Method for sharing transportation means, e.g. cars, motorcycles or bicycles, among a plurality of users, comprising the steps of - providing an electronic control unit, comprising a database of providers of vehicles, a database of said vehicles comprising database fields for a plurality of time schedule data for each vehicle and a database of users, - providing a plurality of protective access units provided in connection with each of the vehicles, - providing a plurality of mobile communication devices, wherein each mobile communication device is associated with a user from the plurality of users, wherein the request of a user for use of one of the vehicles comprises the steps - transmitting, directly or via a mobile communication device, a request of said user for use of one of the vehicles to the electronic control unit, - identifying the user, his mobile communication device, the requested vehicle and the corresponding security device in the databases of the electronic control unit, - providing an original encapsulated message to the mobile communication device of the user comprising timeslot information for the requested time of use of the vehicle, wherein the original encapsulated message comprises two layers of protection, - providing a forwarded encapsulated message from the mobile communication device of the user to the protective access unit associated to said vehicle comprising the timeslot information for the requested time of use of the vehicle, characterized in that the timeslot information for the requested time of use of the vehicle is digitally signed by the electronic control unit of the system, wherein the encapsulated message is digitally signed by said electronic control unit, wherein the outer layer of protection of the encapsulated message is encrypted through a public key of the mobile communication device, wherein, upon decoding of the outer layer of protection and of the original encapsulated message, the mobile communication device checks the received original encapsulated message whether it originates from the electronic control unit of the system, and in the affirmative result, the remaining message is used as said forwarded encapsulated message, wherein the layer of protection of the forwarded encapsulated message is encrypted through a public key of the protective access unit; wherein the protective access unit, upon decoding of the layer of protection of the forwarded encapsulated message, checks the received forwarded encapsulated message, whether it originates from the electronic control unit of the system, and in the affirmative result, opens, unlocks and/or starts the vehicle for use. - providing an electronic control unit, comprising a database of providers of vehicles, a database of said vehicles comprising database fields for a plurality of time schedule data for each vehicle and a database of users, - providing a plurality of protective access units provided in connection with each of the vehicles, - providing a plurality of mobile communication devices, wherein each mobile communication device is associated with a user from the plurality of users, wherein the request of a user for use of one of the vehicles comprises the steps - transmitting, directly or via a mobile communication device, a request of said user for use of one of the vehicles to the electronic control unit, - identifying the user, his mobile communication device, the requested vehicle and the corresponding security device in the databases of the electronic control unit, - providing an original encapsulated message to the mobile communication device of the user comprising timeslot information for the requested time of use of the vehicle, wherein the original encapsulated message comprises two layers of protection, - providing a forwarded encapsulated message from the mobile communication device of the user to the protective access unit associated to said vehicle comprising the timeslot information for the requested time of use of the vehicle, characterized in that