I have a new book published on 1 September, one in a series of short books on policy and economics topics described as ‘essays on big ideas by leading writers’. My contribution is a critique of the inconsistencies of transport policy in recent decades, which I attribute to the shortcomings of conventional transport economic appraisal in identifying the benefits that arise from investment. A column in The Spectator magazine of 26 September described my book as ‘excellent throughout’.

The Office of Rail and Road has responsibility for monitoring Highways England’s delivery of the Government’s Road Investment Strategy. This involves investment in England’s Strategic Road Network of £15bn over five years, with more to follow. The ORR has been consulting on how to carry out this task. My response to this consultation is as follows.

The economic rationale for investment in the road network is to generate benefits for users, including in particular the saving of travel time. It would therefore be appropriate for the benefits to users of Highways England’s investment programme to be evaluated as part of ORR’s monitoring process.

In general, traffic congestion on the Strategic Road Network (SRN) arises in or near populated areas, where local traffic adds to long distance traffic; remote from such areas, the traffic generally flows freely. From the perspective of orthodox transport economics, a congested road is an opportunity to invest by adding capacity. But how do road users experience the benefit?

Highways England has evaluated the outcome of ‘major schemes’ five years after opening. It finds that average time savings are small, 3 minutes at peak periods.[1] The economic case for investment depends on multiplying such small time savings by a large number of vehicles (and by monetary values of time saved). Nevertheless, it is relevant to ask how road users experience such small time savings.

While a few minutes time saving would not be material for long distance users, it could be significant to local users on short trips, in particular by allowing more opportunities and choices when changing job or moving house. Indeed, it seems likely that the main benefit of investment in additional capacity on the SRN would accrue to car commuters.[2]

It would therefore be important to understand the nature and distribution of the benefits of the investment schemes of Highways England, as experienced by different classes and locations of road users.

Transport Focus commissioned an Independent Analytical Review for a Road User Satisfaction Survey in 2015. This recommended the development of a continuous online survey of satisfaction using a representative panel of road users. Repeated surveys of a panel would allow trends in satisfaction to be monitored over time. Transport Focus is currently piloting this approach.[3]

Such a survey technique could in principle be used to track the subjective user experience of improvements to the network as a whole. Moreover, relating user experience to specific investments would allow the benefits of these to be understood, as experienced by different classes of road user.

Another approach, also using a volunteer representative panel, would involve monitoring individual travel patterns, based on mobile phone GPS location. This would provide an objective measure of changed travel patterns as the result of investment, and would allow identification of which users benefit, both as regards location, journey purpose and socio-economic characteristics.

Average travel time has been measured for the past 40 years by means of the National Travel Survey. It is noteworthy that average travel time has remained unchanged at about an hour a day, despite many £billions of investment in the road network. This indicates that there are no time savings to users in the long run. There is a therefore a question about the nature of long run benefits, which are mainly to be seen as changes in land use and land value, as land is made more accessible for development that can contribute to economic growth. Travel time savings are therefore short run and their duration needs to be monitored.


Given the very large expenditures planned for the SRN, it is important to understand the nature and distribution of the benefits of investment. There is an opportunity for the ORR to improve value for money by taking an analytical approach – tracking the experience of road users as this is improved by investment in the road network. Both subjective and objective change should be monitored, to understand the nature and distribution of the benefits of investment.










[1] http://assets.highways.gov.uk/our-road-network/pope/major-schemes/POPE___meta_2011___main_report___final.pdf

[2] http://peakcar.org/valuing-travel-time-savings-problems-with-the-paradigm/





I have a new book published on 1 September, one in a series of short books on policy and economics topics described as ‘essays on big ideas by leading writers’. My contribution is a critique of the inconsistencies of transport policy in recent decades, which I attribute to the shortcomings of conventional transport economic appraisal in identifying the benefits that arise from investment.

The Transport Committee of the London Assembly is holding an inquiry into growing traffic congestion in London. The evidence I submitted is below.


Although London’s population has been growing quite rapidly, road traffic in London has not increased over the past two decades, both cars and all motor vehicles, as Department for Transport statistics show (see Figure).

Road traffic growth has been inhibited by the retention of London’s historic street pattern, more road space allocated to buses, cycles and pedestrians, controls on parking in inner boroughs, and congestion charging. The public has accepted constraints on road traffic growth because of investment in public transport, particularly rail, which generally provides speedy and reliable travel for commuting and for work-related journeys in central London. As the population has grown, car use, as a share of all trips, has declined from a peak of 50% in 1990 to 36% currently, projected to decline to perhaps 27% by mid-century with continuation of present policies.

