Pavement Design for Carriageway Construction

(d) Lateral WanderThe cumulative number of commercial vehicles using a pavement during itsdesign life shall be corrected for the positive effect of lateral wander of vehicleswithin or across the traffic lanes. The lateral wander correction factors (W f ) forflexible pavements are shown in Table 4. For an intermediate lane width, anappropriate factor may be derived by interpolation.Table 4 - Lateral Wander Correction FactorsLane Width (m) Lateral Wander Correction Factor (W f )3.00 1.003.37 0.963.50 0.953.65 0.923.75 0.90(e) Step-by-step Calculation of Design Traffic LoadThe anticipated number of equivalent standard axles for structural design isdetermined according to the following steps.Step 1 - Determine the design initial average daily traffic flow (AADT d )AADT d = AADT b x (1 + r) m [vehicles/day]where AADT b = base annual average daily traffic flow [vehicle/day]r = annual traffic growth rate [in decimal], from past trafficfigures or from Transport Department (typical valuesranging from 0.01 to 0.04)m = length of period between timing in AADT b and the timethat the road is expected to open to traffic [years]Step 2 -Determine the initial daily number of commercial vehicles (C e ) in theslow lane in one directionC e = P s x P v x D s x AADT d [no. of commercial veh./day]where P s = percentage of commercial vehicles using slow lane= 1 where there is only 1 traffic lane in the directionconcerned; or0.65 for other casesP v = percentage of commercial vehicles in AADT b ,RD/GN/042 Pavement Design for Carriageway Construction Page 15 of 42