The main costs of a public transport company are the salaries of the drivers and the operational costs related to the use of the vehicles.

The transport service
The service provided by a Public Transport Company is made of a set R of transportation activities performed by a set of vehicles that travel to execute a service within a given geographic area. These vehicles may be of different types according to the kind of service provided (i.e. bus, coach, long bus, etc.). A vehicle is driven by a driver or, more generally, by a crew. A transportation activity is named trip (or ride) and it is characterized by a route that links two points in the geographic area. Thus each trip is a point-to-point link that occurs at predetermined times.

Vehicle Scheduling problem
The vehicle scheduling planning phase aims at optimizing the usage of a fleet of vehicles. This phase defines which trip of R must be assigned to which vehicle.

Crew Scheduling problem
The salary of the drivers usually covers a percentage between 50% and 75% of the total costs. Therefore it is important to minimize the number of drivers using efficiently all the available resources. The crew scheduling problem (CSP) presents as many similarities with the MDVSP as many differences due to the presence of constraints modeling safety conditions and law requirements. The CSP is aimed too at planning activities with well defined time and place. Generally speaking a vehicle shift does not correspond to one and one only crew shift, as the legal constraints that determine whether a shift is feasible or not are different and aim at ensuring good working condition, by interleaving properly periods of work and periods of rest.