Two routes connect an origin and a destination, and the flow is 15,000 veh/h. Route 1 has a performance function tl = 4 + 3x1, and route 2 has a function of t2 = b + 6x2, with the x's expressed in thousands of vehicles per hour and the t's in minutes.
(a) If the user equilibrium flow on route 1 is 9780 veh/h, determine the free-flow travel time on route (b) and equilibrium travel times.
(b) If population declines reduce the number of travelers at the origin, and the total origin-destination flow is reduced to 7000 veh/h, determine user equilibrium travel times and flows.