Saturday, 2 September 2017

I've seen things you people wouldn't believe: Part 2 - Magic Roundabouts

Last week, I introduced a series of posts of highway layouts I saw while on holiday in the Netherlands. This week I'm going to take a look at some roundabouts.

As usual, please remember that there will be context and reasoning behind what I'm writing about which must be an ever present health warning. These are observations from a holiday and not from using layouts on a daily basis for a number of years - David Hembrow makes this very important point here.

Our trip involved driving from Dunkirk to Bruges and then on to Amsterdam and in fact, the first "Dutch-style" roundabout (I think) I encountered was in Belgium, just as we entered East Flanders near the town of Maldegem;


The reason I say "Dutch-style" is that many of the roundabouts I encountered in Flanders (which borders the Netherlands) appear influenced by the Dutch layouts, but they are not quite there - many seemed to enable entry and exit speeds which did not reflect the real Dutch provision. As an aside, the Flanders region is definitely upping its game when it comes to providing for cycling and it's a place which needs a visit in its own right!

Anyhow, back across the border. There isn't a single off-the-peg type of Dutch roundabout (as locations and contexts vary), but there is a high level of consistency, especially at the more rural locations. There are also some poor layouts (one of which I'll cover later). First, I'll introduce you to the Hugo de Grootplein roundabout in Amsterdam in the neighbourhood of Frederik Hendrikbuurt which is just under a mile to the west of the centre of the city.


This roundabout has been given an entire blog post by Mark Wagenbuur on his Bicycle Dutch blog and it is a fascinating piece of urban infrastructure. At first glance, it looks utterly mad, but it's a very neat solution for when two relatively busy roads meet; plus the north-south axis carries a tram just to make life interesting! In fact, the tram issue is easily dealt with as it runs through the centre roundabout with full priority afforded by stopping everyone else with traffic signals and so the tram is actually a distraction in terms of how the junction operates.

Roundabouts are efficient in terms of moving motor traffic and in comparison with a signalised junctions, there are far fewer points of conflict. The problem is, roundabouts don't provide the pedestrian priority which can be incorporated into signalised junctions and they have a poor safety record for people cycling.

As you might expect, the City of Amsterdam have built cycling into this roundabout by providing dedicated (and largely protected) cycle tracks.


One important aspect of the design is that as the cycle tracks reach the roundabout, they form into a larger "cycle roundabout" which means that there is a distance of about a car length between the edge of the "traffic" roundabout and the "cycle" roundabout (or an annular cycle track). Coupled with some fairly tight geometry, this means that drivers turning (right) to leave the roundabout will see people cycling on the outer cycle roundabout and they will cross the cycle track at 90°. Being an urban area, people cycling have priority over those driving and in fact, the crossing of the arms are a series of parallel crossings with people walking having space on the outside of the cycle roundabout and are thus afforded a touch more physical protection.


I've simplified the layout above for clarity, stripping out inset parking bays, landscaping and so on. Of course, the Dutch drive on the right and with the cycle tracks around the roundabout being one-way, so do people cycling. A very important feature of this roundabout is that it is strictly one traffic lane in and one traffic lane out otherwise there is the risk of people being masked where one line of vehicles is slower than the other. The one lane in/ out is reinforced by there being a central island between each traffic direction. Not only does this force drivers to approach the roundabout squarely and so slowly (in contrast to UK roundabouts which help people drive on at speed), the islands help people walking and act as a further buffer.


The circulatory area for drivers falls out from the centre (so drainage is on the outside of the circulatory area). This introduces a little adverse camber which helps to keep circulation speeds down and makes drainage a doddle. The cycle tracks tend to fall towards the centre of the roundabout which also makes drainage easier (as the gullies in the road and track are closer together) and the fall into the roundabout is slightly more comfortable for cycling (rather than feeling pushed outwards).

Those cycling into the annular cycle track must give way to those on it (you can see Dutch give way triangles in the photo above) and for people on foot, the crossings are all marked as zebra crossings, although at least in Amsterdam I found worse compliance from people cycling than in smaller towns and villages. Some of the pedestrian refuge islands are also very narrow so there is always room for improvement. Bearing in mind I was a tourist cycling a cargobike around the city I felt very safe and comfortable using this roundabout. Here's a little video of it in action;


I did ride (and drive) through similar roundabouts during the holiday and those tended to have a narrower circulatory area with an over-run for larger vehicles, but the principles were the same and the road layout was nice and predictable. If you want to see this type of roundabout in operation, then Nigel Shoesmith has suggested watching a live webcam of this roundabout in Purmerend - it really shows the elegance of the design.


The question is whether we could bring this design to the UK? The answer is a qualified yes. In fact, as Mark Wagenbuur explains in his blog post, a test version inspired by the Hugo de Grootplein roundabout was built at the Transport Research Laboratory (above) when TfL was testing various infrastructure ideas. Since these tests, we have the UK parallel zebra crossing layout available in the Traffic Signs Regulations and General Directions 2016 which means we can prioritise people cycling as well as walking. The qualification to my yes is that the same principles of tight geometry, adverse camber, set back of a car length and so on must be followed. I would also strongly reinforce the need for the cycle tracks to be one-way as this reduces potential conflict.

However, there is a lot going on and we should appreciate that going through this type of roundabout is pretty tasking in terms of watching for other vehicles, people cycling and people walking; it is therefore not a fail safe design and it is certainly not applicable in out of town/ rural locations (as I will explain). It was a response to a particular location and care should be used in copying it. For example, driving though Maastricht, I had to go through this roundabout which was not tight or slow because of its spiral layout and multiple circulatory lanes. I remember feeling worried that I was not watching for people walking and cycling while I looked for the right road position to exit.


