It’s a major artery into Michigan for the auto industry, so that means a lot of trucks. Plus, two of Ontario’s biggest towns (Hamilton and Toronto) are on the 402 and in both it transitions from rolling farmland to big city rather quickly. Thirdly, the 402 via the Queen Elizabeth Way (QEW) is a popular “shortcut” for trucks transiting from the northeast US to the midwest. All the above translates into fairly heavy traffic volumes as well.
CC
Hamilton and Toronto are nowhere near the 402.