The section of 581 with the grass median is crawling with police at all times. Be aware that when merging with 581 from I81 the speed limit drops to 55 although the traffic flow is heavy and fast. 581 thru down town where the concrete barrier exists is harder to enforce due to the divider and narrow shoulder. This section is patrolled by motorcycles and unmarked cars driving in traffic, although it is usually during the day that I’ve seen them the most. It is possible at night to drive this section at a very high rate of speed with out too much risk.