The best of the new cycling infrastructure in London is almost entirely composed of bi-directional cycleways, placed on one side of the road. This includes pretty much the entirety of CS3 and CS6 – the former running from Parliament Square to Tower Hill, the latter from Elephant and Castle to just north of Ludgate Circus.
Bi-directional cycleways are often not the best design solution, but the decision to go with bi-directional cycleways is not an accident. Undoubtedly people at Transport for London have thought long and hard about the best way to implement cycling infrastructure given current UK constraints, and have plumped for two-way as the most sensible approach.
To be clear, bi-directional cycleways do have serious downsides – they can lead to more conflict at side roads as cycles will be coming from unexpected directions, and pedestrians in particular may find them harder to deal with. Head-on collisions with other people cycling are also more likely. On ‘conventional’ streets – one lane of motor traffic in each direction – uni-directional cycleways are clearly preferable, all other things being equal.
However, bi-directional cycleways do also have advantages, and one in particular that has probably swayed the decision-makers in London. It’s touched upon in this excellent summary of the advantages and disadvantages of bi-directional and uni-directional approaches by Paul James –
Depending on the roadway in question you could have less junctions to deal with, if you have many turnings on one side of the road, running a bi-directional cycleway on the opposite side so as to save on conflicts might be a good idea.
This is clearly the reasoning behind putting a bi-directional cycleway on the ‘river’ side of the Embankment. There are no junctions to deal with, cycling in either direction, so even though people are cycling on the ‘wrong’ side of the road, heading east, that’s a lot safer (and also more convenient) than having to deal with all the side roads that do exist on the non-river side of the road.
Cycling on the ‘wrong’ side of the road, heading east. But no side roads to deal with, so safer, and more convenient.
But this isn’t the only type of conflict-avoidance that explains why bi-directional cycleways have been chosen in London. Bi-directional cycleways also reduce conflicts at junctions that have to be signalised, by ‘bundling up’ all the cycle flows on one side of the road. This is actually very important, thanks to the limitations of current UK rules, and it’s the subject of this post.
In all the countries in mainland Europe (and also in Canada and the United States) it is an accepted principle that motor traffic turning right (the equivalent of our left) with a green signal should yield to pedestrians (and people cycling) progressing ahead, also with a green signal. Here’s a typical example in Paris; the driver is turning off the main road, with a green signal, but pedestrians also have a green signal to cross at the same time. The driver should yield (and is).
Two ‘conflicting’ greens, circled
This approach actually makes junctions very straightforward, and efficient. A complete cycle of the traffic lights at a conventional crossroads requires only two stages to handle all the movements of people walking, cycling and driving. In the first, walking, cycling and driving all proceed north-south (with all ‘turning’ movements yielding to ‘straight on’ movements), and in the second, the same, but in the east-west direction.
Motor vehicles, red arrows; cycling, blue; pedestrians, green
Compare that with a typical UK junction, which will have three stages (if it takes account of pedestrians at all) and ignores cycling altogether, lumping it in with motor traffic. First, motor traffic (with cycling included in it) going north-south; then, motor traffic heading east-west; then pedestrians finally get a go on the third stage, with all other movements held.
Motor vehicles in red; pedestrians in green
This arrangement obviously doesn’t allow any turning conflicts (apart, of course, from motor vehicles crossing each other’s paths) – pedestrians don’t get to cross the road until all motor traffic is stopped, with an additional third stage. (This is, effectively, a ‘simultaneous green’ for pedestrians, although we are rarely generous enough to give pedestrians sufficient signal time to cross the junction on the diagonal).
And this gives us a clue to the problem when it comes to adding in cycling, when these kinds of turning conflicts aren’t allowed. You either have to add in stages where motor traffic is prevented from turning, or you have to stop pedestrians from crossing the road while cyclists are moving. Both of these approaches would add in a large amount of signal time, and would make for inefficient junctions.
One possible answer is including cycling in the ‘simultaneous green’ stage, but with sensible design – cycles moving from all arms of the junction at the same time as pedestrians have their green, and pedestrians crossing cycleways on zebra crossings. For whatever reason (from what I hear, DfT resistance) this kind of junction is still not appearing in the UK, forcing highway engineers to improvise within the constraints of the current rules. As Transport for London have done.
If we are trying to build uni-directional cycleways, those UK rules effectively mean we either have to ban turns for motor traffic, or we have to employ very large junctions indeed, to handle signalising different movements. Take the Cambridge Heath junction on Superhighway 2, which has to use three queuing lanes for motor traffic in each direction. One for the left turns (which have to be held while cyclists and motor traffic progress ahead), one for straight ahead, and one for right turns (which have to be separate from straight ahead movements, otherwise the junction will clog up).
That’s an awful lot of space when you add in the cycling infrastructure – space not many junctions in urban areas will have.
In an ideal world – and with sensible priority rules – these junctions could just be shrunk down to two queuing lanes in each direction. A left turning lane combined with a straight ahead lane, and a right turn lane. All these lanes would run at the same time as cycle traffic progressing ahead (as well as pedestrians), with the left turners yielding.
Unsurprisingly this is – of course – how the Dutch arrange this kind of junction.
A typical Dutch junction with separated cycling infrastructure (flipped for clarity). Motor traffic from this arm will have a green in all directions at the same time as cycling running in parallel.
This is much more compact than the kind of ‘Cambridge Heath’-style junction that we are forced to employ in Britain.
But, given that we unfortunately can’t do this, and that we rarely have the kind of space available that there is on Superhighway 2, bi-directional cycleways are the most obvious answer. As I hinted at in the introduction, this is why they’ve been used by Transport for London – they’re not stupid!
Let’s take one of the junctions on the North-South superhighway, at Ludgate Circus. Space here is much more limited than on CS2 – we can’t add in multiple turning lanes – so that means, given the constraints of UK rules, a bi-directional cycleway is the most sensible option.
‘Ahead’ movements running in parallel with ‘ahead’ movements for cycling. (Arranged with North at the top).
Only two queuing lanes for motor traffic are required, in each direction, making this arrangement much more compact. It helps, of course, that a bi-directional cycleway is more space-efficient than two uni-directional ones, but the main win here is the fact that all the potential conflicts are ‘bundled’ on one side of the road. That means motor traffic flowing south doesn’t have turning conflicts on the inside.
Clearly, as I’ve outlined early on in this post, bi-directional cycleways will, more often than not, be less desirable than uni-directional ones, in urban areas. But they are currently – thanks to UK rules – probably the best way of building inclusive cycling infrastructure when space is genuinely limited, as they are the simplest way of side-stepping around British priority rules. (An additional benefit is that they will typically only involve converting, at most, a single lane of motor traffic, which helps when it comes to persuading reluctant local authorities worried about retaining capacity for drivers.)
Perhaps the way forward is to continue building bi-directional cycleways, but keeping in mind the possibility of adapting bi-directional designs into uni-directional ones, if and when UK rules become more flexible, or if and when ‘simultaneous green’ arrangements start to appear.