Distracted driving is the biggest reason for automobile accidents and fatalities. Our highways would be much safer if people were not distracted while driving. But how much do the different distractions influence driving performance? We meta-analyzed 30 empirical studies that used interventions to distract drivers and then measured their driving performance. The four primary distractions used were texting, eating, drinking alcohol, and smoking marijuana. For each type of distraction, we computed the standardized mean difference (effect size d) that compared a baseline condition or control condition to a distracted condition, and then we computed the weighted average effect size for each treatment. Not surprisingly, drinking alcohol and sending text messages were the two distractions that had the largest effects on driving performance. Eating and smoking marijuana had less effect, but these two distractions have been studied less frequently than alcohol and texting.