Eventually, the "Hiawathas", "Zephyrs", and the "400" ran 6¼-hour service between St. Paul and Chicago, and for a time the "Morning Zephyr" from Chicago reached St. Paul in six hours flat. In the 1950s, the federal government began imposing stricter rules for high-speed operation, and expensive advanced signaling was installed along the routes to the Twin Cities, though trains generally traveled a maximum of . Unable to keep up with an increasing automobile speeds on an improving road network and other factors that kept passengers away from trains, train ridership declined and the five daily fast trains became unprofitable.