National Infrastructure Commission: advice on interurban roads

The National Infrastructure Commission has published an Advice Note, directed to the government, on roads policy, to help inform plans for the Third Road Investment Strategy (a five year investment programme for strategic interurban roads). I found this rather disappointing in its analysis of the problem.

The need to decarbonise road transport is obligatory, yet investment in new road capacity is counterproductive, whatever is achievable through the switch to electric propulsion. The Department for Transport’s draft National Networks National Policy Statement, recently issued, persists in addressing carbon emissions at scheme level, where they can continue to be treated as de minimis. There should be a requirement to estimate carbon emissions for the whole future programme (RIS3), when announced.

Given the conflict between road building and achieving decarbonisation, a critical look is needed at the econometric analysis of the relationship between interurban road investment and GDP growth, which is less than convincing. Likewise, scepticism is justified as regards projections of the growth of future traffic growth based on demographic and economic factors; per capita car use did not increase for twenty years prior to the pandemic. The main factors determining car use per capita are speed of travel, time available for travel and household car ownership, none of which seem likely to increase in the future.

The benefits of road construction are subject to diminishing returns. Arguably, the UK has a largely mature road network. For instance, cities such as Stoke-on-Trent and Wakefield, which would see themselves as lagging economically, are well located in relation to the Strategic Road Network. For devolved regional governments able to decide priorities for infrastructure investment, new road capacity may not be high, except where it is required to permit major site-specific development.

The Advice Note argues that effective prioritisation of road projects requires a focus on the links that will be most significant for trade between major regional cities. However, interurban roads are used by commuters travelling into cities. It is a common situation for traffic on interurban routes in or near populated areas to show pronounced morning and evening peaks, the consequence of commuting. If capacity is increased to alleviate congestion at these times, this will attract commuters from local roads on account of the faster travel made possible – one type of induced traffic, and one reason why we cannot build our way out of congestion. This diversion of commuters on to new major road capacity is facilitated by the wide use of Digital Navigation (generally known as satnav), which makes fastest options clear. The increased local commuting pre-empts the additional capacity intended for longer distance business users.

The proposal for a systematic analysis of the road network to see which routes are slow or unreliable is reminiscent of the approach of US highway engineers to categorising levels of service as the basis for proposals to increase capacity, thus justifying multilane freeways that attract more traffic. Yet there is a conflict between accepting the need for further road construction and demand management measures to reduce carbon emissions from the sector.

We no longer add to urban road capacity to accommodate growth of demand for road traffic; indeed, the trend is to subtract carriageway available for general traffic in favour of more space for buses, cyclists and pedestrians, plus investment in urban rail, traffic management and demand management measures. Yet the focus of interurban roads policy continues to be on investment in new capacity (although the Welsh Government has taken a different view). Given the demands of decarbonisation, a reconsideration of this traditional focus is desirable.

The prospects for autonomous vehicles as a source of economic benefit are unclear. Yet Digital Navigation is widely use and is changing travel behaviour. Road freight operators take advantage of similar digital technologies to manage their fleets effectively. There are opportunities to exploit digital technologies to improve the operational efficiency of the mature road network, which would be far more cost effective than civil engineering technologies employed to increase capacity.