Congestion Maps for Cyclists?

I'm thinking of creating a road map for cyclists, colour-coded by the likelihood of congestion.

Some background ... I've been plotting a route from the West End to the Kingston area. On the map, Fulham Road looked like the most direct route, a relatively straight diagonal to the SW. But then I hit heavy traffic with no room to filter ... The moral being that the most direct route is not always the fastest.

Now, I record all my routes via GPS. In theory, if I looked back at the extract I would see that some roads were fast and others were slow, by working out the average speed between splits.

I could turn that GPS data into a nice colour-coded map: red roads for slow, and green roads for fast. Anybody who looked at that map would know to avoid Fulham Road at the time I hit it.

Now what if thousands of cyclists did this, and the data was aggregated? You'd eventually(!) have a road map of the British Isles, colour-coded by the likelihood of congestion given the time of day.

Taking it further, you could ask for a suggestion of the route from A to B which is least likely to be a wall of steel and exhaust fumes. Or get warnings/suggestions from your smartphone in real time.

This does rely on having access to a large number of GPS recordings from cyclists, so there needs to be an incentive to participate. That's where the route suggestions come in.

I don't know how practical this would be. There are certainly a number of snags with linking average speed to congestion ... Ttime of day, hills, fitness levels, filtering abilities, RLJing etc.

I get the impression that Tom Tom works in a similar way - collecting time-stamped GPS data from all users. But Tom Tom is fairly closed, commercial and car-centric I believe.

Does anybody know if such a thing exists for cyclists? Would something like this be useful to you?