Technical precisions


Vias institute publishes a quarterly dashboard www.vias-modalsplit.be that reflects the most recent developments in mobility in Belgium. The dashboard provides information on the distribution of the modes of transport used for travel in Belgium. More specifically, the following indicators are shown:

Via the "controls" on top, the indicators can be displayed for different subgroups. The filtered variables are the age group (18-34, 35-54 or 55+), the gender and the place of residence (Flanders, Wallonia or Brussels) of the respondents. Furthermore, you can filter on the day on which the trips were made (week or weekend) and finally you can select a number of travel modes that can be compared in more detail. 1

 

Methodology


This information is based on a monthly online survey that is conducted among 1,000 Belgian respondents. These respondents constitute, on the basis of their age, gender and place of residence, a representative sample of the Belgian population aged 18 and over.
The survey asks about journeys made the day before. More specifically:

  • Which modes of travel did you use yesterday?
  • Were you a driver, a passenger, or both?
  • How many kilometres did you travel yesterday using each mode?

The survey runs one week per month and includes both weekday and weekend trips.
Based on the data collected, the number of kilometres travelled by the respondents on one average day can be calculated, broken down by mode of transport. Finally, a weighting is applied which ensures that the sample is extrapolated to the entire adult population. In this way, the number of kilometres travelled on an average day by the entire population of Belgium can be calculated.


Limitations of the data


When interpreting the data, some limitations should be kept in mind.

  • It concerns self-reported data, and is subject to a certain bias. For example, people do not always have a correct idea of the journeys they have made and the number of kilometres they have travelled.
  • When the data is filtered to show certain subgroups, one has to be careful when interpreting data that is based on few respondents. Especially when several filters are used simultaneously (e.g.: women from Brussels in the age category of 55 years and older), the sample on which the data is based becomes very small.
  • The data are collected for one week per month. Due to some external factors such as weather conditions, the estimated usage and travelled kilometres might be overestimated or underestimated depending on the external conditions encountered during the rest of the month.

 


1 When a selection is made of a number of travel modes, the selected modes together make up 100% when calculating the modal split. The other, non-selected modes are no longer taken into account.