Welcome!
It was awhile since I played this one, so I don't remember specifics that well. If I recall correctly I have gotten the gold medal when I chose the electric option. I think I was careful to keep my track away from the mountains using wide sweeping curves to keep speeds up, and also to mainly connect cities that were further apart. I didn't run many cars per train, don't remember how many, but definitely double track wherever more than one train had access to the line. Also paid attention to reliability and tried to prevent breakdowns as far as possible.
I am not saying that this map is impossible or harder with diesel, just that I chose electric. Either way, because extra investment is needed to make high speed rails (double track, more engines, etc.), the profit available from investment in them (return on investment (ROI)) is poorer than normal. This makes industries attractive to build up a revenue base in the first 5 or so years of the game. Later on this revenue base will finance a steady expansion of quality rail network. There are many different strategies for industry investment, but building is often preferable to buying. However, in the first year there may be some excellent buying opportunities as industries on the map are getting established.
I would tend to get a good income going with industries first, but your question was about how to prevent clogging up your lines. I didn't use these when I won this map, but here's some ideas which have been invented/adapted/re-designed by various members around here:
One idea would be to plan to have more than one station in some of the cities (larger/more industrial ones to begin with). This isn't great from a profit stand-point so I would do it later in the game. But you need to plan to leave room when you expand initially. If not to make alternative connections (make the map look like a spiders web) these can be used to make parallel connections in high traffic areas.
One of the strategies that will make this map seem easy is the use of dedicated maintenance spurs. That is, spurs near stations that are off the main-line. This method requires extra stops are added to the trains roster so that it makes short empty runs from the station out to the service facilities (holding down the Ctrl key will enable you to select them for the train's roster) and back to the station where it will then load for its normal trip. There are different ideas about the best way to setup these spurs, they work best if you have them beyond a station on straight track, but it is debatably easier to make them on short curves of track leaving both entrances to the station free for connecting to other cities. Also, some people prefer to add both maintenance facilities as stops in the roster, others like me are lazy and only place the furthest one in the roster. If you only add the furthest facility on a curved-away-from-main-line spur type MAKE SURE you leave some space between the junction and the first maintenance facility, if not the train may be confused by the junction and SKIP this facility. For diesel and electric I think it is pretty safe to leave sand as an optional stop. With steamers it is a case of going Water-Oil (automated Water), or Oil-Water where some will add both stops to the roster.
Here's a few screenshot examples. This is the most common way I use spurs. This is where care needs to be taken to leave enough room before the first facility.
- Maintenance Spurs curved-track.jpg (20.74 KiB) Viewed 157458 times
This is a method I have used mainly as an experiment. Traffic flow is pretty good without building two stations. Visible is the routing setup I was using.
- Maintenance Spurs alternative end-of-line.jpg (56.37 KiB) Viewed 157458 times
Combining everything. It takes a little planning to make everything fit nicely in larger cities.
- Maintenance Spurs with double stations.jpg (18.35 KiB) Viewed 157458 times
Notice how the track junctions are pretty smooth. To get this effect always make a junction from the existing track side. If the track connects two existing tracks make the curves at either end separately first and then connect up the middle last. Freaky joins can slow trains considerably. All these screenshots are from Age of Steam Blue Streak IV (1.06).