Using expert surveys for scenario development in ‘decide-and-provide’ transport planning processes: Lessons from public transport network planning in Cape Town

The City of Cape Town has adopted an approach to city transport planning geared to accommodating future uncertainty. This approach has generated new data needs, and necessitated new forms of transport surveys. In addition to household travel surveys required to calibrate models, surveys of diverse disciplinary experts are required to develop plausible scenarios of future travel demand against which the robustness of public transport system improvements can be tested. The aims of this paper are to share experiences in surveying experts to assist in scenario building, and to draw lessons from this experience for future planning cycles. The expert survey was administered using the Delphi panel technique, in two waves. The first wave sought expert insight into: (1) plausible scenarios of Cape Town’s future from the perspective of different fields of disciplinary expertise; and (2) the implications these plausible scenarios may have for travel demand characteristics. The second wave sought to: (1) test a set of propositions about the future arising from the first wave; and (2) establish the extent of divergence within and across disciplinary experts on these propositions. Panellists in some categories found extrapolating current trends into the near future easier than estimating a range of possible and plausible outcomes in the far future. In future planning cycles this limitation might be overcome by a combination of facilitated expert focus groups and anonymous expert Delphi panels that enables both panellist training and promotes unbiased independent thought.