Hard to troubleshoot without a picture, but making cargo which walks taking your trucks usually isn’t that hard.
So:
- Are the stations actually freight stations? (You won’t be the first one to accidentally place a passenger station on a cargo route. :))
- Are there no missing pieces of road (i.e. your trucks are able to make the full round)
- Is taking the truck actually faster? Waiting time is considered, so you may try adding a few trucks to decrease the frequency a bit.
- Once the line is running, make sure that you have sufficient capacity to actually transport all the cargo. If cargo piles up at the truck stop, the industry will stop using your line again. Best to keep your trucks spaced out a bit (if necessary using ‘Full Load (any)’) to make sure cargo gets removed from the truck stop regularly.
Mixed transport (i.e. Truck -> Train -> Truck) is harder to pull off especially starting from 0 production, but can still be done reliably in my experience. All of the above applies, but especially keep in mind all the waiting times involved. Typically the train takes the longest and also incurs the biggest waiting penalty – so make sure your train is frequent and fast enough. Some simple experiments have indicated you have about 35 mins to get your cargo from source to destination, but your mileage my vary on that number.
If starting an industry chain from 0 production using a truck -> train -> truck route, be prepared to take some significant losses in the first couple of years though!