The Met Office has issued a Yellow Warning for freezing fog across the Westcountry including the M5 in Somerset.
The area covered by the alert stretches from Wellington through Somerset and across the Midlands into the North of England.
The warning is in place from 2am until 11am on Saturday.
A spokesperson for the Exeter-based forecaster said: "Freezing fog is expected to lead to some travel delays on Friday night and Saturday morning."
The Met Office said people should expect slower journey times with delays to bus and train services possible, and a chance of delays or cancellations to flights."
Travel Somerset urged drivers to "respect the conditions" and advised motorists to slow down, allow extra time, travel on major roads, have at least a quarter of a tank of fuel in case of delays, clear windows and ensure the windscreen is fully demisted.