As you said, OP, if a judge is asked to rule, they will look at the specific facts of the case.
If the arrangement is 50/50, then presumably DM and DF live fairly close and there isn't a long commute for either. In this case, the question of who transports the kids could hopefully be resolved fairly without a judge. Esp if the short time travelling with the kids is seen as a positive - a time to chat, listen to music. Or changeovers could be at end of school day and neither parent would be 'commuting'. But I totally understand that resolution is often much harder in RL than on paper.
For what it's worth, I would say that in a 50/50 care situation it would be reasonable to have a starting assumption that the commuting also be shared, subject to some other relevant considerations (rough list off the top of my head below).
Some considerations for maybe departing from 50/50 share of the commute:
- is the hard work (as well as the number of nights over) shared 50/50 or does one parent do more? e.g. laundry, clothes/shoe shopping, mending broken stuff, care when ill, visits to GP, dentist, school, hair dresser. If one parent is doing more, the burden could be evened up by the other parent doing more of the commuting?
- are the children's costs shared 50/50 or is one parent chipping in more money? The parent putting in less money might even up contributions by doing more commuting. Might need to think about financial earning power here.
- is the commute as logistically easy for each parent? i.e. do they both have a car and a driving licence?
- does either parent have other caring responsibilities that makes the commuting task harder (e.g. other children elderly parents)
- what paid work hours are both parents doing that might make it difficult to manage the commute times?
A lot of the considerations above would also apply in situations where care is not 50/50. Plus you might also think about:
- how different are the physical care burdens? Is care 60/40 or 90/10?
- how different are the financial care burdens of both parents? 60/40 or 90/10?
- did one parent move?
- is the "NRP" paying child maintenance?
[these aren't meant to be exhaustive lists - just some ideas that come to mind]
If it is proving hard to share the commuting on a weekly basis, maybe could agree to take turns each month? Or one parent could agree to do X trips per month or per half-term, (so they do a percentage greater than zero but not half)? Or one parent could agree to help with the trips during school holidays but not during school term.