Mitigation of Traffic Congestion

Average travel time is invariant as measured in the National Travel Survey: over the past 40 years, it has remained steady at about an hour a day nationally, 1.1 hours in London. Accordingly, traffic congestion is self-limiting: as traffic speeds fall, journey times rise, and flexible road users change the timing, mode or destination of their trips. Gridlock can generally be avoided through Active Traffic Management measures.

The origin of the recent observed increase in congestion is unclear: it could be a short-term response to particular developments, such as the Cycle Superhighways or the construction boom, with congestion expected to lessen in time as the more flexible road users adjust.

Of the of possible means for mitigating congestion:

  • Investment in rail to accelerate mode shift is likely to have the biggest impact.
  • Flexible road users could be encouraged to avoid peak congestion by providing them with good information on expected journey times via mobile phone apps. This would reduce congestion for those whole are less flexible.
  • A workplace parking levy might be beneficial, particularly by generating funds to support investment in public transport.
  • More bus priority measures, including Bus Rapid Transit, would increase the speed and reliability of buses, thus attracting people from cars.
  • It would be worth investigating the scope for fine-tuning road layouts, on-road parking restrictions, permitted turns and Active Traffic Management, based on suitable traffic modelling methodologies.
  • Car sharing in place of personal ownership results in people making less use of the car, which is helpful.

Other possible means for mitigating congestion seem less attractive:

  • The extension of congestion charging to the Western zone in 2007 and its subsequent withdrawal in 2011 had little impact on congestion. A substantial increase in the charge would pose problems of public acceptability.
  • New road infrastructure, such as the proposed East London River Crossings, would add to traffic without reducing overall congestion. We know from experience that we can’t build our way out of congestion (and understand why).
  • Regrettably, investment in cycling infrastructure is unlikely to get people out of their cars. In Copenhagen, 30% of all trips are by bike, but car use at 33% is only a little less than London: walking and public transport take the hit. However, investment in cycling infrastructure would reduce crowding on public transport. (Relevant to Q4,14)
  • Driverless cars, as being developed by Google for instance, are essentially taxis with robot drivers. More use would be made of such taxis if they were cheaper, as they might be if robots replaced human drivers, which would increase demand. Parking requirements for privately owned cars might reduce in residential districts and in off-street car parks, but not for on-street parking in central areas, so the impact on congestion seems unlikely to be substantial.

Increased vehicle occupancy

One longer term approach to mitigating congestion would be to encourage increased vehicle occupancy. For instance, UberPOOL offers ride sharing for people going in the same direction, sharing the cost. In the long run we might envisage a system of driverless shared-occupancy taxis. This could be facilitated by (a) demand management measures to prioritise shared over single occupancy (as High Occupancy Vehicle lanes on US freeways or the exemption of taxis from congestion charging in London); and (b) traffic management that takes advantage of developing vehicle-to-infrastructure communications to smooth flows and avoid conflicts (analogous to Air Traffic Control). While implementing a system of this kind would face formidable challenges – technological, institutional, commercial, public acceptability – it offers the prospect of a more efficient road network that provides reliable, uncongested, door-to-door travel at the user’s time of choice.


Traffic levels in London as a whole are stable, despite population growth. Congestion is self-limiting, as flexible road users adjust to slower speeds. There is scope for accelerating the shift away from car use, without detracting from London’s success, particularly by further investment in public transport, which could ease traffic congestion. In the long run, driverless shared-occupancy taxis may allow a significance increase in efficiency of the road network.



I recently participated in a study visit to Copenhagen, organised by the Young Urbanist Network of the Academy of Urbanism. This proved to be an excellent opportunity to understand the impact of pro-cycling policies in Denmark.

The Bicycle Account records that Copenhagen is very friendly to cyclists, with 45% of all journeys to work or education made by bike, up from 36% ten years ago. For residents of the city, the figures are 63%, up from 52%.

It is interesting to compare Copenhagen with London as regards mode share for all trips: bike C 30%, L 2%; car C 33%, L 37%; walk C 17%, L 24%  ; public transport C 20%, L 37%. So compared with London, promotion of cycling in Copenhagen has reduced public transport use markedly, walking significantly and car use just a little.

The Bicycle Account estimates that there is a net socioeconomic benefit of DKK 1.62 per km (£ 0.18) for a cycle trip during rush hour, in comparison with the journey not having taken place. The main benefits are convenience (time saved) followed by health. For a car, there is a loss of DKK 5.63/km.

The main feature of cycling in the city and beyond is the general provision of dedicated cycle lanes, located between the pavement and the carriageway, separated by kerbs from both. Only on residential roads or narrow historic city centre streets do cyclists have to share space with cars. In addition, there are traffic signals for bikes with give them a head start (typically 6 seconds). Car drivers defer to bikes when they need to cross a cycle lane.

