Sunday 12 June 2016

A Waste Of Space

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.


  1. Time to refuse the refuse trucks! I'd support a ban on HGVs over 7500 kg from leaving the motorway and motorway style roads, except to directly to a distribution centre, and a ban on vehicles over 3500 kg from going into the roads that should be Dutch style access roads.

    I also suggest angling the kerbs that are next to the carriageway. On roads as minor as these, we could lower the speed to 30 km/h and restrict access, and if a bike tyre hits the kerb, ugh, not good. And if a car really needs to overrun the pavement, if shoved off the road or a firetruck comes along, then it won't damage the kerb as much.

    And can someone explain to me what priority pedestrians have over motor vehicles in the UK? Where I live they always have priority except over emergency vehicles and when a traffic light specifically says they don't, but not midblock where most cities and towns have outlawed midblock unofficial crossings.

  2. TBH I'd like to make the junction of every residential street with a main road into a continuous footway(and cycleway, if they were present). We would then physically divide residential spaces from the through route - and crossing over what would essentially be a speed table would help remind drivers of that fact whilst giving peds (and cyclists) priority and also removing the poorly laid out dished footways we seem to now get when we put in dropped kerbs at crossings.

    Andy R

    1. I couldn't agree more.

      When we ask for this from our LA, their greatest concern is that the turning vehicle will be hit from behind by a speeding vehicle.
      This would exacerbated by pedestrians/cyclists crossing the junction in front of the turning vehicle forcing it to wait. "Much safer to force the pedestrians to wait for the car."

    2. "This would exacerbated by pedestrians/cyclists crossing the junction in front of the turning vehicle forcing it to wait."
      Drivers actually having to follow the recommendations in the Highway Code, you mean? Scandalous.
      As a road safety auditor I have recommended the use of continuous footways to help slow down traffic and give the message to drivers that they're the guests - albeit in a residential development - but where there was also intended to be a primary school. Also better to put the onus on adults (with road sense??) to look out for hazards rather than children.

      Andy R.

  3. Doesn't even help this:
    "This is the shocking motorist a dog walker was also decapitated"
    Does no-one proofread ?