Although instrumental to the city's early growth and economy, the railroad inhibited its expansion. In the 1920s smoke abatement experts reported that the combination of high hills, low wind velocity, and frequent railroad traffic, created air quality problems for the city and its business district, which was adjacent to the area of intense railroad activity. The resulting smoke from the railroad industry was a chief factor in hindering the growth of the city. Restructuring of the railroads and heavy industry through the late 20th century resulted in the loss of more jobs and, ultimately, population. People moved elsewhere for work.