  Ramp metering is one of the most effective tools to combat traffic
congestion. In this paper, we present a ramp metering policy for a network of
freeways with arbitrary number of on- and off-ramps, merge, and diverge
junctions. The proposed policy is designed at the microscopic level and takes
into account vehicle following safety constraints. In addition, each on-ramp
operates in cycles during which it releases vehicles as long as the number of
releases does not exceed its queue size at the start of the cycle. Moreover,
each on-ramp dynamically adjusts its release rate based on the traffic
condition. To evaluate the performance of the policy, we analyze its
throughput, which is characterized by the set of arrival rates for which the
queue sizes at all on-ramps remain bounded in expectation. We show that the
proposed policy is able to maximize the throughput if the merging speed at all
the on-ramps is equal to the free flow speed and the network has no merge
junction. We provide simulations to illustrate the performance of our policy
and compare it with a well-known policy from the literature.
