This is the first part of a two parter. I apologise in advance for the length and dryness of this content and the colourfulness of my drawings. Enjoy.

I usually try to keep the content of this blog specific to London or to the urban realm in general, but I do think it’s useful to use real world examples once in a while, and so I’m going to talk about a public realm issue close to my heart.

The London Borough of Richmond-Upon-Thames (LBRUT) have been working through a multi-year process of coming up with a plan for the future development of Twickenham town center, the Twickenham Area Action Plan. They have spent the last 18 months doing that thing that committees do, trying to please everyone and in the process pleasing nobody.

Part of the Twickenham Area Action Plan is the catchely named Twickenham Street Scene and Highways Scheme Consultation which outlines the public realm changes:

Over the last 18 months the Council has undertaken extensive evidence gathering and consultation with local people around the future of Twickenham Town Centre. The public supported the general principles within the Twickenham Area Action Plan to improve the town centre environment by reducing the dominance of traffic. Proposals have now been developed that take these principles forward with a detailed scheme.

The overview document gives the main objectives of the plan to of which I broadly agree:

Overall aim of the scheme is to regenerate the town centre by creating higher quality streets, helping pedestrians and reducing the dominance of traffic.

• The scheme seeks to improve the town centre for all users. The impact on traffic has been carefully assessed to ensure changes would not unacceptably delay vehicles; 
• A 20 mph limit throughout the town centre will reduce the impact of motor traffic and improve safety, but maintain a steady flow of traffic;
• Bus lanes in King Street will be removed and bus stops relocated to create room for the footways to be widened.  It will also not be possible to turn right into Water Lane from King Street during the busiest times of the day; 
• Footways will be widened and street clutter removed as part of a comprehensive scheme of new paving, street furniture, lighting and landscaping, which takes account of needs of all users including disabled people;
• Pedestrian ‘countdown’ will be provided at all signal junctions to indicate the time allowed to cross the road;
• Advance cycle stop lines will be provided at signal junctions and the level of cycle parking will be increased;
• The quality of bus stops will be improved and screens at stops will show when buses are due to arrive;
• The number of car parking spaces and loading bays will remain the same; and
• There will be CCTV enforcement of moving traffic contraventions.

All very noble and worth while improvements (except maybe for pedestrian countdown). I won’t go into the details of the action plan, Tim Lennon has done an excellent job of that already, instead I want to look at how the plan was come up with, or rather, look at how, using my brief understanding of the Dutch principles of Sustainable Safety, we might arrive at a plan.

Investigate street usage

The first step is to identify the major traffic routes and desire lines, and decide the function of each street.

Usually you’d do this by observing and asking people where they go and what they do, where’s easy and where’s hard to get to, etc. but I’m not in a position to carry out such research so I’ll do it the old fashioned way and make it up.

So let’s look at the territory.

Map of Twickenham town center, showing the three main through routes, shopping streets in purple, areas of residential housing in yellow, and schools in pink.

Twickenham town is centered around King Street, which is not only the main shopping street but also the crossing of the A310 and A305. To the north we have the main through route of the A316 which links the M3 to the southwest with A4 to the northeast and kind of acts like a bypass other than for traffic heading down the A310 (Cross Deep) towards Kingston. To the southeast we have the river Thames forming a natural barrier which is only crossed in the north at Richmond (A305) and Twickenham (A316) bridges and 2 miles to the south at Teddington lock.

The main problem Twickenham town suffers from is the through traffic of the A310 and A305 having to travel down King Street. The A305 is partially augmented by the A316 and so should be a good candidate for traffic reduction techniques, but traffic travelling from Richmond and Isleworth to Kingston have to no option but to travel down through the town center down King Street. Since this traffic can not be moved and is unlikely to be able to be reduced purely by the Twickenham scheme alone, it must be catered for within King Street.

Church Street is a small shopping street opposite the end of London Road that has been given a tactile road surface and is (in theory) closed to traffic other than deliveries and blue badge holders. It has been a huge success for the businesses along the street and for the vibrancy of the town center and the riverside area. This success should be looked on to be magnified into the towns other shopping areas.

The railway, as well as providing excellent links to surrounding areas and central London, also acts as a northern boundary to the town being an obstruction with limited places to cross.

Identify street types

With this information we can now prioritise each road in the town based upon it’s desired usage. The first principle of Sustainable Safety is that of mono-functional roads, so our aim is to define each road with only a single use.

This also leads to the idea of reducing the number of conflict points on the network. Conflicts occur where vehicles meet, so by reducing the number of junctions on busy roads, we can reduce the danger and at the same time improve traffic flow.

Through routes are shown in dark blue, distributor roads in dull orange. Shops are in purple and the railway in cyan.

Here we have identified the two main through routes, the A316 to the north of the town center acting as an east/west bypass, and the A310 going north/south through the town center. Although traffic will want to use the A305, this route is better served by the A316 and so by redesigning the A305 through the town we can promote the idea that the other route is the better/faster through route.

