Saturday 30 September 2023

Voorrangsplein! Part 3

One of the things that constantly impresses me about Dutch highway engineering is that they are not afraid to experiment and improve.

I was lucky enough to visit the Netherlands again a few weeks ago and my nerdy highlight was a cycle infrastructure safari around Utrecht with Mark Wagenbuur of Bicycle Dutch blog fame and our ride took us through a type of junction which has been intriguing me for ages - the voorrangsplein or "priority square" junction.

This post is actually part three of a series in which I wrote about the junction form back in February and March of 2021 as we were still grappling with Covid and I was wondering when I might venture back across the North Sea. Fortunately I have been able to visit several times since and each trip gives me further insight into the kind thinking that we could easily import into the UK and that includes the voorrangsplein design.

My first two posts looked at the design from first the motor traffic point of view (because it is a motor traffic feature) and then how walking and cycling could be added. My trip to Utrecht allowed me to see a couple of examples in the flesh and Mark provided some additional local knowledge. 

The other little development is I put out a little slideshow of my latest trip which included one of the junctions and that prompted a discussion with a Dutch colleague who pointed me and another UK colleague at the general design guidance for the junction type as featured in the CROW ASVV Recommendations for Traffic Facilities Within Built-Up Areas 2021 which is a much larger piece of design guidance than the CROW Design Manual for Bicycle Traffic which many in the UK will have heard of. I have the 1998 English version, but the current one is only in Dutch and so I've had to do a bit of translating with Google!

I will add my usual health warning that Dutch guidance has no legal standing in the UK, although lots of it will be of interest to a UK audience and many practitioners use it for inspiration and ideas (myself included - more on law and guidance here). Some of the tools, techniques and layouts are not compatible with UK legislation, but in my view we could very easily import the voorrangsplein design.

As we found out in the second post of this series, the layout was first used in Hilversum in 2007 to replace a signalised junction. The design developed from the LARGAS idea - langzaam rijden gaat sneller or driving slowly goes faster.

Since 2007, the junction has become a feature of guidance and the design has popped up all over the Netherlands. In Utrecht, it has been used at a couple of junctions which are part of the Western City Boulevard project which is squeezing out some motor traffic capacity in favour of more space for people and green space on the city's ring road. I made a video of a section of the project from my recent visit in which you'll see a couple of voorrangsplein junctions.

The project still has retained a fair chunk of capacity at the larger junctions and given these are largely the flow constraining features, removing a lane in each direction between them isn't a huge problem from a capacity perspective. Before we take a closer look at one of the Utrecht examples, it's worth taking a slightly deeper dive into some of the features of the junction type. 

The guidance suggests that the design should be used at intersections of distributor roads with access roads, and that the main road can operate with a maximum of 25,000 vehicles a day. As you might recall from the previous posts, the junction is part of a single carriageway layout (locally dualled or with a very large traffic island on the approach) and so 25,000 vehicles a day is a very high flow indeed. 

When the main road is running clear, the guidance also suggests that the main road can feed up to 1,200 vehicles a day in each direction through the junction type (just under 10% of the daily flow). In some situations this might be seen as potential constraint because peak hour flow might be a touch higher, but as I have suggested, 25,000 vehicles is very high for a single carriageway road and we really need to be designing for traffic reduction in my view. 

The junction type is not for high speed roads and indeed, the guidance suggests that it is a useful "gateway" feature for stepping driver speed down. Because of the horizontal deflection it provides on the main road and for the side roads being mainly for access, it's a chance to reinforce a change of environment. Above is a simplified layout I have flipped for the UK and I've annotated some of the key features. The main thing to consider here is that it can be easily seen that drivers are able tackle the junction in stages, dealing with other traffic streams in bite sized chunks - it is an easy junction to drive through!

The lane widths are interesting. The guidance suggests they be in the range of 2.9m to 3.5m. The narrow lanes help keep driver speeds down, but there are options to add overrun areas to accommodate larger vehicles - rammelstrook or rumble strips. I can see some UK network managers shuddering at the narrow and locally dualled sections which might be a problem in the event of a breakdown, but we probably shouldn't design for what is a fairly irregular event.