I took the opportunity to try the electric bikes available for rental on the streets, equipped with an iPad-like display for login, payment and satnav route. This behaved like a normal bicycle, with a boost from the power-assist – very pleasant.  These electric bikes seem aimed at tourists since residents all have bicyles and the city is flat, so little need for a power-boost.

The question I had in mind at the start of this trip was: how can we get people out of cars onto bikes? – something that seems difficult in Britain. What I learned is that, with vision and perseverance, and in particular by segregating cyclists from general traffic, it is possible gain a very substantial share of trips for bicycles, but largely by switching from public transport and walking. It is still hard to get people out of their cars, even in such a cycle-friendly city as Copenhagen.

The article below appeared in Local Transport Today 699, 10 June 2016. It was prompted by discussions at a workshop event organised by colleagues at the Transport Institute of University College London, who are carrying out a study for the Department for Transport of social and behavioural impacts of autonomous vehicle.

There is much interest in the possibilities for autonomous vehicles, in particular driverless cars. Focus is mainly on technological feasibility, role of the driver, risks and insurance. What has not yet been sufficiently considered is the implications for traffic. How much difference would autonomous vehicles make?

There are two broad routes to driverless cars. Mainstream auto manufacturers are equipping vehicles with devices that assist the driver. Adaptive Cruise Control automatically adjusts the vehicle speed to keep a safe distance from the vehicle ahead. Lane Keeping systems alert the driver if the car is drifting out of its lane and assist in steering back. Self-Parking systems allow a vehicle to park hands-free. Such devices are contributing to a reduced role for the driver, which ultimately could lead to driverless vehicles. The crucial transition is from high automation to full automation. Because many manufacturers, BMW for instance, market their cars on performance, they are likely to encourage hands-off-the-wheel only in situations where there is little challenge to the keen driver – such as long motorway trips or slow-moving urban traffic. Otherwise, driving is to be enjoyed.

Google’s pods, lacking a steering wheel, exemplify the other route – the great leap forward to full driverless. While these electric vehicles could be privately owned, they seem particularly suitable for shared ownership, given that they are, in effect, taxis with robot drivers. Taxis are popular, and we would make more use of them if they were cheaper, which they might be if robots replaced humans. This could increase demand, adding to traffic congestion in urban areas. But possibly the technology might allow the safe distance between moving vehicles to be reduced, packing more into the available carriageway.

The main impact on traffic of shared driverless cars is likely to be via parking. Privately-owned cars are generally parked for 95% of the time, seemingly an inefficient use of resources. Sharing would allow more time in use and so fewer parked cars. But the main impact on road space would be in the suburbs and car parks, not city centre streets where congestion is most acute and where parking is limited to avoid impeding traffic.

Driverless vehicles would contribute to congestion when they are on the move empty, as do black cabs plying for business. Programming your personal driverless car to cruise round the block empty while you transact business in a shop – in effect ‘parking’ on the move – would need to be regulated, possibly banned, in city centres (although this could lessen the attractions of driverless vehicles). A two-car family might economise with one driverless car, taking the breadwinner to work, then returning for use by the house wife/husband and children, before collecting the worker at the end of the day. But this would double the number of work trips, adding to traffic.

Altogether, it seems likely that the overall impact of driverless cars would be to increase urban traffic. It would be desirable model traffic flows under a variety of driverless scenarios to understand better the implications, since there may be conflicting policy objectives.

The UK Government is keen on driverless cars. The ministerial introduction to the Department for Transport’s 2015 action plan, The Pathway to Driverless Cars, starts: ‘Driverless vehicle technology has the potential to be a real game changer on the UK’s roads, altering the face of motoring in the most fundamental of ways and delivering major benefits for road safety, social inclusion, emissions and congestion.’ The Chancellor of the Exchequer, in his 2016 Budget, made a point of announcing trials of driverless cars on the Strategic Road Network by the end of 2017.

It could turn out, however, that benefits of autonomous vehicles on inter-urban roads could be offset by increased traffic on urban roads. One way of mitigating such traffic would be to increase vehicle occupancy significantly. This may be possible though what might be termed the ‘shared-squared-driverless’ mode, involving both shared ownership and shared use.

So rather than one or two occupants, the aim would be to fill the vehicle at peak times with passengers travelling in the same direction. This would reduce urban traffic congestion through high occupancy requiring fewer vehicles, with one study suggesting that this could remove 9 out of 10 cars in a mid-sized European city. Uber has introduced uberPool, a shared taxi service with lower fares, and uberHOP, which facilitates sharing along commuter routes at peak times. Their success will depend on the ability to match enough passengers going in the same direction, and also on the willingness of people to share.

