It's good to hear that WMATA is set to expand MetroExtra service adding new routes for these faster buses that stop less frequently and have "signal priority" technology that lets them briefly hold green lights so the bus can make it past the intersection. Given the flexibility and relative lack of expense involved in buses, these are the kind of measures that jurisdictions all across the country should be looking at.
The next step, and the one that could really change things, would be the implementation of dedicated (and well-enforced) bus lanes. As pictured above, an equal number of people can fit into a vastly smaller space if they're riding a bus than if they're in single passenger cars so ultimately the best way to deal with the problem of a large number of people wanting to pass through a limited roadspace is to make it more appealing to take the bus.
A dedicated bus lane means that your bus can go faster (especially when combined with signal priority) which makes for a shorter commute, thus making the bus a more attractive option. But a faster bus also means it reaches the end point sooner and then goes back the other way. That means that, even holding the number of buses constant, a dedicated bus lane makes bus service more frequent which makes taking the bus a more attractive option. And, of course, if the bus becomes more attractive there'll be more demand on the route and therefore more fares, which makes it more viable to run buses more frequently which, again, will make it a more desirable option.