Route 4 in Calvert County is aggressively patrolled along its entire length, with many speed traps that change location very frequently, by both county sheriffs and state police. The number of traps and patrolling cars, with and without radar, marked and unmarked cars including vans etc., is greater per mile than anywhere I have seen in almost 6 decades of driving all over the USA. Generally you can exceed the limit by 10 or even 15 mph, but not always.