Parliamentary inquiry into strategic road investment

The House of Commons Transport Committee is holding a timely inquiry into investment in strategic roads, following a critical report from the National Audit Office about progress with the £27 billion Road Investment Strategy 2 (RIS2) programme, now at midpoint. I submitted evidence as follows.


This submission is concerned with whether the Government’s road investment programme is meeting the needs of users, whether the programme aligns with other policies, and the relevance of technological developments. These are matters in which I have taken an interest for many years, starting when I was Chief Scientist at the Department for Transport.

Here I argue that:

  • the economic benefits of road investment have been overstated;
  • there is conflict with other Government policies, particularly Net Zero;
  • technological opportunities to improve the operational efficiency of the road network are neglected.

Economic benefits of road investment

The main economic benefit of investment in new road capacity is supposed to be the saving of travel time. The benefit-cost ratio of a proposed scheme, a measure of value for money, largely depends on the estimated value of time savings to business users and others, in relation to the cost of construction. However, there are now available evaluations of outcomes of smart motorway schemes 3-5 years after opening that find no time savings, in part on account of traffic volumes greater than forecast.

I have compared the traffic and economic forecasts with the outturns for the two smart motorway schemes for which data is available: M25 Junctions 23-27 and M1 Junctions 10-13.[i] A salient feature of the forecasts is that the value of time savings to non-business users (commuters and others) is almost entirely offset by increased vehicle operating costs. This is the result of local users diverting to the new motorway capacity to save a few minutes travel time, for instance from home to work, not fully recognising the additional fuel costs arising from the longer trip. Such diversion is facilitated by the widespread use of Digital Navigation (generally known as satnav), which makes clear the fastest routes.[ii]  Increased use by local users pre-empts capacity for longer distance business users, for whom the additional capacity was intended, and based on which the economic case for investment depends.

It is likely that these examples are representative of the general situation in that the Strategic Road Network comes under greatest stress in or near areas of population density where local and long-distance traffic compete for carriageway. Remote from such locations, for most of the time traffic generally flows freely. Investment in additional capacity that is prompted by peak hour congestion serves to accommodate more local users, who have the flexibility to choose from a number of routes.

There is a maxim that we cannot build our way out of congestion, which we know from experience to be generally true, and to which the wide use of Digital Navigation contributes. It is common for the public justification of investment in new strategic road capacity to claim the relief of congestion and boosting the economy through improved connectivity. Yet such effects are very short term, negated by the local traffic induced by the new construction that restores congestion to what it had been. Accordingly, we have been deluding ourselves about the economic benefits of road investment.

Lack of alignment with other policies

The Department for Transport recently published new National Road Traffic Projections that include a Core Scenario plus seven variant scenarios. Traffic is projected to grow in all scenarios, by between 8% and 54% by 2060, which contrasts with the widely held view that car use needs to be reduced to meet the Government’s commitment to Net Zero by 2050. Projections of traffic growth would support a future road investment programme, yet would conflict with decarbonisation policies.

The Core Scenario, based on ‘existing firm and funded policies only’, projects 22% increase in traffic to 2060 and 42% decrease in carbon emissions. Yet Net Zero by 2050 is surely a firm government commitment. The Department for Transport published its Transport Decarbonisation Plan in 2021 which claimed that this commitment could be achieved, implying that future funding and policy development would need to constrain carbon emissions from road traffic to zero by 2050. So there is an apparent inconsistency between the 2022 National Road Traffic Projections and the 2021 Transport Decarbonisation Plan.

