VIDEO - How Ramp Metering Works
If you have tried to enter the freeway in the lower mainland, you may have encountered a traffic signal on the on ramp. Why would there be a red light at a freeway entry? During times of congestion, controlling how vehicles enter the freeway can actually keep the traffic on the freeway flowing. A small wait on the on ramp is traded for what could turn out to be a significantly long wait in gridlock.
This is known as ramp metering and it also serves another purpose, preventing closely spaced groups of vehicles trying to squeeze into the freeway when gaps of the necessary size don't exist.