The Dumbarton Rail Corridor seems like a good idea, but it's not going to work. The problem is that Dumbarton commuters have a large "fanout"; that is, they come from all directions in the east side, and commute to locations in all directions in the west side. A single point-to-point link between Redwood City and Union City isn't very useful because of all the connections that would need to be made. Yes, there are connections to Caltrain, BART, and Amtrak, but those services are also linear and don't fan out well.
Two easy fixes to the Dumbo would do a lot more to reduce idling in traffic: (1) direct connection to 101 on the west side which was originally blocked by the city of Palo Alto, and (2) increase the capacity. But while there is plenty of appetite to charge bridge commuters exorbitant tolls, there is no appetite to do anything that helps them.
Two easy fixes to the Dumbo would do a lot more to reduce idling in traffic: (1) direct connection to 101 on the west side which was originally blocked by the city of Palo Alto, and (2) increase the capacity. But while there is plenty of appetite to charge bridge commuters exorbitant tolls, there is no appetite to do anything that helps them.