Protip: Be aware of your industrial sectors and how they are linked by train. I have 3 main sectors of industry, and before they would all be linked by train in every direction. But then I noticed that some cargo trucks were going all the way across town to export their goods via the highway instead of dropping off their cargo at the perfectly fine train station right next to them.
What I noticed is that the train station wasn't focused on exporting goods. It was focused on transporting any intermediate goods from one industry sector to another, which wasn't necessary. Those intra-city trains would only be carrying 10% cargo from one industry section to another.
So, what I did was delete my triangle train track intersection things, so that all my train stations only had a route to the outside, and no way to interact with each other. This set their behavior to export only. Then, all my cargo trucks went to the nearest train station to export goods and my efficiency went up by a lot.
HOWEVER
That is not to say that all cargo train communication within your city is bad. It is probably inefficient if you don't have any specialization industry, but if you do, then intra-city train communication can be very efficient too, as long as it doesn't interrupt your communication between regular industry sectors (if you have more than one).
Since you can't choose where specialized industry will be due to the placement of resources, it's likely that your forestry industry, for example, will be in a separate location than your regular industry.
Your industry supply chain works like this:
1. You mine ore/pump oil/cut trees/farm produce with your specialized industry gatherer buildings.
2. They transport the raw materials to the secondary specialized industry buildings for processing. This is usually not a problem since processing buildings usually spawn right next to the gathering buildings too. (or they export the raw materials if you don't have enough secondary buildings to process it all)
3.The secondary processing buildings then transport their intermediary materials to regular industry for final processing. (or they export the intermediary materials if you don't have enough regular industry to process it all)
4. Your regular industry accepts the secondary materials, and creates the finalized goods that are then shipped to your commercial areas (or they export the finalized goods if you have more than your commercial zones can accept)
Without any train connection to each other, your specialized industry takes the intermediary materials to the regular industry for final processing by truck. It's not so bad if your specialized industry is close to your regular industry. However, it can become a problem if your specialized industry is far away from your regular industry. It can become a big problem if those trucks have to pass through any road bottlenecks, or through any residential areas.
This is where the train comes in. Have your specialized industry be connected to your regular industry by train. The specialized industry takes the secondary materials to the train, the train then takes those materials to your regular industry, bypassing all the traffic, and then trucks at the train station unload the secondary materials to your regular industry for final processing.
I hope someone finds this useful.
