Did you separate your dataset correctly?
It seems that the test dataset will have different drivers from the ones that we get to train on. If you don’t create a good validation set, you might be getting very optimistic results. Your validation set should not contain any drivers from your training set.
If you want a few good pointers like this one, I recommend visiting the Statefarm thread: Statefarm kaggle comp
In the upcoming videos, Jeremy will show you a bunch of different ideas you can try with this dataset 
Cheers, and good luck!