Add in option to manually give orders to a truck.

Imagine this scenario. Both source and destination have priority 1.
A truck is sitting idle next to a source storage and destination needs that resource desperately (think Power station with no coal shutting down half your buildings because of no power). and the truck sits there next to the coal storage doing nothing. Then a few moments later heads off to the other side of the map.
Frustration fills you with anger and you kick your poor helpless computer for being dumb.
Solution: Have a button to temporarily give an order to a truck to pick up cargo A from Source and deliver to Destination.