  Two diversion schemes that apportion demand between two on-ramps to reduce
congestion and improve throughput on a freeway are analyzed. In the first
scheme, drivers choose to merge or to divert to a downstream on-ramp based on
information about average travel times for the two routes: (1) merge and travel
on the freeway or (2) divert and travel on a surface street with merging
downstream. The flow, rate of merging at the ramps, and the travel times
oscillate strongly, but irregularly, due to delayed feedback. In the second
scheme, diversion is controlled by the average mainline velocities just
upstream of the on-ramps. Driver choice is not involved. If the average
upstream velocity on the mainline drops below a predetermined value (20 m/s)
vehicles are diverted to the downstream ramp. When the average mainline
velocity downstream becomes too low, diversion is no longer permitted. The
resultant oscillations in this scheme are nearly periodic. The period is
dominated by the response time of the mainline to interruption of merging
rather than delayed feedback, which contributes only a minor component linear
in the distance separating the on-ramps. In general the second scheme produces
more effective congestion reduction and greater throughput. Also the travel
times for on-ramp drivers are less than that obtained by drivers who attempt to
minimize their own travel times (first scheme).
