Answer:
The Question is incomplete, the complete question is as follows:
Consider the freeway in Problem 1. At one point along this freeway there is a 4% upgrade with a directional hourly traffic volume of 5,435 vehicles. If all other conditions are as described in Problem 1, how long can this grade be without the freeway LOS dropping to F?
A six-lane rural freeway (three lanes in each direction) has regular weekday users and currently operates at maximum LOS C conditions. The base free-flow speed is 65 mi/h, lanes are 11 ft wide, the right-side shoulder is 4 ft wide, and the interchange density is 0.25 per mile. The highway is one rolling terrain with 10% large trucks and buses (no recreational vehicles), and the peak-hour factor is 0.90. Determine the hourly volume for these conditions
Step-by-step explanation:
Make the assumption Base continuous flow velocity (BFFS)= 65 mph.
Pitch width= 11 ft.
Decrease in lane width pace,fLW= 1.9 mph.
Complete Lateral clearance= 4 ft. Lateral clearance speed reduction, fLC= 0.8 mph.
Complete Width of the Ramp= 0.25 mile.
Velocity reduction proportional to the ramp height, f ID= 0 mph.
Assume lane number to be = 3.
Reduction in speed corresponding to no. of lanes, fN = 3 mph
Free Flow Speed (FFS) = BFFS – fLW – fLC – fN – fID = 65 – 1.9 – 0.8 – 3 – 0 = 59.3 mph
Peak Flow, V veh/hr
Peak-hour factor = 0.90
Trucks = 10%
Rolling Terrain
fHV = 1/ (1 + 0.10 (2.5-1)) = 1/1.15 = 0.8696
fP = 1.0
Peak Flow Rate, Vp = V / (PHV*n*fHV*fP) = V/ (0.90*3*0.8696*1.0) = 0.426V veh/hr/ln
Average speed of vehicles, S = FFS = 59.3 mph
Level of service C
Density of LOS C lies between 18 - 25 veh/mi/ln
Maximum density = 25 veh/mi/ln
Density = Vp /S = 25
0.426V = 25 * 59.3
V = 3480 veh/hr
b) V = 5435 veh/hr
LOS dropping to F
Max density = 45 veh/mi/ln
Density = Vp/S = 45
Vp = 45 * 59.3 = 2668.5 veh/hr/ln
V/(PHF * n * fHV * fP) = 2668.5
fHV = 5435/(0.9*3*2668.5*1.0) = 0.754
1/(1+0.10 (ET -1)) = 0.754
ET = 4.26 ~ 3.5
For 4% upgrade and 10% trucks with ET = 3.5, length of the grade is Greater than 1.0 miles