ADD: Private cars will disappear from the map as soon as the estimated time of the car journey that gave rise to them being spawned has expired
FIX: Errors in the calculation of private car journey times
FIX: Ensure that the origin and destination for passengers and mail is never identical
CHANGE: Reduce the generic road speeds (used for private car journeys in cities and all private car journeys if always_assume_everywhere_connected_by_road is set) to reflect the lack of maximum speed at all times and the indirectness of road routes