A system for calculating a desired time of arrival to a target destination (304, 406, 506) of a working site for a working machine, comprising a device mountable to a first vehicle being a working machine (306, 410, 502), the device comprises: - a transmitter; - a receiver; and - a logic unit configured to receive signals for determining a current position and a current vehicle speed of the first vehicle (306, 410, 502), the logic unit being further configured to determine an estimated time of arrival at a target destination (304, 406, 506) for the first vehicle (306, 410, 502) based on predetermined route information, the current position of the first vehicle and the target destination of the first vehicle (306, 410,502); wherein the device is configured to: - transmit the estimated time of arrival at the target destination (304, 406, 506) for the first vehicle (306, 410, 502); - receive, from a second vehicle (308, 412, 504) being a working machine, an estimated time of arrival at the target destination (304, 406, 506) for the second vehicle (308, 412, 504); characterized in that the device is further configured to: - receive signals indicative of a weight of a load on a platform of the respective first and the second vehicle; - calculate a desired estimated time of arrival at the target destination (304, 406, 506) for the first vehicle (306, 410, 502) based on the received estimated time of arrival at the target destination (304, 406, 506) for the second vehicle (308, 412, 504) and a weight ratio between the weight of the load on the platform of the first vehicle and the weight of the load on the platform of the second vehicle; and - calculate a desired vehicle speed for the first vehicle (306, 410, 502) for achieving the desired estimated time of arrival at the target destination for the first vehicle (306, 410, 502). - a transmitter; - a receiver; and - a logic unit configured to receive signals for determining a current position and a current vehicle speed of the first vehicle (306, 410, 502), the logic unit being further configured to determine an estimated time of arrival at a target destination (304, 406, 506) for the first vehicle (306, 410, 502) based on predetermined route information, the current position of the first vehicle and the target destination of the first vehicle (306, 410,502); wherein the device is configured to: - transmit the estimated time of arrival at the target destination (304, 406, 506) for the first vehicle (306, 410, 502); - receive, from a second vehicle (308, 412, 504) being a working machine, an estimated time of arrival at the target destination (304, 406, 506) for the second vehicle (308, 412, 504); characterized in that the device is further configured to: - receive signals indicative of a weight of a load on a platform of the respective first and the second vehicle; - calculate a desired estimated time of arrival at the target destination (304, 406, 506) for the first vehicle (306, 410, 502) based on the received estimated time of arrival at the target destination (304, 406, 506) for the second vehicle (308, 412, 504) and a weight ratio between the weight of the load on the platform of the first vehicle and the weight of the load on the platform of the second vehicle; and - calculate a desired vehicle speed for the first vehicle (306, 410, 502) for achieving the desired estimated time of arrival at the target destination for the first vehicle (306, 410, 502). - transmit the estimated time of arrival at the target destination (304, 406, 506) for the first vehicle (306, 410, 502); - receive, from a second vehicle (308, 412, 504) being a working machine, an estimated time of arrival at the target destination (304, 406, 506) for the second vehicle (308, 412, 504); - receive signals indicative of a weight of a load on a platform of the respective first and the second vehicle; - calculate a desired estimated time of arrival at the target destination (304, 406, 506) for the first vehicle (306, 410, 502) based on the received estimated time of arrival at the target destination (304, 406, 506) for the second vehicle (308, 412, 504) and a weight ratio between the weight of the load on the platform of the first vehicle and the weight of the load on the platform of the second vehicle; and - calculate a desired vehicle speed for the first vehicle (306, 410, 502) for achieving the desired estimated time of arrival at the target destination for the first vehicle (306, 410, 502).