This is NOT the definitive history of Viennese cycling infrastructure and I do not know the full story but here are two great films and my understanding of the context.
Back in 1969 the city was full of cars! The City realised this was not going to be a future-proof solution. What Vienna needed was an underground network and so they built one. Vienna now has the best Public Transport in the world (my world at least).
The focus on public transport, the dismantling of cycle infrastructure and the cultural aspirations of motor car ownership meant bikes were bullied off the road.
Then came the 70s and the problems of car use and oil dependence reignited the mobility discussion. By then there was 0.01 % modal share for bikes and those that rode used illegal routes and survival tactics.
Since then the City has had some good initiatives to accommodate cycling with some very good bits of cycle path and some very nice cycling environments. However these initiatives are like the current network, half hearted, disconnected and do not really join up or have any consistency or quality.
Cycling is back in fashion across the developed world as more and more realise the mobility potential cycling brings to urban spaces. Vienna has marketed cycling well and modal share is at about 5%. There have been some pathetic attempts to improve the cycling infrastructure and to connect up the network which fail as soon as there is any resistance due to a lost parking space.
Cyclists that have coped with and perfected cycling in the Vienna cycling environment are resistant to more poor quality cycling infrastructure which often disadvantages them compared to riding on the road.
Pedestrians and cyclists fight for space on the once illegal survival routes but now official cycle/foot paths.
Austrian traffic planners are influenced by German Cycle planning which is very orientated to deigning roads for cars and footpaths for pedestrians and no understanding of human factors or their Dutch neighbour's solutions.
Austrian political cock blocking and the 23 Vienna district micro politics creates an environment that is very resistant to change.
Again the City is at a turning point as it considers mobility for the future. It realises that the city is truly saturated with cars there is nothing it can do to accommodate more, so it hopes to half the number of cars in 15 years. That leaves public transport, cycling and walking as the only realistic mobility options.
Public transport costs billions but Vienna is very good at it and the politics for public transport are very well established and unquestionable. Cycling is nothing but problems and conflict but it is very cheap, promotes health, inclusive.... bla bla bla...
If you were Mayor what would you do? Invest in public transport help your friends and profit from established relationships and structures or tackle the cycling mess and make a real difference with a coherent connected quality network despite resistance from all groups (even cyclists!)?
So it looks like we will get the U5. Vienna has underground lines from U1 to U6 but the U5 never got built. When it does we will have to find a new joke to play on tourists who ask "how do I get to ....". "You take the U5".
If Vienna really wants to half the car use and improve mobility it will have to invest heavily in public transport and cycling infrastructure and combine them to provide multi modal solutions. I believe cycling levels will increase (across Europe) but it seems that they will have to be increased as a result of individual sacrifice and determination rather than political leadership and technical expertise.