If priority were given to shared-squared-driverless vehicles through road pricing or similar demand control measures, it might be possible to avoid urban traffic congestion while offering speedy and reliable door-to-door travel. This would be facilitated by some central oversight of such vehicles to minimise conflicts and maximise efficient use of the road network (analogous to air traffic control). The outcome could allow the car to compete with rail in urban areas, in terms of speed and reliability, and could help cities without rail infrastructure better to meet the mobility needs of their citizens. However, the technological, institutional and commercial challenges to the shared-squared-driverless concept are substantial, and practical feasibility is unclear.

Colin Buchanan’s seminal report, Traffic in Towns, was published 50 years ago, decades before the possibility of driverless cars. How much difference would autonomous vehicles make to urban traffic congestion? In the medium term, congestion could worsen, unless action were taken to regulate the movement of vehicles without occupants. In the longer term, the possibility of higher vehicle occupancy offers the prospect of mitigating urban traffic congestion.




I was invited recently to speak at a research conference of investment analysts and asset managers concerned with the automotive industry. My presentation summarised my thoughts about the future of the car:

Car use in big cities will decline, as a share of all travel, as exemplified by London. Successful cities attract those wishing to share that success – businesses, people to work, study and live. Population grows, population density increases, which generates economic gains known as agglomeration benefits, with analogous cultural and social benefits. The city authorities recognise that the road system cannot cope with potential demand for car travel and so invest in public transport, particularly rail which provides speedy and reliable travel compared with the car on congested roads.

Beyond city centres, the car will remain popular where there is road space to move and to park. But per capita car use is unlikely to grow in the developed economies.

Income growth no longer drives the growth of average distance travelled. The main determinant of the growth of travel demand is population growth. Corresponding growth of car ownership and use will depend in where the additional inhabitants are housed: more car ownership for greenfield sites, less for urban locations.

The car has developed incrementally since the original mass-market Model T Ford that hit the road a century ago. Despite enormous improvement and refinement, we still employ nineteen-century-originated mechanical engineering in modern cars. Electric vehicles use twentieth-century-originated electric propulsion and storage, which is being improved and refined to increase market penetration. Only with driverless vehicles do we get to a twenty-first century technology.

Digital technologies are being adopted incrementally by the motor manufacturers to ease the task of driving – the advanced driver assistance systems. Ultimately, these could permit full hands-off mode. But the manufacturers who market cars based on performance would promote driverless travel only when driving was tedious, as on long motorway trips or in congested urban traffic. In contrast to these evolutionary developments, we have Google’s revolutionary attempt to take a giant leap forward to a car lacking controls for a human driver. This is essentially a taxi with a robot driver. Taxis are useful: we would make more use of them if they were cheaper, as they might be if robots replaced human drivers. But they would not constitute a fundamentally new form of road transport.

More generally, application of the fast developing, disruptive digital technologies to road travel is constrained by the slow-to-evolve nature of the mechanical engineering technologies that still define the car. Nevertheless, there are possibilities for disruptive innovations that would affect car ownership and use:

Mobility-as-a-Services (MaaS) is a concept that would allow us seamless travel via the most appropriate mode, all arranged via a smartphone app (not dissimilar in concept to the traditional travel agent’s offering for long-haul trips). Feasibility of MaaS depends on being able to integrate the availability of the most appropriate mode – whether taxi, train, tram, bike – under different ownerships, with paperless ticketing, including at times of peak demand. This could be challenging, but if successful, would lessen the attractions of the personal car.

While role-out of simple driverless taxis would not be a fundamental innovation for road transport, the addition of shared occupancy to share ownership (‘shared-squared driverless’) would permit the more efficient use of road space. UberPOOL already offers shared trips at lower cost to those heading in the same direction at the same time. Two additional measures would further increase the efficiency of the urban road network: demand managemen that would give priority to shared occupancy vehicles, following the precedents of the High Occupancy Vehicle lanes on US commuter routes and zero charge for taxis in London’s congestion charging zone. Plus an urban road analogue of air traffic control that serves to avoid conflicts between aircraft and smooth flows, which would become possible as vehicle-vehicle and vehicle-infrastructure communications are developed. A shared-squared-driverless scenario with minimal congestion could offer door-to-door travel at time of choice with speeds comparable to urban rail, again lessening the attractions of personal car ownership.

The present state of battery technology constrains electric car sales, hence much effort is being expended to develop better batteries. Batteries based on the current Li-ion electrochemistry are being refined to improve performance, reduce costs and increase market penetration of electric vehicles. But it is possible that a new electrochemistry will be developed with superior performance – energy density, rate of charging, lifetime and cost. Much then depends on who owns this new battery: if a single battery manufacturer wishing to maximise sales, then all auto manufacturers could take advantage; but if an auto manufacturer had teamed with the battery manufacturer in developing the innovative product, that team could have a disruptive advantage.


