Traffic Signal Pie - Time For T

I've been grappling with an issue of what we can do where a cycle route in a quiet network of back streets meets a busy urban mixed-use A-road.

There is a real-world site I have in mind, but I won't name it as it is too close to work. However, this doesn't matter as the geometry is more important that location and it has been good to flex my brain on the issue.

The main road in question is a typical long-distance single carriageway A-road which was never planned as such and so ends up connecting a series of shopping centres with housing between each; plus the occasional school and community facility. In fact, these mixed-use streets are everywhere and often end up being the de-facto long-distance road network.

The existing layout is shown above. The main road runs east-west and carries around 20,400 vehicles per day (over 24-hours), with 17,500 of them being cars. There are (unsurprisingly) 200 people per day cycling, 500 bus/ coach movements and the rest various sizes of HGV.

The total highway width gets up to around 20.5 metres with about 11.5m being carriageway (with advisory cycle lanes). To the south of the junction, we have a primary school. The side street 7m wide, flaring out to a huge 21m as it means the main road - probably because of the former industrial estate (now housing with a couple of small workshops). The side street feeds a residential area and because of modal filters, it's the only motor vehicle entrance into the estate. There is also a signalised pedestrian crossing to the west of the junction on the main road.

Aside from the main road being pretty awful to cycling along, the principal issue is one of helping people cycling to turn right into and out of the side street. The main road needs cycle tracks to do anything about the woeful cycling numbers and the twice a day congestion, but the links are pretty simple, the junctions are the challenge.

My starting point was a junction I had studied in Amsterdam;

The junction of Middenweg with Zaaiersweg is not a million miles away from my study location. Aside from the central bus/ tram lanes, there is only one general traffic lane in each direction and the road is flanked by one-way cycle tracks and footways. The cycling here feels nice and safe. The issue here is one of turning left (i.e. UK right) from the side street (Zaaiersweg) which is the main access to a filtered estate. 

Turning left required people cycling to cross the entire carriageway to get to the cycle track going in the opposite direction (towards the city in this case). At least when I was there, the main road was quiet enough to find a gap to cross in one go, but I could imagine times when this would be harder. After mooching around in Streetview, I found a junction with Postjesweg elsewhere in the city which provided space to cross the road in two parts (with cycle space) and a pedestrian crossing on one side and this gave inspiration for my crack at a UK version;

Although I hadn't been to this junction, I have crossed large urban Dutch Roads with a refuge and priority remaining with drivers such as here;

As you can see from below, the highway space has been reworked as you might expect to see in a place such as Amsterdam.  

For people cycling, the side street has a similar entrance treatment to Zaaiersweg and so the right turn out (Dutch left) has people cycling coming from the shared carriageway of the side road and across the cycle crossing point with motor traffic retaining priority. Those turning right in have a similar provision, but they end up in the shared carriageway (blue is right out, purple is right in);

People on foot retain a crossing, but it's now a zebra rather than being signalised.  I put the sketch out on Twitter and as usual it provided for some good debate. David Hembrow did sound a note of caution in terms of the UK probably having far more motor traffic than the Netherlands and so it might not be suitable, also citing Dutch experience with the same. He also flagged the issue of needing to divert the traffic [from the main road] before trying to 'civilise the street'.

This is where the UK constantly comes up against a wall. In my example, there is a high-speed (parallel) dual-carriageway about 750m to the north and to reduce through-traffic on the main road, we would have to divert it to the trunk road. This would mean having people driving longer distances switching to the trunk road and at the same time making it less favourable to use my main road example as a long-distance route. The problem is (at least for now) is the trunk road is often heavily congested at peak times and a major change like this would need political cooperation across a number of boroughs and Transport for London.

So, I wondered if a pragmatic approach could be signalising the junction with the justification that it helps feed a quiet cycle route to the north. If a borough were going it alone (like one of the mini-holland boroughs) then this could be a treatment which protects those who we would like to get cycling (such as children going to the primary school) and as such, any loss of capacity for long-distance drivers is given back to local people who will want to cycle.

