NextGEN is the Federal Aviation Administration’s program to upgrade the nation’s air traffic control systems from the traditional radar+radio communication to modern satellite based GPS with automated data exchange.  The net effect is that airplanes will be able to take more direct routes to their destinations and have less need to stack up, reducing effects like the Downey Rush.  Because airplanes can now take more direct routes to LAX than via Downey, areas around LAX will see an increase of low altitude flights.