“Prediction is very difficult, especially if it’s about the future”

In this second post about the work of the Commission on Travel Demand I will explore the challenges posed by the quote from the scientist Nils Bohr that headlines this article.

Lets start by looking at the state of practice in the UK. All major infrastructure schemes are subject to an economic appraisal with an appraisal period of 60 years (which is 30 years longer than it used to be a decade ago). We produce long term estimates of demand using the National Trip End Model and a suite of other tools such as the National Transport Model and the Passenger Demand Forecasting Handbook. However, the demand futures upon which decisions are based are largely determined by what are deemed to be ‘reasonable assumptions’. The case for HS2 for example includes the following acknowledgment: “Despite the economic downturn there is little evidence to suggest the recent strong growth in long distance rail travel is about to stop. We therefore assume further growth in long distance rail travel but on a conservative basis that growth will stop in 2043” (HS2 Ltd 2011)

It’s a truism that the only thing we will know about any forecast is that will be wrong but that is not particularly helpful. So what is our history on forecasting? Phil Goodwin has long established the tendency of forecasts from the days of Roads for Prosperity to tend to overestimate road traffic with, at best, demand following the low growth ‘option’ as shown in Figure 1.


Figure 1: A history of forecasting difficulties for car traffic (Image courtesy of Phil Goodwin)

It is not that transport forecasters are bad at forecasting, it is just difficult to anticipate how the various variables in the models might move and which important variables that are not in the current approach will start to matter more. As an example, the National Infrastructure Commission is currently consulting on what the most likely population estimates will be. They review forecasting accuracy as shown in Figure 2. Look familiar? Clearly if the population forecasts are wrong then so will the travel forecasts be given the importance of population growth to total demand growth in our current approaches.


Figure 2: Previous ONS projections versus actual population 1955-2014 (Source: National Infrastructure Commission, 2016)

So, how do we deal with uncertainty about the factors that have underpinned our approaches to demand forecasting such as oil prices, population, income changes. The Department for Transport has been developing the National Transport Model to try and consider those trends which might be important. It led in 2015 to the production of five ‘scenarios’ of travel demand futures. They are not scenarios in the true sense of the term, more sensitivity tests on oil price, economic growth and the extent to which declining trips rates might persist. These are shown in Figure 3.


Figure 3: Range of potential demand futures from National Road Traffic Forecasts (DfT, 2015)

This shows us that there is a range in 2040 traffic levels between the highest and lowest projection of 100 billion vehicle miles. Yes, 100 billion vehicle miles. That is 40% of the miles on our roads today. How do we deal with this kind of range of uncertainty? Currently we don’t, we adopt a preferred ‘scenario’ and continue with our demand analysis on the basis that this is the future under which all projects should be assessed.

None of the above allows for the changes to mobility that will come from social change such as the radical reshaping of the retail sector or changing travel expectations for the over 65s. Nor does it consider the transport system changes such as the introduction of TNCs such as Uber and Lyft, vehicle automation or electrification of the fleet which are being aggressively promoted.

An alternative to simply adding more and more sensitivity lines that incorporate these factors is to try and develop scenarios which capture a plausible set of alternative futures under which decisions can be evaluated. Glenn Lyons and the New Zealand Department for Transportation underwent such an exercise producing a set of four scenarios (see Future Demand where Figure 4 is drawn from – well worth a read). The scenarios were then quantified and the headlines shown below.


Figure 4: Different demand scenarios for New Zealand: Source Lyons et al, 2014

Here again however the range of possible futures goes from a growth in traffic of +10% to –62%.

So, one of the questions we need to ask is whether the relatively near future of 2040 is so uncertain that we have to present decision makers with a range of outcomes which are this wide? Are there not some aspects of everyday life which root some parts of travel demand and are harder or slower to change? Which aspects, which areas, which communities are most and less open to change? Buchanan was surely faced with uncertainty on a level that parallels that which we face today as Traffic in Towns was assembled  in the early 1960s. Many of the key insights were right or close approximations as to how demand might play out.

So, we must find a way forward which accepts that there are some demand uncertainties but which provides insight as to what and how much and equally importantly why? Some of these uncertainties are not somehow ‘out there’ waiting to happen but will be created by policy pathways we choose. Which aspects of future demand are most amenable to influence by transport policy and which will happen anyway? I hope the Commission will make progress through the call for evidence and our first three sessions on these questions so that we can move forward the debate on what this really means for decision-making.


