Interstate 5 near Terwilliger
The Portland Police have been using this trap for years. They have even gotten "parking" for their cruisers and motorcycles built into the freeway along the stretch of I-5 known as the "Terwilliger Turns" or "Terwilliger Curves".
The posted speed limit is 50 MPH, although this stretch of interstate can be navigated safely at moderately higher speeds. The police like to sit on either end of the curves and wait for people to speed into them, then they pull them over.
Sometimes a motorcycle officer will sit at the bottom of the Terwilliger on-ramp to catch people speeding OUT of the curves while going northbound.