National Highways failing nature

When National Highways plans and delivers road schemes, it is meant to avoid harming nature and then minimise any impact, which it is then supposed to compensate for. This is called “mitigation” and is a legal requirement.

In addition, new rules about Biodiversity Net Gain (BNG) require developers to create more biodiversity than they destroy. The amount of harm, mitigation and BNG are important considerations when deciding whether a scheme should go ahead.

It is very easy to make promises when you are trying to persuade a decision maker, or to buy off or weaken opposition. But what happens when these road schemes are opened? Are the measures delivered, and does the mitigation actually work?

The reality seems to be that National Highways regularly promises new trees in mitigation and then fails to deliver and look after them.

The A14 debacle

The £1.5 billion A14 Cambridge to Huntingdon road scheme opened to great fanfare in 2019, a year earlier than scheduled. To make way for the scheme, 400,000 trees and shrubs were cleared¹, but National Highways said they would replant more trees than they had felled. However, Sky News revealed in 2023 that three-quarters of the 850,000 saplings planted to replace veteran trees felled for the project had died². This would be around 600,000 dead trees. National Highways said it would replant the trees at a cost of £2.9 million.

In November 2023, National Highways had to backtrack and apologise after one official claimed that the high numbers of dead trees on the A14 happened because the government had pressured it to open the scheme early³.

Meanwhile local environmental group the Great Ouse Valley Trust not only criticised the failed tree planting, but also the littering caused by thousands of discarded plastic tree guards⁴. It said it was also concerned about river bank erosion caused by the road scheme.

In June 2025, the BBC reported that residents had taken to planting their own trees along the side of the road to replace dead ones⁵. At the same time, Cambridgeshire County Council complained⁶ National Highways had failed to update them on the replanting plans despite “numerous requests”. and that replanting “appears to have been in a few limited areas”.

The Guardian picked up the story⁷ in July 2025 stating that three attempts at replanting had failed, with local councillors asking the very good questions: “How can they be allowed to get away with this? How can anyone have confidence in promises about environmental mitigations in any national infrastructure projects in the future?”.

National Highways’ track record elsewhere

A freedom of information request by The Times in 2023 revealed that more than 400,000 trees planted to compensate for road projects had died within years⁸, including what National Highways said was 45% of the trees on the A14 scheme.

The newspaper pointed out that National Highways only provided data for nine of its 38 big road projects, so the actual number could be significantly higher.

The worst outcome by percentage was at the Chowns Mill A45/A6 junction, where 75% of the 2,800 trees planted died. A further replanting effort has also failed, with a third attempt scheduled to take place in November 2025⁹

Experts criticised National Highways for focusing too much on planting large numbers of many trees, rather than looking after them subsequently. John Parker, chief executive of the Arboricultural Association, said “the focus still needs to move further towards tree establishment than planting, looking at ensuring maintenance and tree aftercare plans are in place for such projects.”

Post Opening Project Evaluations

National Highways carries out reviews on major road schemes to measure their impacts against its original objectives. These are called Post Opening Project Evaluations (POPE). The POPE studies include evaluating whether environmental mitigation has succeeded or failed.

POPEs are done one and five years after road schemes are opened, although National Highways does not publish them promptly and is now moving to three-years after reports. Recently published five-year POPE reports show that promised mitigation on three schemes had failed.

A23 Handcross to Warninglid

In this scheme, the road was widened from a dual two-lane carriageway to a dual three-lane carriageway. It was completed in 2014 but National Highways released its five-year POPE 10 years later – in 2024¹⁰.

The report showed that some of the scheme’s proposed mitigation had failed, which it blamed on the 2018 collapse of contractor Carillion: “The project was constructed within the existing highway boundary as far as possible and new landscape mitigation planting was provided. However, the collapse of the construction contractor meant that at five-years after, the landscaping was in poor condition.”

