method of horse and streetcar transit. The model of Lowell was abandoned in favor of that of Pittsburgh, a great river town with a strong urban center. Retail and commerce was encouraged in downtown Moline, and higher density housing began to appear there. The historic street names were replaced by a numerical system in which north–south roads were dubbed "streets" and east–west ones were re-christened "avenues". Though some complained "the corner of Ann Street and Bass Street… is now merely 17th Street at 6th Avenue", the new system, inspired by an alderman's visit to Philadelphia in 1876 for the Centennial, was generally regarded as a great urban innovation. Moline was a successful, if somewhat boring, turn-of-the-20th-century city. It was clean, well maintained, and prosperous, and unlike Rock Island and Davenport, contained no slums, congestion, or red-light districts. Despite the occasional conflicts between native-born and immigrant leaders, the Puritanical, serious temperament of the city had not changed in the half-century since Moline's founding. The city became known as "Proud Moline" to its neighbors, a somewhat derisive nickname that touched on Moliners' sometimes haughty, holier-than-thou attitude. The electric streetcar system expanded as the city did, and by 1915 there were over of paved city streets and of sidewalks. Recognizing a need for more recreational space, Riverside Park was established in 1902 near present-day 34th Street on the waterfront, and the Tri-City Railway Company opened Prospect Park in the southern part of the city in 1911 as an amusement park. The widespread prosperity attracted wave upon wave of immigrants, and Moline's immigrant workers often sent for their extended families in the Old Country to join them in America. The 1910 census showed the Tri-Cities metro area to have the second highest per-capita income in the United States. By the 1920s and 1930s, the appearance of East Moline in Illinois and Bettendorf in Iowa reflected the further growth and diversification of the region. Moline emerged as a retail, transportation, and cultural hub on the Illinois side of the river. The first metropolitan airfield, the Moline Airport, opened in 1926 and later provided commercial air service to Chicago and St. Louis. With federal funds from the Works Progress Administration, the Iowa-Illinois Memorial Bridge, a single-span, two-lane highway bridge built for automotive traffic, was concluded between Moline and Davenport in 1935 and quickly became the preferred method for interstate transit. A bustling retail sector emerged in