Missouri’s Dept. of Transportation and engineering consultant HNTB are investigating why a section of interstate highway ramp in southern Kansas City collapsed on July 17. The earth beneath a ramp that connects I-470 with I-435 gave way, collapsing part of a 42-ft-high retaining wall and creating a 35-ft-wide, 200-ft-long hole in the pavement. The highway serves some 35,000 vehicles per day. MoDOT engineer Jesse Skinner says MoDOT and HNTB are analyzing geologic data to see whether the failure occurred in the soil or underlying shale. The answers will help HNTB design the repair. Skinner says MoDOT plans to bid the repair to contractors on a basis that combines speed and quality. The bid is expected to be let by July 23. Repairs could take at least several weeks, according to MoDOT.