A proposed North American “super corridor” would relieve overburdened highways and promote economic growth in three countries, supporters say. But others wonder whether the proposal might bring in cheap exports and put unsafe Mexican trucks on U.S. roads. The issue takes center stage at a three-day conference that begins today in Fort Worth, Texas. More than 350 transportation, logistics and economic development specialists from the United States, Canada and Mexico are meeting. The conference is sponsored by Dallas-based North America’s SuperCorridor Coalition. The nonprofit coalition, whose members include public- and private-sector organizations, wants to develop an integrated transportation system linking...