There are an increasing number of uncertainties that will affect the long-term development of the auto industry: changes in travel behaviour, attitudes to driving and personal car ownership, demographic developments, new technologies and new business models. It’s hard to take a view about investment outcomes. Given the greater risks involved in investing, larger returns will be sought. But then the question is what will motorists be willing to pay for driver assistance technologies that add significantly to the cost of cars, particular mass market models. The answer remains to be seen as these technologies percolate down the model price range.




I visited Bournemouth to participate in a day-long seminar on transport arranged by the Council for councillors and officials. My fellow speakers were my UCL colleague, Peter Jones, and Phil Jones, a consultant transport planner. My presentation Metz Bournemouth 14-4-16

We  see that big cities such as London attract people to work, study and live, which results in higher population density and prompts investment in rail-based public transport since growth of mobility  cannot be met by more cars on the road network. But for smaller cities and larger towns like Bournemouth, the route to more sustainable transport is less clear. Cars are popular and responsible for 67% of commuting trips in Bournemouth, substantially higher than the 44% for Brighton, another prosperous south coast resort, perhaps reflecting thre latter’s more youthful demographic profile and better co-operation between the local authority and the bus operators. There may be lessons to be learned from Brighton’s experience.

More generally, my sense is that smaller cities and larger towns need to decide what kind of a place they want to be, and then work towards that aim incrementally, using stick and carrots.  A traditional aim has been to accommodate the car with plenty of cheap parking, thus attracting the trade of visitors. But then the volume of urban traffic lessens the sense of place and attractiveness of the destination. Pushing back the cars, for instance through higher parking charges, may be unpopular in the short term, but may generate a source of revenue that would allow attractive improvements to be made to the urban realm. Fostering bus services and cycling by means of appropriate infrastructure investment is the carrot to balance the stick of parking constraints.

Breaking down the customary distinction between carriageway for vehicles and footway for pedestrians can be helpful in reducing conflicts and accommodating both, as the example of Poynton, Cheshire demonstrates.

In my presentation, I drew attention to evidence that travel in the twenty-first century is turning out to be different from travel in the twentieth, in particular that growing prosperity is no longer necessarily associated with increasing car use. This creates opportunities for policy initiatives in towns like Bournemouth that go with the grain of more sustainable trends.

Transport technologies are remarkably slow to change. The first modern mass-produced motorcar took to the road in 1913 – the Model T Ford. In its fundamentals, it was little different from current models: internal combustion engine, gearbox, pneumatic tyres, amateur driver at the steering wheel. Contemporary cars are of course vastly improved in all respects, as are modern trains compared with the locomotives of a century ago, although the steel-wheel-on-steel-rail technology persists.

Speed limits

One consequence of this technological conservatism is that we have run out of the means to travel faster at acceptable cost and impact. Whilst high performance cars are built for enthusiasts, there is no general scope for faster travel on public roads, safely and with tolerable carbon emissions. On the railways, high speed rail routes are planned, but rail is responsible for a minority of all travel and high speed rail would be a minority of a minority, so its impact will be modest. There are more adventurous technologies such as Maglev and Hyperloop, but these seem expensive and inflexible, and therefore likely to be confined to specialist applications if deployed at all.

Why this reluctance to change? Why is nineteenth century technology still found under the bonnet of our cars – pistons, cylinders and crankshafts? Part of the reason is the interconnectedness and mutual dependence of the technologies – mechanical and electrical engineering, fuel supply, road infrastructure, and related safety regulation and road use legislation. The applications of all these technologies are path-dependent, in that we are not free to start again with some theoretically better approach on account of the huge investments that have been made. One particular constraint is the high energy density of oil fuels, which has made the modern car possible and still competes strongly with alternative energy sources. A switch to electric powertrains is going to be expensive, even if the problems of battery technology are solved.

Open and closed

For surface transport, the fundamental distinction is between roads that are open to all and so prone to congestion at times of peak use, and the railway – a closed system that can offer speedy and reliable travel. The nineteenth century was the great age of rail, offering station-to-station travel according to the timetable. In the twentieth century, the motorcar became predominant, providing door-to-door travel at the time of choice. But the very popularity of the car has limited its attractiveness in urban areas where population density is high, so that rail has experienced a revival.

Digital technologies

But while transport technologies evolve slowly and incrementally, the digital technologies and the applications that depend on them leap ahead. How might this change the pattern of transport? There are four broad areas of application of digital technologies to transport:

  • improve and enhance the operation of vehicles, including the possibility of driverless cars;
  • improve and enhance the operation of public transport, including convenient payment, apps for real time information and online advance booking;
  • facilitate travel on the road network, including satnav routing, advance journey time information, and urban traffic management;
  • facilitate seamless journeys across the modes.

