Plausible deniability. The feds use this technique a lot. They do things against you illegally but also have plausible deniability so they can claim they didn't do something illegal. So yea, tossing the tracker on the side of the road is perfect.

In reality, they don't need GPS trackers anyway. They simply get your cell phone carrier to give them your cell phone's location data. Or they go to the carrier of your car's onboard communication system. All of this should be illegal, but they get around that easily enough. As a last resort, they can track you with video cameras they have access to.

The video suggests that it 'fall off' while the car is driving over a bridge.