Navigation system and method

A method of providing navigation instructions to a mobile unit 4 the location of which can be automatically identified wherein:<BR> the mobile unit 4 transmits a reference to a destination to a route-finding means (the central vehicle routing system) 1;<BR> the route-finding means acquires the location of the mobile unit 4;<BR> the route-finding means calculates a preferred route from the location of the mobile unit to the destination; and<BR> the route-finding means transmits information concerning the preferred route to the mobile unit. The central vehicle routing system comprises a database 2 and a processor 3. An arrangement for traffic congestion monitoring is also disclosed.