TL;DR
Change trains / rail research so players aren't encouraged to rush most of it at once.What ?
Rail, Automated Rail, and Rail Signals research should have their costs re-worked, to incentivize players using each tier of research without always rushing. (Signals could probably stay separate, to avoid confusing players, but that could probably be solved with more mini- / popup-tutorials.)There could also be more types of research similar to Fluid Wagon, which allow different types of railway. As possible examples, there could be:
- Crude Locomotive. Slow, inefficient, weak, but early research, and cheaper to build. (See this mod.)
- Diesel Locomotive. Can burn crude oil (inefficient), light oil, heavy oil, and petroleum gas. (See this mod.)
- High-speed Locomotive. Can burn "solid fuel", rocket fuel, and nuclear fuel. (Would require limiting the "normal" locomotive to only burn wood, coal, or maybe "solid fuel".)
- Electric Locomotive, powered by overhead lines, or an accumulator wagon. (See this mod, this mod, and this mod.)
- High-speed + electric research unlocks high-speed electric locomotives.
- Etc!
Why ?
The current rail research seems like it doesn't fit with the rest of the game. Everything except the guns, car, and tank, is about automation. The most basic transport belts and inserters let you set up an automated (if slow) system. Trains on the other hand, require you to drive manually for the first research topic, and only allow automation after the second one. Complex automation requires the third research topic (signals), rather than simply being limited by the player's ingenuity and logic. That last part is the key, in my opinion; The other researches generally allow complex or space-efficient automation when the player figures out the puzzle, and the different research generally gives flat speed boosts or flat efficiency boosts.Railway research costs (1 red, 1 green, 30 seconds) * 75. Automated Rail Transportation is the exact same cost; Neither slower, nor more resources. Rail Signals is slightly more expensive at * 100 instead of * 75, but that's only 33% more expensive. Hardly a disincentive to simply researching all three of those at once. Contrast that with Fluid Wagon research, which is 266% times the cost of Railway research, which is at least a sizable increase. Braking Force research, starts more expensive and only goes up - 133% of the red and green, plus blue bottles - later ones add other colors!
Together, this means that players are encouraged to research all of the rail technologies before laying down any track at all. They certainly can start using trains with the first research, but it's a big hassle - you need to have entirely separate and non-overlapping tracks, in order to have your trains work. Additionally, if you wanted to drive something manually, you've already got the car and the tank - neither of which limit you to tracks! Manually-driven trains overlap with cars' and tanks' use-case, and do it poorly!