How Truck Escape Ramps Stop Out-Of-Control Big Wheelers

Oh! He took it! He took it, dude! Gravel is flying! Dirt is flying! Narrator: If you’ve driven any one of the many highways
crisscrossing the world, chances are you’ve seen one of these: a truck escape ramp. Some escape ramps slope upwards. Others are flat. Some contain sand, others gravel. But regardless of design,
they all serve one purpose: to bring vehicles with
malfunctioning brakes to a safe stop. Just how do they work? When designing a new
ramp, state authorities consider factors specific to the road, like how steep the grade
is and what road conditions look like at the bottom of a hill. Though they may look different depending on where you see them, escape ramps around the world
do have some things in common. Most escape ramps make
use of arrester beds, pools of sand or gravel. The material in the bed is selected for their low coefficients
of interparticle friction, meaning when a wheel or
axle touches the bed, the material in it moves
away from each other, allowing the truck to sink into the gaps. Like a swimming pool, escape
ramps are shallow at entry, anywhere from 3 inches
deep, and get deeper, to around 48 inches at 100 to 200 feet in. When a truck enters the bed, it meets little resistance at first, then more as it travels. This means the truck
decelerates gradually, reducing the risk of injury to the driver, and stands less risk of
flipping over, or capsizing. When observing escape
ramps around the world, three designs stand out: the sandpile bed, the gravity escape ramp, and the mechanical arrester ramp. This is a sandpile bed. This type of escape ramp
contains loose rows of sand perpendicular to the direction of traffic. As a truck collides with the pile, the energy of the truck is
transferred to the sand. As the sand is sent flying
away at high speeds, an equal and opposite force
acts against the truck, reducing its velocity. Impacting sandpiles, though, is… jarring, putting the driver at
higher risk of injury, which brings us to the
gravity escape ramp, distinguishable by its
gradually ascending slope. In addition to the friction
of material in the bed, gravity works on the truck,
pushing it down and back. The sloped gravity ramp is more effective than a flat arrester bed. A 10% grade could allow a truck to halt anywhere up to 85 feet sooner. Gravity ramps are the most cost-effective where natural rises occur
adjacent to the road. Some terrains, though, simply do not allow for a naturally occurring
gravity escape ramp. So, state agencies have turned to a more experimental
form of escape ramp. The mechanical arrester ramp
can be installed on flat ground or even downward slopes. Unlike other designs, this ramp does not have an arrester bed. Instead, it contains a series
of stainless-steel catch nets. The nets absorb the energy
from a truck collision. Like a rubber band being pulled taut, the force exerted on the
truck increases exponentially the further the truck travels. The mechanical arrester
ramp then can stop a truck more quickly than gravel
or sand arrester beds. Entering a truck escape
ramp is a one-way trip. If the ramp works properly, a truck will either end
up submerged or damaged, needing a tow to recover. Despite the expense,
agencies urge truck drivers and other motorists to
use the escape ramps.