The webpage of the California Public Utilities Commission oversight of rail transit systems

Rail Transit Systems. From the webpage:

The PUC's Rail Transit Safety Section is responsible for overseeing the safety of public transit guideways. The Commission's program ensures that transit agencies have and follow system safety programs that integrate safety in all facets of transit system operations. Every three years staff audits the transit agencies on the agencies' adherence to the system safety programs. Commission staff also review the design of new systems and system extensions, work with transit agencies to mitigate safety hazards, inspect construction to ensure conformance with applicable standards, and audit the safety certification practices of transit systems. Commission staff oversee the safety of operations, including accident investigations and resolution of safety related complaints.)

The following Commission General Orders (GO) pertain to light rail systems:

• GO 26-D: Clearances on railroads and street railroads as to side and overhead structures, parallel tracks and crossings
• GO 95: Overhead electric line construction
• GO 118: Construction, reconstruction and maintenance of walkways and control, of vegetation adjacent to railroad tracks
• GO 143-B: Design, construction and operation of light rail transit systems
• GO 164-D: Regulations governing state safety oversight of rail fixed guideway systems

There is nothing to prevent DC, Maryland, and Virginia for jointly creating a commission structure to do this, under the current structure of utility regulation.

The key is providing the oversight structure and appropriations necessary to create and staff the unit.

At the same time, the board of WMATA needs to be upgraded too. Local political officials with short term considerations generally focused on keeping fares down and minimizing the amount of money allocated to the transit system may not be the best people to represent the needs and requirements of the transit system independent of the local political structure.
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Thanks to Christopher for this, based on our e-conversation related to this article from the San Francisco Chronicle, "Muni on the spot over safety in wake of crashes." He writes:

... So if there was a failure of the local board on safety CPUC would be the ultimate voice. But Muni is the responsibility of the Board of Supervisors. Similarly BART is the responsibility of its own elected board. Remember also that BART is regional -- like Metro -- while Muni only operates within the City/County of San Francisco with small trips to ease connections into San Mateo.

Why in the 1970s CPUC ordered that safety change? I can't be sure. Perhaps. An investigation was ordered -- the system was brand new at that point. It happened right before or right after revenue service began.

Never in any time I lived in California did CPUC step in to look at problems at BART, but there wasn't an accident in the 6 years I lived in California on BART.

In the early 00s, Muni specifically was restructured after system wide failures to not be the responsibility of the Mayor's office, but to live within the SFMTA and be overseen by Board of Supes.

Either way, had their been accidents of the type that WMATA has experienced -- I think the board of supervisors would have demanded that at the very least questions be answered in front of them.

So there are really multiple pieces of oversight.