Transport Insights

National Highways has reiterated its commitment to improving around 250 sites where road runoff provides a high risk of polluting the environment, despite a lower target in the Road Investment Strategy (RIS 3) and advice from its regulator that it should come clean about what can really be afforded.

As I wrote here, although the company’s 2030 Water Quality Plan sets that date to mitigate all confirmed high-risk outfalls and soakaways, the commitment in the new RIS is to mitigate 190–250 high risk sites, implicitly by 2031.

This is subject to “reviewing a deliverability plan by the end of 2027/28” and “includes those outfalls and soakaways mitigated during Road Period 2 and 2025/26”.

As defined by the bottom of the range, the RIS pledge is significantly less ambitious than the 2030 plan but higher than what the company said it could afford, as quoted in its regulator’s November 2025 advice on its draft business plan:

National Highways estimates that between 110 and 130 mitigated assets will be delivered from the allocated budget as part of this programme in RP3.

However, appearing before the Transport Committee on Wednesday, chief operating officer Duncan Smith said:

We’re very pleased to say that we’ve been given funding in RIS 3 to mitigate those locations where they have the highest potential risk to the environment. So it’s not saying they are polluting, but based on the receiving watercourse and some of the topography and dynamics of the road that they are supporting, those are ones that are the highest priority for us to invest in. And we think that by 2030, we will have improved around 250 of those locations to ensure that the receiving waterourses are protected.

I asked National Highways whether this meant that it was sticking to the 2030 plan. A spokesperson referenced the plan and said the company estimated that by the end of 2030 it will have mitigated around 250 sites, adding:

We are committed to reducing the risk of pollution from road run off and our Water Quality Plan 2030 sets out a high-level programme of work to achieve this.

As part of the plan, we have identified and published details on the high priority outfalls and soakaways that need new or improved treatment systems, and we are committed to delivering those upgrades by 2030.

The problem is that, as I have reported, the Office of Rail and Road (ORR) said in its advice that estimated costs per asset mitigated had more than doubled to between £900,000 and £1.2m against a budget of £159m and stated clearly:

This means National Highways will not deliver ~250 outputs by 2030 which it previously proposed and committed to in its 2030 Water Quality Plan. The company estimates that between £186m and £294m would be required to deliver all the mitigated assets by the end of RP3. National Highways should seek to work with the department to manage expectations where it has previously committed publicly to deliver a bigger programme and the reasons this is no longer feasible.

According to the ORR, the company forecast that between 75 and 95 assets will be carried over for mitigation during the next RIS “taking into account the nine scheme being delivered in 2025-26”.

This implies that around 45 mitigations were delivered before RIS 3 began this month, although I make it around 18, and would see a total of 155-175 delivered by the end of the RIS, at an average cost of just under £1m.

What can actually be delivered is dependent on the cost of schemes and what the actual budget is for the National Programme under which they fall, which the RIS does not state.

The interesting twist here is that, even after the ORR said National Highways should manage expectations, it cast doubt on its cost estimates:

Despite the revision in per unit cost estimates, National Highways explained that cost data in this area remains limited, in terms of the unit cost of the solution, and associated requirements such as traffic management. In addition, the company indicated that it has not undertaken external benchmarking, as its priority is to understand performance within its own operating environment. To date, evidence has been drawn from a limited number of retrofit projects delivered through Designated Funds.

In overview, the evidence to support National Highways’ plans is high-level, making it difficult to assess whether the proposed delivery commitment has been set at a challenging and deliverable level. On balance, based on evidence of the cost of recent interventions, we consider that the proposed commitment, in terms of the number of outfalls treated, is conservative and should be revised such that it represents an appropriately challenging commitment.

It looks here as if the regulator thought National Highways may have exaggerated the cost per unit in support of a relatively low “proposed delivery commitment” in the RIS.

Comparing the bottom end of the range required by the final RIS with what the company is still saying it can do, it seems to have largely succeeded.