How is braking on a wet road affected by using tyres having tread wear exceeding maximum safety limits?

An excessively worn tyre tread drastically increases the braking distance on a wet surface. The grooves in the tread channel water away, and when they are too shallow, the tyre can float on a cushion of water (aquaplaning), losing grip. By law, the minimum tread depth is 1.6 mm, and its condition can be checked using the Tread Wear Indicator (TWI) shown in the picture.