The junction form is still space hungry, but compared with a signalised junction of a similar capacity, the layout tends to be elongated and provides space for landscaping where being used in retrofit. So, the Utrecht examples are interesting because the overall highway footprint remains, but the elongated nature of the junction and the general road diet means an awful lot more space is released for landscaping as well as walking and cycling space.

Let's take a look at one of the junctions - Marnixlaan with Royaards van Den Hamkade/ Van Egmondkade (above). In the photograph the main road (Marnixlaan) splits either side of the kidney shaped central island. Around this island you can just see a left turn lane and the black car to the left is entering the other left turn lane coming towards us. To the right there is a black car emerging from Royaards van Den Hamkade just out of shot that car has also cleared the cycle track to wait in a pocket before joining the main road.

Above is a photograph where I turned a little more to the right and the cycle track and footway can be clearly seen, both with priority over the main side road. The video below is a pan across the junction from its south east side and then a quick look at how the Royaards van Den Hamkade arm works. It's worth watching a couple of times to see how well things flow for all users.

Royaards van Den Hamkade is part of a route which connects to the city centre and so arguably it is more of a distributor road than an access road, although the route does tend to fizzle out as it meets the city's ring-canal. The Van Egmondkade arm is also more of a distributor road which continues as a route to meet the regional road network. 

The other thing to note is there are two way cycle tracks on both sides of Marnixlaan whereas the guidance shows (but doesn't require) with flow cycle tracks. Of course, walking and cycling is an additional to the basic motor traffic junction and locally, the two way tracks make sense at a network level. 

The photograph above is the the left of the first one which shows an uncontrolled crossing for walking and cycling of the main road which is in accordance with the guidance (but signalised crossings are used elsewhere) and you can just make out that the cycle track coming in from the left is one-way as is the crossing by virtue of the no entry signs. For cycling, this junction is the interface between one-way cycle tracks coming from the southwest and the two side roads and then becoming two-way on both sides of Marnixlaan off to the northeast so save having to cross the main road further on.

The final piece of interest here is the set of traffic signals on each approach to the junction on the main road. I have already said that the junction form is unsignalised, but in this case, the signals are used to hold traffic for a very short time if the junction has started to hit capacity which in theory could be from traffic on the side streets, turning right in the junction or perhaps lots of people cycling across. The photograph above shows the signals on the southwestern approach and you can note the one-way nature of the cycle track.

You can also see the signals here which are just red and green aspects when in use and some traffic loops for drivers and cyclists here. The traffic signals only switch on when needed and are set away from the junction so they don't create any confusion that they are part of the junction.

And there you have it. Hopefully this has helped get under the skin of the voorrangsplein to show lots of little things working together to create a really useful junction design.

Friday 25 August 2023

Railton Revisited

Just over a two years ago, I paid a visit to the Railton Low Traffic Neighbourhood, to the southeast of Brixton town centre in south London. I revisited because I had seen photos on social media of the project being made permanent and I wanted to have a look myself.

Functionally, the project is the same as it was on my last visit with restricted motor vehicle access to Atlantic Road from Coldharbour Lane at the northwestern end (below), with that first section essentially creating a cul-de-sac just beyond. At the southeastern end, a bus gate has been retained near Herne Place which means there is a low traffic link from Brixton to Herne Hill station. 

Crucially, Shakespeare Road remains closed to motor traffic at Mayall Road and so with pretty small scale work, an entire area has been freed from being a cut through for motors while maintaining full access to buses, emergency vehicles and service vehicles.

A shopping street with lush planting areas on both sides with a bus driving away in the distance and a person crossing from right to left with a buggy.

So on that basis, this post is actually quite short because the previous one went into a bit more of that detail. The key thing is how the London Borough of Lambeth has made the project permanent and so let's look at the Atlantic Road end a bit more closely. The first 35 metres (from Coldharbour Lane) is only for buses and loading permit holders, and it is dominated by new planting (above).

A bench in a quarter circle with timber slats for a seat and back with metal legs and armrests. A grey bike with an orange bag on the front rack is parked just behind.

