Saturday, 16 November 2019

CD195 Designing For Cycle Traffic

A couple of weeks back I wrote about how the Design Manual for Roads & Bridges (DMRB) was changing and this week I'm doing to have a dig through CD195 - Designing for Cycle Traffic.

The first thing to say is the DMRB is a standard to be used on Highways England and devolved administration schemes. It is a useful document for trunk road style roads and caution should be exercised when using it for local roads and streets because much of the information is not applicable.

That stated, CD195 has plenty of general application within its pages because the physical space, design speed and user requirements for cycle traffic apply everywhere. It's also an important point that the term "cycle traffic" is being used because we are dealing with a distinct mode of transport which is not motor traffic and it is not walking traffic. As Professor John Parkin says, "cycles are vehicles capable of speed"!

In terms of overall layout, there is a brief initial section for matters which all apply to Highways England, Transport Scotland, the Welsh Government and the Department for Infrastructure. The document then splits into four annexes, one for each for each of the four administrations. 

For England, the national annexe is a set of detailed information for the design of cycling infrastructure on the Highways England network. The annexes for the other three administrations are extremely short with only a couple of clauses each. The key ones are;

NI/1.1 Direction on the design of routes and facilities for cycle traffic in Northern Ireland shall be obtained from the Department of Infrastructure.

S/1.1 The design of routes and facilities for cycle traffic in Scotland shall be in accordance with Cycling by Design.


W/1.1 The design of routes and facilities for cycle traffic in Wales shall be in accordance with Active Travel (Wales) Act 2013 Design Guidance.

So in practice, the bulk of CD195 only applies to the English annexe and the three other administrations use their own guidance which in my view is a problem because of the age of the Scottish and Welsh documents and the absence of anything for Northern Ireland (at least to the best of my knowledge).

In the first part of the UK-wide introduction, we are reminded that the scope of CD195 is for the "design of routes and assets used by cycle traffic" - it's not for shared paths and this is an immediate problem where the default design choice is for shared designs. I'm hoping that in due course there will be better direction in this matter (which will sit elsewhere) because in many cases, there's nothing wrong with sharing if pedestrian traffic is very low and cycle traffic low to moderate.


The photo above is a cycle track on the Danish North Sea island of Fanø. I was the only person walking here and cycle traffic was low. Of course in rural areas there may be walking connections to local services and bus stops for example and in that situation, I'd expect the design to change for a section. For me, this is an issue that needs dealing with, especially as the DMRB standards on sharing are yet to be updated.

The second part of the UK-wide introduction simply refers the reader to other parts of the DMRB which should be read in conjunction with the text. In this case, just one reference to the introduction to DMRB.

So, to the English Annexe, which is set out under the following headings;
  • Foreword
  • Introduction
  • Abbreviations
  • Terms and definitions
  • Types of cycle route
  • Cycle design vehicle
  • Cycle route design
  • Crossings
  • Junctions
  • Signing
  • Normative references
  • Informative references
  • Appendix E/A - One-way and two-way cycle tracks
The introduction repeats the point that the standard is for routes used only by cycle traffic because of higher design speeds (notwithstanding my comments above). The abbreviations and terms/ definitions are helpful to get tuned into the language.

The types of cycle route are a couple of tables. The first looks at the minimum provision for traffic speeds and flows;


The second looks at the five conditions for good cycling infrastructure which will be familiar to students of the Dutch experience;


The cycle design vehicle section recognises that there are many types of cycle and many types of people using them. A "Cycle Design Vehicle" (CDV) of 2.3m in length by 1.2m in width is given to cover most situations;


Frankly, most designers could do with looking that the first two tables and the cycle design vehicle diagram! The point about the CDV is that people need space within which to cycle in terms of forward movement, curves and corners; this idea flows through the annexe.

