It would be great to have the following process:
1) Search A-B-C-D from a client with a Car ;
2) Search A-B with a Car - OK ;
3) Search B-C with a Car - Fail ;
4) Retry B-C with Foot - OK ;
5) Search C-D with Foot (not Car because you fall back on Foots) - OK ;
6) Return the given itinerary.
It would be great to have the following process: 1) Search A-B-C-D from a client with a Car ; 2) Search A-B with a Car - OK ; 3) Search B-C with a Car - Fail ; 4) Retry B-C with Foot - OK ; 5) Search C-D with Foot (not Car because you fall back on Foots) - OK ; 6) Return the given itinerary.