Here’s an idea; two types of cart.
Push carts are not as fast, but don’t require tracks, can be used to move large quantites of items elsewhere, but cannot be used to move hearthlings.
Rail carts require rails which are made by using a special type of road. When you place a minecart on this road it “activates”, allowing hearthlings or items to ride the minecart on the road. If the road splits it uses regular hearthling AI to find where it wants to go, and minecarts either clip through each other or you have to build the track to avoid possible clogging or a crash.
Using a special road is better than having additonal items, since it can handle slopes through the use of stairs, and doesn’t hinder regular hearthings tunneling since it’s walkable on top of, gets built faster, and doesn’t clutter your view of the tunnels.
Alternatively, you could have a solution like a track maker, where you place two ends and either draw or autogenerate a path to each end, with special pieces like jumps and elevators for that extra entertainment value. This solution could also be useful for determining how much a path would cost, especially since something that increases hearthling speed should be expensive, but not too expensive for short distances.
Either way, we shouldn’t do the place track one piece at a time thing, especially since that would get annoying fast.