CVRPLib Capacitated Vehicle Routing Problem Library

VRPTW Best Known Solution Challenge

Introduction

Following the success of the 2026 CVRPLib Best Known Solution Challenge for the Capacitated Vehicle Routing Problem (CVRP), the CVRPLib team announces a new challenge, this time on the Vehicle Routing Problem with Time Windows (VRPTW).

The 2026 CVRP Challenge brought together 19 teams and generated 1,932 improved best known solutions over its 30 days. Beyond substantially improving the solutions available for the XL benchmark, the competition stimulated the development and refinement of new algorithms and provided an arena for comparing classical optimization approaches, hybrid methods, and emerging AI-assisted algorithm design techniques.

The new VRPTW Best Known Solution Challenge will follow the same general philosophy. Its goal is to obtain extremely high-quality solutions for a new set of large-scale VRPTW instances and, at the same time, stimulate the development of new methods for solving vehicle routing problems with thousands of customers.

The XLTW Set

The challenge will introduce XLTW, a new benchmark set for the Vehicle Routing Problem with Time Windows, with instances ranging from 1,000 to 10,000 customers.

The XLTW instances are closely related to the XL instances introduced for the 2026 CVRP Challenge. They retain the same depot and customer locations, while incorporating the additional data needed to define time-window constraints.

This connection between XL and XLTW makes it possible to preserve the wide range of spatial structures represented in the XL benchmark while introducing one of the most important additional constraints arising in practical vehicle-routing applications.

As with the XL set, the objective is to provide challenging large-scale instances that remain useful for algorithmic research for many years. The official XLTW instances will remain confidential until the beginning of the competition.

The Competition

The competition will follow the basic format of the 2026 CVRPLib BKS Challenge.

Before the competition starts, the organizers will perform extensive computational experiments to obtain strong initial Best Known Solutions (BKSs) for all XLTW instances. The official instances will then be released at the start of the Challenge, and participating teams will attempt to improve these initial solutions.

During the competition, teams will be able to submit solutions through the CVRPLib website. Submitted solutions will be automatically checked for feasibility and their objective values will be computed by the platform. For each instance, a real-time leaderboard will record the progression of the BKS and the teams responsible for each improvement.

As in the previous Challenge, the solutions themselves will not be made public while the competition is running, preventing teams from directly improving solutions obtained by other participants. Final solutions will be released after the competition.

Evaluation of Algorithms Before the Challenge

A BKS competition necessarily rewards the ability to find the best possible solutions, and teams may differ substantially in the amount of computing power available to them. This is part of the nature of such a competition, but it makes the final leaderboard an imperfect instrument for comparing the intrinsic quality of algorithms.

In the 2026 CVRP Challenge, the experiments used to produce the initial BKSs already provided an evaluation under comparable computational conditions: publicly available methods were run by the organizers using a common computational environment and experimental protocol.

For the VRPTW Challenge, we will expand this process by making an explicit open call to algorithm developers. Authors who would like their VRPTW algorithms to be considered in the experiments used to establish the initial XLTW BKSs may make their implementations available to the organizers. These submitted implementations will be considered together with other relevant algorithms already publicly available.

Participation in this pre-Challenge evaluation and participation in the BKS competition are independent. A research group may make its algorithm available for the initial BKS experiments without subsequently participating in the competition. Conversely, a team may participate in the BKS competition without having submitted an algorithm for the pre-Challenge evaluation.

After an initial screening to exclude methods that are not competitive with the current state of the art, the selected algorithms will be run by the organizers under the same computational environment, computational budget, and experimental protocol.

This evaluation is complementary to, and separate from, the BKS competition itself. Once the competition starts, teams will remain free to use the computational resources and algorithmic strategies of their choice. The Challenge therefore pursues two related but distinct objectives: establishing extremely strong BKSs for the XLTW set and providing meaningful evidence about the performance of algorithms under comparable computational conditions.

Timeline

The present announcement provides the general outline of the Challenge. Detailed competition rules and further technical information will be released on October 26, 2026.

  • September 30, 2026 – Initial announcement.
    Publication of the general format, objectives, and timeline of the VRPTW Best Known Solution Challenge.
  • October 28, 2026 – Detailed rules and technical information released.
    The complete competition rules will be published. We can already anticipate one important point: the Challenge will use the classical VRPTW objective, lexicographically minimizing first the number of vehicles and then the total traveled distance. The set XLTW-Test with instances similar to those of the official XLTW set will also be made available, allowing researchers to develop and test their algorithms before the official instances are released.
  • December 16, 2026 – Registration and algorithm submission open.
    Team registration for the BKS competition opens. Submissions of algorithm implementations for consideration in the pre-Challenge computational experiments also open.
  • January 16, 2027 – Deadline for algorithm submissions.
    Last day for authors to make their implementations available for consideration in the experiments used to generate the initial XLTW BKSs. A companion report presenting the results on the XLTW-Test instances is mandatory; the organizers will use these results to determine whether the algorithm will be employed.
  • February 24, 2027, 15:00 GMT – Challenge begins.
    The official XLTW instances and their initial BKS values are released. Submission of improving solutions opens, and the competition begins.
  • March 26, 2027, 15:00 GMT – Challenge ends.
    The competition closes 30 days after the release of the official instances.
Organizers
  • Rafael Martinelli (PUC-Rio)
  • Eduardo Queiroga (UFBA)
  • Anand Subramanian (UFPB)
  • Eduardo Uchoa (UFF)
  • Igor Malheiros (Sorbonne Université, CNRS, LIP6)