A second bridge across the Potomac from Gaithersburg on an arc towards Dulles Airport would divert a large amount of traffic from the American Legion Bridge. It will never happen with all the movers and shakers who live near the river on both sides of the Potomac.
I remember folks advocating a 2nd crossing of the Potomac above (west) of the Point of Rocks/American Legion Bridge when I was first assigned to the Pentagon by the Army in 1980. It was opposed then, as now, by the NIMBY folks.
If I lived in Montgomery County, I too would be opposed to turning Montgomery into Fairfax North. Suburban sprawl has become a cancer. A new Potomac River crossing would simply spread the cancer 20 miles further out.
I know, I know … immigration to the United States is a global entitlement, and advocates of sprawl think we can just keep building roads to accommodate a doubling of the population every 40 years.
Who else are we building these new suburbs for? The native born U.S. population is below replacement rate in fertility. We dump the illegal immigrants into the cities and build suburbs as refuges for fleeing native born citizens.
I'd rather attack the problem at the front end. Our cities are quite big enough already. We don't need to import the rest of the world so that we can live in an antheap.