As of the end of WWI, what was a significant milestone achieved in trucking?

Answer: B — One million heavy-duty trucks in use

The achievement of having one million heavy-duty trucks in use by the end of World War I marked a significant milestone in the trucking industry. This development demonstrated the growing reliance on trucks for transporting goods across the country, highlighting a shift in logistics and supply chain operations. The increase in truck utilization was driven by the advancements made during the war, where trucks played a crucial role in moving troops and supplies, showcasing their efficiency and reliability compared to traditional transportation methods like horse-drawn wagons. This milestone not only signified the maturation of the trucking industry but also set the stage for the post-war economic boom, as commercial enterprises began to adopt trucks to enhance their distribution capabilities. The expansion of the trucking fleet was instrumental in the evolving landscape of American transportation and commerce, ultimately leading to the establishment of infrastructure that would support the growth and development of the trucking sector in the following decades. In contrast to this significant achievement, the other options focus on aspects that either emerged later or weren't directly linked to the immediate outcomes of WWI. Electric trucks were not widely introduced until later in the 20th century, safety regulations developed gradually over time, and trucking unions took shape as the industry progressed, but they were not a direct result of the war itself. Hence, the