Why we should worry about travel demand

Today marks the launch of a new Commission on Travel Demand which I am chairing. This is the first in a series of blog posts where I will explore the thinking behind the Commission and share insights from events, evidence and public meetings the Commission hosts during 2017.

I start by looking at why we should be interested in travel demand. There are certainly greater short run policy priorities out there such as job creation and promoting productivity and competitiveness in a post-Brexit world. In fact, talking about demand can be politically quite challenging as the idea of limiting growth in demand or managing demand in particular places or times of day can be contentious.

However, I would argue that we are in a period of significant change and uncertainty where there are numerous opportunities to shape the course of the future growth in travel demand. Many of these influences will also come from outside the transport sector. Some pathways will be more mobility intensive than others and that matters to the amount we will need to spend on infrastructure expansion and the extent to which we can meet our future environmental obligations.

Starting with environmental obligations reminds us that we may need to pick less mobility intensive pathways in order to meet our carbon obligations. The UK Committee on Climate Change in its 2016 annual report to Parliament noted that whilst the UK as a whole has achieved CO2 emissions reductions of 38% on 1990 levels this has almost entirely been achieved through the power sector. If it is to remain on track for the fourth and fifth carbon budget periods to 2032 it requires major action in other sectors.


As the figures show, transport has shown comparatively little overall reduction and there is a very significant gap between what the Committee on Climate Change believes is a cost-effective reduction pathway and the set of transport policies we have in place today.


Whilst new technologies such as electrification of vehicles and increased biofuels offer reductions in emissions, the scale and pace of the transition from where we are today to an entirely technology-led solution seems unrealistic. In transport terms therefore this could mean travelling less far or less often, more by non-motorised transport and by more shared forms of mobility. To do this though, whilst maintaining social and economic progress, requires thinking well beyond just the transport system but to how participation in society is changing. This will help to understand where transport interventions could shape those futures in less rather than more carbon intensive ways.

In the next article in this blog series I will be reporting on insights from the US Transportation Research Board Annual Meeting in Washington which begins on Sunday 8th January. I’ll be talking at TRB on what different demand futures mean for infrastructure planning and maintenance and on what the changing employment market might mean for youth mobility. There will also be lots of debate about shared mobility and increasingly autonomous futures.

If you are interested in what you have read here and would like to contribute to the work of the Commission then please submit to the call for evidence which is open until mid February.

Professor Greg Marsden

Open Letter to Secretary of State for Transport

Below is the full text of an open letter, sent today, to the Secretary of State for Transport from 32 Transport Professors in the UK and two professional societies (Transport Planning Society and the Royal Town Planning Institute)  asking for a fresh look at where transport strategy is heading and to look again at investment priorities.

The Rt Hon Patrick McLoughlin MP

Secretary of State for Transport

Department for Transport

Great Minster House

33 Horseferry Road



Dear Secretary of State

Transport strategy – where should we be heading?

We write to you as a collective voice of professional concern and advice in relation to UK transport policy and investment plans.

Undoubtedly, the task of planning for the future mobility of the UK is more challenging than when we wrote to your predecessor in 2002. Operating within significant fiscal constraint the Department for Transport is seeking to stimulate economic recovery, tackle climate change and improve the well-being of the population. However, we are concerned that a perception of the economic imperative is leading to a series of important decisions on all of the major transport modes being taken in the absence of a coherent and integrated national policy framework for passengers and freight.

Recent evidence from the UK and internationally shows signs of road traffic growth leveling off, even after accounting for lower than anticipated economic growth. These trends are something which the Department for Transport has never forecast and which we are only beginning to understand. Whilst a growing population may well exert an upward pressure on demand, the basis for major infrastructure spending decisions appears to be changing.

There exists a range of views as to the importance of new transport infrastructure in stimulating economic growth. The evidence base is not as strong as you, or we, might wish it to be. Where real and substantial gains in connectivity and accessibility can be achieved (for example with city based investments such as CrossRail) the potential to unlock employment seems clear. As the 2006 Eddington Review pointed out however, the UK is already comparatively well connected, rendering the employment gains promised for many schemes difficult to realize.

