A vehicle passenger restraining system is basically comprises a plurality of passenger restraining devices, a deformation detecting device and a passenger restraining device operating unit. The skate further includes a skating device mount for mounting the skating device to the boot, wherein the skating device can rotate 360 degree under the boot. In the closed position the first and second device members overlap such that the first device member blocks access to the second io element. Another signal line 13 is provided on the cathode 4; the signal line 13 extends straight from the cathode 4 and is connected to a Y axis wire 14. The first effective refractive index being associated with the first mode and the second effective refractive index being associated with a second mode of a second optical signal having the wavelength. Still further, the method comprises determining whether the first testing element has corroded through.