This is recollection from when I last went along this path (approx 14 years ago), but there's footbridges with gates on and a pond around here (ie, between the river and the sports-ground).

What is the purpose of this building?

I think that the marked parking bays in one of the two lanes on these carrageways are being mistaken for a cycleways. I don't remeber any cycleway being marked on the ground (hence with a set width when I whent there yesterday but I'll recheck before changeing osm data.
It is confusing for some maybe as the fourlaned dual carageway often has so much parking that the lane closest the "sidewalk" often resembles a cycleway passing a perment seperate lane of stopped traffic.
I think the route was originaly intended to be a local dual-carageway with four lanes [down to st clements] that replaced the old route to london that went up cheney lane.

Mentor when are you going to resolve these two lines which are drawn with an offset from each other?

I suspect that this footpath doesn't match reality (as mapped it suggests that there's no access to the road, whereas I suspect you could actually just step from the pavement onto the road). Needs survey.

Bicycle access on osm.org/way/57833863/history is set to a non-value. Presumably some local knows the legal situation?

Roads missing speed limits:

http://www.itoworld.com/map/124?lon=-1.21748&lat=51.74922&zoom=15&fullscreen=true&fullscreen=true