Vastly increased computing capacity and data collection have led to big advances in digital applications. The mobile internet allows the reporting of system performance to be crowd-sourced from smart phones, as well as the sharing of vehicles.

The speed and ubiquity of digital technologies also allows travel to be avoided where business can be done through internet telephony and videoconferencing. On the other hand, the ease of establishing digital communication allows more extensive networks of friends and colleagues, with whom face-to-face contact is sought to reaffirm relationships. So the net effect of digital technologies on travel behaviour remains unclear.

Data sources

A recent review commissioned by the Transport Systems Catapult made a valiant effort to get to grips with the rapidly growing range of transport data sources. I liked the idea of ‘digital exhaust’, the data generated through the operations of transport companies and customer interactions, used to understand better individual and aggregated travel intention

One route to exploiting these burgeoning data streams is by private sector companies either selling services of value to consumers, or providing such services free of charge, cross-subsidised, in line with a high ‘expectation of free’ – although this works against smaller providers. The other route is provision by public bodies, of which Transport for London (TfL) is an outstanding example.


In contrast to TfL, Highways England (successor to the former Highways Agency) is lagging in the provision of convenient information to users of the strategic road network. The Department for Transport’s Road Investment Strategy, which commits £15bn over five years, earmarked only £150m to an Innovation Fund for future technologies, the vast bulk of expenditure being devoted to civil engineering work. This Strategy may have been appropriate to the twentieth century, but not to the digital twenty-first.

The Rees Jeffries Road Fund, a charity, is supporting a study, Major Roads for the Future, led by David Quarmby. A Discussion Note on Technology outlines future possibilities and raises worthwhile questions. The challenge is to map the way forward in the face of considerable uncertainty.





I gave a talk on this topic at a recent meeting of the Transport Economists Group, one theme of which was the subject of the previous article. My overall conclusions are set out below.

A number of new trends emerged in the 1990s, or in some cases are still emerging:

  • There has been no growth in average distance travelled in Britain for more than 20 years, whether by all surface modes or by car alone. Available data suggests that this holds for the developed economies generally. This contrasts with the previous century and more during which average distance travelled increased steadily.
  • One reason for this cessation of growth of distance travelled lies in technological constraints on faster travel. We cannot drive faster on the roads, safely and with acceptable emissions. We have high speed rail to come, but rail is responsible for a minority of trips, and high speed rail for a minority of a minority. These technological constraints mark the end of an era that began in 1830 with the first passenger railway, which harnessed the energy of fossil fuel to permit travel at faster than walking pace.
  • Car-based mobility or access to good public transport allow high levels of choice of many regularly used types of destination, thus lessening the need to travel further.
  • Travel demand per capita has ceased to be driven by growing incomes. Total travel demand is now determined largely by population growth. However, the pattern of such demand will depend on where the additional inhabitants are housed – if on greenfield sites, more car use; if within existing urban areas at higher density, then more public transport.
  • Car use in big cities has passed its peak, in term of mode share, and is now declining. Successful cities attract people to work, study and live, so population density increases. The city authorities recognise that the road network cannot be enlarged to accommodate increasing car use, so investment in urban rail is needed to meet the mobility needs of the population.

So travel in the twenty-first century will be different from travel in the twentieth century, quite apart from the impact of technological developments such as driverless cars.

In contrast to these new trends, one unchanging feature is average travel time of about an hour a day, found for all settled human populations. This constitutes a sound basis for forecasts or scenarios of future travel. Travel/transport models should be constrained to hold average travel time constant in the long run. They also need to recognise the new trends outlined above as regards both model structure and calibration. Most existing models are obsolete.



I gave a talk to the Transport Economists Group in London on 28 October 2015. Much of the material covered can be found in recent articles on this website. One new theme is set out here.

The Government has announced its Road Investment Strategy that commits £15 billion expenditure over the next five years. One stated aim is a ‘free-flow core network, with mile a minute speeds increasingly typical’. How realistic is this?

Let’s consider the past pattern of travel behaviour that has been tracked over the past forty years by the National Travel Survey. Average travel time has stayed steady at about 370 hours a year, or an hour a day, a finding that holds true for all settled human populations. What has changed over the period is the average distance travelled, which increased from 4500 miles a year in the early 1970s to 7000 miles in the mid 1990s, since when this has ceased to grow. Increased distance in unchanged travel time is the result of investment in the transport system that has permitted faster travel – private investment in cars, public investment in roads and railways.

