From 5 November 2025, a targeted legal tweak adds teeth to air‑quality protections for Epping Forest. The A122 (Lower Thames Crossing) Development Consent (Amendment) Order 2025 updates the project’s Register of Environmental Actions and Commitments (REAC), enabling and funding enforcement of a 60mph westbound limit on the M25 between junctions 26 and 27 and tightening how results are reported. The 60mph safeguard and monitoring framework originate in the 2025 Development Consent Order and were refined by a September correction order.

The amended commitment requires National Highways to resource the highway and enforcement authority to set and police the limit and to run a defined monitoring programme for nitrogen oxides (NOx), nitrogen dioxide (NO2) and ammonia (NH3). Monitoring must begin shortly after construction starts and continue for at least four years after opening, with annual reports reviewed in consultation with Natural England. If evidence shows increases in nitrogen deposition or relevant pollutant levels that would risk an Adverse Effect on Integrity (AEoI), the control must be in place from the start of operations; the Secretary of State can stand it down only where pre‑operation evidence shows it is not needed. The REAC already embeds four‑year post‑opening monitoring and Natural England’s review role; today’s change tightens timing and clarity.

Epping Forest is a 1,630‑hectare Special Area of Conservation dominated by ancient beech woodland and valuable heath, with internationally important dead‑wood invertebrates including the stag beetle. Lichens and mosses here are sensitive to reactive nitrogen, which makes traffic emissions a persistent pressure on site condition.

The numbers that matter are straightforward. UK law sets 40 µg/m³ as the annual mean limit for roadside NO2. For vegetation, the critical level for NOx is 30 µg/m³. Aligning monitoring to NOx, NO2 and NH3 means results can be read directly against human‑health standards and the ecological thresholds used in habitats regulation decisions.

How far can a 60mph cap help? National Highways’ own air‑quality trials found measured NO2 dropped network‑wide over the study period, largely due to cleaner vehicles, with limited additional signal from the speed cap alone. Independent modelling by the University of Birmingham indicates that cutting motorway speeds from 70 to 60 mph could reduce roadside NO2 by 7–12%, with modest PM2.5 benefits up to one kilometre away. Taken together, the evidence supports speed management as a sensible back‑up while fleet turnover continues-making continuous monitoring essential.

Responsibility and funding are explicit. The REAC locks in provision of enforcement technology and appropriate funding for the highway and enforcement authority, with Natural England consulted on design and reporting. The September correction order clarified the ‘if required’ trigger for enforcement and confirmed who pays. Today’s amendment closes remaining gaps on timing and oversight so measures can be switched on quickly if risk to the Forest rises.

For local planning, the signal is clear: traffic emissions remain a material risk to site integrity. Natural England’s conservation advice and Catchment Sensitive Farming data list Epping Forest among priority areas where nitrogen critical loads or ammonia critical levels are exceeded, supporting the case for transport controls that secure measurable reductions.

What to look for in the published data now is transparency and comparability: annual time‑series for NO2 means, NOx and NH3 concentrations, set alongside traffic volumes and fleet mix. That allows communities and NGOs to test whether results stay under the 40 µg/m³ NO2 limit and keep vegetation below the 30 µg/m³ NOx critical level-and to press for enforcement if they do not.

The Lower Thames Crossing remains the UK’s largest road scheme, with scrutiny rightly focused on construction impacts, induced traffic and habitat outcomes. But a funded, enforceable 60mph control with a clear monitoring plan gives Epping Forest stronger protection while wider questions on the scheme continue through delivery.

For practitioners, the lesson is practical: tie mitigation to thresholds, publish the datasets, and agree an enforcement path with the statutory nature adviser from the outset. That blend of legal authority, measurements that track the right pollutants, and a timetable that accelerates decisions is how this package can turn promises into protection on the ground.