In theory the only way in for loading permit holders would be from the opposite arm of Atlantic Road given the banned turns from both arms of Coldharbour Lane and so only those in the know would go that way. Other deliveries can be made by accessing Atlantic Road via other routes. Because this first section restricts motor traffic, additional footway space has been provided along with seating (above) and cycle parking.

A street with a road narrowing on both sides to create a pair of lush planting beds with an informal crossing point beyond. A person on a small folding bike has just passed through.

The modal filter just south of Marcus Garvey Way has also been upgraded (above) so it is more obvious that people shouldn't be driving through southbound. Northbound is allowed due to the way the local traffic circulation plan has been arranged. This is a bit of a theme and while needing to allow buses through, the road layout has been changed to help reinforce the prohibition of general traffic intention of the design.

The pair of buildouts from the other direction showing no motor vehicle signs and the words BUS GATE on the road.

One issue I have is with the signage which in common with the entrance from Coldharbour Lane uses the written "BUS GATE" marking with the no motor vehicles traffic sign (above). I'm afraid that this is not an approved combination and Lambeth needs to either remove the markings or swap the signs to one of the 953 series (one for the sign geeks) within which exemptions to the traffic regulation order can be made for "authorised vehicles" but not permit holders.

A section of street with a rail bridge over it in the distance. The road has been coloured buff and there are staggered planting beds on each side and a group of timber and metal chairs to the left. There is a no motor vehicles traffic sign to the left.

Other main change has been at Shakespeare Road where a short section of street has been essentially pedestrianised with the temporary materials giving way to permanent materials which work to explain to drivers they shouldn't be here (above). To the north of the railway, Shakespeare Road is now a quiet cycle route up to Loughborough Junction station.

The same as above, but a closer view of the seating which has an armchair and a pair of two person benches.

The street layout in the wider area is a bit awkward due to the railway cutting through, and so from an emergency access point of view, the pedestrianised section of street has space for vehicles to pass through with CCTV enforcement. The layout is such that there isn't a clear view of the route ahead which is another design reinforcement to drivers that they are not permitted to pass. The seating and planting work to block this view through while allowing a route that standard fire engines can tackle.

The street closer to the railway bridge with a pair of no motor traffic signs and the planting on both sides.

The photograph above is from the north looking south and again, the winding nature of the emergency route can be seen with the planting providing the visual break. Below is a closer look at the planting here which are all rain gardens with a square of granite blocks providing a bit of water energy dissipation before the planting.

A close up of a small squarish rain garden with a square of granite blocks closest to the viewer.

There are also poems from local poets within the area as part of a local heritage trail (below).

A poem in yellow and white on black asphalt: "we make the place trendy, vibrant Brixtonians make a Splash, never silent. When injustice arises to fight us we fight back with a roar that's righteous. The youth stay current, Electric Pattern up 'cause life can get hectic. We grieve loved ones no longer here. We kiss our teeth to conquer fear. We rise, Elevate above friction. Respect the village, love Brixton. BRiES.

So, while the project hasn't functionally changed from my last visit, the permanent materials and planting don't just look good, they help reinforce the layout to make it a bit more self-explaining to drivers which I think is a good thing. Even though people driving should understand traffic signs, making it easy to understand counters the often claimed confusion argument. So, I shall leave you with a quick video of the project and I wonder if you'll see the little surprise (just before the 3 minute mark)?

Sunday 13 August 2023

Battersea Bridge: What Can Be Done Quickly

Bridges are often contested spaces simply because they very rarely contribute to dense street networks and as a result, they funnel users to specific points which might be off their general desire lines into situations where trying to manage different users with different energy is a challenge.

It is against such a backdrop that this week, a woman cycling lost her life on Battersea Bridge in London after being hit by a lorry driver. It has been a notorious crossing of the Thames for many years with a terrible safety record. The London Cycling Campaign sets out the litany of failure in its blog.

As is the general case in many UK cities, the layout and classification of the road network has somewhat evolved and in many cases, those designated as A-roads come as a result of that evolution. Battersea Bridge is the A3220, although in a London context, it is not classed as part of the Strategic Road Network (SRN). The specific classification is somewhat moot given the bridge carries some 25,000 motor vehicles a day - sitting here today it is a busy motor traffic route and it is important for bus traffic too. Around 8% of vehicles are either buses or HGVs and this scales to nearly 26,000 if we convert to passenger car units (PCU).

