The best repository is CVRPLIB. This repository contains Capacitated Vehicle Routing Problem instances in an easy accessible way.
Taxonomy of test-instances is explained in Eduardo Uchoa et al. (2017). Below is a summary of the notation used for the instances.
Depot positioning
Customer positioning
Demand distributions
This contains several new instances and mirrors test-instances from other repositories. Go to download folder
A collection of test-instances prepared for the multiple Travelling Salesmen Problem (mTSP). These are available as Matlab files. They were used to gain insights about the Balanced-Dynamic (BD) mTSP. Go to download folder
Some of the above mentioned test-instances were used for:
The VRP Web contains many test instances, including explanations and other material. (NEO=Networking and Emerging Optimization): CVRP instances.
fixed areas, fixed routes, period routing, single period, site-dependent multi-trip period routing, sparse feasibility graph, two-echelon.
ABEFMP instances were popular up to about 2010 (ABEFMP each letter represents a class, from Augerat, Eilon, Fisher, Mingozzi, etc.)