I'm sure that Sherrardk (the mother of twins, who used to have to struggle with a double buggy) wouldn't support the narrowing of footpaths. I doubt that Woodelf (who's totally blind and who has to navigate his way around other pedestrians, street furniture and advertising signs) would be too keen either.
The mathematics involved in studying traffic flows is incredibly complex. (I've got a maths degree but some of the research on the subject published in the journal of the Institute of Mathematics and its Applications sends my head into a spin). However experience has shown that lowering traffic speeds can often result in a reduction in congestion. (e.g. the use of variable speed limits on the M25). Reducing speed limits to 20mph in built-up areas (and then rigorously enforcing such limits) can significantly improve road safety and again (as research has shown) REDUCE congestion.