Capacity utilization is a description of how much of the vehicle capacity is utilized.
In the dialog window it refers to either volume or weight, whichever is the limiting factor. Freight companies of course always try to utilize as much of the capacity as possible. However, sometimes there are different goods co-transported in the same truck delivered to different destination, leaving the truck under-utilized during part of the trip. Sometimes trucks return empty. The average utilization factor is therefore lower than 100%.
The distribution truck has a default setting of 50 % capacity utilization and the semitrailer has a default setting of 90 % capacity utilization. If you have more information on the capacity utilization for a specific transport/distance in you product chain you can change the capacity utilization yourself. When doing that, please consider the transport both to and from the destination. For example: If the truck is 100 % loaded one way and empty the way back, the capacity utilization will be 50 %.