Question

freeway design.

• Demand volume = 60,000 veh/day; Proportion of Peak Hour AADT : 0.08

• Directional distribution: 60/40; Mountainous Terrain and target LOS = C

• FFS 60 mph; 10% trucks; 5% RVs; PHF: 0.95 and fP =1

Answer 1

calculate the directional design hour volume as below:

DDHV=K₁*D*AADT

here, K₁ is the factor used to convert annual average daily traffic to a specified annual hourly volume.

D is the directional distribution factor

AADT is the annual average daily traffic

substitute 0.148 for K_1, 1.5 for D and 60000 for AADT.

DDHV = 0.148*1.5*60000

=13320 veh/h

for 60 mi/hr operating condition LOS C the capacity is 2300 pc/h/ln.

calculate the heavy vehicle adjustment factor as below:

f_hv=1/1+P_T(E_T-1)

here P_T is the proportion of heavy vehicle and E_T is the passenger car equivalent.

for rolling terrain E_T is 3

f_hv= 1/1+0.15(3-1)

=0.434

assuming a four lane calculate the v_p as below:

v_p = V/PHF*N*f_hv

here V is the hourly volume in vehicles/hr

N is the no. of lanes

f_hv is the heacy vehicle adjustment factor

v_p = 13320/0.95*2*0.434

=16124 pc/h/ln which is greater than 2300 pc/hr/ln so assume more number of lanes.

assume 8 lanes

v_p=13320/0.95*4*0.434

v_p=1752 [pc/h/ln

so eight lane is acceptable.