The view over Battersea Bridge from Google Street View. Traffic in both directions and high kerbs with railings between the road and pavement.

From a walking, wheeling and cycling point of view, the bridge has a pair of fairly narrow footways and a carriageway width of about 7.5 metres (at least from Google maps) or a running lane width of about 3.75 metres which puts it in the "sweet" spot of widths which should be avoided for mixing cycle traffic with general traffic (7.2.5 in LTN 1/20 for those interested). It's a width which some drivers think they can still squeeze past someone riding, especially if they are in the gutter and on Battersea Bridge, there are containment kerbs (with barriers behind) protecting what I assume is a weak parapet from vehicle incursion which is not a nice feature to be near on a cycle.

The bridge also carries 3,800 cycle movements a day and so the combination of lane width and volume of buses/ HGVs does immediately create the conditions where people cycling are exposed to risk and at least in terms of absolute numbers, around 25% of collisions involve someone cycling on the bridge. If you throw in the junctions at each end, then this rises to around 28% and in terms of collision risk per daily trip, (and very crudely) a person cycling is about 5 times more likely to be hurt than a motor vehicle occupant (excluding motorcycles). 

It is worth noting that using casualty numbers can be volatile, especially the more serious collisions as the numbers for a section of road are usually low and can drastically change year on year, but we do have a situation which I think is reasonable to conclude that this is a place which is both subjectively and objectively riskier to cycle than it is to drive (or be driven) and not even the prevailing 20mph speed limit is enough to mitigate this.

If we return to LTN 1/20, Figure 4.1 suggests that even at 20mph, we need below 2,000 PCU/ 24hrs and so with 26,000 PCU/ 24hrs we need physical protection. With the width available and keeping two-way motor traffic (which buses at least require) means we have some hard decisions. In the short and medium term, I cannot see there is an infrastructure solution which is going to be politically easy to deliver on Battersea Bridge. "Just ban cars" really isn't a solution here.

400 metres east of Battersea Bridge is Albert Bridge (above). It is quieter at around 10,000 vehicles a day, although that's from estimated flows, but allowing for data quality, it is still going to be way over what most people would feel happy cycling with. However, with a carriageway of maybe just wider than 8 metres, it does give a little more overtaking space, although there are plenty of collisions involving people cycling here. 

My actual interest in this bridge is an historical quirk and that's the fact the bridge is currently subject to a 3 tonne structural weight limit. This is physically enforced by a 6'-6" (2 metres) width restriction, and that's after a strengthening project over a decade ago. My suggestion is that Albert Bridge be made a walking and cycling bridge and potentially (subject to structural engineering input) left accessible for ambulances. Yes, this means motor traffic displacement to Battersea Bridge in the short term, but it's far quicker to roll out than a new walking and cycling bridge or anything clever and radical at Battersea Bridge.

Of course, it's not just about a safe crossing, it's about the network and so such a plan to repurpose Albert Bridge needs to consider the local cycling networks either side. For example, to the south, some filtering could create some quiet routes to the bridge and to the north, maybe a two-way cycle track on Chelsea Embankment on the river-side would provide a really handy way of plugging into the bridge. 

If the network design were clever in how cycle traffic is dealt with through traffic signals on both sides of the river, the loss of time for some trips diverting to Albert Bridge could be offset with priority measures to keep people moving and essentially unravelling the motoring and cycling networks locally.

However, the main problem with all of this (as is usually the case) is political. To the north and owning Albert Bridge, we have the Royal Borough of Kensington & Chelsea which I think it is fair to say has an administration which is actively hostile to cycling. Transport for London owns Battersea Bridge which connects to TfL-managed roads, RBKC streets and to the south, streets managed by the London Borough of Wandsworth which traditionally hasn't been too bothered about cycling (it might be changing slowly).

This means that there are three organisations are intimately connected with varying levels of political backing for cycling which is why the response to collisions on Battersea Bridge has been so stop-start over the years.

