 Trains can climb grades of up to 6.5% and economize the most energy when following a humped-station profile (track profiles that descend to accelerate after leaving a station and climb before entering the station).Steel-wheel train technology has undergone significant advances and can better round tight curves, and climb and descend similar grades and slopes but despite these advances, steel-wheel trains still cannot operate at high speeds () on the same steep or tightly curved track profiles as a train equipped with rubber tires.All lines but the Yellow Line are equipped with automatic train control.