They are actually determined for each stretch of road for a combination of reasons. Once you've exceeded the posted limit you are not only making an illegal moving violation, but putting yourself, your family, and others on the road in potential danger. How you react to something unexpected in the road will make a difference. Driving without additional distractions should better allow you to stay in control of your vehicle when you are faced with any of these situations. If you do 'jerk' the steering wheel to try and 'swerve' quickly to avoid the pending obstacle, this will place your vehicle in a potentially hazardous position depending on your center of gravity and your forward speed - the momentum of which will then be transfered horizontally to the most forward side of your vehicle when you pull the wheels away from driving straight forward.
Prevention can go a long way.
This is not ignoring that accidents happen, and happen quickly, and sometimes an impact situation cannot be avoided. It is hopeful that the SUV structure and design will help you survive an impact, in any case you simply MUST be wearing your safety belts to take advantage of the original intent of the manufacturers design to keep you safe inside the vehicle in case of impact. Try not to get to the point where your reaction would be to swerve in the firstplace. Seat Belts . Check on the statistics if you don't believe us.