I am reminded that when cars were first invented, there were laws put in place mandating that someone walk ahead of any self-propelled vehicle waving a red flag, for fear of scaring horses and making people uncomfortable.
Not automobiles as we know them.
Steam powered road tractors, mammoth agricultural tractors and heavy construction equipment. Ca. 1860-1896. Think township or county roads that were dirt or gravel tracks barely more than a single lane wide. Now do you know why you needed a flag man?