Significant is not severe: refusing on highway grounds.

The appeal and the challenge

Cherwell refused the scheme with 15 reasons, many on highways. After a nine-day inquiry, the inspector made a series of findings that, on their face, favoured the appellant. Queues on the Junction 11 slip road would stay within acceptable limits and raised no unacceptable safety issue. The residual cumulative impact on the local network would be significant, but not severe.

The difficulty lay in Banbury itself. The modelling predicted significant extra congestion on Southam Road and Hennef Way. The appellant offered a contribution of about £907,000 towards Hennef Way, but no specific scheme had been identified. The inspector could not tell whether the money would work, found that effective mitigation had not been demonstrated, and held that the contribution failed the regulation 122 tests. He dismissed the appeal.

The appellant argued that this was a refusal on highway grounds, made after the inspector had found the paragraph 116 threshold was not met. The Secretary of State argued that the refusal rested on a wider mix of harms, so paragraph 116 did not apply.

What the court decided

1. Paragraphs 115 and 116 are read together. Where paragraph 116 applies, it supplements paragraph 115. Development should not be refused on highway grounds unless the safety impact is unacceptable or the residual cumulative impact is severe (judgment, paragraph 21).
2. "On highway grounds" does not mean "only on highway grounds". Most refusals rest on several reasons. Confining paragraph 116 to cases where highways is the sole reason would make it almost meaningless (paragraph 23).
3. The minimum test. Paragraph 116 applies at least where highways impacts are the principal or main reason for refusal, and the balance would probably have come out differently without them (paragraph 26). The court considered other possible tests but did not need to choose between them.
4. That test was met here. Highways was the only harm given substantial weight, and the inspector's own reasoning showed it drove the outcome (paragraph 27).
5. The error. The inspector should have asked two questions at the balance: am I refusing on highway grounds, and is the paragraph 116 threshold met? The answers were yes and no. He then had to recognise that national policy said permission should not be refused on that basis. He could depart from that with a rational planning reason, but he did not consider it at all (paragraph 28).

A separate ground also succeeded: the inspector had not weighed the scheme's biodiversity net gain in the balance. It made no difference to the outcome, because the decision was quashed anyway.

Why it matters

Practitioners have long worked with a two-tier vocabulary. Below the threshold, traffic harm is real but tolerable. Above it, refusal is justified. Greystoke confirms that the distinction has practical consequences. An inspector who places an impact below the threshold cannot then refuse mainly because of it, at least not without confronting paragraph 116 and giving a reason to depart from it.

Equally important is what the court did not say. Highways impacts below the threshold still count. They must be weighed under the statute, and the weight is for the decision-maker (paragraph 28). Non-severe harm can still tip a balance when other harms are also in play. What it cannot do, without explanation, is carry a refusal on its own.

The case also exposes a tension that many schemes run into. The inspector's real concern was not the size of the impact but the absence of a credible fix. An unidentified scheme funded by a contribution failed regulation 122, so the mitigation fell away. Yet the impact without mitigation was still judged not severe. Having made that finding, the inspector could not treat the absence of mitigation as an indirect basis for refusal without addressing paragraph 116.

The limits of the judgment

The decision was quashed for a failure to consider policy, not because the outcome was wrong. On redetermination, the inspector may still dismiss the appeal, provided the balance confronts paragraph 116 and any departure is properly reasoned. The court also set a minimum test, not a complete one.

There is a further complication. The judgment applies the December 2024 Framework. Since August 2026, the transport tests sit in policy TR6 of the new 2026 NPPF. If TR6 keeps the structure of a threshold for refusal on highway grounds, the reasoning in Greystoke should carry across. Check the current wording before relying on it.

What to take into the next scheme

• Address severity directly. For a promoter, a clear finding that the residual impact is not severe carries greater significance following this judgment. The modelling should be capable of supporting that finding on its own terms.
• Tie contributions to a scheme. A sum of money towards an unidentified improvement invites a regulation 122 failure. Identify the scheme, its cost and how it addresses the predicted queues.
• Consider how the harm is framed at the close of the case. Where the objection has narrowed to traffic harm below the threshold, paragraph 116 should be put squarely before the inspector at the planning balance.
• For councils: make sure refusals stand on more than non-severe traffic harm, or set out a reasoned case for departing from national policy.
• Present the modelling transparently. The inspector relied on average queues across seed runs while noting variation between runs. The averaging and any outlying results should be explained.