Driving rules matter. These small changes can make a difference.

Every parent wants to make a difference in his or her teen driver’s safety, but it’s not always easy to know if what you’re doing is working.

Will having another teen in the car really lead to a crash? Will 10 extra practice hours really make your new driver safer? Is it that big a deal if your teen stays out driving until 10 p.m., instead of 9 p.m. We designed our New Driver Deal to help you set these rules and limits, but we also know how difficult it can be to stick to them (especially when your teen wants just a little more freedom behind the wheel).

Fortunately, there’s a tool to help. Known as a Graduated licensing calculator, this resource from the Insurance Institute for Highway Safety shows you the real-world impact of adjusting the driving rules for your teen in clear terms: crashes and fatalities.

We’ll use our home state of Illinois as an example to see how small changes can increase or decrease these risks.

In Illinois, the state-mandated driving curfew for teens is 11 p.m., but let’s say you want to change it to a still-reasonable 9 p.m. Your teen might argue that those two hours don’t make a difference, but this would actually decrease your teen’s fatal crash risk by five percent. If you’re considering going the other way, however, and rolling back your teen’s driving curfew to midnight, you’d actually be increasing your teen’s risk of a fatal crash by two percent.

Those numbers might seem relatively small, but in a dangerous situation they’ll mean everything. Consider the rules around passengers in the car. Illinois allows teens to drive unsupervised with one teen passenger, but banning these passengers would reduce your teen’s risk of a fatal crash by 16 percent. Allowing two passengers, on the other hand, actually increases this risk by seven percent.

In fact, just making these changes – no passengers, setting the curfew at 9 p.m. and racking up 70 practice hours – reduces your teen’s fatal crash risk by 21 percent. That’s not just a number, it’s a reality that could literally save your teen’s life.

We encourage you to try this tool out and see what changes you can make to better protect your new driver. We know it’s not always easy to put your foot down and stick to these rules, but hopefully this gives you a new perspective on the difference you can actually make.

Article originally found on nsc.org.