Transportation Theory and Planning

Working under the assumption of rigid demand, we can define two different methods to estimate the mobility demand in the actual situation:

1) Census

The census is usually performed by a government department or a public agency. In Italy, the census is provided by the public agency ISTAT, which is the Italian national institute of statistics, whereas in the state of New York City, it is provided by the NYCDOT. The census provides useful information that can be used to estimate the mobility demand.
These information are briefly listed in the following:
-the internal demand, that is the movements for study or work purposes within the study area;
-overall inflows and outflows between cities or provinces, that is the movements with origin or destination outside of the study area.

Regarding the flows between cities or provinces, the data provided by the census are usually inadequate because they provide the total flows without other information which allow the analyst to distribute these flows on the link of the network. That is why to estimate the “external demand”, which is represented by the movements that have the origin or the destination outside the study area, it is better to perform direct investigations at the boundaries of the area. If this option is not viable, a criteria to distribute the flow is accounting for the employment rate of each sub-area of the study area.

2) Direct demand estimation through interviews

We can distinguish three different type of direct investigations:

-at home: with this approach, the analyst interviews randomly (in this way he/she will be able to extend the result of the investigation) a sample of users which live within the study area. [...]

- on board: these are interviews performed on the streets; every users that travel on a certain street, the interviewer interviews an user which is travelling on that street. In this case, the entire population is constituted by the number of vehicles that travel using that street, during the investigation period.

- on the boundary: these are on board interviews performed on the links which represent the boundary of the study area. These interviews are aimed to estimate the exchange demand between the study area and the external environment, and the non-systematic movements.

- at destination: the interviewer ask the users which is his/her origin, destination, departure hour, and arrival hour.