Question

A 5% grade with a length of 3,000 ft is meeting a 2% grade with a length of 4,000 ft. If a truck starts at the beginning of the first grade at a speed of 50 mph, determine the following:

1. Speed at the end of the first grade
2. Speed at the end of the second grade

Answer 1

since the directio of grade is not given hence it is auumed that both grades are positive in nature: [ refer figure attached below]

as per AASHTO, the verticle curve as per Passenger Comfort is given by:

Where: L = length of verticle curve in ft

A = Grade diffrence in percent

V = speed of vehicle in mph

1. speed of vehicle as end of first grade:

  

2. speed of vehicle as end of second grade:

the net grade = 5%-2% = 3%