Participants take a simulated driving test twice, in one condition they have no alcohol, in the other they have enough alcohol to take them over the legal limit. this design is:

The correct answer is repeated measures design.

Repeated measures design refers to an experimental design that involves making all participants of the study subject to each condition or variable of the study. Each participant is measured multiple times in a repeated measures study. In this example, the participants are subject to both conditions - a simulated driving test without alcohol consumption, and a simulated driving test after alcohol consumption.