How do you calculatemodeling the formula for the correction

How do you calculate/modeling the formula for the correction factors of the calculated saturation flow rate?

Solution

STEP 1 : First we will understand the formula & terms involved in it

Saturation flow rate

S = S_o x N . F_w . F_HV . F_g . F_p . F_bb . F_a . F_LU . F_{LT .} F_RT . F_Lpb . F_Rpb

where,

S - saturation flow rate for subject lane group, expressed as a total for all lanes in a lane group (veh/hr)

S_o - base saturation flow rate per lane (pc/hr/lane)

N - Number of lanes in lane group

_Fw - adjustment factor for lane width

F_HV - adjustment factor for heavy vehicles in traffic stream

F_g - adjustment factor for approach grade

F_p - adjustment factor for existence of parking lane and parking activity adjacent to lane group

F_bb - adjustment factor for blocking effect of buses which stop within intersection lane

F_a - adjustment factor for area type

F_LU - adjustment factor for lane utilization

F_LT - adjustment factor for left turn in lane group

F_RT - adjustment factor for right turn in lane group

F_Lpb - pedestrian adjustment factor for left turn

F_Rpb - pedestrian adjustment factor for right turn

STEP 2 : Now we will see how to calculate each adjustment factor

1. Base saturation flow rate

2. Adjustment for lane width

F_w = 1 + (w - 12)/30

where w - lane width in ft

3. Adjustment factor for heavy vehicles & grade

F_HV = 100 / [ 100 + %HV(E_T - 1) ]

F_g = 1 - %G/200

where,

% HV - % heavy vehicles for lane group volume

E_T - passengar car equivalent = 2

%G - % grade on lane group

4. Adjistment for parking

F_p = [N - 0.1 - (18N_m/3600)]/N

where,

N_m - no. of parking manouvers per hr

N - no. of lanes

5. Adjustment for bus blockage

F_bb = [ N - (14.4 N_B/3600) ] / N

where,

N_B - no. of bus stopped per hr

6. Adjustment for area type

F_a = 0.9 for Central business district and 1 for all other areas

7. Adjustment for lane utilization

F_LU = V_g / (V_g1 . N)

where,

V_g - unadjusted demand flow rate for lane group (veh/hr)

V_g1 - unadjusted demand flow rate for single lane with highest volume in lane group

N - no. of lanes in the group

8. Adjustment for left turn

F_LT = 0.95 for exclusive lanes

= 1 / [ 1 + 0.05 P_LT ] for shared lanes

where, P_LT - proportions of left turn in lane group

9. Adjustment for right turn

F_RT = 0.85 for exclusive lanes

= 1 - 0.15 P_RT for shared lanes

= 1 - 0.135 P_RT for single lane

where, P_RT - proportions of right turn in lane group

10. Adjustment for pedestrian left turn

F_Lpb = 1 - P_LT(1 - A_pbT) (1 - P_LTA)

where,

P_LT - proportion of pedestrian left turn in lane group

A_pbT - permitted phase adjustment

P_LTA - proportion of LT protected green over total LT green

11. Adjustment for pedestrian right turn

F_Rpb. = 1 - P_RT(1 - A_pbT)(1 - P_RTA)

where,

P_RT - proportion of pedestrian right turn in lane group

P_RTA - proportion of RT protected green over total RT green