This is my solution to the ridiculous M1, M6, A14 Catthorpe interchange, probably the worst in the country. The current A14 relies on a single carriageway road with dumbell roundabouts where two major streams of traffic cross each other on one of these roundabouts (M6 to A14 and A14 to M1) and this along with local traffic between villages.
A new A14 extension is built to the south with the A5 involved in a subordinate short merger; the once added slip roads from the M6 eastwards are removed. A bridge takes local traffic over the A5 with a new spur to join it, and a new roundabout is made around a public house to assist other local movements.
M1 traffic for the A5 would still have to use the A303 north of this map segment, and indeed where traffic was going would decide which roads they used. No more would M6 to A14 traffic cross the path of A14 to M1 traffic, on a minor roundabout. M6 north to M1 would use the A426, east of the map segment. M6 from the west to M1 south would travel to the end of the M6 returning back to a simplified merger. M6 to the A14 would use a new southern spur road that would also give improved and immediate access to the A5, without having to use the M1 and need to come off it many miles south using the A428. The A14 traffic from the east would also enjoy better access to the A5. The catthorpe to Newton road would have a safe bridge over the A5 and only join it via a new spur road south. This would also become the new local access to the M6.
I think this is arguably more elegant, capacity of traffic enhancing and in keeping with other road use than other solutions, for example within the Society for All British and Irish Road Enthusiasts (SABRE - such useful modern and old maps there). The disadvantage is that traffic from the A14 north still has to slow down to use two roundabouts, though two lanes in one direction can be available throughout, including on the single lane road under the M1.
The maps shown derive from the Ordnance Survey both as is and then as altered by me. I am claiming fair use of a minimal amount to illustrate my idea, but if this is an abuse of copyright please inform me and I will redo the map diagram. See previous entry for comment on this and a response.