A server of a vehicle request management system, comprising: communication means arranged to communicate with a plurality of first devices and a plurality of second devices, each of the second devices being associated with a vehicle, the communication means being further arranged to receive a vehicle request from one of the first devices, the vehicle request comprising a first location, and the communication means being further arranged to receive a second location from the first device or one of the second devices that has accepted the vehicle request; data storage means comprising digital map data having a plurality of navigable segments representing roads of a road network in a geographical area covered by the map; and processing means arranged to calculate a route on the road network between the received first and second locations to be travelled by the vehicle associated with the second device using the digital map data, wherein said communication means is further arranged to receive positional data relating to the position of the second device over time, characterised in that: the processing means is arranged, during the journey of the vehicle between the first and second locations, to: compare the received positional data with the calculated route between the first location and the second location; determine if the vehicle deviates from the calculated route; and select a new second device that is able to fulfil the vehicle request when such a deviation is determined; and the communication means is further arranged to transmit data indicative of the vehicle request to said new second device. communication means arranged to communicate with a plurality of first devices and a plurality of second devices, each of the second devices being associated with a vehicle, the communication means being further arranged to receive a vehicle request from one of the first devices, the vehicle request comprising a first location, and the communication means being further arranged to receive a second location from the first device or one of the second devices that has accepted the vehicle request; data storage means comprising digital map data having a plurality of navigable segments representing roads of a road network in a geographical area covered by the map; and processing means arranged to calculate a route on the road network between the received first and second locations to be travelled by the vehicle associated with the second device using the digital map data, wherein said communication means is further arranged to receive positional data relating to the position of the second device over time, characterised in that: the processing means is arranged, during the journey of the vehicle between the first and second locations, to: compare the received positional data with the calculated route between the first location and the second location; determine if the vehicle deviates from the calculated route; and select a new second device that is able to fulfil the vehicle request when such a deviation is determined; and the communication means is further arranged to transmit data indicative of the vehicle request to said new second device. the processing means is arranged, during the journey of the vehicle between the first and second locations, to: compare the received positional data with the calculated route between the first location and the second location; determine if the vehicle deviates from the calculated route; and select a new second device that is able to fulfil the vehicle request when such a deviation is determined; and the communication means is further arranged to transmit data indicative of the vehicle request to said new second device.