What’s most likely to cause tiredness?

Explanation: Tiredness will affect your concentration. Don't allow yourself to become tired through not taking proper breaks or rest periods. As a professional driver, you have a responsibility either for goods or for passengers, as well as for overall road safety. Make sure your vehicle is well ventilated, so you don't become drowsy between rest periods.

Category: Drivers' Hours and Rest Periods

References: The Official DVSA Guide to Driving Buses and Coaches: Section 3, The Official DVSA Guide to Driving Goods Vehicles: Section 4