The majority of speed bumps I encounter are not the full width of the road but are discrete bumps sloping on all 4 sides and about the width of the car. If you car has enough ground clearance you can take these at 30+ mph as long as you position the centre of the car with the centre of the bump. On busy roads this may be impractical and you may have to position the vehicle with the nearside to miss the bump and the offside (drivers) side takes the full height if the bump.