I want to add a KPI to calculate the percentage of occupancy of vehicles (: the total of travel time of occupied arcs (where the capacity of a vehicle different of zerois non-zero) over the total travel time.
How can I represent that consideringusing three variables : the xij$x_{ij}$ variable equal to 1$1$ if there is an arc between i$i$ and j $j$, the qi$q_i$ the capacity of vehicle after serving vertex i$i$ and the bi$b_i$ the starting time of service for vertex i.$i$?