A42?, the A42 presently lies between Measham (near Tamworth) and Nottingham. The problem with this is that is is completely out of the correct numbering zone, and by all rights should begin with a 5. It isn't unusual for a road to be entirely out of zone, but usually this is because of gradual renumbering which erased the section of the road connecting it to its rightful zone, whereas the A42 was dropped directly into the wrong zone and no portion of it in its present alignment has ever been in the 4-zone.
5.1.3 Where was the original A42?
When roads were first numbered, the A42 was a major road from the A4 at Reading, through Oxford and up to Birmingham. It was renumbered very early on so that the A34 trunk road could be extended over its route and onwards to Manchester. The remaining part from Reading to Oxford was changed too, and is now the A329 and A4074. For a long time the number was unallocated.
In the 1970s the M42 was built, presumably numbered so it wouldn't be associated with another road anywhere else. When the 1980s extension towards Nottingham was built, it was designated an all-purpose road, not a motorway, and fortunately the A42 number was available to match its motorway counterpart.
5.1.4 Why is part of the A30 called the A303?
No section of the A30 is called the A303. Parts of the A30 from the M3 to Honiton are, however, of a very low standard, and long-distance traffic is directed onto the A303 instead. Originally, the A30 formed the main route from London to Penzance on its own, but as traffic increased and the road had to be improved, the routing of the A303 was picked as superior for whatever reason and this road was improved instead where it ran parallel. As a result, the A30 is a non-primary locally maintained road through the section where the A303 runs parallel, whereas the A303 is a national trunk road.
5.1.5 What happened to the road numbers around Cambridge, and where did the A604 go?
Large-scale renumbering of the roads around Cambridge means the city's road numbers have changed completely since 1990. The A604 has been completely wiped from the map, both at Cambridge and everywhere else it once ran. In brief, this is due to the A14, which has obliterated the need for the A45 and A604 in the area by trying to do both their jobs (though, between the M11 and A1 at least, it isn't doing very well at this).
5.1.6 Which is the shortest A or B road?
The simplest answer is that nobody knows. SABRE has been attempting to catalogue all the numbered roads in the UK since early 2002, but has yet to produce a definitive answer to this question. From their research it is also known that the Department for Transport no longer keeps an accurate and up to date record of all classified roads; in fact, even in its current state as a work in progress, SABRE's listing is alsmost certainly the more accurate and up to date of the two. Despite this, because the very shortest roads are extremely difficult to spot on maps, and because they almost never appear on signs, SABRE can never be sure it has found them all. Probably the shortest one found so far is all of 105 metres long.
5.1.7 Where is the greatest vertical separation between two carriageways of the same road?
On some dual carriageway roads, particularly in hilly terrain, the opposing directions of traffic might find themselves split across two levels, with one carriageway higher than the other. The M5 south of Bristol has a famous section like this, running for several miles with about 9m (30 ft) vertical difference between the northbound and southbound carriageways, as it passes through the Gordano Valley.
The greatest difference is actually in a much less mountainous area. It is believed to be on the A282, which forms the link between the two ends of the M25 east of London. Northbound traffic is carried in twin two-lane tunnels under the river, while southbound traffic crosses over the water on a four-lane cable-stayed bridge. There is the entire depth of the River Thames, plus space above it for shipping clearance, between the two opposing directions of travel.
5.1.8. What are bar code signs for?
On some trunk roads (and former trunk roads) small signs placed parallel to the kerb are mounted after junctions. They are a disused system for accurately tracking the location of maintenance vehicles. Mark Thorne writes:
During the 1990s, the Transport Research Laboratory were carrying out trials of condition surveys of the roads using lasers, cameras etc. and they needed a simple method of locating where they were on the road network. They could measure the lengths of road by means of the equipment on the vehicle carrying out the survey, resetting the chainage (length) at known points as they drove over the 2 white dots (known as Node Points) you see at the start & end of slip roads, centre of junctions etc.
These days GPS is used to locate the survey data to a great degree of accuracy, typically to the nearest centimetre.