In playing with the space, it was clear that space was tight into the side road and so providing a set of three parallel crossings with "floating" crossings couldn't quite fit. The sketch below shows my thinking (ignore the southern cycle-only arm).

This approach would make for a simple method of control whereby the east-west motor traffic runs together, then the side road (north) runs an then finally the three parallel pedestrian and cycle crossings run together. I had to think a bit differently;

The image above shows the side street as having those cycling and driving mixing as opposed to the separation in the example above. The traffic signal method of operation took some thinking about, but it runs like this;

1. East-west motor traffic runs together (black),

2. Traffic released from side street. Motor traffic joins carriageway of main road (black) and cycles enter the cycle tracks (purple),

3. Pedestrians cross both arms of the main road (red) and cycle traffic turning right from the main road into the side street runs in parallel,

4. East-bound and left turning cycle traffic runs with pedestrians still crossing both arms of the main road.

3 and 4 could be swapped so that eastbound/ left turning cycle traffic runs before cycle traffic turning right into the side street, but either way, 3 and 4 are essentially a single pedestrian stage within which two cycle sub-stages are squeezed because people cycling need less time to cross. Don't ask me what the timings might be with this as I am not a traffic engineer!

The drawbacks of this design are that people cycling east are going to have their progress halted (and there will be red light jumping). In the UK, we couldn't have people cycling ahead being put into conflict with left turning drivers within traffic signals, although for some reason this is perfectly acceptable at uncontrolled side roads with advisory cycle lanes!

Alternatively, left turning drivers could be held on red signals (so-called 'hold the left turn'), but this requires stacking space which isn't available in my example - see the layout here in Mile End, East London;

The cycle track on the left can run with the ahead motor traffic movement when the left turning motor traffic is held. It is all very complex and needs lots of motor traffic stacking space!

So where does this leave us? Signalisation can be costly and not very flexible for walking and cycling (after all, signalisation is generally about stopping conflict with motor traffic). With the first sketch, we could have parallel zebra crossings, but having one on each side of a junction in such close proximity would be extremely unusual (if not unheard of in the UK).

I don't have the answers, just suggestions and so it is going to have to be down to the context. On a mixed-urban A-road, we are not going to be able to signal every single side street, although we can be clever with filtering them. As David Hembrow has said, the motor traffic reduction is key - how we get there is one for the politicians. 

ALARM 2018

I've been following the ALARM survey for some years now and for the first time in a very long time, the one-off cost to clear the backlog has reduced.

The Annual Local Authority Road Maintenance Survey (ALARM) undertaken by the Asphalt Industry Alliance (AIA) has shown that the backlog has reduced from £12bn to £9bn. That's not because £3bn more has been invested in road maintenance, it is far more complex than that. One point to make is that this survey is just about carriageways and cannot reflect the true needs of highway maintenance as a whole and it is only England & Wales.

Above, gives some of the key headlines from the full report which gives the headlines. The inference is that main roads are generally those which get the most investment (which makes sense given their traffic volumes), but local roads are being left out. Even lightly used local roads will still be at the mercy of the elements, but the reality is that many (especially in urban areas) are expected to be release valves for the main roads.

The structural condition reinforces this as we can see a polarisation between "good" and "poor" roads as the "adequate" roads percentage shrinks.

I have often said similar, but there is a realisation in the industry that the situation remains unsustainable and my own view is we need to start trying to get the best out of what we have now. This is summed up in a comment in the report;

"We need to think long and hard about building new roads. If we don’t have enough money to maintain the existing roads, how are we going to be able to maintain new ones?"

One point Londoners might be interested in, especially after the cuts to London's road maintenance funding, is that the shortfall has increased compared to last year. This will undoubtedly get worse.

One of the main problems is that roads are hugely political. At one end of the scale, we have the government dogmatically tied to the notion that building roads is essential for continued growth. That in itself is patently nonsensical because because growth cannot be infinite. 

