Deadly traffic accidents involving large trucks have surged over the past decade. FRONTLINE and ProPublica examine one gruesome kind of truck accident — underride crashes — and why they keep happening.Trucking industry representatives and the government's lead agency on traffic safety have said that their top priority is safety. Drawing on more than a year of reporting — including leaked documents and interviews with former government insiders, trucking industry representatives, and families of underride crash victims — the documentary reveals how, for decades, federal regulators proposed new rules to try to prevent underride crashes. Over and over, pushback from trucking industry lobbyists won the day, leaving drivers of smaller vehicles vulnerable.