The MinMax-COVRP is a variation of the COVRP (Capacitated Open Vehicle Routing Problem) where the objective is to minimize the duration of the longest route.
In the reference given below, we presented a matheuristic for the MinMax-COVRP. Using this algorithm, we were able to solve several instances to optimality.
The optimal solutions that we identified are given in a zip file which can be downloaded here. The zip file contains a separate solution file for each instance. Moreover, the zip file contains the file named "fileformat.txt" which explains the format of the individual solution files.
Corrigendum, September 2023: Continued research has shown that, unfortunately, the results for three instances in Tables 3 and 4 in the paper were based on incorrect data. The corrected results are provided here.
Reference:
J. Lysgaard, A.D. López-Sánchez & A.G. Hernández-Díaz (2020): "A matheuristic for the MinMax capacitated open vehicle routing problem", International Transactions in Operational Research, vol. 27 (1), pp. 394-417. DOI