I was thinking of asking on sabre.
Am especially puzzled by the slip road situation. Tomtom does drop the
limit to 60 on slip roads, which I had always assumed is an error.
One place I have noticed it recently is going from the A41 to the A55
westbound near Chester. At some point, before the traffic joins warning
signs it drops its limit to 60. At what point are you supposed to assume
you are no longer on a dual-carriageway?
I think that's a mistake. The A41 is definitely dualled westbound as it
meets the A55.
I think it's also a mistake in general. A slip-road having a different speed
limit to the main carriageway would be a ludicrous situation. Surely the
whole point of a slip road is that you use it to accelerate up to the speed
of the traffic on the main carriageway, or to decelerate from speed without
having to drop 10mph on the mainline? Would an HGV really have to drop its
speed to 40mph before it enters the off-slip?
A sliproad isn't just another one-way street. In fact, sliproads are not
usually signed as a one-way street when you enter one - yes there's a
no-entry sign at the exit, but no "one-way" sign at the entrance - they're
just signed as if they're just another part of the main (dual carriageway)
road. They're effectively part of the main road, they do segregate traffic
(if you consider the opposite sliproad - then they're segregated by a
~40-50m gap...), so they ought to be under a 70mph limit.
There are a few examples where there are very wide central reservations in
some roads, there are roads where you can get more than two carriageways
each separated by a barrier to the others.
(e.g.
-->
-->
<--
<--)
I doubt any of those wouldn't be 70 just because of a wide reservation, or
because the carriageways split apart for a time.
I think the point I'm trying to make is that it's not a standalone road on
its own which happens to be one-way. It's an integral part of the main road.
If the main road has traffic in both directions at that point, and traffic
can only move in one direction on the part of the road you're on - you're on
a dual carriageway and the NSL is 70.
I would be very surprised if SABRE give you a different answer.
RichardB
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