I have not been able to get a positive cash flow. I've tried trains and wagons. I've had a decent production chain, but it won't stay in the black.

It really depends on what year you start in and which train set you're using. ( American is better for cargo, European for passengers)

It's pretty difficult to do more than break even using railroads before the 1870's/1880's trains come out. they just aren't fast enough and can't haul enough to make much money. Profitability comes even later for road hauling. (Ships are virtually useless in most cases)

I usually spend the time from 1850 to about 1910 heavily in debt while slowly developing 1 -2 industries (food or fuel) and getting my core towns connected and growing. Once I have 3+ towns demanding at least a hundred of each product I start expanding more quickly, it's hard to lose money once you have several full trains hauling more than a hundred items.

I should add that low line frequency and over production can both disrupt production chains because of the way product demand is handled.

Are you saying we are doomed to losing money early on? Having a few vehicles rather than trying to spam vehicles is the way to go?

Losing money isn't inevitable but it's easy to get over extended if you try to grow too fast.

If you start in 1850 you need to be very careful in planning your initial lines. Start with 1 or 2 passenger lines between cities but keep them flat and straight, no bridges or tunnels and make sure you cover the towns with carriage lines so people can get to the trains. Don't let your debt get over 3 - 4 million.

Don't build your first cargo line unless you can haul things both ways. A town near an oil well can haul oil to a refinery and then fuel back to the city in the same tanker cars ( livestock --> food works the same way ) but don't bother doing this until you have customers for it 40 - 50 units won't make a profit. Passenger lines grow cities but cargo pays 2x as much per unit.

If you want a quicker start try starting in 1920 or 30. You have a much higher starting debt limit and the the trains are a lot more profitable. You still have to be careful until you have a steady cash flow but it's a lot more forgiving than an early start.