This week saw the first evidence session of the Commission on Travel Demand bringing together stakeholders from local and national government, academia and industry to discuss approaches to understanding demand in the sector. It ended with a debate on whether forecasting as had its day. The motion was defeated but that is not the same as saying we don’t need to re-examine the practice of thinking about travel demand in the future.
Robin Hickman shared the following image on uncertainty, time and techniques that match to the space you are operating in.
In the transport sector we largely deploy forecasting and, even where we use scenarios to think about different policy options, we return to making our decisions based on estimates of demand derived from a forecasting approach. Such an approach seems likely to risk biasing prioritisation of options towards those that are most compatible with the trends which underpin the forecasts. That is a problem if the futures really are potentially significantly different from where we are today.
It seems critical therefore to understand whether there already have been some important structural changes to travel trends which we have missed and whether there are likely to be more which fundamentally change how mobility is tied in to how society works. The evidence session shared several examples of trends which seem to be somehow significantly different to previous decades whether that is between central, inner and peri-urban areas or between different groups in society or for different journey purposes but what there is less evidence on is why that is happening. As an example, the chart below comes from evidence submitted to the Commission by Transport for Greater Manchester showing very different trends in traffic inside, outside and on the motorway network.
Some of the gap between projections and outturn was attributed to it being impossible to correctly foresee the ‘input conditions’ (wealth distributions, oil prices and congestion effects) and that structurally things aren’t perhaps so different. Even were that to be the main explanation, that line of thinking could marginalise whether the changes that result then create a different pathway for society as a result of the new conditions. Some of the change was attributed to completely new ways of doing things such as retail and work which is having a profound impact on what we travel for and how we might value travel in different activities.
It is important to make headway on these arguments. Despite there being widespread acceptance that in some way things are different this does not mean that there is acceptance amongst those taking decisions that this actually makes a difference to how we should take decisions. The assumption that demand in the future will be best supported by the assumptions of links between capacity growth and GDP growth remains intact and the attraction of a single central point forecast also remains strong. Greater clarity on the extent and reasons for an underlying change to how demand is evolving that challenges the current view would be necessary to convince that business as usual planning assumptions are built on sand.
Whilst I think there is a strong case to change the way we approach long-term planning I think we need to proceed with caution and build the arguments very carefully. In the debate I argued that forecasting is not dead. I did so for several reasons (other than that the purpose of a debate is to mount a coherent argument for whatever you are given to discuss!):
- There remain many decisions in the transport sector which are more short term in nature and/or which get revisited over time and therefore can be adapted. Longer-term uncertainty here is less important (see the earlier diagram)
- The approach to forecasting allows one to see how different explanators are changing over time and provide a baseline from which to understand stability and divergence from trends (incidentally no-one argues that forecasting is perfect and that it could not be improved)
- Even if we determine that other approaches would be better for longer-term decisions (and there does seem great potential here) there remain risks that those approaches would be hijacked to support the political will of the day as some critics suggest has happened with our current approach. There would need to be more work done to underpin the analytical rigour which supported decision-making in a world where more pluralistic futures were accepted (and there are examples being deployed in other sectors that may help).
- In short, we must not confuse the practice of decision-making that has built up around forecasting with the benefits that can be derived from the development and appropriate use of forecasts. They should be part of a toolkit of futuring rather than the only tool.
So, to conclude, there seems to be a growing body of evidence that suggests that there is a change in the role of mobility in society and therefore a level of uncertainty in future demand which goes beyond whether or not we have used the right GDP and oil price assumptions in a forecast. The future policy picture for mobility looks certain to add further uncertainty with the increasing automation of transport and changes to mobility service provision. Still greater change can be expected outside of the transport system which will also have profound impacts on what we travel for, where, when and how. That will be true whatever approach we adopt to decision-support and decision-making.
One of the uncertainties that we certainly face is whether decision-makers are ready to not just recognise this but to accept that it matters. A key challenge for research and practice is whether we can prove the need for change, persuade them of the evidence and provide tools which help them to understand and communicate this uncertainty to the various constituencies and systems to which they are accountable.