  In densely populated-cities, the use of private cars for personal
transportation is unsustainable, due to high parking and road capacity
requirements. The mobility-on-demand systems have been proposed as an
alternative to a private car. Such systems consist of a fleet of vehicles that
the user of the system can hail for one-way point-to-point trips. These systems
employ large-scale vehicle sharing, i.e., one vehicle can be used by several
people during one day and consequently the fleet size and the parking space
requirements can be reduced, but, at the cost of a non-negligible increase in
vehicles miles driven in the system. The miles driven in the system can be
reduced by ridesharing, where several people traveling in a similar direction
are matched and travel in one vehicle. We quantify the potential of ridesharing
in a hypothetical mobility-on-demand system designed to serve all trips that
are currently realized by private car in the city of Prague. Our results show
that by employing a ridesharing strategy that guarantees travel time
prolongation of no more than 10 minutes, the average occupancy of a vehicle
will increase to 2.7 passengers. Consequently, the number of vehicle miles
traveled will decrease to 35% of the amount in the MoD system without
ridesharing and to 60% of the amount in the present state.