Not time savings

People have taken the benefit of investment by travelling further to more distant destinations, not by saving time in reaching unchanged destinations. This is contrary to what transport economists suppose when they estimate the main benefit of investment as time savings, valued for the extra work or leisure supposedly made possible. In reality, people travel further to have more opportunities and choices. For instance, by travelling faster on the journey to work, you have more choice of jobs accessible from where you live in the time you allow yourself for travel, more choice of homes accessible from your workplace, and similarly more choice of shops, schools and so forth.

So people take advantage of road improvements that permit faster travel to make longer trips as part of their daily routine. This is particularly the case in areas where demand for housing exceeds supply, creating an incentive to travel further in search of affordable properties.


Daily travel is an important component of traffic on parts of the Strategic Road Network (SRN). Congestion on this network arises near to populated areas, where local users interfere with long distance users. Half the traffic on the M25 is local. Remote from populated areas, the traffic generally flows freely. The conventional response to congestion on the SRN is to add capacity – an extra lane, conversion of the hard shoulder, or an improved junction. Conventional economic appraisal involves multiplying small time savings from such capacity increases by a large number of vehicles and by standard values of time to generate monetary benefits that can be compared with the costs of the extra capacity, to assess value for money.

Small savings

The time savings per vehicle are quite small. The Highways Agency (now Highways England) carried out evaluations of around 120 completed major improvements and found the average time saving to be three minutes at times of peak congestion. There has been debate about the value of such small time savings. One view is to disregard these as too small to change behaviour. Against that, it is argued that small time savings can accumulate as more improvements are implemented, so in logic all need to be counted.

While three minutes is too small to matter for a long distance trip, it is not insignificant for a local journey. So if we add carriageway to a congested section of the SRN, it is the local users who take advantage of the faster travel to make rather longer trips, particularly for greater choice when they change jobs or move house. These lengthier trips generate extra traffic,  which restores congestion to what it was previously. Long distance users are no better off.

Induced traffic

This extra traffic is what is known as ‘induced traffic’, about which there used to be debate – did it arise and if so why? We can now see that induced traffic is the extra traffic that arises because people take the benefit of road improvements that allow faster travel as more opportunities and choices at greater distances, consistent with the evidence of the National Travel Survey, rather than as time saved.

Occurrence of induced traffic is the basis for the maxim: ‘You can’t build your way out of congestion’, which from experience we know generally to be true. This is what transport ministers at one time used to say, when they did not have a big budget for road construction. Current ministers tend to speak rather vaguely about new road schemes ‘creating opportunities for hardworking people across the nation and driving economic growth’, but no doubt hoping that congestion would be lessened, as is seemingly implied by the time saving rationale.

What road construction can achieve is to make land accessible for development. But this needs to be led by planners and developers identifying sites suited for development that are commercially attractive. If such sites require improved road access, then this should be a candidate for funding, whether from a local transport investment budget or a national funding programme, subject to a value for money test. Such local initiatives fit with devolved funding, not as part of a national Road Investment Strategy for which local development is inadvertent or incidental.


If we can’t build our way out, what do we do about congestion? Surveys of road users find that the main perceived problem arising from congestion is unreliability, rather than increased time taken. We can tackle the unreliability problem by providing road users with good predictive travel time information before they set out, so reducing uncertainty in arrival time. This is becoming increasingly possible through digital technologies, which are far more cost effective than traditional civil engineering technologies in meeting the needs of road users. In Britain, we are familiar with roadside variable message signs predicting the time to the next junction – although this tends to be too late to be of much use.

One example of useful predictive travel time information is found at Seattle, where you can input the postcodes of your home and workplace, and the time you want to arrive at work, to be advised of the time to leave home to arrive on time nineteen times out of twenty. A more ambitious example has been in operation in Nordrhein-Westfalen in Germany, where a simulation model of the autobahn network predicted journey times for any kind of trip (although this website seems no longer to be active). Such simulation models may be expected to improve their predictive accuracy as computers become more powerful, faster and cheaper and can process increasing amounts of input data.

Two kinds of driver

Predictive journey time information can be used by the two kinds of driver on the roads. Those who need to be at their destination at a particular time will know when they need to set out – whether to get to work or a meeting, or deliver time-critical goods. Those who are more flexible may be able to use such information to avoid peak traffic – for instance when on shopping or leisure trips or visiting friends. The more the flexible drivers can avoid peak traffic, the less congestion for those who have to be on the roads at that time – which is win-win.

Anecdotal evidence of the usefulness of digital technologies is to be found in Just-in-Time delivery, offered by efficient road freight haulage businesses who understand the road network well and can manage their vehicle fleets to perform rather precisely. For instance, a haulier working for a supermarket business to deliver from the central warehouse to the stores may be contracted to deliver within 30 minutes time slots, and can do so.

