Cycle Traffic and the Strategic Road Network – Junctions (2)

This post is the last in a series looking at the new Highways England standard on designing for cycling, Cycle Traffic and the Strategic Road Network, or IAN 195/16. The previous three posts can be found herehere and here.

As mentioned in my previous post, designing for cycling at junctions is important, and consequently junctions (rightly) occupy around half the length of the Cycle Traffic and the Strategic Road Network. I’ve split my coverage of junctions into two posts; this second post will look at roundabouts and ‘grade separation’, or in layman’s terms, ‘putting cycling at a different level from the road network’. That means bridges or underpasses – or a hybrid of both.

Given that this is a Highways England document, grade separation will naturally be particularly important, due to the type of most of the roads covered by the Highways England network – fast, busy roads where grade separation is likely to be the most appropriate option. As IAN 195/16 itself states –

Grade separation of cycle traffic from motor traffic is the preferred solution for the crossing of all high speed road links and junctions.

Referring back to Table 2.4.2 in the document (covered in the previous post) we can see that grade separation is the only option for crossing roads with a speed limit of 60mph or higher.

screen-shot-2017-02-06-at-15-28-42

It is also the ‘preferred’ type of crossings of 40mph and 50mph lanes of traffic with over 10,000 vehicles per day (or crossing two or more lanes with >6,000 vehicles per day), and for 30mph roads (or single lanes) carrying more than 8,000 vehicles per day. As mentioned in the previous post, designers ‘shall’ use the ‘preferred’ type of crossing unless other options make more sense in terms of route continuity. So clearly grade separation is important (and required) in situations with fast and/or heavy flows of motor traffic.

Naturally the two types of grade separated crossings are underpasses and bridges, although this document describes them respectively as ‘underbridges’ and ‘overbridges’, which I think is an important reframing. Good underpasses will resemble bridges, in that the cycle traffic is passing under a bridge carrying the motor traffic above it.

Grade separation in the form of an underbridge in the Dutch city of Assen.

Grade separation in the form of an underbridge in the Dutch city of Assen.

As in the photograph above, these ‘underbridges’ are clearly a much more attractive proposition than the kind of subterranean tunnels that ‘underpasses’ usually resemble in Britain. Explicitly framing this kind of grade separation as a ‘bridge’ is therefore very helpful. The photograph of an ‘underpass’ included in IAN 195/16 makes this obvious too.

screen-shot-2017-02-06-at-15-40-47

The minimum width for cycle traffic through this kind of underbridge is set at 3m, with only a suggestion that designers should ‘consider’ increasing this dimension to increase natural light. I don’t think that’s good enough; it allows ‘boxy’ underpasses of this type –

A relatively new Highways England underpass, under the A23 near Handcross in West Sussex.

A relatively new Highways England underpass, under the A23 near Handcross in West Sussex.

These are much less attractive than the Dutch stipulation that ‘walls should recede towards the top’. Here’s a path of equivalent width, but with sloping walls, in the Netherlands –

screen-shot-2017-02-06-at-16-27-39Much more open – so it would be good to have some stipulations about tunnel dimensions, beyond the 3m width recommendation.

We have similar width stipulations for overbridges – at least 3m, with 0.5m margin clearance at each side. There are useful recommendations on gradients; ramps approaching or departing grade separation should meet the design requirements set out earlier in IAN 195/16 –

screen-shot-2017-02-06-at-16-55-19

It is recommended that the steepest part of a ramp (if it is unavoidable) should be located at the start of the ramp, where people are likely to be carrying most speed. Given that this has been taken into account, it is slightly disappointing that IAN 195/16 does not have anything to say on the matter of overbridges versus underbridges in general.

Underbridges should generally be preferred, mainly because the speed that a person cycling carries into them (on the downslope) can be used on the upslope; this isn’t the case with overbridges. Underbridges should also be preferred because they require less slope in general; they only need to accommodate the height of a human being, rather than the height of the large vehicles a bridge has to pass over. This is missing from IAN 195/16.

At the rear of the document there are extensive ‘grade separation’ diagrams, showing the appropriate way to separate cycling and motoring at junctions, particularly those with slip roads, which present a major safety hazard. Here’s just one example, showing cycle traffic (the dark line) routed under the slip roads, and under the roundabout.

screen-shot-2017-02-06-at-17-04-47

This kind of design removes any interaction with fast motor traffic altogether, something IAN 195/16 requires for 60mph+ speeds and for heavier flows of motor traffic. So we should expect to see this form of grade separation at new junctions being built by Highways England (but unfortunately not retrofitted to old junctions, as yet).

The one final ‘junction’ element covered by IAN 195/16 is roundabouts. Britain has a long history of failing to design for cycling altogether at roundabouts, and we still haven’t really managed to do so in the last few years, despite increasing design attention being paid to cycling. So the advice (and indeed requirements!) contained within IAN 195/16 is welcome, even if (unfortunately) there is very little UK good practice to draw upon.

Happily, on-carriageway perimeter cycle lanes on roundabouts are explicitly ruled out –

On-carriageway cycle lanes shall not be provided on the perimeter of the circulatory carriageway, as they encourage cyclists to take up a nearside position where they are vulnerable to being hit by vehicles exiting the roundabout.

The only options are a ‘compact’ (i.e. a continental-style) roundabout with no lanes or markings, combining cycling with motor traffic, or a ‘separate cycle track’ around the perimeter of either ‘compact’ or ‘normal’ roundabouts, with a recommendation that the latter is preferable ‘because most cyclists will prefer off-carriageway provision as they will perceive it to be safer and more comfortable.’ Indeed, off-carriageway cycle tracks ‘shall be provided’ once the total throughput on a compact roundabout exceeds 8,000 vehicles per day.

