the speed of the passing vehicle 108 is increased the vertical force generated by the viscous damper unit 112 increases and beyond certain speed speedbump speed setting the total vertical force exerted by the panel 100 on the tire 108 a becomes greater than the weight of the vehicle 108 on the passing tire 108 a and the tire 108 a and the vehicle 108 will experience a vertical motion speedbump action and a deceleration thus the speedbump also serves to slow down the vehicle 108 if it is moving too fast over the panel s 100 a similar device for decelerating vehicles is described in co pending u s patent application ser no 10 372 496 the disclosure of which is incorporated herein in its entirety by its reference in an adaptive version of the speedbump of fig1 a sensor 114 is provided in the roadway 106 before the panel s 100 that is the sensor 114 is positioned in the roadway 106 such that a vehicle 108 approaching the panel s 100 will first pass over the sensor 114 before passing over the panel s 100 as the vehicle 108 approaches the panel s 100 the sensor 114 is crossed the sensor 114 is of a type.