McALLEN — State transportation officials are still months from making a final decision about the location of the much-heralded Interstate 69 superhighway from Canada to Mexico. Still deep in the preliminary study phases of an environmental impact assessment, Texas Department of Transportation officials are making headway toward a decision on whether to use existing U.S. highways 77 to Harlingen, 281 to Edinburg or 57, which connects to Laredo, or build an entirely new road. I-69, known as Trans-Texas Corridor 69 in the state of Texas, is a proposal for a 2,600-mile highway system running from Canada to Mexico. About 1,000...