No person shall drive any vehicle, or ride, drive or lead any horse, mule, cow or similar animal, across, upon any sidewalk or clearly marked pathway or walkway intended for the use of pedestrians, or any parkway, which is defined for purposes of this chapter as that unpaved portion of a street right-of-way between the roadway curbline and the adjacent property line, excepting over any sidewalk adjacent to a freeway underpass and permanently constructed driveways and excepting, in the case of motor vehicles, when it is necessary for any temporary purpose to drive a loaded vehicle across a sidewalk; provided further, that in such latter instance the sidewalk area is substantially protected by wooden planks two inches thick, and written permission is previously obtained from the city traffic engineer. Such wooden planks shall not be permitted to remain upon such sidewalk area during the hours from six p.m. to six a.m. (Ord. 80-7 § 1, 1980)