These are permanently installed axle sensor (class II) or weighing grade (class I) axle sensors manufactured by North American Philips.
The sensor element is secured in an extruded aluminum channel with sand filled epoxy or flexane 80. The sensor is normally available in 6' (one wheel path) or 11'6" (both wheel paths) length with 65' of RGU 58 coax cable.
Longer lead in coax cables are available. Normal output voltage is in the 300 millivolt range. Normal life expectancy is 4-7 years.