There are all the elements in place in IAN 195/16 for Dutch-equivalent design of cycleways around roundabouts – how wide cycleways should be; when (and when they shouldn’t) have priority over motor traffic when crossing the arms of the roundabout. Unfortunately all this good advice (and requirements), much of it covered in previous posts, does not appear in the form of a useful diagram. There aren’t any illustrations on how to design for cycling at priority roundabouts (i.e. roundabouts that are not signal-controlled), which is a pity.

This isn’t too much of a problem for Highways England roads, where I doubt these kinds of designs would be used, but it is a design gap that needs filling, and this document could have provided design requirements and advice that local authorities could have copied, or drawn from.

As it is, we have some diagrams on how to design for cycling at signal-controlled roundabouts, including complete signal-separation, the use of holding exit motor traffic (the approach used at the ‘Dutch’ roundabout in Wandsworth) and the ‘cycle gate’ ASL (or ‘always stop’ ASL), favoured by Transport for London at a number of locations. IAN 195/16 has some useful suggestions on the appropriateness of each of these, in turn – pointing out, in particular, that the ‘cycle gate’ ASL

introduces a time penalty for cycle traffic and will therefore be less suitable for cycle traffic movements that pass through a number of signalised nodes

… but it is unfortunately hampered by the UK not doing any of this particularly well, anywhere. The only concrete example it can draw upon is the Wandsworth ‘Dutch’ roundabout, which is far from ideal.

And that’s pretty much it for IAN 195/16! I think this has been a fairly comprehensive overview. However, there may have been some elements or aspects of it that I have missed, and (in particular) I think there is some scope for examining how useful it might actually be in practice, in terms of improving the way England (and the UK) designs for cycling in general. So there is potential for a ‘summary’ post covering these kinds of issues, including those raised in the comments to all four posts.

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11 Responses to Cycle Traffic and the Strategic Road Network – Junctions (2)

  1. Clive Durdle says:

    Terraced housing in 19c tower hamlets was built by digging out half the depth of the basement and using the spoil to raise the road height, create my a full depth basement .

    The other trick used in Stevenage is that raise the road level.

    As Crow revised is now out, how does Ian compare?

  2. Clive Durdle says:

    Terraced housing in 19c tower hamlets was built by digging out half the depth of the basement and using the spoil to raise the road height, creating full depth basement .

    The other trick used in Stevenage is to raise the road level.

    As Crow revised is now out, how does Ian compare?

    • Bmblbzzz says:

      Georgian Bath was built in the same way. The cellars are at ground level, and the road is a couple of metres above the level of the back gardens. This allowed them to build a series of vaults at ground level, put a road on top with iron covers and hey presto, each house has its coal cellar accessible by coal merchants without disturbing the householders!

  3. Paul Luton says:

    I suppose that a snag with the Dutch examples in an urban environment is that both involve raising the road making it more visually dominant and spreading road noise. For Highways England schemes this may not usually be an issue but as your last paragraph implies it would be good to have these as de-facto standards for all roads.

  4. Bmblbzzz says:

    The terms underbridge and overbridge are used on railways too. They’re not quite so clear as underpass and bridge, since you have to know which is your reference point: if the road passes above the cycleway, is that an overbridge for the road or an underbridge for the cycleway? Perhaps the reference point is whichever is at ground level (if either).

    In terms of sensation while riding, bridges are more pleasant (to me) than underpasses in general. You’ve still got the sky above you, you still get a view. Plus it allows you a feeling of superiority over the motor traffic rushing beneath you!

    • Paul Luton says:

      Yess but ; Possible lorries etc are taller than bicycles so there will be a long/steep climb unless the road is below ground level (I can see that being a problem in the Netherlands).

  5. Matthew Phillips says:

    The junction diagram you show (Figure 2.8.1.1) does not seem to allow for all possible routes someone might want to take on a bike. Referring to the top of the diagram as north, it is not possible to go north-south or south-north on the minor road (but perhaps you are expected to be travelling on-carriageway?). Nor is it possible to go from west to south, north to west, east to north, or south to east.

    Am I missing something?

    • bigK says:

      Well noticed. Unfortunate if this is the new standard.

      • HivemindX says:

        Personally I wouldn’t have a problem with this so long as the connections at the North and South of the junction are designed to control the speed of traffic. If a car leaving the main road (motorway) has to approach a roundabout to join the minor road then I would have the opportunity to merge in to traffic and circulate to join the minor road heading south. There are similar junctions on one route I regularly take. Traffic leaving the major road approaches a roundabout and they slow and yield as normal.

        If this is designed (like so many major road junctions) to facilitate traffic leaving the motorway to maintain a speed of 100kph on the minor road by making the slip a high speed curve then I would have no safe opportunity to cross this traffic. Any cyclist who wants to go from West to South or from East to North has no way to do so. A lane populated with motorists who are concentrating on transitioning from a steady stream or traffic at 120kph to a steady stream of traffic at 100kph, or vice versa, is no place for a cyclist. One route I tried had multiple junctions where a lane appears on my inside in which traffic slowing from 120kph was trying to merge in to the road I was on at 100kph. I go 5k out of my way to avoid that road now.

        • Paul Luton says:

          Traffic lights where vehicles from the main road enter the roundabout would be a solution – and are not unknown.

  6. Pingback: Cycle Traffic and the Strategic Road Network – Junctions (2) | As Easy As Riding A Bike

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