In a Bay Area that seems to reinvent itself by the week, few things have remained more constant or recognizable over the past half-century than the BART logo.

Big lowercase black “b” overlapping a big lowercase blue “a.” Small uppercase “BART” on top.

But in 1970, less than two years before the first trains carried passengers in the East Bay, the design was undecided. And the transit agency arguably avoided disaster, nearly choosing a futuristic-thinking logo that brings to mind a toilet bowl flushing.

After talk of a San Francisco subway began in the 1940s —Marc Benioff’s grandfather Marvin Lewis was a main proponent —momentum for a Bay Area transit system increased in the 1960s. Transit officials distributed all kinds of utopian concept drawings during the early years of BART planning, including photos of stations that looked pristine enough to eat off the floor, and images of trains passing underneath the Golden Gate Bridge.

But one thing none of these images featured was a consistent Bay Area Rapid Transit logo. The design was downplayed until April 1965, when BART officials dropped several prototype cars in urban centers, showing them off like mobile homes.

“BART’s Dream Car: The Luxury Route for Commuters,” The Chronicle headline read.

Lost in that hype surrounding the futuristic/sleek design was the first live look at a BART logo, mocked up by the company making the cars.

The Chronicle published a photo of a cigar-smoking executive, straight out of a “Mad Men” three-martini lunch, leaning against a car with a mid-century modern “ba” design. The letters were skinnier than the current design, and framed around two interlocking ovals that looked like a Venn diagram.

That temporary logo was seen again weeks later when the cars were formally unveiled. Interested citizens who visited the cars probably thought the logo had been finalized.

But in September 1970, less than two years before the system debuted, BART officials announced they were still deciding on their symbol. Three images were sent to The Chronicle, and were discovered a couple of years ago in an archived folder of early BART designs.

“The BART Public Information committee decided on three designs as finalists in the choice of a new symbol for display on equipment and advertising,” The Chronicle reported on Sept. 3, 1970.

One of the logos was a bulkier, less stylized version of the early logo, submitted by the designers of the original cars. The second showed the words “BART” above a white arrow framed by black — a simple and classic design submitted by San Francisco-born architect and designer Ernest Born —who designed BART’s Balboa and Glen Park stations.

And then there was the BART vortex logo. Also designed by a local architect, the design featured a font an alien might choose for their spaceship in a lesser 1970s science fiction movie. It overlapped a swirling circle that looked like either a black hole or a toilet bowl flushing.

Both were unfortunate metaphors for a system that was about to go way over budget before opening to the public —then struggling to meet ridership goals through much of its first decade.

Less adventurous heads prevailed. After a failed bid to change the logo to a “T,” hoping it would catch on as an international symbol for subway entrances, the “ba” design was chosen as the permanent logo.

“Meanwhile, signs warning of the dangers of the electrified third rail in the BART system in southern Alameda county already are posted in Spanish as well as English, and additional languages may be needed as the line into San Francisco becomes electrified,” The Chronicle reported.

In a later meeting, the staff asked for the word “BART” to be added to the logo, and wanted to see the “ba” symbol in a variety of colors. Blue was chosen.

Born’s arrow design was used for some signage, and his influence can still be seen in the interior and exterior of BART stations across the Bay Area. And what about that swirling circular logo of the future? It spent the next 45 years in the Chronicle archive, buried with other forgotten near-miss blunders from the past.

The winning logo hasn’t aged a day in 50 years, appearing unchanged on BART’s new replacement cars. The logo that then-president Richard Nixon encountered during his 1972 ride is the exact same design on your 2019 commute.

It was never the boldest choice, but it was clearly built to last.