For what it's worth, I have had a quick look at trying to design a little bit of a network around Albert Bridge which you can look at here, but essentially we have the following;
  • Filtering the area between Battersea Bridge Road, Prince of Wales Drive and Battersea Park.
  • Albert Bride becomes walking and cycling only.
  • South side of Chelsea Embankment becomes a two-way cycle track.
  • The southern end of Oakley Street (maybe 100 metres) becomes one way for general traffic south with a pair of one-way cycle tracks which crosses Chelsea Embankment to connect to the two-way cycle track and bridge.
Of course, that doesn't deal with the wider network, but it is a start and longer distance routes would converge on the quieter version of Albert Bridge Road which could become a cycle street to reinforce its priority as a key cycle route. Just my thoughts, but I do think this is the kind of thinking we need.

Sunday 30 July 2023

SuDS In The City: Esther Road, Leytonstone

In the southeast corner of the London Borough of Waltham Forest, a little project is nearing completion which is designed to alleviate a local flooding problem.

Esther Road is an unremarkable street in the north of Leytonstone, a community which was severed by the A12 in the 1990s as part of the M11 Link Road project, one of the last large road schemes in London of that era and which was bitterly protested against.

A street with car parking on both sides. A very long section on both sides are surrounded with kerbs with slots every metre or so leading to lower areas filled with soil.

What makes the street more interesting than the others in the area is some sections of the car parking on both sides have been repurposed for surface water management using a Sustainable Drainage Systems (SuDS) feature commonly known as "rain gardens" (above).

A coloured contour map with two red circles where the streets in question are situated.

The project covers three streets in the area which were hit by floods in 2021 and which are in a bit of a valley circled in red above - taken from the London Topographic Map. It's a problem which is only going to get worse with climate change and the project demonstrates that we're going to need lots of these little localised interventions in order to adapt to the warmer wetter conditions the UK faces.

A kerb line with gaps flush with the road surface through which water can flow into the rain garden.

In terms of design, the layout is pretty common whereby the rain garden areas are bounded by kerbs to retain the adjacent carriageway and there are regular slots to take the flows from it. In theory, the kerb could be flush with the road surface, but usual practice is to keep an upstand to dissuade drivers and to provide a detectable edge should someone walking require it (above).

A closer view showing the painting bed lower than road and footway level.

A closer look along the rain garden shows the existing kerbline (left) and new kerbline (right) supported with concrete backing, and what is nice here is the edge of this concrete has been neatly formed and faced with stones set into it. These stones not only look nicer than formed concrete, they'll also do a little bit to dissipate the energy of water entering the rain garden.

A view of the same pair of features from one side of the road a small circular feature can be seen with a red dome and a square manhole.

Elsewhere, we can see chamber covers set into the rain gardens and curious red domes (above). I'm not entirely sure how this all fits together for this project, but the covers will provide maintenance access to chambers which provide the ultimate connection to the sewer network. 

A closure view of a round saucer feature which has a smaller red slotted dome which is a water overflow.

The red domes are overflows (above) with a pipe extending downwards. Designs vary, but the general arrangement of a rain garden like this will be that water enters at the surface and soaks into the soil and then down into a stone layer and the ground itself. 

The stone layer is specially graded to provide 30% voids and so provides storage for flood water. If the inundation exceeds the ability of the surrounding soils to absorb, then the stone layer fills with water, then the soil layer fills and then it finally overflows to the sewer. The soil layer is also specially selected for the job to be free-draining, and in fact, rain gardens need plants which can cope with long dry spells!

A technical drawing cut through a rain garden showing a low level perforated pipe and an overflow structure.
© City Infinity

In ground where water infiltration is likely to be very slow, the bottom of the stone layer will have a pipe (called an underdrain) with lots of little holes to allow water to percolate into and drain away after the storm event, otherwise the stone layer will stay saturated and so be useless if another storm event occurs in a short time. Above is a typical detail of how that would look in long section - there will also be a layer of geotextile around the stone layer (a cloth-like material) which stops fine particles getting in and clogging the voids needed for water storage.

