United Airlines is testing a two-line boarding system at Chicago O’Hare International, Houston George Bush Intercontinental and Los Angeles International airports. One line will be for priority passengers, like those in first and business class, and the other for Economy and Basic Economy passengers. The system is a return to the previous system for United, which used to board two groups before switching to five as various new classes of service and boarding priority based on elite status and other considerations were introduced. The five-line system did speed up boarding but also led to crowding. The two-line system was facilitated in part by the launch of Basic Economy, since those passengers more frequently travel without carry-on bags and so don’t compete with other travelers for overhead bin space. United plans to roll out the two-line system to other airports this summer.