No problem, I saw Andrew's more detailed comment on your other changeset after I'd posted here.

With pedestrian routing applications built upon OSM data, we have to hope that it will be sensible and assign a high cost to edges which have maxspeed=70 mph and/or and maxspeed:type=GB:nsl_dual (already mapped here) and no sidewalk or verge (not yet mapped).

If you felt inclined, you could add appropriate sidewalk and verge tags where they're missing. I've linked to the documentation for these tags below.

Happy mapping!

https://wiki.openstreetmap.org/wiki/Key:sidewalk
https://wiki.openstreetmap.org/wiki/Key:verge