I do not like to use tractors and trucks for transporting resources; instead preferring to use them as scouts since they do not carry as much cargo as a train does; in addition to the glitchiness of truck/tractor wheels, where the tiniest bump sends it flying.
Therefore I would like to request a tiered train system, much like IRL.
The way I envision this happening is as follows:
Tier 1 of trains will be unlocked at Tier 3, on dual-rail tracks made with concrete and iron rods. They will be steam locomotives, requiring any burnable fuel + water. Locomotives, cars and infrastructure (train station, freight station, liquid freight station) will be made of iron plate and wood.
Tier 2 trains will be unlocked at Tier 5, and upgrade steam engines to gas turbine engines. This will eliminate the use of water in trains, but retain the need for fuel. Same construction materials as Tier 1 for locomotives, track and railcars, except steel will replace iron.
Tier 3 trains will be the current, all-electric monorail trains and track, unlocked at Tier 6.
A fuel tender car will be used on the Tier 1 and Tier 2 trains to allow for longer run without the need for fuel and water stops. Auxiliary fuel tenders for additional fuel and water can be added as necessary. Loading of fuel into fuel tender will be done at the train station. Tier 1 and Tier 2 trains will also not transfer electricity along the track.
I would also like to see the creation of maintenance facilities for vehicles. This would allow for the automatic upgrade of trains, track, infrastructure and cars to the latest tier, without having to manually do it. (It would also allow people to repair road vehicles.)