Briefly discuss the different methods by which freeway entrance ramps can be controlled. Clearly indicate the advantages and disadvantages of each method, and give the conditions under which each of them can be used.

Question

What will be an ideal response?

Answer 1

The methods for controlling freeway entrance ramps are closure, simple
metering, traffic responsive metering, and integrated system control.
Closure entails the physical closure of the ramp by using “Do Not Enter”
signs or by placing barriers at the entrance to the ramp. This form of control is the
simplest, but also the most restrictive and should be used only when absolutely
necessary.
Simple metering consists of setting up a pretimed signal with extremely
short cycles at the ramp entrance. Simple metering can be used to reduce normal
ramp capacity (about 1200 veh/h) to about 250 veh/h, by changing the signal
timings of the ramp meter. This type of metering can be used to improve flow on
the mainline freeway by determining the difference between the downstream
volume and the upstream capacity and setting the metering ramp to match this, or
to improve safety at the merge area by allowing only one vehicle at a time to
merge.
Traffic-responsive metering systems are based on the same principles as
the simple metering systems but add the ability to base the metering rate on
current traffic conditions rather than predetermined timing plans based on historic
data. This type of system therefore has the ability to respond to short-term
changes in conditions.
Integrated system control brings several ramps together and controls them
as a group rather than individually, without concern for how they are impacting
one another. This allows the metering rates to be set to maximize the available
mainline capacity and improve overall system flow.