At the other end of the scale, we have local authorities being hammered by the gradual removal of funding from central government with their responsibilities growing. In many ways social care is vastly more important than filling potholes, but the local highway network is the one asset that a local authority has which binds the rest of its activities and responsibilities together. We need a different conversation about all of this.

Five Simple Things We Can Do for Walking

Here are five simple things which we can do to make walking easier and accessible for all. Doing it right does not cost any more than designing and implementing poorly.

In many cases, doing something right is actually cheaper than doing something wrong and so my message is to pause, think and get it right first time.

Barriers
Why take a perfectly good path and block it with barriers? Staggered barriers, K-barriers and kissing gates might in theory stop mopeds and scramblers, but they will completely prevent access for many and provide a poor level of service for everyone else. The anti-social use of powered two-wheelers is an enforcement issue and in any case, they will just be lifted over the top of barriers. If car access is an issue, then carefully designed bollards with 1.5m clear space will deal with the problem, but make sure bollards are positioned carefully to maximise unobstructed clear space.

Pedestrian Guard Rail
It is there to control pedestrians, saving them from themselves, especially where a road layout for maximum motor capacity cannot accommodate the desire lines of people moving under their own power. If we provided for pedestrians and their desire lines properly, then guard rail wouldn't be needed. However, we are stuck with lots of it, but it doesn't have to be this way. Anywhere it has been provided to stop parking or footway over-run is a failure for pedestrians as the solution will be a combination of enforcement, parking controls and community engagement with the odd bollard as a last resort. In places where safety is perceived as an issue, then a structured audit approach will give confidence where it can be removed.

Dropped Kerbs
If we are laying dropped kerbs for pedestrians, then please make sure they are laid flush. The kerbs are flush to assist people using wheelchairs and mobility scooters, people pushing buggies and prams; and people with other mobility impairments. It costs the same to lay a kerb correctly as it does incorrectly and can make all the difference. A flat-topped road hump can be better as pedestrians don't need to contend with ramps and at side roads, continuous footways are even better (although perhaps not as simple as a dropped kerb). Don't forget tactile paving is needed, laid correctly with blisters and cut properly to prevent those silly little pieces popping out and causing a trip.

Vehicle crossings
Where vehicles need to cross a footway, we can provide a vehicle crossing. We need to remember that it is the vehicles which have the engines and so we shouldn't be dropping the footway down to meet the road. It is hard work to keep going down and up ramps and steep crossfalls can tip people from wheelchairs and mobility scooters. By keeping as much as the footway longfall and crossfall constant, the very front can be ramped for the vehicle. Where the footway is narrow, then quadrant kerbs can be used to maximise the footway for people walking. We can (and should) go further as this type of design approach can be equally applied to junctions where a continuous footway can be provided across the side road. Paved in a different material to the carriageway, a continuous footway will have a good level of visual priority, showing drivers that they are the visitors.

Clutter Buster
Many of the traffic signs out there are provided to manage and regulate motorised traffic and invariably get stuck on posts in the footway creating obstacles for those walking. The key here is that everything in the street has to earn its place and that includes traffic signs. Perhaps a street audit could be undertaken to check what should really be there and then put a plan into place remove what shouldn't. If a sign gets hit, the first question the maintenance team should be asking is if needs to go back. If signs are really needed, then can they go on lighting columns or be attached to walls (especially parking signs). A little thought here can go a long way.

Traffic Signal Pie: Just Rephase the Lights

I don't hear this every day, but "just rephase the lights" has become a shorthand for people who cannot see or refuse to see that they are part of the problem.

First, let's get the terminology right and I have the irrepressible Brian Deegan to thank for this wonderful three word description of how traffic signals are arranged;

"Phases make stages"

Phases come from the electronic set up of the signal control computer, essentially they refer to where traffic (drivers or cyclists) or pedestrians are are controlled through a junction on a predictable path with the control being the signals themselves. With pedestrian crossings and situations where opposing traffic flows always run together, then they are taken as single phases.

