Three Democratic U.S. senators on Monday said they are introducing legislation that would require U.S. regulators to mandate installation of driver-monitoring systems to ensure motorists pay attention while using systems like Tesla's Autopilot.Senators Ed Markey, Richard Blumenthal and Amy Klobuchar introduced the measure on Monday, saying they hope to get it included as part of infrastructure reform legislation. The National Highway Traffic Safety Administration has opened 28 probes into Tesla crashes to date, with 24 pending, where Autopilot was suspected of being in use.The measure also requires the agency "to study how driver-monitoring systems can prevent driver distraction, driver disengagement,...