The trucking industry turned to sealed speed recorders on the trucks, (Congress mandated properly installed and maintained units to be Evidence, SCOTUS agreed), and the Crooked Coppers just turned to other violations.
The one thing the Crooked Towns couldn't beat was the Feds bypassing the town with an Interstate Freeway because the Feds worked together, kept records and had complete control of construction.
Bypass meant certain economic death for a town.
There were several I watched rot for years in California, my dad pointed 'em out when we drove by on the freeway, and told me why.