Originally posted by slartibartfast01 Still intrigued to know how long a full road train takes to stop. Aren't there regulations about that sort of thing?
I don’t think there are regulations, but there is the design and engineering of the brakes, just like on any vehicle. Brakes must be sized to be able to dissipate the forward motion of the expected mass, and be able to absorb and dissipate the heat created when operating, without failure.
I believe the manufacturers publish the designed stopping distances of vehicles, based on the maximum designed weight capacity and speeds. A fully laden tractor trailer rig will always have a stopping distance much greater than that of the family car.
I’ll add some more here:
The Federal Motor Carrier Safety Administration (FMCSA) calculates the stopping distance of semi-trucks vs. cars as follows:
A normal passenger vehicle driving at 65 miles per hour will need about 300 feet to stop.
A fully loaded commercial truck driving at 65 miles per hour will need about 600 feet to stop.
For a more visual comparison, a car takes about the length of a football field to stop, while a semi-truck needs the distance of approximately two football fields to stop.
I believe the more common road train configuration Down Under is a prime mover and four trailers. So given the above, a road train should take around 1,200 feet to stop, about four football fields.
Additionally, stopping distance can vary significantly based on road conditions and other factors.
Reaction time. Most drivers take about 1.5 seconds to react after seeing a hazard that requires action. Since truck drivers sit a bit higher, they may have a slight advantage over drivers in cars or pickups, but the advantage is minimal.
Vehicle weight. A fully laden tractor trailer weighs around 80,000lbs, a car around 4,000, so a truck is 20 times heavier than a car.
Road surface and grade. A downhill slope will increase stopping distances dramatically, and exponentially based upon the weight. Gravel, rain, snow or ice also increase stopping distances, again, influenced by the weight.
Speed. Newton’s law, an object in motion tends to remain in motion, unless acted upon by an opposing force. The faster the object, and the greater the mass, the larger the required opposing force to slow or stop it, and the longer it will take.