OT: road building regs

[sm_jamieson]

Near me two new major road alterations are taking place, both involving the lead up of dual carriageways onto roundabouts. In both cases the orignal c arriageway gradients have been modified so that the road rises up a "hill" which then dips down for the last, say 25 metres, towards the roundabout. A part from this new "hill", the levels are the same and the road could have been left as before, with a single gradient slowly sloping up towards the r oundabout. There hills do not appear to be bridging anything. The works *are* part of other changes - they are not just changing the grad ient. So, I wondered if some sort of (EU ?) regulations have been changed to mand ate that the lead-up to roundabouts should be level or downhill - for exanp le to save fuel usage, clutch where, etc. Anyone know ? Simon.

[charles]

a slight guess. they are to stop people driving round the roundabout as if it wasn't there. Basically to slow down the traffic.

[Nightjar]

Probably to improve visibility on the approach. A climbing approach to a roundabout can make it difficult to see traffic approaching from the right of the entry.

If you fancy wading through reams of traffic design data, there might be something in the Design Manual for Roads and Bridges:

[Nightjar]

That should be achieved by a horizontal deflection of the route through the roundabout.

[Robin]

May not be relevant in this case but, while I don't think it is a "standard", I think highways people do to try to avoid drivers having to do "hill starts" onto roundabouts.

[Bob Minchin]

I think this could be the case. A couple of big roundabouts near me have newly erected screens on the entry roads so that you just cannot see if the way ahead is clear until you are right on the point of entry to the roundabout. Frustrating, as outside peak times the road is lightly used and drivers used to be able to see the whole roundabout and judge the right speed and time to enter for an unimpeded route from entry to exit. Now use of brakes and acceleration is essential with extra consumption of fuel.

[charles]

Not necessarily easy if there are busses using it. You need lots of extra land.

[Andy Burns]

They tried that in the name of safety on a roundabout near here, they've just taken the fences down again ...

[Roger Mills]

Maybe. But it seems to me that that having a slope *down* to the roundabout increases the risk of not being able to stop if the road is icy.

[Nightjar]

Roundabouts have to be designed to take an articulated vehicle with a single axle at the rear of the trailer and a length of 15.5m. If it will take that, it will take a 15m bus or 17.9m bendibus comparatively easily.

[Mathew Newton]

It has been standard policy for many years to restrict visibility on the runup to roundabout to roundabouts however not necessarily to the point of entry.

Para 8.8 of

refers:

[Capitol]

Don't know, however, locally, roundabouts have caused a lot of HGVs to fall over as their suspension doesn't like changes in direction at certain speeds. The road cambers have been changed in order to reduce the accidents, but only last month an HGV shed it's load over a number of a car dealers cars parked on the grass verge at the exit from the roundabout. The Dealer has now moved his display away from the grass verge for some reason.

[Robin]

Fair point but I think it must be a matter of trading one risk against another as the design manual for roundabouts certainly used to include "Roundabouts should preferably be sited on level ground or in sags rather than at or near crests because it is difficult for drivers to appreciate the layout when approaching on an up gradient."

Or perhaps they've been told that icy roads will soon be a thing of the past in the UK :)

[The Other Mike]

The surrounding road surfaces are maybe being drained at one common point at the centre of the roundabout

[Jethro_uk]

Would that render the road builder liable, should an insurance claim be required ? Would the dealer be able to recoup any expense incurred in making amendments due to the incorrectly built road ?

[steve robinson]

No, the lorry driver is solely at fault, approaching the junction/ round about too quickly , driving without due care, having an insecure load

[fred]

It's good that they see that as a possibility but bad that they ignore the possibility that those more likely to be involved in excess speed roundabout errors could well be the same group that are likely to be oblivious to restricted visibility situations and plough on regardless, resulting in the same or greater number and severity of collisions. That plus the greater inconvenience for the majority seem to be quite able to balance the natural visibility and road speed issues.

[Capitol]

Locally a roundabout which had a significant number of HGV rollovers was redesigned as a roundabout with a N/S dual cariageway through the middle and lots of traffic lights. This means that if you wish to turn right from the dual carriageway, you have to take a slip road to the left which puts you onto the roundabout, traffic lights then control your progress, or lack of it. If you are coming into the roundabout from the road crossing the dual carriageway and wish to turn right, you have to go around the roundabout, traffic lights permitting and then turn left onto the dual carriageway when you reach the correct turning. Confused, you aren't the only one! It is possible to turn onto the dual carriageway from the roundabout as the signage is not that good, but it is a very sharp turn. It was interesting to see the upside down 4 x 4 on the dual carriageway shortly after this road improvement was opened. I was nearly pushed off the road by a truck driver who did not realise that he was in the wrong lane until 50ft from the traffic lights. I've not seen another roadway like this so far.

[sm_jamieson]

Any chance of a location or link on google maps so we can have a look at the layout ? Simon.

[Capitol]

Google maps are not current, so it doesn't show.