This case highlights the dangers of National Highways devolving responsibility to contractors for maintaining planted trees, long after the construction. What guarantees are put in place to ensure that saplings and other landscaping are properly maintained? Why didn’t National Highways have safeguards in case Carillion went bankrupt to ensure that the trees were looked after?

A11 Fiveways to Thetford dualling

National Highways’ five-year POPE found a catalogue of failures with the promised mitigation for this project, which passes through The Brecks, an area of East Anglia of international and national nature conservation status.

The project was predicted to initially have a “large adverse” impact on landscape, which was expected to reduce to “moderate adverse” after 15 years as mitigation planting matured. However, the landscape was evaluated as “worse than expected” with a risk that mitigation measures may not reach their potential.

With mitigation in place, the impact of the project on biodiversity was predicted to be neutral overall. However, the POPE found poor record keeping, as well as “no evidence of recent species-rich grassland management or maintenance having been undertaken” and “little evidence of woodland management taking place”. As a result, ecology and nature conservation were also “worse than expected”¹¹.

A21 Pembury to Tonbridge dualling project

This scheme caused the destruction of nine hectares of ancient woodland, of which just over three hectares were designated as a local wildlife site and a potential site of special scientific interest for fungi. It was nevertheless predicted to result in a “moderate adverse” impact on biodiversity after proposed mitigation including “translocated” woodland and hedgerows, enhancement of 26 hectares of woodland and new species-rich grasslands and new heathland.

However, the five-year after plan noted that species-rich grasslands and two woodland plots were “struggling”, implicitly because of poor long-term aftercare, while the “experimental” translocation of fungi had failed and the heathland was in such poor condition that it was planned to turn the area into a grassland.

What’s the solution?

Of course the best way to protect nature is not to cause harm in the first place, by not approving large road schemes that trash habitats and woodlands. For road projects, tree planting is not an easy fix. Ancient woodland and veteran trees are literally irreplaceable, and should always be avoided, however road schemes like the Lower Thames Crossing will damage several ancient woodlands. If tree planting is proposed, trees need to be planted at the right time of year, and need careful maintenance and monitoring for years afterwards to thrive, especially with extreme weather becoming more common with climate change. National Highways needs to write guarantees into its contracts so that contractors have to both deliver and maintain mitigation measures, with safeguards in case they go out of business.

It also needs to monitor completed schemes more frequently so that any problems can be caught at an early stage. Otherwise, these important and legally required mitigation measures risk failing time and time again.

Planning Inspectors and ministers must also be more sceptical and vigilant about the promises made by National Highways. Too often, environmental destruction is ignored, as decision makers are all too willing to accept National Highways’ promises on mitigation and compensatory planting or habitat creation, despite their abysmal track record.

Photo: Shutterstock

1. Highways England to replace hundreds of thousands of failed trees from A14 Cambridgeshire upgrade – ITVX, 19 March 2023 ↩︎
2. Half a million trees have died next to one 21-mile stretch of road, National Highways admits – Sky News, 18 March 2023 ↩︎
3. National Highways ‘sorry’ over A14 Cambridgeshire tree-death claims – BBC News, 3 November 2023 ↩︎
4. Protest after A14 project left dying trees and plastic waste – The Hunts Post, 9 April 2023 ↩︎
5. Residents plant own trees to replace dead A14 ones – BBC News, 17 June 2025 ↩︎
6. Report to Cambridgeshire County Council on A14 Cambridge to Huntingdon Improvement Scheme,17 June 2025 ↩︎
7. How a £1.5bn ‘wildlife-boosting’ bypass became an environmental disaster – The Guardian, 5 July 2025 ↩︎
8. 400,000 trees planted in roadwork schemes have died – The Times, 4 August 2023 ↩︎
9. More dead plants on A45 Chowns Mill roundabout leads to concerns from councillors and MP, Northamptonshire Telegraph,13 February 2025 ↩︎
10. a23-handcross-five-year-post-opening-evaluation.pdf ↩︎
11. a11-fiveways-to-thetford-five-year-post-opening-evaluation.pdf ↩︎