# Fixed cost associated to SlackVar(waiting time cost) [CVRPTW]

I'm modeling a CVRPTW with some features:

• Each type of vehicle has a cost per km and a fixed cost per trip. To calculate these costs, I am using these methods for this: setSpanCostCoefficientForVehicle and setFixedCostOfVehicle.

• Each customer has a time window where they can be visited. I'm using this method for this: solver.addConstraint(solver.makeNotMemberCt(transitTimeDimensionCumulVar, forbiddenWindow.starts, forbiddenWindow.ends)

So far, everything is working correctly but now, a requirement has arisen to add an extra fixed cost if a vehicle has been idle(slacking) for more than 4 hours at a customer. A vehicle can wait for the opening time of the next customer before leaving.

I'm in doubt about how I can add a fixed cost for SlackVar on each node or something like setSlackVarSoftUpperBound. Is it possible to add a fixed cost associated with each customer's SlackVar? This cost does not apply to waiting at the depot.

I'm using ORTools 7.6 with Java