The non-exact algorithms for the VRPTW have been very active-far more active than that of exact algorithms. The field of approximation algorithms and heuristics one sometimes classifies
an algorithm as sequential and parallel. In a sequential algorithm one route at a time is constructed, while a parallel algorithm may build more routes at the same time. This conflicts
with the notion of a sequential algorithm and a parallel algorithm. We will therefore avoid the use of this classification of heuristics.