Systems, devices and methods for managing mobile assets at a worksite. A system computer creates a geofence relating to the geolocation of a first communication device disposed in a first mobile asset, the data points of the geofence periodically updated according to the geolocation of the first communication device such that changes in the geolocation of the first communication device are proportionally reflected in the updated geolocation of the datapoints of the geofence. The cycle time of a second communication device disposed in a second mobile asset can be determined by determining the amount of time lapsed after the second communication device triggers the geofence. Various triggering events are described. Various shapes of the geofence are described to avoid unintended triggers of the geofence by assets, including polygonal shapes.