Locomotive's

Have to add bridges so your trucks could go over the tracks.

Trains are pretty much a must have now we have bigger maps, and they use essentially the same tech as roads so there isn't much reason not to implement them, they should be appropriately expensive compared to roads, I'd like to see multiple tiers, steam (slow and available early), diesel (moderate speed, mid game) and hydrogen (high speed, end game), maybe electric as a higher maintenance alternative to hydrogen or diesel.

Some ideas for trains. 3 Tiers: Coal, Diesel and Eletric. Modular Train Stations like the cargo ship ones, Train Depots for creating locomotive with it's wagons. Signaling. Catenarys for the electric trains.

I just want to move my wheat from one side of the island to the other.

Like previous comments already states the maps are too small for it to make sense. Having one Tier 3 U-shape conveyor is 450 ore/min, thats 600 iron plates per minute at the output. If you need more just add another conveyor but i don't think many will reach that level before exhausting all iron on the map.
With a much bigger map (x100 something) (edge of map 10 times bigger) it starts to make sense, then you could mine at different locations at iron deposits that is the same size as the whole island in the current game and have a train go and collect at the different stations and deposit at the iron/steel factory but this would be super end game stuff, and the obvious step would be to be able to transport everything this way by having a train network.

Trains are planned for update 3 (late this year or sometime next year per Marek) https://www.captain-of-industry.com/post/cd-44