We are at present midway through the second five-year road investment programme, known as RIS2, worth £27bn over the period 2020-2025 when announced. RIS3 is now being planned. Yet there are headwinds:

  • The potential economic benefits are likely to be overstated, as discussed above.
  • Any increase in road capacity is counterproductive for the Net Zero climate change objective since both tailpipe and embedded carbon would be increased.
  • There are public anxieties about the safety of Smart Motorways in the absence of the hard shoulder, reflected in a critical report from the House of Commons Transport Committee, to which the Government responded by halting new schemes until five years of safety data is available.
  • The Government’s Levelling Up White Paper, published in early 2022, identified a dozen ‘missions’ across departments. The single mission for the Department for Transport is aimed at improving public transport in regional cities towards that achieved in London, a sensible political and social objective. There was no reference to road investment, which is appropriate, given that congestion delays on the Strategic Road Network are less in the Midlands and North than in the South East.
  • Current pressures on public expenditure.

Given these impediments, there is a good case for treating the Strategic Road Network as mature, with the future focus on improving operational efficiency. This is the situation for urban roads, which in the past were enlarged to accommodate more traffic, but nowadays the policy direction is to reduce capacity allocated to general traffic, to encourage active travel and facilitate public transport. Similarly, the aviation sector focuses on operational efficiency – airlines maximising flying time of aircraft, use of allocated routes and passenger load factors; airports (struggling recently) optimising throughput of passengers and baggage; and air traffic management making best use of crowded airspace. The underlying discipline is operations research, not civil engineering, together with modelling and economic analysis of operations, rather than of long-lived investment.

Technological developments

A focus on operational efficiency of the Strategic Road Network would naturally prompt consideration of how best to take advantage of the huge investment in Digital Navigation that has been made, both by providers of the service and by road users. Here a very odd phenomenon is the apparent disregard of Digital Navigation by road authorities, at least as judged by their publications – no reference to satnav in those of National Highways, the Department for Transport, or local authorities (with one exception known to me, Transport for London’s collaboration with Waze). Possible explanations include: preoccupation of highways engineers with civil engineering works; the need to spend the large budget allocated to road investment; the lack of staff with professional background to cope with digital technologies; and road authorities being monopolies, so not subject to competitive pressures to maximise efficiency.

The one constituent of road users that is highly competitive is road freight, particularly that forming part of integrated logistics businesses, which makes extensive use of digital technologies to manage HGV fleets on major roads and delivery vehicles on local roads. We are conscious of this when we order goods online, with a specified delivery date and often a time slot, the ability to track packages, delivery confirmed on the doorstep, and our feedback sought on the experience – all done by algorithm. This kind of operational efficiency needs to be brought to bear on the totality of traffic on the road network.

Road network operators with such experience would naturally want to take advantage of Digital Navigation, one aim being to better cope at times of stress – major incidents, bad weather, peak holiday flows. A second aim would be to optimise use of the network in normal times, including avoiding routing traffic through unsuitable minor roads.

When road users are asked why congestion is a problem, their main concern is the uncertainty of journey time. Digital Navigation provides estimates of journey time in advance, so those who need to be at their destination at a particular time can decide when best to set out; those who are more flexible can avoid the worst of congestion; and all can choose the fastest route. Digital Navigation is vastly more cost-effective as a means to mitigate the impact of road traffic congestion than costly and ineffective civil engineering investment.

While the Department for Transport and National Highways disregard the impact of Digital Navigation on traffic flows, they do pay attention to the possible impact of autonomous vehicles. The National Road Traffic Projections includes a Technology Scenario that envisages autonomous vehicles entering the market in the 2020s and making up 50% of it by 2047. And the government intends to introduce comprehensive legislation governing driverless vehicles when parliamentary time allows.

However, any significant impact of driverless vehicles on use of the road network seems a long way off at best. Eventual benefits would be experienced by vehicle occupants whose time might be available for non-driving tasks, with little scope to increase the operational efficiency of the network. The preoccupation with this future digital technology seems perverse when an existing digital technology, Digital Navigation, is widely used and is capable of changing travel behaviour in ways that are far more cost-effective than civil engineering.

[i] Metz, D. Economic benefits of road widening: Discrepancy between outturn and forecast. Transportation Research Part A, 147, 312-319, 2021.

[ii] Metz D. The impact of digital navigation on travel behaviour. UCL Open: Environment. 2022;(4):05.