The main explanatory factors of changes in public transport patronage are supply (in quantity and quality), economic variables (prices and income), but also structural factors (growth and ageing of population, urban sprawl, etc.). These structural factors, which are often neglected, have a negative impact on public transport use, which is lower for the inhabitants of the suburbs and for the new generations of elderly who keep their car as long as possible. This impact can be measured through a simple demographic model, by weighting each population group by its public transport usage rate. Thus a structural indicator could be introduced in an econometric equation explaining the public transport use rate (number of trips per inhabitant and per year) by usual explanatory variables such as volume of supply, frequency of services, density of network, fares index, etc.
Samenvatting