Assume you are an observer standing at a point along a three- lane roadway. all vehicles in lane 1 are traveling at 30 mi/ h, all vehicles in lane 2 are traveling at 45 mi/ h, and all vehicles in lane 3 are traveling at 60 mi/ h. there is also a constant spacing of 0.5 mile 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 and space-mean speed for this traffic stream?