Even were one to accept an economic imperative to invest in significantly expanding the strategic road network there is a well established evidence base that demonstrates that this will generate more traffic. Our cities are simply not equipped to take further growth in road traffic and the benefits of faster journey times on the strategic network risk being lost in greater congestion on local urban roads where the majority of journeys are undertaken. Across all of our networks we would urge a continuation or acceleration of smart demand management measures to ensure we get the best use of the infrastructures we already have – including our telecommunications infrastructures. The UK is a world leader in many aspects of this. Our service and knowledge-led economy should not be assumed to be as tightly coupled to road traffic for its success as it once might have been. There is substantial recent evidence, including the Local Sustainable Transport Fund and the Olympics, on the success of travel behaviour change programmes, underscoring demand management potential.

Integration across government is also important. On land use, changes to policy could well store up traffic problems for the future rather than encouraging economic growth. In reality, good transport and land use planning has prevented congestion and supported the economy, not held it back.

On funding, no progress has been made in the debate on how we should pay for improvements to the transport system. Understandably perhaps, your predecessors and the Treasury have ducked the issue of establishing a new congestion based system of pay as you go motoring. This could continue, but for how long? Tax revenues are forecast to fall as vehicle fuel efficiency improves to fulfill a major plank of your carbon reduction strategy. Increases in fuel duty to fill this hole have been a temporary fix, lack public support and fail to establish a stable platform for transport investment. There is a need to find a new way of charging for motoring as we move away from fossil-fuels.

We conclude, as we did in 2002 that policies on infrastructure, land-use, operations and prices must be consistent with each other if they are to offer a realistic chance of making things better instead of just accumulating long term problems. The past decade has shown how difficult integrated transport planning can be, but it remains the best hope to tackle the challenges you face. We urge you to work with us and the professional institutions in establishing a clear long-term national policy framework.


Full details of the letter and a press release will be posted on the Transport Planning Society website www.tps.org.uk

The Climate Change Act and Transport – 4 Years On

The Climate Change Act (2008) celebrates its fourth birthday today. The Act  sets a world-leading target for reducing emissions of carbon dioxide (CO2) by 80% by 2050 compared to 1990 levels. Four years on I reflect on what this has meant to the transport sector drawing on an on-going research project (http://www.its.leeds.ac.uk/transport-carbon/). Much more detailed analysis is available through the Committee on Climate Change website.

Transport is described as the sector that is most difficult to tackle, being so dependent on fossil fuel as its primary input. The evidence at least bears the lack of apparent progress out, with only a 1.7% reduction in emissions since 1990 despite quite significant improvements to vehicle fuel efficiency. These have, until recently been offset by traffic growth and by upsizing of the vehicle fleet. But has the Act galvanized new sorts of action and thinking in the transport sector?

To answer this we need to look at what the Act actually means. When it was first introduced, the then Labour government set about establishing departmental budgets as well as a series of interim overall carbon reduction targets. The Conservative-Liberal  coalition has dropped sectoral targets and instead gone for a ‘Carbon Plan’ which provides indicative assessments of the impacts of a series of proposed policy tools. Of course, when set badly, targets have the potential to corrupt policy making, forcing actions to chase the end goal whatever the cost. That is not good policy. However, targets also provide a strategic focus which draw organizations together to meet common goals. Does it matter that the Department for Transport does not have a target for CO2 reduction?

This question has been explored through interviews with 59 governmental and non-governmental stakeholders in four city regions in England and Scotland joint with colleagues at the Universities of Sheffield, Glasgow and Lund. There seems to be little coherent or comprehensive action towards carbon reduction at a local level and, whilst the 80% by 2050 target is clearly known, there is a lack of clarity about what is expected locally. Even where local carbon targets are set they are deemed to be more a statement of hope than true intent.

Have local authorities failed then in their mission to support carbon reduction? This is complex. In part, they are muddling through on the back of limited evidence and significant uncertainty. For example, if there are major technological breakthroughs in decarbonising the car fleet then their role in reducing vehicle miles is diminished. No-one knows what will happen or how fast. Nonetheless, it seems that the imperative of economic growth has demoted discussion of travel demand reduction policies relative to that of promoting travel demand growth, albeit with some emphasis on public transport.