5.2 Central London
5.2.1 What's so complicated about central London's roads?
Heated debates on the SABRE forums started when someone asked where the roads go in Central London. Theoretically the A-roads A1-A6 radiate from London to form zone boundaries for road numbering purposes, but what exactly happens where they all theoretically meet is not simple. The following is a breakdown of where each road goes and where the zone boundaries go. Other important roads are also here. Descriptions start from the North or South Circulars.
5.2.2 The route of the A1
The Great North Road runs from London to Edinburgh. It enters from the North, along Falloden Way, Lyttleton Road, Aylmer Road, Archway Road, Holloway Road, Upper Street, Goswell Road, Aldersgate Street to end infront of St Paul's Cathedral on Newgate Street, which is A40 to the west and unclassified to the east.
5.2.3 The route of the A2
Enters along Shooters Hill Road, Blackheath Hill, Blackheath Road, New Cross Road, Old Kent Road and Great Dover Street to end on the A3 Borough High Street
5.2.4 The route of the A3
Common North Side, Long Road, Clapham High Street, Clapham Road, Kennington Park Road, Borough High Street, London Bridge to end at Monument. North of this point, the road is the A10.
5.2.5 The route of the A4
Cedars Road, Ellesmere Road, Hogarth Lane, Great West Road, Talgarth Road, West Cromwell Road, Cromwell Road, Brompton Road, Knightsbridge, Piccadilly, Pall Mall, Strand, Fleet Street, Ludgate Hill, Cannon Street to end at Monument with the A3 and A10.
5.2.6 The route of the A5
Edgware Road, Cricklewood Broadway, Shoot Up Hill, Kilburn High Road, Maida Vale, and Edgware Road to end on the A40 Bayswater Road at Marble Arch.
5.2.7 The route of the A6
The A6 doesn't, and never has, actually reached London. Historically it started on the A1 at High Barnet, where the A1081 forks off the A1000 today. The construction of the M25 meant that it was cropped short and now starts even further north at Luton.
5.2.8 The route of the A40
Western Avenue, Westway, Notting Hill Gate, Bayswater Road (from here forming the 1/5 zone boundary), Oxford Street, High Holborn, Newgate Street to end at St. Paul's Cathedral along with the A1.
5.2.9 The route of the Inner Ring Road
Within the Inner Ring Road, no other road numbers are signed, which is why the above was so fiercely debated. It takes on a lot of numbers in its erratic route around the city's streets (and it is literally city streets too, not purpose-built road).
6. Technical Terms
An explanation of most technical terms used by road enthusiasts can be found in the CBRD Dictionary. Explanations of these terms are no longer held in this FAQ.
7. More Information
7.1 Other roads websites
Other websites about British roads can be found in the first section of the Links page. Outside Britain some sites are found on the Links page, but a much better resource is AAroads who have links to the international roads community.
7.2 Discussion forums and newsgroups
The single biggest forum for the discussion of UK Roads is the SABRE Forum, part of the SABRE website. These boards are the central part of the Society for All British Road Enthusiasts (SABRE), and indeed this FAQ list has been adopted as their official FAQ. Other UK forums are the Usenet newsgroups uk.transport and uk.rec.driving, though both these tend to be concerned with wider motoring and political issues. Internationally the most active roads group is misc.transport.road (MTR), though international discussion is frequently drowned out by American voices here.
I afraid I haven't kept a full record of those who have contributed and so the following is sadly a partial listing. Many thanks to those listed below and anyone else who has lent a hand.
Harry Strong, Chris Armitage, David McMahon, Ian Carr, Chris McKenna, Martin Radford, Terry March, Brian Freeman, Wesley Johnston, Tristram Grevatt, Peter Courtenay, Andrew Jackson, Alan Williams, Nick Booth, Ian Duff, Toby Speight, Jonathan Winkler, Simon Hollins, Ben, Patrick, Tony Baker, Jon B, Phil Baines, Richard Bullock, David D Miller, Tim Lidbetter, Ben Smithurst, Paul Martin, Guy Barry, Paul Berry, Simon M4Man, Adrian "Dadge", and of course the ever-knowledgeable members of SABRE.
- Maps showing zone boundaries above: Reproduced from Ordnance Survey map data by permission of the Ordnance Survey © Crown copyright 2001.
- Photograph of Pre-Worboys sign by Tony and used with permission.
- Picture of sign on the A74(M) showing "M6" courtesy of John Mullen.