The section on cycle route design is concerned with the different types of provision given the traffic conditions (lanes, tracks, protection etc) and it recognises that effective widths of provision are eroded by high kerbs, vertical features and gullies. There is advice on visibility, gradients, transitions between types of provision and dealing with bus stops (which should have cycle bypasses). The section contains all of the physical information one could need - a good point is made that two-way cycle tracks should have a centre line to enable people understand that they are two-way.

Because of the CDV and the need to make our infrastructure accessible, we are also treated with this group of clauses which I fully endorse!

E/3.32 Cycle tracks shall be clear of street furniture and obstructions with the exception of features to prevent motor traffic access.

E/3.33 The gap between posts and other physical constraints on cycle tracks shall be a minimum of 1.5 metres to restrict access by motor traffic while retaining access by cycle traffic.

E/3.34 Bollards on cycle tracks shall be aligned in such a way that enables a cycle design vehicle to approach and pass through the bollards in a straight alignment.

E/3.35 A frame and K frame type barriers, often used to prevent motorcycle access, shall not be used on cycle tracks.

Within the section on crossings, there is a large table which sets out the traffic conditions which lead to each type of crossing. For uncontrolled situations, we should not be expecting people to cross multiple traffic lanes. For higher speed roads, the inescapable conclusion is people need either signals to cross or grade separation (the latter where flows and speeds are at the higher end).

One issue I do have an issue with is where cycle tracks are running adjacent to the carriageway or bent-in (from a position away from the road to being adjacent) and the designer is invited to return cycle traffic to carriageway level within a lane before the junction in order to ensure people cycling are in a position which makes them visible.


The document is aimed at trunk road and motorway schemes and so inevitably, this will lead to changes on local roads as part of interface or legacy works. Although this is only for 30mph and lower situations, this type of layout is a cop-out because project sponsors need to work harder to ensure enough land is provided for decent layouts. 

Junctions are treated to detailed advice with emphasis on roundabouts. We're reminded that we should not put cycle lanes on the perimeter of roundabouts because it's dangerous. For compact roundabouts (essentially smaller roundabouts with single lane entries and exits) with more than 8,000 vehicles a day, cycle traffic should be taken around on cycle tracks. I don't think daily traffic flow is a detailed enough metric because in situations with heavy peak flows and very quiet off-peaks, it's still going to be awful to mix with traffic.


The photo above is a standard Dutch compact roundabout with a two-way cycle track, set back crossing points (about 10m), tight vehicle geometry (including HGV overrun around the centre). We can safely copy this approach, yet we don't and nonsense like this layout in Cambridgeshire keeps getting built;


Larger roundabouts (known as normal roundabouts) have a variety of solutions for cycling;
  • provide cycle tracks around the junction, with cycle track crossings of each arm;
  • remodel the junction as a compact roundabout, where permitted by CD 116;
  • provide grade separated cycle tracks around and/or across the junction;
  • introduce signal control to the roundabout, with appropriate cycle track provision;
  • replace the roundabout with a signal controlled junction or another form of junction, with appropriate cycle track provision.
Of course, when crossing each arm, we refer back to the section on crossings and we'll realise that once we have multi-lane approaches/ exits, high speed limits and higher flows we're into signals or grade separation! CD116 is for roundabout design which is a separate blog post in its own right!

The section on signing is mainly about directional signing strategy (so people can follow a decent route to where they are going to) and how the signage should be laid out. After the references, the table on one-way and two-way cycle tracks is useful to explain the advantages and disadvantages of the approaches.

So, there you have it, a blast around the new standard. Frankly, if every designer of trunk road style schemes started using this tomorrow, we'd see a big improvement and actually, there application in suburban areas too. 

The standard is based on an earlier interim advice note which was published in 2016 and so there will be people out there wondering why crap is still being built. It's a two-fold problem. For Highways England schemes, there are various stages where processes are fixed and one of them is on which standards are being used. With many current schemes, the standards fix predates 2016. 

The second issues is one of project scope. While CD195 will be used on new schemes, it's important that issues are brought into project scope in the first place and in my opinion, this also includes matters of historic severance. This is an issue to be tackled away from design standards and will no doubt need political weight brought to bear.