Our research found little difference in the ambition or effectiveness of carbon reduction policies across the different case study areas or countries. Although the Climate Change Act promises legally binding targets, it seems that it has done little to really stimulate a step change in thinking in the transport sector. Carbon certainly is not yet acting as a constraint in any meaningful way and it appears to have lost traction as an agenda since the downturn.

We will be meeting regional and national stakeholders in the coming months to develop policy recommendations and we would be happy to hear from any interested parties. Events will be held in:

  • Leeds (29th November)
  • Manchester (28th February)
  • London (5th March)
  • Glasgow or Edinburgh (9th April)

If you want to find out more or get involved please contact me g.r.marsden@its.leeds.ac.uk

Flood Survey Reflections

A team of researchers spent the weekend out interviewing people in Cawood, Naburn, Acaster Malbis and York talking to households and businesses affected by the flood. Fortunately the number of houses affected in the areas I visited were small compared with 2000 in part due to the slightly lower water levels and in part due to small improvements to the flood defences which, for example, kept one road out of Naburn open. Driving and walking around now, it is hard to believe that there was a flood, with the exception that Cawood bridge remains closed and riverside fields and caravan parks remain under water.

It is early days to be able to generalise about what the interviews found. However, the ones I did showed how varied the responses might be. For those who have jobs where work can be done flexibly from home there was little direct impact. That is, unless one also had children who were due to attend the school which was closed. This led to a series of traded favours amongst the community in the case that both parents worked. Arrangements were in some instances quite fragile. Interestingly no-one I spoke with described there as being anything other than an immediate loss, with work being flexible and understanding and workload simply being “caught up” over the coming week or two.

Food shopping patterns changed, particularly as home deliveries were unable to be delivered. Most people actually had enough in their fridges and cupboards to be able to get through with a little top up shop at a nearby garage or en-route home. Some of the longer-term residents had stocks of food in the freezer for just such an eventuality. It was surprising to a degree just how ‘normal’ this event was. For someone new to the area there was a sense of calm as the rising waters followed a pattern which others knew and understood.

We’ll find out more about business impacts over the coming weeks. I met with a farmer who had to make significant adaptations to their livestock housing and who lost a lot of arable crops at various stages of planting. It will take 2 to 3 years to get back in cycle there. A local caravan park was significantly affected but still had spaces on one high area. However, the lack of local bus service meant that those with motor homes that usually accessed York by bus left the site.

This will be my last blog post on the flood – we are moving now into a phase of data analysis and then feedback – both to the local authorities and parish councils and to the Disruption project www.disruptionproject.net

Football pitches at Tadcaster

Floods stretch on – what are people doing to cope?

Friday afternoon. I’m lucky in that my kids are being looked after by friends in the village – all arranged during the various handovers that happened yesterday. I am in debt again so had better plan not to be working on the next school inset day!

Some reflections from people I’ve seen. Long diversions in place for cyclists and cars but its a nightmare getting into York with the A19 shuty and parts of the inner ring road. A neighbour suggested it would be faster to walk to York (we are 5 miles out). I reckon they are right. My daughter said last night and today. Can we keep it like this, its good fun, I’ve kind of got used to it. Perhaps its the fun of making it round the village in a dinghy or maybe not being at school. However, there is a sense in which this has all become quite normal – we are only using one car and need to share it. It takes a bit longer to get places and we’re probably doing a bit less than we were. Well that wouldn’t be so bad given how much we are overdoing it anyway.

I should add life would be a whole lot less complex if my wife wasn’t away for the weekend and I wasn’t trying to organise surveys to find out more about how everyone else is coping.

Been Affected by the Flood Like Me? – Take Part in Research

Many residents of York and North Yorkshire will have had and still be having travel plans upset by the current high water levels. I am leading a research project which tries to understand what happens to people when they are faced with Disruptive events of a whole range of different types (more details at www.disruptionproject.net). We would like to have short interviews with anyone who has been affected by the flood in any way – cancelled activities,missed work, school closure, long journeys and just more generally to understand how you coped.

To take part please contact Jeremy Shires


W: 0113 3435347

M: 07957 333 817

We hope to be surveying over the weekend and are happy to provide more details. In the meantime, hope you enjoy the photo below – and if anyone knows who is looking after my kids tomorrow that’d be good to know too!!!

The only way to travel!!!