Langer Lane? Didn't think there was much of a problem there Slacker?
Only for people who live on Grangewood
There isn't really a problem except during the rush hour if you are turning towards Chesterfield but turning towards Clay Cross can be a bit more problematic. The main benefit would probably be to the people of Wingerworth who would no longer get through traffic going down to the Tupton roundabout it if was easier to turn right at Langer Lane.
As for the original design of the bypass. It's easy.
Roundabouts are about 90% cheaper and quicker to build than flyovers.