Ginjan, since I have only been on insulin for nine months, I am still learning how my body reacts to it. Things change from day to day, but I am getting more settled with it. I do test before driving, but I keep it a little higher than 100; usually about 120. I used to keep it even higher around 150, when I first started until I felt mre familiar with things. As time goes on I will keeping trying lower readings and see how it goes. Thanks.