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Why did automobiles and buses create serious congestion in older parts of cities?

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Aerial view of Paris showing broad, radiating boulevards lined with historic buildings, demonstrating Baron Haussmann's city planning design. — urban planning Georges-Eugène Haussmann's modernization plan transformed many areas of Paris through the addition of wider boulevards, better lighting and water sanitation, new parks, and improved rail transportation.

In older parts of cities, the introduction of automobiles and buses created significant congestion because these vehicles were forced to operate in mixed traffic on existing street networks that were not designed to accommodate them.12

Unlike rail-based systems that utilized exclusive guideways to separate transit from other urban activities, buses and automobiles shared the same limited road space as pedestrians, vendors, and other vehicles. This lack of separation meant that buses could not travel faster than the surrounding traffic, and their frequent stops further impeded the flow of vehicles.32

The automobile, in particular, rapidly increased in both speed and volume compared to earlier horse-drawn transport, overwhelming the capacity of traditional, compact city layouts. Because these older urban areas were often characterized by roads that funneled traffic toward a single central point, the surge in motor vehicle use exacerbated existing bottlenecks, making traffic control a persistent and characteristic challenge of 20th-century industrialized society.1