Final answer:
The majority of single-car fatalities have been linked to opioid and heroin use, with a significant rise in overdose deaths involving these substances surpassing those from car crashes between 1999 and 2014.
Step-by-step explanation:
The drug responsible for the majority of single-car fatalities is commonly linked to the use of opioids and heroin based on trends observed over the years. In the period between 1999 and 2014, accidental deaths from drug overdoses increased significantly, surpassing those from motor vehicle crashes. This increase was driven largely by the misuse of prescription opioids as well as the use of heroin. These findings are supported by data indicating a sharp rise in deaths due to heroin, outpacing fatalities related to other substances such as cocaine.
Moreover, additional factors contributing to automobile accidents include driver error and potentially other drugs that could impair driving abilities. However, opioids and heroin remain the predominant substances associated with accidental overdose deaths, reinforcing their impact on road safety and public health.