When a safety device has been installed in the traveled portion of a street at a railroad grade crossing for the protection of the traveling public, the municipal corporation shall place a warning sign not less than two hundred feet from the crossing. The driver of any vehicle shall place his vehicle under control at the location of said warning signs so as to be able to bring said vehicle to a complete stop at said safety device. Colliding with such safety device at the crossing is prima-facie evidence that the driver is a reckless driver.