Saturday, 9 November 2019

Traffic Signal Pie: Automatic For The People

This post is part of an occasional series on traffic signals. This time, I'm discussing push buttons at crossings.

We all know about push buttons at crossings (stand alone or at junctions). They are there to register a demand from people who wish to cross the road;


They are the familiar boxes with the yellow shells (see a toucan crossing above) either attached to the traffic signal post or as a separate post. You also see them as slightly smaller boxes where a second push button is provided such as this chilly example;


There are various push button layouts for various situations;


There are two things to accept when we talk about people having to push a button to register their demand to proceed;
  • Traffic signals are there to manage motorised traffic.
  • The ultimate decision on highway space is political.
So, we end up with the simple act of wanting to cross the road being bumped down the pecking order by both traffic and politics. because we've seen the car as freedom and the politics supported this leaving it harder to cross the road in some places.

Detection for general traffic is pretty much universal using sensors in the road and on the traffic signals. It can be very clever counting vehicles through junctions and the control computers can adapt on the fly. Cycle traffic gets a bit of this where dedicated space is provided, although push buttons are still common.

People on foot (and I include those using wheeled mobility aids) get the raw deal because they have to press a button. Because of the way we configure space and that push buttons are mainly on poles near the kerb, we often make it hard or impossible for some people to press the button. In this film, Esther shows us that poor positioning of push buttons at this crossing makes it impossible for her to reach the button when using her wheelchair;


The problem here is the layout of the island with the push button on a post behind a kerb, so she cannot get close enough to press and so this could potentially be solved with some works, but is does show how easy it is to install something which is useless for many people.

It's also a problem for users of non-standard cycles where the push button cannot be reached without sticking the front of the cycle into the road or for hand cyclists and recumbent users, they are also seated lower down;


The above photo is a little bit of fun, but from my seated position, there is no way I could reach the button and unlike me, there are people who cannot easily dismount or dismount at all.

At multi-stage crossings where there is only one direction people are going to leave the central island (like where Esther was crossing), I think that the signal push buttons should be linked. There is no technical reason why pushing a button cannot register demand at the right time from the island.

Elsewhere, we have to think about how we can avoid people having to push a button at all. It would be possibly to run signals on a timer so the green man (and/ or bike) comes in every so often, but people should be able to turn up and cross and like drivers, we need detection.

I have never seen one myself, but pressure mats have been used in the UK to register someone waiting to cross - there is a report from the early 1990s on the testing of puffin crossings, although this was more about detecting that someone had walked off so the demand could be cancelled. The problem with this technology is that having stuff recessed into the ground puts it at risk from water and failure.

Modern crossings now use clever detection to sense people standing at a crossing using infrared or video with artificial intelligence tracking people through a space. There are companies looking at technology and in London, a pedestrian version of SCOOT is being tested which can extend green times where there are more people wanting to cross.

In time, we should see detection taking over from the need to push a button. I don't know if we'll see the end of the push button completely, but it would be nice to see new displays appearing which can reassure people that they have been "seen" and even better, how long they have until they get to cross (like many other countries manage). Eventually, we need more places were we get rid of traffic to the point where we need far fewer traffic signals, but that's another story!

This post is part of an occasional series on traffic signals - for more posts, search "Traffic Signal Pie" in the search bar or click here.

Saturday, 2 November 2019

Dem Bones, Dem Bones...

Well a tenuous link to Halloween I guess, but this week, I'm looking at the 'dog bone' roundabout which is a bit of a curiosity.

The dog bone junction is a development of the dumbbell junction which is a grade separated (roads on different levels) arrangement consisting of a pair of roundabouts connected by a short road which goes above or below a main road with slip roads connecting the roundabout to the main road, like this junction on the A13 in East London;


The reason for the layout is to keep the high-speed main road flowing without delays and safety risks by having junctions at grade (on the same level). The photo below is a view of this type of junction where the main road is carried on a flyover with the roundabouts and local roads below. The arrangement can be reversed with the main road at a lower level.