A stage is where non-conflicting phases can move together and may or may not be used each time in the signal cycle; with the signal cycle itself being basically where every called stage has had a turn (in a preset order). For the very geeky, a more detailed (and slightly more correct) explanation is available on a Traffic Advisory Leaflet here.

So, when people say "just rephase the lights" they probably mean they want the set up changed to favour a particular stage they have an issue with (the one they feel held up on). Rephasing would essentially come from a physical change to the layout because we are dealing with fixed paths or movements. Perhaps they do know more and think that a dedicated phase should be created for them and that it should always be green!

I am not entirely sure how the phrase has come into common use, but at the root of it is a dissatisfaction with how signalised junctions operate (and I never hear the phrase used with standalone signalised crossings). As the running title of this occasional series of posts suggests, we are dealing with something finite and as with a pie, it has to be divided up somehow. My generalised complainant just wants a larger slice.

The size of the pie is governed lots of variables which go back to physical space, the number of traffic lanes, pedestrian demands, cyclists demands, flows changing throughout the day, type of vehicles passing through etc. In essence, for any given situation there will be an optimum pie size. If we are to efficiently consume the pie, we will be able to scoff 90% of it easily without any problems. The last 10% is where people start fighting over the crumbs and it's not efficiently eaten.

Paradoxically, we can sometimes eat more than 100% of the pie (and to be honest it's where my analogy turns a bit suspect), but its people licking the enamel off the plate. The amount which the capacity is utilised is known as the Degree of Saturation (DoS) and so 90% DoS is generally the most efficient situation and as we reach (or sometimes exceed) 100% DoS we are in the realms of people taking shorter gaps, tailgating, jumping amber or red signals etc.

In busy urban places, junctions regularly run above 90% and in many cases, they regularly run beyond 100% (perhaps up to 105% as a rough idea - "over-saturated" if you will). At this stage, the flows completely break down and we see traffic queues quickly forming and if things don't start to clear, these can start to extend exponentially (in theory). We see drivers blocking crossings and other movements as they try to get through the green signals, despite not having clear exits. Junctions with yellow boxes will generally be running beyond 90% because of the need to try and keep drivers from locking up the junction.

Those who are frustrated with the operation of signals rarely want to face up to the reason why the pie has all gone. People do sometimes suggest tweaks that the experts have missed (and signals people are very clever), but in general they don't want to face up to the reality that the congestion is caused by too many people wanting to get through a junction at the same time and that everyone else's journey is less important than their own.

It is interesting (for me at least) to read transport assessments (TAs) for new developments where signalised junctions are impacted. I have often said that I have never seen a TA that admits a scheme will cause congestion, but that has changed recently. I don't know if it is a shift in presentation or a realisation from my TA-producing colleagues, but the arguments being put forward have subtly changed.

What seems to be happening is that more is being made of national forecasting data (i.e. traffic is growing) and where junctions are over-saturated, the argument is being advanced that although queues do in theory grow exponentially, people will change their behaviour and travel at different times, using different modes or not travel at all. They are not quite admitting the development will stuff the signals, they are saying that the junction is either stuffed now or it will be soon, so the development doesn't really change the inevitable.

I don't think this is people throwing up their hands and giving up, but there is a realisation that we can't built ourselves out of the problem - well we could, but we would have to start demolishing our town centres to make their junctions larger. In many cases we did just that to create gyratories which now have had their capacity used up.

Just rephase the lights is an easy opt-out for the public who think there are cheap and simple solutions to our congestion problems. The politics of it doesn't seem to explain the difficulty there is because it is often also too simplistic and not wanting to face up to the challenges. Whether this is because we don't want to be honest with people or whether professionals aren't very good as explaining complex issues plainly, but our problems go way further than those which can be solved by a traffic signal engineer fiddling with traffic signals to give a couple of seconds more green time.

It's Snow Joke: Redux

I didn't think I would be revisiting snow again so soon after my blog in December last year, but this week's weather cannot pass without comment.

December's post was about "winter service" (gritting to most people), but this week, I'm going to broaden the discussion as there are other issues to think about and learn from.

