and be immune to lifting because of air currents and turbulence application_number US 90462392 A description referring to fig1 a pair of piezoelectric sensor cables 10 and 11 are embedded in flexible carrier 12 which is a roadway grade rubber such as neoprene carrier 12 maintains the spacing between sensor cables 10 and 11 a fixed distance apart in the embodiment shown in fig1 the overall width of the carrier is about 4 inches and the center to center spacing d between sensor cables 10 and 11 is slightly less carrier member 12 can be of the type shown in tyburski application ser no 07 880 410 in this embodiment a uniformly distributed linear weight 14 is secured by an adhesive 15 to the lower surface 16 of carrier 12 linear weight 14 and carrier 10 has a weight per unit length sufficient to maintain the device on the surface of the roadway and as disclosed in the above identified tyburski applications which are incorporated herein by reference the weight per unit length for high speed roadways is at least about one pound per foot for lower speed highways the weight can be less lead metal has been found to be particularly useful because it molds itself to roadway undulations so the flexible carrier hugs the roadway and at the same time assists in maintaining an accurate spacing d between piezoelectric sensors 10 and 11 thus while the sensor is flexible and coilable it.