Speed cameras in work zones are for revenue (Dec. 29, “Automated Speed Monitoring to Start in Work Zones”). If not, then why do we not do things like adopt the zipper merge, and post 85th percentile speed limits? Low speed limits cause a speed variation between the vehicles, which promotes tailgating, constant passing and rapidly approaching a vehicle.
Here is Michigan’s strategy. Most freeway work zones have workers behind concrete barriers, so they are not at risk from passing cars. Drivers see the workers are safe. Freeway limits are usually 70 mph, but are sometimes reduced to 60 mph if warranted (if the work areas are close to the travel lanes or there are some minor lane shifts, the basic limit drops by 10 mph.)