Question

Problem #2 A section of a six-lane highway (3 in each direction) with a two-way-left-turn lane (TWLTL) is being designed. Determine the level of service if the following data are applicable to this section. Traffic Data: • • • Directional design hour volume = 3600 veh/h (all are passenger cars) Peak-Hour-Factor (PHF) = 0.94 Base Free-Flow-Speed (FFS) = 55 mi/h Geometric data: • • • • • Urban setting Rolling terrain Lane width = 11 ft Shoulder width = 4 ft (right side) and 1 ft (left side) Average access point spacing= 12 points per mile on each side

Answer 1

Ans) We know,

v_p = V / (PHF x N x f_HV x f_P)

where, V = hourly volume =3600 veh/hr

PHF = peak hour factor = 0.94

N = number of lanes in each direction =3

f_HV = Heavy vehicle adjustment factor

fp = Driver population factor = 1

Also, f_HV = 1 / [1 + P_T(E_T -1) + P_R(E_R - 1)]

where, P_T and P_R are proportions of trucks and RVs respectively

E_T and E_R are passenger car equivalent for trucks and RVs respectively

Since , all the vehicles are passenger cars, P_R = 1 and P_T = 0

For passenger cars, E_T = 1

=> f_HV = 1 / 1 + 0 + 0 = 1

=> v_p = 3600 / ( 0.94 x 3 x 1 x 1)

=> v_p = 1276.6 $\approx$ 1277

Now, determine free flow speed (FFS),

FFS = BFFS - f_LW - f_LC - f_N - f_AD

where, BFFS = base free flow speed = 55 mph

f_LW = adjustment for lane width = 2 mph for 11 ft

f_LC = adjustment for lateral clearance = 0.80 mph for 4 ft shoulder width and three lanes

f_N = adjustment for number of lane = 3 mph for three lanes in one direction

f_AD = adjustment for access point density = 3 mph for 12 access point per mile

=> FFS = 55 - 2 - 0.80 - 3 - 3 = 46.2 mph

According to speed vs flow curve, for v_p = 1277 and FFS = 46.2 mph, level of service is LOS D