Early Warning Reporting System Improvement Act of 2018 This bill expands early warning reporting requirements for manufacturers of motor vehicles and motor vehicle equipment. It requires such manufacturers to provide additional information on accidents that involve a serious injury or fatality and on settlements in civil actions that restrict disclosure of information. The bill requires the Department of Transportation (DOT) to make certain improvements to the publicly accessible vehicle safety databases of the National Highway Traffic Safety Administration. It also requires DOT to provide public notice of each inspection or investigation related to motor vehicle accidents and make notices relating to enforcement actions available online.