As the city slowly began filling in the Back Bay tidal estuary to establish the South End and Back Bay sections of the city, the rail line went from being a lone causeway in the middle of said tidal estuary to a major transportation cut through the heart of the western sections of the city. Besides being a physical separator, the railroad was a societal and economic barrier as well; while the South End reclamation project was a municipal project that lacked any form of solid planning, the Back Bay reclamation project was a state-run program that established specific ideas of who would reside within the district. The proximity of the railway also led to an unforeseen effect, suburban flight. With the new rail lines in close proximity to the entire city, many wealthier citizens began migrating to the cities and towns west of Boston. This migration put financial burdens for municipal services such as water and sewer, fire and police on these communities, and helped lead to drives for them to be annexed by Boston, further expanding the city limits. Despite these issues, by the end of the nineteenth century the western railroad and its contemporaries were helping drive the city's economy by assisting local industries to bring products to Boston's port, helping it become the second busiest port on the eastern seaboard.