how to track the current number of shipments in a particular location ?

Hi,

We have a port location L1 with 3 operational locations L1A, L1B, L1C.

We need to update the destination L1 on the shipment, by the operational location that have less shipments at the current time.

If L1A have four shipments, means that there is 4 trucks that have been droppped in, but not yet pickup for a next location L2.

if we have pickup from L1A/L1B/L1C, count should decrease by 1.

similarly at drop off, count shoud increase by 1.

Each shipment is a customer truck with the customer equipment.

Please guide which OTM concept is suitable for our case.