As an employer you have certain responsibilities to your employees, in respect to Health and Safety at Work.  This includes your essential drivers.

The first source of advice that I would suggest for your employees to read is the new version of the Highway Code.  This may sound a bit obvious, but over the years driving has changed considerably, laws, rules and advice has had to change to match this.  Most drivers do not keep up to date with these changes, so the Highway Code is a good starting point.

Another good source of information is "Fleetcraft", written by Jonathan Halliday Philip Coyne Police Foundation and contains some excellent advice.

This book is available from all good book stores.