The layout means that there's less road and structures work than might be the case with a larger junction such as a single roundabout under or over the main road. The example above is slightly unusual because of the length of the main road bridge, but local levels mean it's on a long viaduct. Here's a schematic of the local roads over the main road.

The problem with the arrangement comes when we want to take people walking and cycling across the junction because we are going to have to get people over the slip roads. In my example from the A13, I've sketched the shared walking and cycling routes which run through the junction in red;


This junction isn't too bad as the slip roads have toucan crossings, the usual UK problem though is that they take ages to get a green man/ cycle and so people tend to chance a gap in the traffic to get across.

If you look closely at the aerial images of the roundabouts, you'll notice the marks on the road from vehicle tyres which show the heaviest movements, highlighted here;


Clearly there are very few movements all the way round the roundabouts - in other words, people coming along the local roads, performing a U-turn at a roundabout and going back the same way - this gives a hint of how the dog bone roundabout works.

At the next junction to the west, this little-used area has been filled in (to form two "tear drops") and the roundabout is now one loop - welcome to the dog bone roundabout!


The junction was signalised and converted into a dog bone roundabout in order to provide a cycle route around it and to increase the junction capacity (because the arrangement gives more stacking space). It's arranged so that drivers getting into the correct lane at the approach will pop out at the correct exit. The cycle route taken over the slip roads and the access to the business park from the northern roundabout by toucan crossings again;


It's OK to cycle through , but the stop start of toucan crossings does make it hard work sometimes, although at peak time, there's no way you can find a gap in traffic.

So far, I've given some urban/ industrial area examples. There is a debate on whether we should be building urban roads like this at all, but if the infrastructure is already there, some retrofitting is more likely than a rebuild and of course, signalising gives a great opportunity for walking and cycling space. 

In theory one could take the walking and cycling route through the centre of the junction as shown below;


In this example, those not needing to access the industrial estate bypass the toucan so it's a bit more efficient and there's no dog-leg on the slip road crossings. However, the signalling needs careful thought in terms of where stop lines go for general traffic. 

Where the idea comes into its own is when we can grade separate the walking and cycling route and that is going to be on the edge of town or interurban locations where signals are less favoured; with the increasing use of "free flow" slip roads (known as Segregated Left Turn Lanes - SLTLs) it's even harder to get people through the junctions on foot and cycle (and I'll cover SLTLs in another post soon).

For junctions which are being changed to a dumbbell arrangement being added, I think they should be developed as dog bone layouts with grade separation for walking and cycling, assuming walking and cycling cannot be completely unbundled (and in many cases, the local roads are the desire line). The drawing below has the main road at a lower level than the local roads;


In this arrangement, the walking and cycling route (red) runs alongside the local roads and crosses into the centre of the tear drops before crossing over the main road in the centre of the bridge which carries the central road. This bypasses the slip roads completely and maintains a good desire line. Here's a variation with an SLTL on one quadrant of the junction which shows the scalability of the layout;


Grade separation means that drivers and people walking/ cycling are not held up when using the arrangement, but the key to the layout is the dog bone arrangement couple with taking the walking and cycling route through the centre of the junction - it might be a little less comfortable between traffic lanes passing either side, but with some offset for vehicle restraint barriers, I'd argue the loss of comfort it exceeded by the improvement in directness.

Sunday, 27 October 2019

The Design Manual For Roads & Bridges Is Changing

The UK's design standards for trunk roads and motorways is changing, but there's no fanfare as the Design Manual for Roads & Bridges is rewritten.

It's not a document that I am expert in by any means, but it's essentially a design approach which (in theory) leads to consistent and legible designs which provide for safer roads. The Manual does recognise that there are people using these roads who are not driving - either in parallel or crossing and so if the requirements and advice were followed, I've no doubt that at least on the strategic road network, we'd have a similar standard to that of the Dutch where walking and cycling has to interact with large through roads.

