Avoid if you possibly can the B184 running North.

It's a narrow, twisty road which cars drive down very fast in rush hour. The road through Littlebury has much better visibility and so is much safer for cyclists, even though the cars drive as fast. 

Can users suggest local improvements to the algorithm?

I love this site, and it offers the best routes of any I have experimented with. I just used it to map and then follow a 120 mile cross-country route from Cambridge to Evesham. But there were a couple of points where the cycle.travel suggested route deviated from the NCN route it had otherwise been following. One of them was actually quite nasty and dangerous: in Bedford, the Cycle.Travel app routed me across a really nasty junction onto the main road out of town whereas the NCN route continued for maybe half a mile along the river before crossing back to the same road. 

I imagine this is because there is a misleadingly labelled section of bike path along the main road in the underlying OSM/OpenCycle map. It's actually a lumpy shared use pavement and to reach it you must cross four lanes of traffic (at lights, but still).

Is there some way to feed into this site/algorithm a note to avoid specific junctions like that one, or should I try to edit OSM in some way to warn others?