Assume that you are an observer standing at a point along a three-lane roadway (in one direction). All vehicles in lane 1 are travelling at 40 km/h, all vehicles in lane 2 are travelling at 60 km/h, and all vehicles in lane 3 are travelling at 60 km/h. There is also a constant spacing of 1 km between vehicles. If you collect spot speed data for all vehicles as they cross your observation point for 30 minutes, what will be the time-mean speed (km/h) for this traffic stream? O 50.0 km/h O 55.4 km/h O 600 km/h O 64.4 km/h O 70.0 km/h