National Highways Failing Nature

When road schemes are proposed, National Highways is meant to avoid harming nature in its designs. What it can’t avoid harming, after it has minimised any impact, it is supposed to compensate for. This is called ‘mitigation’ and is a legal requirement, especially with the introduction of Biodiversity Net Gain (BNG), where developers are required to create more biodiversity than they destroy. The amount of mitigation and BNG are important considerations when deciding whether to approve the scheme or not.

However, 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?

In fact, it seems that National Highways promising new trees in mitigation and then failing to deliver them when carrying out the work is something of a regular occurrence. 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 years. The worst outcome was at the Chowns Mill A45 / A6 junction, where 75% of the trees planted died. National Highways only provided data for nine of its thirty-eight big road projects, so the actual number could be significantly higher.


The £1.5 billion A14 Cambridge to Huntingdon road scheme opened to great fanfare in 2019, a year earlier than scheduled. However, it was revealed in 2021 that over half a million trees planted alongside the A14 had died. This was three-quarters of the 850,000 saplings planted to replace veteran trees felled for the project. National Highways initially blamed the Government for pressuring them to open the road early. They then were forced to backtrack and apologise. The cost of replanting the trees will be around £2.9 million and will come from taxpayers. Meanwhile local environmental group, the Great Ouse Valley Trust (GOVT), has not only criticised the failed tree planting, but also the littering caused by thousands of discarded plastic tree guards. It is also concerned about river bank erosion caused by the road scheme.


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) reports.

POPEs are done one and five years after road schemes are opened, although National Highways do not publish them promptly. Two five-year POPE studies were recently published, showing that promised mitigation had failed.

Completed in 2014, the road was widened from a dual two-lane carriageway to a dual three lane carriageway. National Highways released its five-year post opening project evaluation in 2024, 10 years after the road opened!

The five-year evaluation by National Highways shows that some of its proposed mitigation has failed, blaming it on the 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 and as in this case, collapsed and disappeared.

What guarantees are put in place to ensure that saplings and other landscaping are properly maintained to allow them to reach maturity? Why didn’t National Highways have safeguards in case Carillion went bankrupt to ensure the trees were looked after?


Despite this scheme passing through The Brecks, an area of international and national nature conservation status, National Highways’ five year evaluation found a catalogue of failures with the promised mitigation.

The project was predicted to have a “large adverse” impact on landscape and biodiversity, yet the POPE report found that landscape, ecology and nature conservation were all “worse than expected”.

More shockingly, they found “no evidence of recent species-rich grassland management or maintenance having been undertaken” and “little evidence of woodland management taking place.”


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. National Highways also needs to be monitoring 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.


Image used of an aerial view of a new link road under construction in Lancashire by Neil Michell /


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