Earlier this year, as you may or may not know, the Cycle Embassy of Great Britain had it’s first “policy bash”, where a bunch of Embassy members got together to chew the fat. One outcome was that I ended up being the proud keeper of the Embassy copy of the Dutch “Design manual for bicycle traffic” (English language edition). So I’ve been gradually working my way through this tome of knowledge, trying to condense it down into a set of useful notes.
As a result, I’ve discovered some great stuff about the when and where of cycle infrastructure I’d like to share with you now.
The Dutch road system follows the idea of Sustainable Safety, that’s with capital “S“‘s, as this is the name given to a set of guidelines for inherently building safety into the road network that I and others have written about before. When this comes to the purpose of roads and streets, it classifies them usefully into three groups:
- Access roads (aka estate access roads) - streets that provide access to destinations, non-through routes to motor traffic.
- Distributor roads (aka district access roads) - streets that provide access to estate access roads, non-direct through routes.
- Through roads - roads that link distributor roads together and act as main routes for motor traffic.
It also makes a distinction between urban and rural versions of these three road types, leaving us with 6 types in total.
It then looks at the different types of cycle provisions upon those types of roads at different traffic volume levels, both along the road lengths and at the junctions between them.
To measure traffic volume, a measurement called a Passenger Car Unit (PCU) can be used; it is a way of standardising different types of traffic into a single metric. So for example, a normal car has a PCU of 1, whereas a HGV might have a PCU of 3, while a bicycle has a PCU of 1/2. This allows us to talk about PCU’s and ignore the actual different types of vehicles. There are of course times when we might want to talk about HGV’s or bicycles in particular, a road with a low PCU/day but where those PCU’s are made up mainly of HGV’s might need a different treatment than one that is mainly cars, but these tend to be the exceptions rather than the everyday situations so the PCU is a good starting point to build up from.
So for roads, following the CROW advice, we can come up with the following table where we show the type of cycle infrastructure that should be provided for each road style at different levels of traffic volume.
Easy peasy, let’s quickly run through these options and what they might look like:
When we have access roads with low volumes of traffic, all types of traffic should be combined together. Speeds should be kept low by various traffic calming methods.
Cycle lanes should be used where there is no space for a cycle track.
Cycle tracks are as the name suggests, roads for cycles that run parallel to a motor vehicle road but are separated from it by a verge or curb (or hedge). They can be uni-directional, with one on each side of the road, or bi-directional where the roads are bigger, the distances greater, and the need for cyclists and pedestrians to gain access to the other side of the road less of a concern.
The final option is the parallel road. When we have a large distributor or through road, to provide access to properties a parallel access road is often added, this can then be used for bicycle traffic and linked together with cycle tracks to provide a complete network solution.
Knowing what to do on each stretch of road is a good start, but what happens when these roads have to come together at junctions? Well, we can derive another table for those based again on the type of road and the volume of traffic:
This one is slightly more complicated, so lets look at the options.
When access roads meet, the traffic is moving at a slow and careful speed. To reinforce this and the idea that traffic should negotiate the space, junctions between access roads are not regulated but instead priority is given on an ad-hoc basis to those coming from the right (or left in the UK).
Find out more about unregulated junctions on access roads.
Right of way intersection
Where a relatively quiet distributor road meets an access road, a normal intersection can be built. Traffic along the distributor should have priority while that on the access road should yield, both on the main carriageway and on the distributor cycle lane or track. Ideally, a cross roads should be turned into two T-junctions where space allows.
Find out more about right of way junctions between distributor and access roads.
Right of way intersection + supplemental measures
Supplemental measures should be added where the volume of traffic on the distributor make crossing it difficult. This usually means adding a central island to the distributor so as to allow a two stage crossing, but could also mean adding a road table or carriageway narrowing to slow traffic speed.
I think we all know what a roundabout is, they are a good choice as they minimise the number of conflict points and act as natural traffic calming. Cycle tracks should be segregated and continued around the outside of the roundabout.
Find out more about the single lane roundabout, turbo roundabout and mini-roundabouts.
Roundabout with cycle tunnel
On busy distributor roads with main cycle routes crossing them, it is desirable to add a foot and cycle tunnel to pass underneath the distributor road.
Images courtesy of David Hembrow
Find out more about large roundabouts.
Traffic control system (TCS)
Otherwise known as traffic lights. A light controlled junction has many benefits and limitations depending on traffic volume and situation.
The final solution is to avoid the conflict altogether by separating the traffic directions by height via an underpass or a bridge.
Once you’ve got this shopping list of tried and tested solutions and you’ve got a framework for fitting them into the conditions seen on the ground via the diagrams above, the hard work is done and it’s just a case of realising them.
Each of these road and junction treatments at each suitable level of traffic volume really needs a whole blog post of it’s own, so I hope to continue this post in the future with more information and hopefully some pretty pictures.