The DMRB is a UK-wide document which covers roads managed by Highways England, the Welsh Government, Transport Scotland and the Department for Infrastructure in Northern Ireland). The Manual is set out into a number of volumes and within each one there are a number of documents setting out standards and giving advice. There are also Interim Advice Notes which cover emerging thinking in the time between the individual documents being rewritten.

The Manual's chapters cover an introduction, highway structures, geotechnics and drainage, assessment (traffic engineering, safety audit, walking & cycling), road geometry (layout, links, junctions etc), pavement design (the makeup of the roads), traffic signs and lighting, traffic control and communications, environmental design and assessment, and economics.

The Manual used to be commended to local authorities, but that's no longer the case, but nothing stops anyone using it as a reference and for a roads scheme not being promoted by one of the four owners of the Manual, it would be perfectly reasonable to use it for the same style of road. The Manual is pretty much not applicable to local roads and streets, although there are still useful pieces of advice such as highway structures management which tends to be locally adopted.

For walking and cycling (and in fact horse-riding), some of the terminology has changed. People have become used to Non Motorised Users (NMUs), they are now termed as WCHRs (walking, cycling and horse riding) which is probably just as clumsy given that it lumps people with varying needs together. For WCHR matters, there are some key documents which are concerned with the nuts and bolts of design;
  • TA91/05 - Provision for non-motorised users*
  • HD42/17 - Walking, cycling and horse riding assessment and review*
  • GG119 - Road safety audit
  • CD116 - Geometric design of roundabout
  • TA86/03 - Layout of large signal controlled junctions*
  • TD36/93 - Subways for pedestrians and pedal cyclists*
  • CD195 - Designing for cycle traffic
  • TA87/04 - Traffic calming on trunk roads*
  • TA90/06 - Geometric design of pedestrian, cycle & equestrian routes*
  • CD239 - Footway and cycleway pavement design
CD195 - Designing for cycle traffic

The documents I have marked with a '*' are in the old format and so I expect them to be updated or absorbed into others in the future - the whole thing is being reviewed as reported in Highways Magazine earlier this year. There are inconsistencies and contradictions, so having everything updated (and easier to update going forward) will be very helpful.

With the old format, the letters and number had a meaning. For example TD36/93 was about traffic control (T), a design document (D) and published in 1993. The '36' was just a document reference. The new system drops the publication year as the current version will be digital at the main website. The new format has five digits with the first two relating to where the document is stored in the overall structure and the three numbers are allocated by the policy group dealing with the particular document - most people won't need to worry about this of course!

Because the Manual takes time to be changed, there will be schemes which use older documents for a while, especially those which are already underway in the design phase because of a "design fix" which draws a line from where design work starts. However, as new schemes come forward, they will be using the newest documents. For those campaigning for change out there, it is a slow thing to change direction, but it's good to know what designers are working to in order to hold decision makers to account.

In the next few weeks, I'll take a look at some of the documents to give a more detailed flavour on what they are all about.

Saturday, 19 October 2019

Cargo Joy

One the small pieces of daily joy for me is spotting cargo cycles as I walk in Central London - mainly from the Tube to my office, but elsewhere too.

The problem of course is that cycle traffic is an efficient transport mode which means it's not always easy to be able to notice a cargo cycle and then get a photo of it. However, here are three which I have managed to capture in the last fortnight;

Christiania tricycle

Hercules e-cargo bicycle (Coop Food)

Urban Arrow e-cargo bicycle (Pedalme)

It's pure anecdote of course, but I'm sure I'm seeing more and more cargo cycles and it's testament to their versatility in shifting people and goods with an efficiency of space and within a predictable time. 

Increasingly our towns and cities are densifying which means even more demand for moving people and goods around. It's simply not possible to add road capacity and so we need to make the space we have work smarter and part of that smarter future will be cargo cycles. I fully expect to be seeing a lot more of them in the coming years.