Metered entrances help a bit (I've seen the difference in traffic when they went from being installed to operaring in santa clara county), but you would have to run them very aggressively (long cycles) to eliminate congestion, and people would not be happy to wait for that long.

When the line from the meters spills onto the adjancement roadway, some people will take alternate routes, but mostly people want to get onto the freeway because it's the best route, even if it's congested.