The project isn't just about the rain gardens, it includes a trial of rainwater planters for households as a way of keeping even more water away from the sewers, but there is also something in plain sight that unless you knew about it, you might miss. Have a look at this little video.

Yes, the water is soaking into the asphalt surface! The product is "SuperDrain" and is designed to allow water to drain through; and like the rain gardens, the substructure of the road has been rebuilt with stone layers designed to retain flood water with outfall structures designed to slowly release the water into the sewer system - I don't know the exact details, but I assume there is an underdrain of some sort.

The porous carriageway is an expensive thing to build, but it could be used for new-build developments. For Esther Road, it has been used to deal with an existing problem and in an urban area, we don't have the space to build ponds and other land-hungry solutions so we need to use existing streets. That to one side, rain gardens are a cost-effective measure which can be built all over and it is this kind of diffuse solution that can provide resilience if deployed routinely.

For more technical information on rain garden design, it is well worth looking at Designing Rain Gardens: A Practical Guide from Urban Design London, although if used outside of London, you need to use appropriate local storm intensity information - one for designers!

Saturday 3 June 2023

A Seaside Safari: Clacton-on-Sea to Jaywick Sands

I have a list of things to go and have a look at, and in April, I added the new Clacton-on-Sea to Jaywick Sands path to that list after seeing Danny Williams tweet about it. It didn't stay on my list long!

I was in the town of Clacton-on-Sea visiting family, and as I had my folding bicycle with me, I was able to take a couple of hours out for a morning ride before meeting them for lunch. I headed down to the seafront and then west towards the village of Jaywick.

The new 1km path is shared for walking and cycling which contrasts with the 2.3km route for driving on roads most people won't cycle on. At 3 metres in width, it's going to be tight when busy and so it would have been nice to have seen a little extra space. To be fair, the project did had to fit between the coastal defences. As can be seen in the photograph above, space has been taken from the back of the revetment to the defensive wall (left), plus the path runs in front of the secondary flood wall along Selsey Avenue

A black asphalt path with a sea wall left and another wall right with houses beyond.

The photograph above is a little further west at Burnham Court which gives a better view of the main coastal defence. The large concrete kerbs on the left of the path have been incorporated into the base of the landward side of the defence to create the space and on the other side of the path, there is a gravel drain for surface water.

A black asphalt path with a sea wall left and open land to the right. There is a large circular brick building looming large on the right..

It's a pretty featureless route given the flood defence on one side and golf course for most of the length on the other, but it passes a Martello Tower (above) which is of local interest.

A black asphalt path with a sea wall left and open land to the right. There are railings on the left which drop down as a high level path meets the main path.

Further west still, the edge of Jaywick can be seen (above) and to the left of the flood defence, the sand dunes marking the eastern end of Jaywick beach.

A black asphalt path with a sea wall right and open land to the left. A woman walks along in the distance next to someone using a mobility scooter with a covered "cabin".

The engineering of the path is excellent with a perfectly smooth surface and so even on a windy and chilly (for June) morning, there were people using wheels other than on cycles (above). The distance advantage over driving or trying to use the often narrow footways on the alternative road route, plus the path's quality gives people a real option to get to Clacton under their own, or e-assist power.

A lighting column to the right of the new path with long solar panels clamped to the side and a small wind turbine on top.

The route is lit using pv-solar and wind (above) which saved having to add power cables to the route which would have been very costly. I have used the system to power flashing traffic signs in the past and it proved reliable back then, so the technology must have improved by leaps and bounds since I last specified it.

A concrete path integral to a seawall to the right with a "beach bar" kiosk to the left with a beach. The path runs behind houses to the right.

Just beyond the end of the new path, the route joins the existing sea wall path which runs behind The Close and where the official NCN150 will turn north from to join Broadway via an existing ramp, although it is possible to just carry on west for a while longer.

The project was part-funded by the Getting Building Fund and is aimed to help provide better access for citizens in Jaywick (one of the most deprived places in the UK) to access employment and education as well as eventually providing a safe cycling route to Clacton station. More can be found on Essex County Council's project website.

I'll leave you with a video of the route from Clacton to Jaywick and then back again.