It's Biffa's term; he has a bunch of youtube videos talking about "Lane Mathematics".

Specifically here, it would mean downgrading the highway between the offramp and the onramp to only be 2 lanes, so that the 3-lane highway ends up with 2 lanes for going straight and 1 lane for going off, rather than having the rightmost lane be able to do two things. And similarly at the merge point, a 2-lane highway plus the 1-lane onramp going to a 3-lane highway means no conflicts because all the incoming lanes have their own outgoing lane.

@me22ca thanks for the feedback!
There is one small thing I don't understand: what do you mean by writing: "Lane Math'd", what does that mean?

Good looking map! Not a super-fancy one, but that's fine -- a mostly flat one with a nice river is often what I'm looking for. This'd be a good "default choice" map. Nice job on the river bridge, too.

Some minor tweak suggestions:
- it's great that the western interchange is Lane Math'd; you should do it on the trumpet in the start square too. (Maybe even have the roads into the start square just be 2-lane highways.)
- the most-southern branch of the river around the islands is a bit stop-start. I think it needs to be a bit deeper in the upstream part, or shallower over the whole thing to go more intentionally for the swampy feel on the whole channel.
- consider softening the terrain a bit around the western interchange.

(N)ice map!

@Maurice604 when you wrote this, I got scared and immediately checked what it means :D Fortunately, it is a good word in this context.

Agir is also a French word

looking good, but unlimited trees mod will burn my pc :D