As old-fashioned keys are being replaced with wireless systems that open doors and turn on the car, questions are being asked about their safety. It turns out that many drivers don’t understand how the system works. In complaints to American regulators, motorists have reported that they were unable to shut down engines during highway emergencies, including sudden acceleration events. Making matters worse, automakers have adopted different procedures for using the keyless ignition systems. As a result, owners may not know how to operate their own cars in an emergency, let alone a rented or borrowed car. “Where you have a second to make an emergency maneuver, you shouldn’t have to search around for the right procedure to use on a switch,” said Henry Jasny, general counsel at Advocates for Highway and Auto Safety, a nonprofit group based in Washington, D.C. that pushes for laws to make roads safer.