For many people in New Glarus, especially on the south side of the village and in the township just beyond it, the sound is familiar enough to wake them before they even fully register what it is: the hard, reverberating growl of a truck engine brake cutting through the valley in the middle of the night.

The term most people use is “jake brake,” though that is technically a brand name that has become generic shorthand for an engine brake. When activated, the system changes how the engine’s exhaust valves operate so the engine helps slow the truck, turning it into what Cummins describes as a power-absorbing air compressor. It is a slowing device, not a substitute for the truck’s regular service brakes.