Gravity Escape Ramp
Gravity escape ramps involve a steep upwards grade that causes
the truck to slow down. These are advantageous when there is a
natural rise already next to the road and can be made at a
relatively low cost. An issue it has is the truck can roll
backwards after reaching its peak height, falling back into the flow of traffic. 
Misiryeong. "Runaway Truck Ramp." Wikipedia. Wikimedia Foundation, 18 Nov. 2014. Web. 18 Apr. 2017.
The Physics
Gravity escape ramps use the force of
gravity in addition to rolling friction to stop the trucks.
You can see the effect grade has on stopping distance in the stopping distance formula (Garber, 55).
You can see the effect grade has on stopping distance in the stopping distance formula (Garber, 55).
U=speed in mph
a=braking acceleration
g=acceleration of gravity
G=grade
So if we use the braking acceleration for an 80,000lb truck on sand that we found for the arrestor bed, an initial speed of 70 mph and an upwards grade of 10%, we can find the stopping distance.
a=braking acceleration
g=acceleration of gravity
G=grade
So if we use the braking acceleration for an 80,000lb truck on sand that we found for the arrestor bed, an initial speed of 70 mph and an upwards grade of 10%, we can find the stopping distance.
Compared to the stopping distance of
a horizontal arrester bed we calculated on the
arrester bed page:
In other words, the 10% grad allowed
the truck to stop 85 feet sooner, which is another
reason why a gravity escape ramp is preferable over a
horizontal arrester bed.