Some of the most dense commercial traffic in the world passes through this region. Heavy ferry traffic from Dover to French ports weaves through the main traffic routes (video, 30 secs). All is managed through TSS, Smaller boats must keep clear of TSS, or only cross in the approved manner. Tidal ranges limit access to many harbours, so most all weather harbours are also busy commercial ports. They all have good provision for leisure traffic, but many have strict traffic control for entry and exit (Dover video) .