Each industrial building gets its own truck to deliver freight. The truck will locate available orders and attempt delivery.

If the truck returns from delivery quickly, it will spawn once per hour - each building has its own timer. This way you get 24 truck deliveries per day.

If the truck is delayed, does not return in one hour (before the next truck would spawn... then the next truck doesn't spawn. The building resets the timer. This can happen when the gets stuck in traffic, or its freight shipment is far away. In this case, you get less than 24 truck deliveries per day.

If you switch to industry view, and you observe an industry building which never hits 0 freight (empty yellow bar) - then you have identified a building that really needs better freight shipping. Either solve the traffic jams, or place a freight accepting building close to the industry. Watch the truck before you try to solve the problem.

Freight accepting buildings include commercial buildings, trade depot with freight attachment, trade port with freight attachment, many service buildings (power, sewage), and the road out of the city (although I haven't seen that last one accept freight yet).

Freight Delivery Truck Respawn

Each industrial building gets its own truck to deliver freight. The truck will locate nearby available orders and attempt delivery. Delivery may involve multiple buildings. All the freight on the truck must be delivered before the return trip starts.

If the truck returns from delivery quickly, it will spawn once per hour - each industrial building has its own timer. This way you get 24 truck deliveries per day.

If the truck is delayed, does not return in one hour (before the next truck would spawn... then the next truck doesn't spawn. The building resets the clock for another hour. This can happen when the gets stuck in traffic, or its freight shipment is far away. In this case, you get less than 24 truck deliveries per day.

For example: if a truck takes 2.5 hours to return, the next truck will spawn in 0.5 hour. The building keeps the timer. If this happens consistently to the same building, you'll get 8 truck shipments per day.

If your city suffers complete gridlock, you may get down to 2 truck shipments per day.

Solving the problem

If you switch to industry view, and you observe an industry building which never hits 0 freight (empty yellow bar) - then you have identified a building that really needs better freight shipping. Either solve the traffic jams, or place a freight accepting building close to the industry. Watch the truck before you try to solve the problem.

Freight accepting buildings include commercial buildings, trade depot with freight attachment, trade port with freight attachment, many service buildings (power, sewage), and the road out of the city (although I haven't seen that last one accept freight yet).