So it looks like King St will have to remain a combined busy shopping street and through route. It also has bus stops for the towns bus routes, so these will also need to be catered for.

We also want to increase the success of the partially pedestrianised Church Street and reduce the dominance of the London Rd/King St/York St junction. We can do this by removing the junction entirely. How do we do that? By removing one of the roads that joins the junction, we can either remove York Street or the end of London Rd too. Time for a close up.

As you can see on this piece of Google Map, the junction is the heart of the town but also a nightmare for pedestrians, cyclists and motor vehicles. But there is a solution, right turns from London Rd into York St and left turns from York St into London Rd are forbidden, they must take place via Arragon Rd which joins both together from their previous junctions. Arragon Rd is a wide non-descript road that does not contain shops or cafes but does contain the entrance to Twickenhams multi-story car park (behind the Waitrose), it is an ideal road for diverting traffic to so as to remove the London Rd/King St/York St junction.

Another problem is that coming from the north via London Road, if you want to get to Hanworth via Heath Road but don’t want to get caught in the rush hour traffic, you can cut through the residential streets instead of going down King Street.

This is easily tackled again by the first principle of Sustainable Safety. These residential roads are access streets providing access to the houses upon them, so following the rule of mono-functionality means that they should not act as through routes to motor vehicles.

This leaves us with the following set of blue through roads optimised for vehicle throughput, green access roads just providing access to residential areas, and dull orange distributor roads linking access roads to the through routes.

The details

Now that we’ve mapped out our domain, we can apply suitable treatments to each road and to the junctions between each road. First we need to know the traffic volume of each road so we know the suitable treatment as laid out in our Cycle Provision Cheatsheet (as derived from the CROW bicycle manual).

As I’m not in a position to sit around counting traffic, that’s something for the council to do on my behalf with my tax money, but a quick Google search later and we do have some numbers from 2011 which if we cross reference with the provision cheatsheet we get the following:

Road          | Type               | PCU/hr | Provision
--------------------------------------------------------------------------
King Street   | Urban through road | 1,738  | Cycle track or parallel road
Heath Road    | Urban distributor  | 656    | Cycle lane or track
Cross Deep    | Urban through road | 720    | Cycle track or parallel road
London Road   | Urban through road | 476    | Cycle track or parallel road
Richmond Road | Urban distributor  | 590    | Cycle lane or track

And then looking at the intersections between each of these roads we get the following junction treatments:

Intersection                     | PCU/hr          | Provision
-------------------------------------------------------------------------------
London Rd, Arragon Rd            | 476, 476        | Roundabout
Arragon Rd, Richmond Rd, York St | 476, 590, 1,738 | Roundabout or lights
Kings St, Heath Rd, Cross Deep   | 1,738, 656, 720 | Roundabout or lights

One alteration from the CROW guidelines is choice of a roundabout on the newly altered junction between London Road and Arragon Road. With the removal of through traffic from London Road and all traffic going via Arragon Road, this junction no longer has to perform the same task as before, but instead has to provide for:

1. Access for deliveries into the pedestrianised end of London Road.
2. Bus services which terminate at Arragon Road being able to turn around.
3. Access into Railway Approach for traffic coming from the north.
4. Provision for pedestrians and cycles to easily continue straight on down London Road.

So instead of just providing a right of way junction into this closed end of London Road, we will instead provide a roundabout to allow buses and traffic to u-turn and to provide safe pedestrian and cycle crossings.

The other two junctions can be either traffic lights (TCS) or roundabouts. I personally prefer Dutch style roundabouts where possible given the choice, but I fear the arms of the York St junction is slightly offset and with road width limited in space for a roundabout able to cope with turning buses. The Heath Road junction is ideal for a roundabout, my only concern would be the lack of right turning traffic from Heath Road into Cross Deep might be an issue for traffic flow. Without further studies of traffic movement we won’t know the answers to these questions, so let’s just go with our gut instinct.

The final junction is the now pedestrianised crossing between Church Street and London Road. This could be a wide Zebra with a center refuge, but with the volume of traffic, a single span Tucan crossing is most likely preferable.

The plan

And so that leads us to our final plan for the town center.

• Blue line: Through route, this should facilitate through traffic and prioritise separation of motor traffic and vulnerable road users.
• Orange line: Distributor roads. Facilitate interchange between through route and local roads, vehicles should be traffic calmed.
• Green line: Access roads, provide non-through route access to destinations.
• Red line: Pedestrian and cycle permeability that is blocked to motor traffic.
• Yellow dot: Single lane roundabout with cycle and pedestrian crossing facilities.
• Black dot: Traffic light control system with cycle and pedestrian crossing facilities.
• Purple dot: Bus stop.

In part two we will look at how this plan might on the ground as we move out of the planning phase and into the design phase.