Plan proposal device, system, vehicle, and plan proposal method

A plan proposal method comprising:

• predicting, by a controller, as a user action, an action of a first user in a certain period, including parking a vehicle in a parking lot shared by a plurality of users including the first user;
• generating, by the controller, proposal data for proposing an action plan in the certain period based on an obtained prediction result and information on the parking lot in the certain period;
• and
• outputting the generated proposal data from the controller, wherein:
• the prediction result includes a first estimated time when the first user is expected to leave the parking lot with the vehicle;
• the information on the parking lot includes an estimated congestion status of an exit of the parking lot or a road around the parking lot at the first estimated time;
• and
• the plan proposal method further comprising, including, in the action plan, an action of leaving the parking lot with the vehicle at a leaving time different from the first estimated time under a condition that the estimated congestion status exceeds a reference congestion level.