Since the start of 2019, the UK’s air quality has well and truly been in the spotlight.  In January the government published its Clean Air Strategy, which has been described as “ambitious” and includes new air quality targets and new powers for local government.
At the launch of the strategy, the Environment Secretary said: “While air quality has improved significantly in recent years, air pollution continues to shorten lives, harm our children and reduce quality of life.  We must take strong, urgent action.”
Evidence for why that “strong, urgent action” is needed, is rife.  Figures from DEFRA show that while Nitrogen oxide emissions fell by 3.4 per cent from 2016 to 2017, emissions of PM_2.5 only fell by 0.1 per cent showing a small decline between 2016 and 2017.
Emissions of PM_2.5 are particularly concerning as these particles are small enough to penetrate and lodge deep in the lungs, which can cause breathing problems and has been linked to asthma, heart disease, stroke, and lung cancer.
Road transport generates air pollution in two main ways: through exhaust emissions and through the particulates that come from wear to tyres and brakes.  The government’s main plan to reduce exhaust emissions is to clean up the vehicles themselves, replacing today’s predominantly diesel and petrol vehicles with ultra-low emission vehicles (ULEVs).  It has previously announced the sale of all new conventional petrol and diesel cars and vans must end by 2040.
Highways England has its own strategy for improving air quality, which includes a series of pilot studies looking at everything from optimising the flow of vehicles on the network to alternative fuels.  One of the pilots is the trial of a barrier that incorporates a polymer material with the potential to absorb nitrogen dioxide, to decide if such barriers should be installed on our network.  “We are also investigating if we can reduce the costs to construct a canopy, which is a tunnel-like structure designed to prevent vehicle emissions reaching our neighbours, to make this a viable solution,” says the strategy.
But Matthew Tompsett, Environment and Sustainability Lead at Kier Highways, says the emphasis on hard engineering solutions is ignoring the vital role green infrastructure could play in cleaning the air near roads. “It is widely recognised that green infrastructure can play quite a big role in removing particulates [PMs],” he explains.
Tompsett says “the jury’s out” on the ability of green infrastructure to deal with NOx emissions, but this will be less of an issue in the future as clean fuel technologies are introduced for new vehicles.  Particulates will still be a problem however, because they are also generated from brake disc and tyre wear.  
Trees and plants have a variety of mechanisms for absorbing particulates.  Some species have pores in the bark, while others have leaves with thousands of tiny hairs on their surface to trap the particulates.  “They end up in the soil or going down gulleys as part of the sediment,” explains Tompsett.  “The important thing is that they are not suspended in the air for people to breathe.  Green infrastructure is not the answer to all the problems, but it must be part of the longer-term solution.”
AECOM Associate Director Caroline Toplis agrees that green infrastructure could play a significant role in improving air quality – particularly to counter the combined effects of climate change and highways maintenance activities.  “With hotter and drier summers, there is likely to be a greater amount of dust and particulates in the air, and the atmosphere is expected to be more ’stagnant’ at times, therefore any highways construction and maintenance activities will worsen this effect,” she explains.  “Ensuring green infrastructure is always integrated alongside and in conjunction with highways infrastructure will help to tackle air pollution, and provide cooling and shading benefits to help reduce some of the other impacts of climate change.”
Toplis also believes highways maintenance firms have a responsibility to make sure their working practices are not contributing to the problem.  “Air quality impacts can be made worse during roadworks due to idling and slow-moving vehicles or can shift the problem to elsewhere as people try to avoid the congestion caused by roadworks,” she says.
This is something the highways maintenance sector is addressing, according to Skanska Sustainability Manager Ed Godsiffe.  “Our key negative impact is how we manage traffic when we are doing the work,” he explains.
VolkerHighways Environmental Advisor, Miles Durrant, agrees, saying one way the highways maintenance sector can contribute to improved air quality is to cut down the amount of time cars are forced to slow down and sit with their engines idling at roadworks.  He advocates using warm lay asphalt rather than traditional hot rolled products so the road can be reopened more quickly once the work has been done.
Godsiffe says the highways maintenance community already has initiatives to help reduce air quality issues related to congestion and traffic management, including better work planning, collaboration with utilities providers, and innovations that improve traffic flows based on better understanding of real-time data.  “We’re using existing data better,” he says. “Now that we can get far more up to date information on traffic, we can plan works accordingly.”
Toplis has identified some simple steps the industry is taking, such as moving from the use of diesel generators on site – responsible for an estimated 25% of site emissions – to hybrid generators; using appropriately sized generators and plant; using mobile lighting rigs powered by solar or hydrogen fuel cells; and planned logistics that lead to fewer vehicle movements and deliveries.”
VolkerHighways is also investing in alternative power options.  Its parent company VolkerWessels has its Sustainable Advantage initiative, to source plant and equipment with lower emissions with the first item being LED lighting towers.  Generators are next on the hit list, says VolkerHighways Environmental Advisor Miles Durrant: “There are hybrid options available, and you can get some that are powered by solar panels, but the concern is whether they are just a novelty, or if they can generate enough power to supply energy in the dark winter months.  But they are definitely part of the future.”
VolkerHighways has invested in electric vehicles, including company cars and vans.  “We did some trials looking at how much the vans are used throughout the day, and worked out that two of them could be replaced with electric,” Durrant explains, “and we have used them on our joint venture in London, but some of our contracts are too rural; the drivers have to go long distances with no option for charging.”
He adds that it is difficult to know whether to commit to specific technologies or fuels: “The manufacturers themselves are concerned about which route to go down.  They don’t want to pile their investment into electric if that’s not what everyone’s adopting.  Are we going to commit to invest in an electric fleet and find out that’s not what is going to be used in two years’ time?”
If, as the government plans, diesel and petrol vehicles disappear completely from our roads, the air pollution problem will be significantly reduced.  But that is some way off, and the entire industry has a responsibility to do what it can to improve air quality – and save lives.
The highways sector has a major part in help tackling the issues around air quality in the way we design, construct and manage the highways network.  This offers both a challenge and opportunity to those who work in this area.  HTMA can play a major role by helping to understand the issues around air quality and by offering and sharing best practice and solutions.  By doing this we feel that we can help tackle both the health and environmental issues posed by poor air quality on our highway networks.”