Pain and Joy of a Panel Survey on Transport Studies

Over ten years ago, it was established that the most frequent reason that motivates a panel survey on transport studies is the evaluation of a change in the transportation system, or a specific transportation-planning project, especially when the project involves novel elements. From a statistical viewpoint, a panel survey has the definite advantage to offer more accurate estimates of changes than cross-sectional surveys for the same sample size. Observing travel patterns of individuals and households over several consecutive days, has offered insights into activity scheduling and travel planning. Variability in travel patterns has important policy implications as well, but how much effort is worth to design a panel survey?To evaluate the effects of the transport policies introduced in Madrid during the last five years, a 'short-long' panel survey was built, based on a sample of a Madrid-worker subpopulation most affected by those recent changes in transport policy. The paper describes both the design and construction of the panel based on GPS technology, and presents some results based on an analysis of its two waves; for example, it registered an increment of public transport use and walking trips in 10%. The panel overcomes the known attrition problem thanks to providing incentives, maintaining contact, using the same interviewer for the same respondents, and conducting face-to-face interviews.