Construction crews are at work in a new section of Summerlin, after the developer of Las Vegas’ biggest master-planned community cleared a key hurdle for more housing tracts. Over the past several weeks, crews have done extensive site work at the western edge of Las Vegas where Alta Drive dead-ends at the desert. Big stretches of open land have now been scraped, showing an apparent extension of Alta past its now-westernmost intersection at Crossbridge Drive. The activity follows the Las Vegas Planning Commission’s approval last spring of Summerlin developer Howard Hughes Holdings’ plans to subdivide more than 400 acres at Alta and Crossbridge into 13 “developer pods” and a dozen parcels of open space. Plans called for a maximum of 2,909 residential units across the sprawling land tract, according to a city staff report at the time.…