Does having a motor vehicle affect your academic performance?

Does having a motor vehicle affect your academic performance? 

Having done some research on this topic I've found a lot of information stating that there is a logical belief that good grades relates to driving privileges. However, if I'm to be controversial, I feel that owning a car or moped potentially is not advantageous for achieving high grades. People I know who had been driving since last year and through year 12 didn't obtain the grades they were predicted or had wanted to attain. 

I myself have been wanting a car ever since passing my test in March but due to the financial side of things its been out of the question. Running costs, maintenance and of course insurance are all drawbacks. Those lucky enough to have a car will need some sort of way to fund these elements of owning a vehicle. The majority wouldn't have parents willing to pay for everything so a job would be needed. Having a job will then take up at least one day of your weekend and possibly a weeknight that could mean work doesn't get finished on time or to the best standard possible. 

The benefits of having a car are numerous. Getting to college/school becomes easier and less stressful and gives you the freedom that you don't necessarily have when relying on your parents or public transport. 

Does this freedom actually entail long-term drawbacks? Is the independence of having your own car really that beneficial if it compromises your chances of future success?