What is a dual carriageway?

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What is a dual carriageway?

Post by pingu » Sun 26 Sep, 2010 16:58

Seems an easy enough question, but I've been reading that a dual carriageway is any stretch of road that is separated from the opposite carriageway by a central reservation. A central reservation is a strip of land with or without barriers (it is not a painted area).

The national speed limit for a dual carriageway is 70mph and a single carriageway is 60mph

This can make life very interesting as 4-lane roads (2 lanes one way and 2 the other) are single carriageways NOT dual carriageways

Single lane sections of road that are separated from the other lane suddenly become a 70mph speed limit. These sections are usually there to slow traffic down.

The same applies to traffic islands that are designed to slow traffic down for junctions :shock: .

Can anybody confirm that what I read is correct?

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Post by billz » Sun 26 Sep, 2010 18:33

Not sure there are any anymore in this country. A610 40, 50 and 70 mile limit even though they run through the countryside with approx 3 foot of land seperating both ways. I think the council now dictates what the speeds are for what ever roads they want.
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Post by Robert T » Sun 26 Sep, 2010 20:05

I would have expected what you have said to be correct - essentially if there is a central division between the two directions of traffic, it is a dual carriageway. I would not expect this to apply to a traffic island though, and you would have to have a very fast car to get from 60 to 70 and back to 60 in the length of a traffic island! :lol:

The 70 limit only applies of course if there is a national speed limit in force - if there is any other kind of limit on the road, that is the limit for the dual-carriageway section as well.

The A556 near me is a classic example of a 4 lane road both with and without central divider - it is now a blanket 50 limit for most of it after some nasty accidents on the undivided section and I presume because the divided section is on an approach to a roundabout. When it is busy, I can see the point, but when it is quiet it is a PITA - especially when all the little narrow side roads now have national speed limit signs on them!

One thing I think I am right in saying is that speed limits always apply to both sides of the road - i.e. you can't have 60 one side and 70 the other, or 70 and 50 or whatever - so you need to look at the road layout on both sides and the limit will be lower of whatever is deemed appropriate.

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Re: What is a dual carriageway?

Post by badboyblue » Sun 26 Sep, 2010 20:17

pingu wrote: The national speed limit for a dual carriageway is 70mph and a single carriageway is 60mph
Your definition of a dual carriageway is correct - additionally if a road has both single & dual carriageways along it's length there will normally be "warnings" at least at the point the change occurs.

I would suggest that your proposal that short "crossing islands" mean the road is dual carriageway - is wrong - as conversely the road length of any turning gaps in the central reservation on a real dual carrigeway wouldn't be dual carriageways - which they are.

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Post by davieb » Wed 29 Sep, 2010 13:16

Don't know if it's still the same but there used to be a section of four lane road between Ayr or Kilmarnock and Glasgow, where there was a spell a few years ago of drivers getting done for doing 70 in a 60. They clearly thought it was 'dual', despite there not being a strip of land between the lanes.

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Post by c_w » Wed 29 Sep, 2010 14:29

Yea it always needs a barrier or divider between them. The A556 as mentioned changes from no barrier 50 and 60, then to "70" where the divider is heading to Northwich.

Don't think I've driven on a "single" lane dual carriage way though!

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Post by Mr Silver » Wed 29 Sep, 2010 15:12

The 'National Speed Limit' applies to all roads in the UK. The national speed limit for a dual carriageway is 70mph - unless other restrictions apply!

This means that the limit on a dual carriageway can be any speed if the road signs so dictate. In effect this means that only if there are no speed limit signs on the dual carriageway the limit will be 70mph.

It is possible that the type of road you mention above (i.e. one lane going in each direction divided by a barrier) is inside another restricted speed limit zone and therefore is subject to that restriction.

Hope this helps.


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Proper Dual Carrageways---in Motown

Post by ZZZEMMCO » Wed 29 Sep, 2010 17:33

I have a dual carrageway section approx 300mtrs long, close to home which is in the middle of single carrageways-ALL NS limits apply. :shock: I luvit!!!
so 60 and then floor it and pass the snails and down to 60 as DC ends. :D

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Post by ZZZEMMCO » Wed 29 Sep, 2010 17:33

Delete No 2

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Post by gookah » Wed 29 Sep, 2010 17:46

c_w wrote:
Don't think I've driven on a "single" lane dual carriage way though!
Try the A442 in Telford, used to be a dual carriageway but now they have turned the inside lane into a giant series of 1/2 mile slip roads for vehicles entering or leaving at different junctions, with a reduced 60mph limit.
Now you get people sitting in the outside lane from the offset, and the inside lane is primarily used by people undertaking, how is that safer?

They have even introduced traffic lights at the roundabouts. I always thought a roundabout was an upgrade to traffic lights to allow better flow of traffic, now, depending on where you approach from, you can sit at a red light on each junction with no other traffic in site.
Bloody road planning w**kers...... :head:

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Post by Zed Carer » Thu 30 Sep, 2010 21:52

Beware the dual carriageway with no speed limt signs and street lights as the limit will be 30 All roads with street lighting are auotmatically a 30 limit unless there is a legal order in place for a higher limit and there are repeater signs on the lamp columns.

Amusing case some years ago on a new bypass that was to have a 60 limit - locals wanted a footbridge - Highways Agency said No - the bypass had street lighting so the legal notices were displayed for the order to go to the 60 limit - locals all objected to the order - had to open a new bypass with the 30 limit.
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Post by Boysie » Sat 02 Oct, 2010 09:07


I have just attendinig a driving course
for being a bad boy and got caught speeding
this is definitely a eye opener
as all sorts of questions cropped up
ie the dual carriageway question being one

I dont like to admit but it opened my eyes
i gained a lot from the course
I've been driving to long time thought i knew it all

Better than 3 points on the license

A question
To all van drivers was you aware you have
have a speed restriction on the road
I didnt :rtm: :rtm:

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Re: What is a dual carriageway?

Post by vzh7gk » Sat 04 Nov, 2017 10:22

Depends on the van.
Car derived vans are subject to the same speed limits as cars.
However those Transit / Movano &c. style are subject to lower limits on most rural roads except motorways...

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Re: What is a dual carriageway?

Post by peter2b » Sat 04 Nov, 2017 18:15

I look at the signs if it says 50-60-70or20-30-40 thats what I try to do I've been on a dual carriageway where the speeds whent from 30 to 60 then back to 40 every 1/2mile for about 3 miles with cameras on each sign ,cash machines

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