As a sibling comment noted, it's not a pressure sensor [1] but an induction loop. The Wikipedia article https://en.wikipedia.org/wiki/Induction_loop#Vehicle_de

As a sibling comment noted, it's not a pressure sensor [1] but an induction loop. The Wikipedia article https://en.wikipedia.org/wiki/Induction_loop#Vehicle_detection https://en.wikipedia.org/wiki/Induction_loop#Vehicle_detecti... has fairly extensive details on modern implementation. [1] These do exist for weight-in-motion systems, however.