SAN FRANCISCO, Calif. (KGO) -- It all started with a Tweet. Then it became a transportation showdown.
Tesla CEO Elon Musk took to Twitter to marvel at the tunnel being created in Southern California and added tunnels are the safest place in the event of an earthquake.
Then things took a turn when he responded to one user essentially saying trains don't belong in tunnels, they are for cars. Trains should be above ground.
BART took notice and its official Twitter account pounced on that statement.
The transit agency put together a graphic saying it carries far more passengers through the Transbay Tube per hour than cars that cross the Bay Bridge.
It put the figure at 28,000 people per hour and says that's nearly twice as much as cars, so trains should be the priority when it comes to using tunnels.
BART capped it off by pointing out that it runs entirely on electricity, which could be taken as a jab at Musk's company, Tesla.
Musk kept asserting his argument as other users chimed in but never directly responded to BART.
RELATED: A Day On BART: What it's really like for commuters
It's a tunnel tussle, BART takes on Elon Musk on Twitter