Bicycle Route 66 does not always follow Historic Route 66. Deviations were made based on present-day conditions. The route begins at Grant Park in downtown Chicago along Lake Michigan. You?ll be riding trails and city streets to make your way through the city and its suburbs. Due to high traffic levels and safety concerns , the route does not follow historic Route 66 leaving the city. The riding through Illinois is over flat to rolling terrain that originally supported the tallgrass prairie ecosystem. Central Illinois is characterized by small towns and mid-sized cities.The route crosses the Mississippi River into Missouri via the picturesque Chain of Rocks bridge which is closed to motorized traffic. The Riverfront Trail goes along the Mississippi River through an industrial area to reach downtown St. Louis, the Gateway Arch, and the end of section one.