Final answer:
The first subways indeed relieved traffic on city streets, as seen with the pioneering London Underground and subsequent subway systems in other major cities, reducing the reliance on surface-level transport and allowing residential areas to expand, thus lessening downtown congestion.
Step-by-step explanation:
The statement that the first subways relieved traffic on city streets is true. The introduction of subways, also known as underground railroads, had a significant impact on reducing congestion on city roads. First, the London Underground, opened in 1863, served as a pioneer of this transition to subterranean transport. Other cities like Glasgow, Budapest, Paris, New York, and Buenos Aires followed, building their own underground train systems. Subways offered not only a quicker and less expensive means of transportation compared to the horse-drawn streetcars and carriages on crowded city roads, but they also helped to alleviate the prevailing traffic and cleanliness issues by removing some of the need for surface-level transport.
The use of electric streetcars also contributed to this relief by enabling streetcar suburbs to develop along the expanding streetcar lines. These advances allowed for residential areas to be further from the city centers, thus reducing the amount of traffic that would otherwise be concentrated in downtown areas. The residential shifts and the introduction of alternative forms of transportation such as the subway systems were instrumental in reshaping the infrastructure and transport dynamics of urban spaces.