[GIS] Downloadable historical traffic data

Question

I'm looking for historical traffic data on a decently large city.
Specifically I need data points that can be used to infer the distribution of vehicle speeds across each road, but I don't want the data to be pre-processed (i.e., it should be coming in the form of individual samples, instead of pre-fit distributions to the data).
It doesn't really matter where the data is from, any major city should be fine — I just need the the traffic pattern to be interesting for analysis.

Is there any source from which I can obtain such data for free and without too much difficulty?
(Ideally it wouldn't be too difficult to map the roads to those from OpenStreetMaps.)

Answer 1

Here is some historic traffic data from San Francisco:

http://www.mtc.ca.gov/maps_and_data/datamart/traffic/

AND

ftp://ftp.abag.ca.gov/pub/mtc/planning/traffic/