Highway Geometric Design

Traffic Characteristics

1. Assuming that a driver with a visual acuity of 20/20 can read a road sign within his area of vision at a distance of 50 ft for each inch of letter height, prepare a table with required letter heights for signs 100 ft, 500 ft, and 1000 ft for drivers with acuities of 20/20, 20/40, and 20/70.

2. A vehicle has a maximum acceleration rate of 10 ft/sec2 is entering a merging area using a 600 ft acceleration lane at an initial speed of 15 mph where the free speed in the merging area is 70 mph.

a) Using basic equations of motion, determine the maximum speed the ramp driver can attain by merging at the end of the acceleration lane.

b) Using basic equations of motion, determine the minimum length of the acceleration lane that would allow the merging vehicle to merge safely with through traffic if the minimum safe merging speed is equal to the free speed minus 10 mph.

3. A driver traveling at 30 mph behind another car decides to pass it and presses the accelerator to the floor. Assuming that the accelerating behavior of the vehicle may be described by

where v is the speed in ft/sec and t is the time in seconds.
a. Find the rate at which the vehicle is accelerating after 3 sec.
b. How long would it take the vehicle to reach a speed of 50 mph?

4. Draw an Excel graph to relate the following:
a) Operating speed versus vehicle density
b) Traffic volume versus vehicle density.
5. You are required to re-design SR 87 from MP 188.83 to MP 190.84. Using data available in the ADOT website and the ADOT Design Manual determine the following:
a. AADT (latest year), K, D, and T
b. What level of service should this road be designed for?
c. What is the design speed?
d. How many lanes are needed in each direction for a 2038 design year assuming a 4% traffic growth per year? Assume a design volume of 1,800 vehicles/hour/lane.
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