Question

The 12.3km Atta Mills road connecting Old Barrier to Kokrobite operates with a
capacity of 2200 pcu/hr and can be traversed within 15 minutes under free flow
conditions. If a flow of 3200 pcu/hr is assigned to the road based on the capacityrestrained approach, what would be the resultant travel time after the traffic assignment
process (AN,5)

Answer 1

Capacity restrained traffic assignment attempts to initially start with all or nothing and then reiterates to re-distribute traffic by iterating between all or nothing and re-calculating link travel times

For capacity restrained, the relationship between linkflow, link impedance is given by

where

t = travel time on the link

x = flow on the link

t₀ = free fow travel time

k = practical capacity

and are parameters which need to be calibrated based on field observations. default values in absence of anything else can be assumed as =0.15 and = 4

So in our case we know t₀ = 15 minutes = 0.25 hours, k = 2200

so we have t = 0.25 * (1 + * (3200/2200))

assume =0.15 and = 4

so we have t = 0.25 * (1 + .15*(3200/2200)⁴) = 0.4178 hours = 25.068 minutes

so travel time after the assignment = 25.068 minutes

---------------------------------------------------------------------------------------------------------------------------------------

Please vote thumbs up to support us to keep learning to keep providign quality solutions. Thanks alot