This means an 85% sample to have accurate and reliable O-D data for the morning peak. Under the same conditions for the whole day (the basis is 30,000 persons) it is necessary to ask 16,771 persons, which means 56% of the users should be questioned.
Literature recommends for such a network with home interviews a sample of 25% [2], [3]. This means 50% of the users under a modal-split of 50% should be asked. This means that every 4th household needs to be questioned.
It is easy to understand that this task (a sample of 50%) is hard or even impossible to perform. Therefore it is clear that there is a need for other methods to produce a time dependent O-D matrix for public transport.