Adjust speed first
The federal recommendation in reduced-traction conditions is to slow to one-third less than your dry-pavement safe speed in light rain or wet roads, and to one-half on packed snow. Drop further on ice — and stop entirely on glare ice if at all possible. The CDL exam will give you scenarios in which the right answer is "reduce speed and increase following distance," even when the prompt suggests other priorities.
Following distance, expanded
The standard one-second-per-ten-feet-of-vehicle-length-plus-one-for-speeds-above-forty-MPH following distance is a dry-pavement minimum. Double it in rain. Triple it on snow. Quadruple it on ice. These are tested numbers — recognize them when you see them in a multiple-choice scenario.
Hydroplaning and what actually works
Hydroplaning happens when a layer of water separates the tire from the pavement, eliminating traction. It can occur at speeds as low as thirty miles per hour with adequate water depth and worn tires. If you start to hydroplane, the correct response is to release the accelerator (do not brake), keep the steering wheel straight, and wait for the tires to regain contact. The exam often tests whether you remember the "do not brake" rule under stress.
Visibility, low beams, and the four-way warning
In fog, dense rain, or heavy snow, low beams reach further than high beams because the latter reflect off the precipitation and create glare. Use low beams. Activate four-way flashers if traffic is moving substantially slower than the posted limit because of conditions, and pull off the road entirely if conditions exceed your ability to safely continue.
For drivers preparing for Driving in Fog, Rain, and Snow, additional context — including federal manual excerpts, employer hiring practices, and DOT medical guidance — is widely available from industry resources. Continue reading on a recommended industry resource for further detail. Always cross-check anything you read with the current edition of your state CDL manual, since enforcement guidance is updated periodically.