Okay, goods and passengers have a maximum travel time of 20 minutes. Your train has a frequency of 9 minutes and it will take a while travel too. Try to put a second or even a third train onto the line.
Secondly, the wood needs a travel time of 20 minutes max, too. So you need:
wood –> (in 20 mins) —> sawmill –> (in 20 mins) —> city.
If all this is connected it should work.