Design Bulletin 32 has a lot to answer for as it is one of the main reasons we have ended up with some of our wide and open estate roads with junctions designed to take the largest possible vehicles.Oh, you've not heard of DB32? Well, here is an archived summary which I almost don't want you to read, but it might be of interest. In essence, it's an old document which set out how to design estate roads and in there you will note some rather large kerb radii when it comes (or came) to connecting two roads.
It was consigned to history by Manual for Streets in 2007 (it should have been killed off far earlier), but its ghost still stalks modern suburbia. If you don't fancy trawling through old design guides, then don't; the point of this post is to discuss some of the legacy we are left with and why it was a problem.
The essence was that we had to make sure we could get all types of vehicle which would potentially use a street into it and in doing so (and by following the guidance as if it was a standard) we ended up with really big junctions which do nothing to ensure people drive slowly through them; barely needing to slow their vehicle in many cases and this is a real safety issue for people walking and cycling.
Have a think about the largest vehicle which might need to use a street; the removal truck (or pantechnicon as it is often called). Generally of rigid construction (as opposed to articulated), the removal truck will often be longer than one would usually expect and so have a large overhang at the front and back. In a cul-de-sac situation, they need lots of space for a three point turn and amazingly, there are residential streets out there designed to fully accommodate them.
How many times you you need to get such a truck into a street? Not very often I'd suggest. A house move is a planned event and a professional moving company is fully able to organise itself to get trucks into tight spaces and as a designer, I wouldn't be too worried about them. If it comes to it, a removal company can use smaller vehicles - they know their business after all.
OK, what do we usually need to get into our streets on a weekly or fortnightly basis? Refuse trucks. So, should we design our streets for them? On a basic level, yes - we need to get them through of course, but we don't need to design our streets at a refuse truck scale.
The designer will often lay out a junction to ensure that large vehicles can stay on "their" side of the road when making turns. This is not necessary - people can swing onto the "wrong" side of the road if they need to - they will have to decide when it is safe and if the streets are not too wide, other drivers won't be able to go too fast. We do need to make sure that fire engines can gain access, but as they will be driven under emergency response conditions, their drivers will be well-trained and will be able to cope with constrained layouts.
Wide junctions are a problem for pedestrians as we will end up with very wide crossing points on the desire line. It will mean that designers will need to decide if to provide dropped kerbs on the desire line (with weirdly cut in tactile paving) or inset them so far into the side road that although the tactiles work and the crossing distance is less, the diversion to get there is longer than the crossing distance was in the first place. Nice tight junctions mean we can deploy continuous footways as well.
Despite Manual for Streets, we still have local authorities insisting on wide junctions because of concerns about over-run by large vehicles at junctions. In my experience, the issue is often parking near junctions and so we can paint yellow lines to keep access clear.
If a junction is wide, it is fairly easy to rework it, but of course if care had been taken from the start, this would mean we could spend our hard-won funds elsewhere.
A ridiculously wide junction. People driving into and out
of it don't even need to brake.
Same junction at the dropped kerbs which have been inset, but
the crossing distance is still huge.
The next junction down has been reworked to provide a
shorter crossing distance with a tighter radius. We could
probably go a little tighter.