Digital futures

These digital technologies need to be made generally available. Highways England has an important role. The investment case for digital technologies requires monetary values for journey time reliability, which might be available from the latest Department for Transport research on the value of time. The investment case also requires information about drivers’ response to predictive information about journey times, which is researchable, albeit not a static situation since positive responses are likely to increase with familiarity.

A further consideration is the information currently made available by specialist providers such as TomTom or general providers such as Google. It is not clear how reliable is this information or what impact it is having on the functioning of the road network. Nevertheless, there is scope for collaboration between Highways England, which has an interest in the overall efficiency of the SRN, and the private sector businesses that provide information to individuals for reward, directly or indirectly.


It is a step forward that Highways England’s recent Concept of Operations recognises the importance of maximising the throughput of people and goods through initiatives such as smart motorways and Intelligent Transport Systems ‘to squeeze every drop of capacity out of what we have’.

So while we can’t build our way out of congestion,  we can manage the problems arising from congestion far more effectively. But to do that, we need a substantial reallocation of planned expenditure within the Roads Investment Strategy. The £15 billion spend over the next five years includes some ring-fenced funds for Innovation (£150m) and Growth & Housing (£100m). However, these earmarks are a tiny proportion of the total, with the bulk of spend devoted to traditional civil engineering work aimed at increasing capacity – a very twentieth-century approach that is not appropriate for the digital twenty-first century.




There is growing interest in the idea of sharing, The ‘sharing economy’ takes advantage of the internet to bring into use excess capacity, whether under-used assets (private cars, spare bedrooms) or labour (people willing to put in a few hours of effort). This is a disruptive economic force that unlocks new sources of supply at lower cost, which will benefit consumers but could be detrimental to traditional suppliers.

For transport, the sharing economy can take various forms. Private parking space can be hired to others. Ride sharing involves people sharing the car and the cost, whether colleagues on regular journeys to work, or new friends on one-off longer trips, for instance using liftshare or Bla Bla Car. Uber has introduced UberPool, a shared taxi service, with lower fares – its success will depend on the ability to match enough passengers going in the same direction. Ride sharing improves the occupancy of cars, a real efficiency gain, and reduces carbon and other emissions per capita.

However, the main opportunities seems to be in shared ownership, taking advantage of the fact that most private cars are parked for more than 95% of the time. Car rental by the day is familiar. Car clubs allow people to avoid owning their own car when their need to drive is limited. One model requires vehicles to be returned to the point of origin, normally close to where you live. Another approach allows return anywhere within a defined area. This kind of short-term car sharing is in competition with taxis, where costs have been reducing under the influence of Uber, which has also made booking and paying convenient.

There is much current interest in the possibility of driverless cars – essentially taxis with robot drivers. These may be particularly suited to ownership models other than the standard private car, since it is supposed that such autonomous vehicles could travel when empty to where needed by the next user.

A number of major car manufacturers have announced Airbnb-style schemes that allow car owners to earn money by renting out their new vehicles to others. This is a response to the disruption of traditional consumer sectors by both the concept of sharing and the declining use of cars on the part of the urban young – both because of the costs of ownership and the alternative modes of transport increasingly available in successful cities.


It makes sense to share under-used assets where that is convenient for those concerned. But how much difference will car sharing in all its forms make to road use, if its growth continues?

  • Car ownership would be reduced but car use would be more intensive, which might make little difference to overall traffic. The implications for the vehicle manufacturers are unclear.
  • Roadside parking could be reduced if personal ownership declines. But this would be in the neighbourhoods where on-street parking is permitted, so the impact on urban traffic congestion would not be great. There would be fewer people driving around to seek a parking space, but more empty driverless cars seeking the next user.
  • Car use could be reduced since those who don’t own their own cars make less use of cars.
  • Ride sharing could reduce car use, or it might take people away from public transport.
  • Driverless taxis might allow cheaper fares, which would increase demand. The impact on congestion would depend on how much reduction in private ownership took place.

Altogether, the impact of car sharing on road use seems unlikely to be substantial, at least in the near term. However, it is possible to envisage for the longer term what might be termed a ‘shared/shared driverless’ scenario – shared ownership of driverless vehicles with shared use. This could reduce urban traffic congestion through high occupancy requiring fewer vehicles. A recent paper suggests one such vehicle could replace nine conventional cars in a US city.

Moreover, if priority were given to shared/shared driverless vehicles through road pricing or similar demand management measures, it might be possible to avoid urban traffic congestion while offering speedy and reliable door-to-door travel. This would be facilitated by some central oversight of such vehicles to minimise conflicts and maximise efficient use of the road network (analogous to air traffic control). The outcome would allow the car to compete with rail in urban areas, and could help cities without rail infrastructure to meet the mobility needs of the citizens efficiently.