Question

A freeway is to be designed to provide LOS C for the following conditions: design hourly volume of 5600 veh/h; PHF: 0.92; trucks: 6%; recreational vehicles: 0%; driver population: commuters and familiar drivers; right side lateral clearance: 7ft; rolling terrain; total ramp

density of 0.75 ramps per mile. Determine: whether eight (four in each direction) 12 ft lanes are enough to provide LOS C.

Answer 1

Answer:

Given that a freeway is to be designed to provide LOS C

Tabulate the PCU (Passenger Car Equivalent) for the vehicles given as follows:

Vehicle	PCU
Truck	2.5
Recreational Vehicle	2.0

Calculate the heavy vehicle adjustment factor by using the relation as follows:

  

Calculate the no. of lanes in each direction by using the relation as follows:

Consider the driver population factor,

Calculate the free flow speed by using the relation as follows:

.............(1)

Consider the following tables for adjustment factors:

Table 1

Right Shoulder Lateral Clearance (ft)	Reduction in Free-Flow Speed, (mph)
	Lanes in One Direction
	2	3	4
>=6	0.0	0.0	0.0
5	0.6	0.4	0.2
4	1.2	0.8	0.4
3	1.8	1.2	0.6
2	2.4	1.6	0.8
1	3.0	2.0	1.0
0	3.6	2.4	1.2

Table 2

Number of Lanes (One Direction)	Reduction in Free-Flow Speed, (mph)
>=5	0.0
4	1.5
3	3.0
2	4.5

Table 3

Lane Width (t)	Reduction in Free-flow Speed, (mph)
>=12	0.0
11	2.0
10	6.35

Table 4

Interchanges per Mile	Reduction in Free-Flow Speed, (mph)
<=0.50	0.0
0.75	1.3
1.00	2.5
1.25	3.7
1.50	5.0
1.75	6.3
2.00	7.5

Substitute the following values in equation (1)

70mph for BFFS

0 for ,

0 for ,

1.5 mph for , and

0 for

FFS = 70-0-0-1.5-0

= 68.5 mph

Calculate the speed by using the relation as follows:

  

  

Calculate the density by using the relation as follows:

According to the LOS-C, the maximum density must be 26 pc/mi/ln.

Therefore, the four-lane in each direction are enough to provide LOS-C.