The first thing to note was that it is hard to forecast snow accurately and so this in turn makes it hard for transport operators to decide whether to put contingency plans into place. On Monday evening, I was catching a train and the announcements were that trains would be stopping earlier than normal because Network Rail needed to run more deicing trains. In the event, Tuesday was snow-free, although cold and the forecast for Wednesday was snow-free.

So on Wednesday, I woke up to snow! Given the amount I go on about cycling, I had to get to work under my own power. I had slipped off my bike on black ice just before Christmas and so I elected to switch to 3-wheels and it was an absolute joy because the morning was clear and sunny with my usual journey not being much slower than normal.

Having two front wheels made for excellent stability and the fresh snow provided no issues with grip. Of course, I had to release the inner geek as I went through a modal filter which, despite the snow, was perfectly legible to use and fully accessible to the tricycle.

Going home was a little more challenging (more of it uphill) and half-way back, I copped the full force of the easterly wind which was driving snow straight at me.

Nonetheless, it wasn't too bad and so I was happy to give it another go on Thursday. Conditions along the shared path I use for part of the journey were a little better as some treatment had taken place, although the on-road cycle lanes were half-covered and I had to move out further than I normally would.

Going home, it was another easterly wind and the low temperatures started to freeze the trike, so progress so slow. For the last 400m, I pushed it up the hill and resigned to getting the bus to work on Friday.

On Friday morning, I put on my walking boots and went to the bus stop which luckily for me, is just around the corner.

As is always the case, the main road was perfectly clear, but the path to the bus stop hadn't seen any treatment. The bus journey was straight-forward because it is direct and on main roads. Because the roads were quiet (snow and the usual Friday pattern) the bus driver had to wait at a couple of stops to let the timetable catch up!

While perhaps not the most impressive examples, I managed to get a couple of "sneckdown" photos on Friday which show that traffic doesn't quite need all the space the designers provide.

A bit more snow on Friday afternoon topped up the untreated side streets.

And as I got home from 3 days of (not that difficult) snow commuting, I hoped that come Monday, the promised thaw would get me back on my usual bike.

As I write this on Saturday morning, the snow here in London is melting away, but other parts of the country are still in its icy grip. As far as transport is concerned, we're seeing stories of people trapped on trains and on motorways for hours, airport disruption and the usual nonsense about the country being unprepared for a relatively rare event.

What we don't hear are the stories from people who have been trapped for several days at home because they are terrified to walk on frozen footways or the snow means they cannot use their mobility scooters, wheelchairs and indeed their cycles as mobility aids. Gritted bus stops are no use if the walking routes to them aren't clear and untreated cycleways aren't going to move significant numbers of people (yes, there is a cycle track under the snow in the photo below).

The sneckdown photos are great, but they also rely on the fact that far fewer people are driving and so as well as showing the space which could be released, they indirectly show us that we need traffic reduction to release the space (and my bus journey shows how things are set up expecting congestion). For those who were out and about travelling actively, the reduction in traffic and the quietness of the streets was noticeable.

Main routes are rightly treated because at the core, we still want to be able to keep buses, emergency services and other vehicle-based public services running. But core walking and cycling routes tend to be treated highly variably and so unless one drives or can get a bus, then for many, local journeys are difficult or impossible.

The people stuck on trains and motorways show the fragility (to a certain extent) of our longer-distance networks which have enabled some to live a long way from work (or where people are priced out of cities) and how when there is a shift in the weather, the whole system can break down. Thankfully, for most of the UK this is pretty rare and so apart from the places which usually get snow, it's pointless keeping huge resources on standby, although there probably isn't the money for local authorities given the continued cuts to funding.

Over the few days, we'll see the thaw spread and some communities will be at risk from flooding, we'll also see a fair bit of surface and structural failure on our highways because of freeze-thaw action from the low temperatures and again, this will disproportionately affect those walking, cycling and using mobility aids.

So, while there has been plenty of fun in the snow, it has cast transport inequality into sharp relief and that's something we should all think about.