From Central City to Star City, the Flash has the run of the town. National City, however, is apparently off limits.

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Ever since Thanksgiving, the Internet has been rife with rumors of a Flash/Supergirl crossover. While Tuesday and Wednesday's Flash/Arrow extravaganza gave ratings an unprecedented boost, The CW DC universe will not expand to CBS's kryptonian endeavor...at least for now.

Previously, it appeared the only speed trap on Barry's (Grant Gustin) way to National City was the simple fact that Superman and Supergirl (Melissa Benoist) do not exist in the world of The Flash. Now, however, it appears the issue is a tad more complicated.

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""There's always those late nights, delirious, semi-high on pizza where you're like, 'You know what would be really cool? If ...,' " executive producer Andrew Kreisberg told The Hollywood Reporter. "But right now there is no legitimate actual plan to bring [The Flash's] Cisco [Carlos Valdes] onto Supergirl or to bring [Supergirl's] Winn [Jeremy Jordan] onto Legends [of Tomorrow]. First of all, we don't even know if we could, legally. And quite frankly, just making the Arrow-verse, which is what we call Legends, Flash and Arrow work and then making Supergirl work, it's enough of a challenge without having to add a fourth player."

Kriesberg said nothing of Barry and Kara, but it's safe to assume the same problems apply.

Are you still hoping for a crossover? Sound off in the comments below!

Find out more when The Flash airs Tuesdays at 8 p.m. ET.