Triple Access Planning

Stress-testing measures against explorative scenarios – how does it work in practice?

By Mojca Balant, Luka Mladenovič, Aljaž Plevnik & Tom Rye, UIRS

Nova Gorica has a long tradition of sustainable urban mobility planning (SUM planning). The city developed its first transport strategy in 2011 and a regional cross-border SUMP in 2015. The second generation of local SUMP was developed in 2017. Currently preparation activities take place for a new generation of the document, which should be developed in 2024/25.

As explained in an earlier blog, in 2022 an exercise was run with transport planners from Nova Gorica and from the TAP for Uncertainty project team which developed a number of explorative scenarios that could be used in future SUM planning. In summary, these scenarios were as follows:

  • Scenario 1: We do what we can but… Commitments regarding the CO2 emission reductions remain on a declarative level. Electric and hydrogen cars are replacing diesel cars, small changes take place regarding public transport and cycling in the city, but most activities remain as they are.
  • Scenario 2: Youth takes over. Bottom-up initiatives manage to engage with wider city population. With strong influence as a result of local initiatives, awareness among residents is raised to the level where people start acting differently even without political, legal, or financial pressure.
  • Scenario 3: Politics leads the way. A strong environmentally oriented administration takes over.  Political decisions lead the way to change. Since the targets regarding CO2 emissions are set very high and not enough has been done in the past years to systematically achieve them, strong restrictions are needed.
  • Scenario 4: Partnership for change. The national government, local politicians and residents reach an agreement that change is needed. They join forces in making the change together. Ambitious policies are put in practice which influence the way we plan, build, and live in Nova Gorica to achieve the net-zero targets.

As the forthcoming TAP Handbook explains, a key possible use for explorative scenarios is to “stress-test” measures proposed in a SUMP, to ensure that they are resilient to several possible futures and, if they are not, to consider changes to them, or possibly removing them from the SUMP altogether.   Looking around the project, it seems however that this stage of incorporating TAP and uncertainty into the planning process has not been tested at other sites. Therefore, in December 2023 the UIRS Transformative Transport Planning research group held a short internal workshop to see how in practice the explorative scenarios could be put to this use.

The measures to be stress-tested were the key measures set out in the 2017 Nova Gorica SUMP.  They are listed below.

  1. Comprehensive mobility plans for key trip generators, especially employers.
  2. Pedestrianisation and missing walking links.
  3. More attractive public spaces.
  4. Elimination of dangerous traffic locations for pedestrians by e.g. slowing traffic, improved crossings.
  5. Better bike connections within city.
  6. Better inter-settlement bike connections within the municipality as a whole.
  7. Better bike parking in residential areas and at destinations.
  8. Promotion of cycling and walking through awareness campaigns.
  9. Improved local public transport, including integration of regular and school public transport.
  10. New vehicle fleet in local public transport.
  11. Parking management and pricing, on-street.
  12. Study to assess demand for more off-street parking, and possible construction of off-street parking garage(s).
  13. Park and ride.
  14. Balancing use of street space between different modes, including in 4 smaller settlements.
  15. More EV charging stations.
  16. Speed reduction especially around schools, traffic calming.
  17. Freight transport management plans

No further information other than these titles was available to the team to understand the measures in any more detail.

Two teams of two people each went through all the measures and related them to each of the four scenarios. The teams were instructed to take a single measure and see how it performed in each scenario both (a) in relation to its impact on objectives in that scenario and (b) in terms of its likelihood of being implemented in that scenario; and to consider about how to adapt the measure in light of these thoughts.

It became obvious fairly early in the exercise that it was a problem that the scenarios developed really only looked at two identified uncertainties (political will and willingness to change behaviour for sake of environment) when there are many others that need to be taken into account. In addition, it may be difficult to have a discussion about the impact of political will on a SUMP with the municipal team that is producing that SUMP. This emphasises the need for a careful choice of key variables in the explorative scenarios, and also the need to ensure that the team doing the stress-testing of measures is the same team that developed the scenarios, so that queries about the validity of and variables in the scenarios are minimised at the stress-testing stage.

As the discussion progressed it became difficult to know whether the exercise should focus on the robustness of the measures in terms of the probability of them achieving objectives in the different scenarios, or their robustness in terms of whether measure would be implemented in that scenario; or both. If anything, the discussion tended towards the latter when on reflection it should probably have focused on the former. In most scenarios, the robustness of measures in terms of the likelihood of their implementation was rather low, because these scenarios are of futures where political and public support for sustainable transport measures is lower than today. In particular, measures requiring significant transformation of roadspace away from cars, or measures increasing the cost of private car travel, were seen not to be robust in terms of likelihood of implementation, in any scenario. This then fed through to the likelihood that they would deliver on objectives; but this was because their poor acceptability made them less likely to be implemented, rather than because the nature of the scenario made it unlikely that their impacts would be achieved. 

The attempt to stress-test measures against the scenarios led the team to question the usefulness of this set of scenarios mainly, as explained above, due to the constraints imposed by the main variables. This made it hard to achieve the main objective of the exercise which was, for the team, to bring a broader approach to the selection of SUMP measures in the light of different possible futures.  Such an approach contrasts strongly with that currently used in Slovenia which is very much a quantitative and predictive one based mainly on the assumption of continuing traffic growth. The value of scenario thinking, but the time that it took Nova Gorica to develop its scenarios and the constraints that those scenarios then placed on the stress-testing measures made the team consider an alternative approach. It could be that instead of an exercise in every municipality to generate explorative scenarios, a set of national scenarios could be developed for everyone (including the national level), to use. These scenarios should be explorative and not just based on the growth of transport demand, but should include things like trends in preferences, ageing, energy prices, land use structure and so on. This could reduce the cognitive effort for municipalities of developing their own set of scenarios and increase their usefulness – including at the national level. 

Thus, in conclusion we can say that the Slovenian exercise in stress-testing measures was not 100 % successful in what it set out to do, but that it generated additional useful thinking about how SUM planning based on explorative scenarios could work in practice.