Since these Solomon’s VRPTW instances vary in vehicle capacity, travel time of vehicles, spatial distribution of customers, time window density and width, they are classified into three categories: R-type (uniformly distributed customers), C-type (clustered customers) and RC-type (a mix of R and C types). Two sets of problems are proposed for each of these three
categories. Problem sets R1, C1 and RC1 have narrow scheduling horizon while problem sets R2, C2 and RC2 have large scheduling horizon. Narrow scheduling horizon problems have vehicles with small capacities and short route times hence only a few customers can be serviced by the same vehicle. Conversely, large scheduling horizon problems use vehicles with large capacities and long travel times so more customers can be serviced by the same vehicle