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Cycle superhighway gets life-saving segregation

With more than 60 injury-causing collisions on London’s cycle superhighway 2 every year, TfL has turned to a clever segregation system to save lives.

Cycle use in London has grown significantly since the introduction of the cycle superhighway network.

CS2, running along the A11 between Aldgate and Bow roundabout, was one of the first implemented and is used by 2,000 cyclists in each direction daily.

Cycle deaths on London roads average 16 a year, having peaked at 33 in 1989. Last year alone, eight cyclist deaths were reported. In light of this, Transport for London announced plans to bring forward its improvements to the CS2 route, in line with updated London Cycling Design Standards.

Historically, traditional materials and forms of cycleway construction involved sequential processes of laying two kerb lines followed by paving infill and reinstatement. This approach would necessitate operations undertaken from each side of the new island, resulting in substantial narrowing of the traffic lanes to accommodate safety zones for working areas.

TfL’s contractor Ringway Jacobs and precast specialist Charcon took a collaborative approach to come up with an innovative solution that would replace the use of these traditional methods.

Radical approach

Technical experts from each of the project partners worked together to come up with a radical new approach that would achieve four core objectives.

These were to safeguard cyclists and other road users, to reduce construction time on site, to use construction methods that reduced exposure to and disruption of traffic, and finally to minimise the project’s carbon footprint.

Charcon London cycle superhighway 0842

Charcon London cycle superhighway 0842

The project is creating physical islands in each direction separating cyclists from vehicles

The biggest proposed change to the cycleway was the introduction of physical islands in each direction separating cyclists and vehicles within the highly constrained strategic corridor.

In partnership with Ringway Jacobs, Charcon’s technical department came up with a 500 mm-wide Eco Countryside Cycle Kerb segregation system as an alternative to the granite kerb and concrete block paving inlay previously used.

The new cycle kerb replicates the aesthetics of natural granite but is made from 82 per cent recycled and secondary material content, including Cornish granite secondary aggregates and washed copper slag.

“Being installed on both sides of the carriageway, the integrated system can safely segregate cyclists from passing traffic, even when on the blind side of a lorry or bus”

Samples of reconstituted granite were manufactured to demonstrate that a uniform, high-quality finish could be consistently and economically produced. In addition, Charcon provided examples of where the material had been used in London to show how it performed over time in similar conditions.

The bespoke kerb’s design features a bull-nose edge running along the carriageway, capable of withstanding vehicular overrun, while a full batter profile on the cycleway side reduces the chance of cyclists catching a pedal.

The top has a patterned finish to give a blockwork appearance. The profile is optimised to include a frog in the base to improve the key into the bedding material, reducing the weight of the unit and helping placement.

Being installed on both sides of the carriageway, the integrated system can safely segregate cyclists from passing traffic, even when on the blind side of a lorry or bus.

The segregation units were manufactured as a one piece unit in a controlled environment so they could be placed in one operation. Using factory manufactured units gave a high degree of quality control for the client’s requirement of a ‘granite-like’ surface to match the materials present on the route.

Huge disruption reduction

To meet the objectives of the project team, the construction methods needed to ensure disruption to road users, cyclists, pedestrians and local businesses was kept to a minimum.

Charcon London cycle superhighway 240815

Charcon London cycle superhighway 240815

Offsite work reduced the impact on road users

The primary challenge to overcome was minimising working width requirements on the traffic side. To achieve this, the units were placed by machine from the footpath, reducing the encroachment into the carriageway from 2 m to 0.5 m.

This eliminated the requirement to saw-cut and break out to virtually full depth to construct kerb lines, reducing the likelihood of damaging existing services and keeping noise and dust generation to a minimum.

Instead, the existing cycleway surface was planed to a depth of 50 mm before placing the new units from the footpath side onto a bed of concrete with 10 mm-sized aggregate, or sand cement screed where depths dictated. Operatives drilled holes for the dowels that were then bonded with resin and the surface sealed.

On completion, alterations were made to the footpath, with the kerb line re-laid as necessary, before the cycleway and main carriageway were resurfaced.

Offsite speed

The one-unit concrete segregation system meant much of the work could be done off site, thereby speeding up construction by around 50 per cent and reducing the impact on road users.

“The bespoke design offered a cost saving of 25 per cent and a 33 per cenr reduction in carbon footprint versus natural granite imported from China”

Fewer materials were required on site, reducing the space needed for storage. Furthermore, the one-unit system ensured surfaces matched both across and along the island. The result was a greater consistency of colour between the units than is usually achieved using natural granite and block paving infill.

In total, 16,000 linear metres of the kerb were supplied for the CS2 project. The bespoke design offered a number of quantifiable benefits, including a cost saving of 25 per cent and a 33 per cent reduction in carbon footprint versus natural granite imported from China.

It also reduced the requirement for raw materials, while manufacturing units in the UK reduced the transportation carbon footprint and delivery times.

Charcon London cycle superhighway Eco Countryside Cycle Segregation System

Charcon London cycle superhighway Eco Countryside Cycle Segregation System

A full batter profile reduces the chance of cyclists catching a pedal

Installation time for the island was reduced by 50 per cent, which in turn had a positive impact on the cost of preliminaries and traffic management.

The project, which began in April 2015, completed in April this year. Overall, the development of the new unit has saved about £150,000 over the traditional approach.

However, when it comes to quantifying the number of lives that will be safeguarded in the future thanks to the new segregation system, the saving is immeasurable.

Mike Davies is specification and major projects manager at Charcon, the commercial hard landscaping division of Aggregate Industries

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