I never had a chance to play Fallout prior to Fallout 3 but have a pretty firm grasp on the story but I've always wondered is it simply a design choice that even though the bombs went off int he future (2077) the era looks very similar to the 1950's. Everything from the music to the architecture, cars music, tv, the technology might be advanced but it is all reminiscent of the 50's. Is it simply a deign choice or is their an in universe explanation?

In the Fallout universe, things shifted style wise in the 50's to focus more on technology. So in that world, technology boomed while the styling stayed around the same as the 1950's. This is why fusion powered cars and robot buttlers were a thing. If you google Fallout Timeline there are some pretty good details to check out, especially on the events prior to Fallout 3

A bit of a debate in the community as to how much 50's mystique was supposed to be present. Some say the originals were only trying to capture te 1950's patriotic optimism before te bombs fell. To others the fallout world is a realization of what "the world of tkmorrow" looked like from the 50's before the bombs

Fallout is future as imagined in 50ties. It's sometimes called retro future. When people 100 years later from now will look at our science fiction movies and games, they will have the same feeling.

And yes, that retro stile is deliberate design choice since original Fallout.

Note that the Fallout world is not our own, but rather one that has diverged from ours soon after World War II. So, while it takes place in the future, it is not our future, but a future as imagined in traditional 1950s style science fiction.

-bold part is important

http://fallout.wikia.com/wiki/Timeline

http://fallout.wikia.com/wiki/Fallout_world

Yep it is suppose to be a vision of the future from a 50's culture. What you have in essense is futuristic tec with a stagnet 50's culture.