Games : Should I build more circular train networks?

On my Scenic playthroughs, I discovered that ring networks may balance the load from each station from the network. However, it also decreases the efficiency when multiple Locomotives (instead of Carriages) are placed. Since Carriages are rare, when should I build more circular train networks?

Here's that Scenic playthrough. Note that the light blue lane has one locomotive, but it holds up relatively fine; The dark blue lane has three locomotives and it doesn't spread the load well. The yellow lane has a locomotive with a carriage and it works pretty well even when the passengers drop off to reach the Hospital (plus symbol).