Decarbonizing Scottish Roads

How can we best manage and maintain existing roads and associated infrastructure? This was the question driving Scotland TranServ, in which WSP worked as a joint-venture partner with Balfour Beatty, collaborated with the independent auditor, PAG and our client, Transport Scotland. The joint venture combined expertise in consulting design, maintenance and construction services to manage and maintain all the motorways and Trunk Roads in the North West and South West of Scotland between 2006 and 2020.

Supporting Transport Scotland’s Transport Asset Management Plan

Scotland TranServ supported Transport Scotland in its delivery priorities:

Meeting Transport Scotland’s wide-ranging priorities for the road network required us to think differently. Our engineers worked closely with the supply chain to devise and develop innovative techniques and solutions to reduce disruption, improve journey times and make our roads safer whilst considering sustainability at every turn. This often required us to push the boundaries of individual products, blend existing systems and develop new software and devices.

A lightbulb moment

For example, on taking over the South West Scotland unit contract, Scotland TranServ conducted an extensive review of assets across the Trunk Road network. The review identified that 47% of the high mast assets were reaching the end of their serviceable life. Some units were up to 50 years old.

The project team could have simply gone with tradition and replaced these ageing assets to ensure they were reliable, but it was important to the team to deliver a generational change in the way our motorways are lit and the way we approach maintenance. In particular, we saw an opportunity to transform the M8 corridor (Scotland’s busiest motorway) into an energy-efficient corridor that will offer long-term environmental benefits, improve safety and represent the best value for money. 

Innovation was key if the project team were to significantly reduce energy usage and future-proof the network. Working with the existing supply chain, our lighting team identified several cutting-edge products that could be combined. The Central Management System (CMS) was born, combining LED lighting with active monitoring and complete control over lighting levels. This enables faults to be reported instantaneously and the most efficient lighting levels to be obtained.

Scotland TranServ replaced 2,000 lanterns in the high masts on the M8 with LED lighting. With the CMS implemented, these cut energy consumption by 70% – enough to power an equivalent of around 600 homes. Compared to the old high-pressure sodium lights, there was a saving of 1,261 tonnes of CO₂e – the equivalent of 232 cars in annual carbon emissions. Our contractors also recycled around 64 tonnes of steel.

The new lighting reduces ‘sky glow’ light pollution, which can impact wildlife and obscure views of the night sky. LED lanterns are perceptibly brighter than high-pressure sodium lights while also directing more of their illumination downwards.

Motoring accident statistics showed encouraging signs. Compared to the previous year, there was a 26% reduction in the number of accidents during hours of darkness.  

The new, longer-lifespan lighting has reduced the maintenance burden. When coupled with energy saving, replacing the lanterns will save around £25 million over the lifetime of the complete system (around 20 years).

Reducing maintenance also improves health and safety, with engineers making fewer visits to the busy motorway to replace lanterns. Resulting in a reduced need for traffic management during these visits, making it better for motorists too. 

Our successful programme on the M8 was subsequently extended to include the A78, M74 and M77. In total, Scotland TranServ replaced over 12,000 lanterns across the South West network.

Minimising carbon emissions and promoting the use of sustainable materials in road maintenance is a shared priority of Transport Scotland and WSP. As Scotland TranServ identified major road maintenance schemes, particularly those on remote Trunk Roads, the project team found that many of them still contained tar. 

Phased out by the 1990s, tar is now classified as special waste and, therefore, a costly disposal process to mitigate its negative impact on the environment. 

TranServ’s pavement team collaborated with their specialist supply chain and researched the market to identify sustainable solutions to this problem– including in-situ and ex-situ methods that had the potential for use on the South West network. In-situ recycling involved a chain of on-site processing and paving machinery that would process the existing pavement materials into new material. Ex-situ recycling involved a similar process, but materials would be taken to a nearby facility for processing. Both could be quickly implemented and were capable of delivering significant environmental, economic and safety benefits. 

For the first time on the Scottish Trunk Road network, the Transport Asset Management project team used a modernised in-situ recycling method at Polneul on the A76. With 758 tonnes of special waste for disposal, 38 construction wagons would have had to complete a 317-mile roundtrip from the site to the nearest disposal facility at Middlesbrough – a total of over 12,000 miles. By using in-situ recycling, we saved the equivalent of lorry miles travelling from Glasgow to Christchurch in New Zealand. This reuse of material also minimised the import of virgin aggregates – conserving resources, speeding up construction and reducing plant and transportation costs.