In most countries, including the Netherlands, the understanding of people?s travel behaviour is based on cross-sectional travel surveys where only one day is surveyed for each respondent. This is not enough to gain a proper understanding of the dynamics in travel behaviour and changes in behaviour needed to reverse the worrying long-term trends of growing mobility, congestion, increasing oil consumption and greenhouse gas (GHG) emissions. The Center for Transport studies is therefore setting up a research programme to examine the implications of the long-run dynamics and temporal variation in individual travel behaviour and accessibility for transport policy making. In a joint initiative with the Netherlands Institute for Transport Policy Research and Goudappel Coffeng, a Mobility Panel (2,000 households) for the Netherlands (MPN) will launched in 2013, using three-day self-completion diaries. Self-completion diaries are however associated with well-known data collection problems. Firstly, there are problems with picking up short-distance walk and cycle trips and accuracy of measurements (in particular trip departure and arrival times). Secondly, multiple-day trip diaries are associated with a high respondent burden. In the Dutch Mobile Mobility Panel project we will examine if GPS-enabled mobile phones are an effective and efficient alternative data collection method, and the value added in examining the variability and stability in individual travel behaviour and accessibility over time. Mobile phones are truly ubiquities having computation, sensing and communication capabilities and are carried by people throughout the day. It may become the most important solution to collect accurate and extensive travel behaviour data at low level of respondent burden in the near future. However, here is little experience yet with using mobile phones as data collection tools in the transport field. In this project we will develop an appropriate mobility monitoring tool to automatically record trips in detail (origin and destination locations, travel times) using algorithms to automatically detect (multi-modal) tours, trip purpose and transport mode. A field experiment will be conducted aiming to collect multiple-week and multiple-year travel behaviour data from 600 Dutch panel members. If monitoring using mobile phones has proven to be successful, it is intended to gradually replace trip diary data collection for specific population segments of the Mobility Panel for the Netherlands.