The next roundabout I'm going to cover is just outside the city walls of the beautiful old city of Hulst in South Zeeland. I am not going to spend too much time on it other than to say that the design should not be copied in the UK.


The roundabout replaced an old crossroads (which had one arm splitting into two close by - image below) and was constructed as part of some major drainage works and the local community were very happy to see it built (thanks for the heads up Roger D from last week's blog comments).


The roundabout has similar characteristics as other Dutch roundabouts with geometry, one traffic lane in/ out, zebra crossings, islands etc, but the cycling provision is an annular cycle lane with low profile kerb protection (light-segregation).
 

For people cycling and leaving the roundabout, the light segregation stops drivers from right hooking and keeps things tight geometry wise.


People on cycles joining the roundabout give way to those already cycling on it as you'd expect.


The issue for me is that those cycling around the annular lane are at risk of right hook by drivers leaving the roundabout (where the black car is) because the one vehicle set back is-missing. I'm told that this is OK in the Netherlands because drivers are used to encountering people cycling, but I don't buy the point that all Dutch drivers always expect people cycling (OK, I'm making a point). A driver leaving a roundabout is the riskiest conflict because it is done so at some sort of speed (whereas a driver joining should be doing so more slowly). The previous example mitigated this by allowing a driver to meet people cycling at 90° and giving space for them to stop.

The final roundabout to talk about can be built in the UK without any major concerns. David Hembrow gives a very detailed account of this approach in this blog post. The elements of tight geometry, camber etc are found on this next type of roundabout, but cycle priority is not given - the convenience of priority gives way to a safer layout where the person cycling decides if it is safe to cross.


The example above is in the rural area to the north-west of Hulst. It is where an east-west section of the N290 (like a UK rural A road) meets some local roads. The A290 has two-way cycle tracks on one side as does the road to the north (which heads towards the coast). Again, a stripped down plan is below.


The road to the south has no cycling infrastructure, but it has a 60kph speed limit (37.5mph) and is part of a local network of very rural lanes. I cycled lanes like this and they were generally very quiet (some are filtered), although you have to watch out for tractors though!


Other than the little rural road, the approaches to the roundabout all had long refuge islands. As well as providing space to cross the road in two parts, the islands meant that drivers approach and leave the roundabout in a straight line. Compare this with the UK roundabout below (Hatfield, very close to where I lived as a student); which despite being one lane in/ out, it has a triangular island and a road which flares to allow faster entry and exit speeds;


As we approach the Dutch roundabout we can see that to turn right, a driver would have to turn the steering wheel far more than with a UK roundabout. The carriageway is fairly tight in order to keep car driver speeds low (no "racing line" driving here"), whilst the large over-run area caters for lorries.


You will also note the roundabout has a grassy mound with hedge planting. As well as being fitting for the location, this stops drivers having too much of a view through the roundabout which is another speed reducing feature.


The photo belows the circulatory area falling out (to create the adverse camber) which helps slow drivers and the distinct over run area which discourages car drivers.


Being a rural location, it would be a very long walk to get to the roundabout and so the layout is for people cycling (no tactile paving for example). In a more urban area, there would be a separate footway and perhaps a formal zebra crossing for pedestrians (but those cycling still give way to motor traffic).


The photo below is of another roundabout in the area (coming out of a bypassed village) which better shows that drivers approach this type of roundabout square on and without a flare.


The photos below show that the drivers of lorries can also cope with the layout. Meanwhile, those cycling are nice and safe!



So there you have it. Three roundabout types. One which can be copied, one which needs care to copy and one which should not be copied. Next week, I'll be looking at junctions more generally.

5 comments:

  1. Slightly, but not entirely, flippant comment. Having, in my nerdy way, superimposed vehicle track trajectories (discolouration on road) for a number of Dutch & UK roundabouts, I'm not wholly convinced by the argument about the angle of approach allowing faster entry of roundabouts in the UK (as in your Hatfield vs Hulst example). Could it be that the offside "straight into the roundabout central roundel" geometry in the Dutch example had to be abandoned in the UK because drivers kept driving into the roundel? ;)

    (very insightful post btw)

    Jitensha Oni

    ReplyDelete
    Replies
    1. I don't know - the "continental" roundabout is in the design manual for roads and bridges. I suspect the Dutch come at it from safety and we've come at it from capacity.

      Delete
    2. Are you sure about that? I haven't driven in the UK but I can't imagine that UK roundabouts slow you down the way continental ones do. Take this one for example, you can draw a straight line through the roundabout from the entrance to the exit. This continental one on the other hand clearly has the central reservation blocking the way (you really don't want to hit the overrun area, especially at speed). You have to make pretty pronounced turns to the right, left and then right again to navigate that roundabout.

      Delete
  2. Do you think that if a cycle-priority roundabout were built in the UK, it would be a good idea to have the zebra crossings and cycle tracks on a raised table when they cross the roads entering and leaving the roundabout? Perhaps this would emphasise the priority and reduce speeds? Would this be allowed?

    ReplyDelete
    Replies
    1. Notwithstanding my qualified support for the layout, raised tables would be perfectly acceptable - it does play with the levels and so the whole "circle" of the cycle track would have to be raised a bit which makes design a bit more complicated.

      Delete