Each required off-street loading space shall be provided with a means of unobstructed ingress and egress to an alley or onto a public street wide enough to accommodate expected vehicles. Where such ingress and egress is made into a public street, it shall be through driveways or openings which meet required standards. Permanent wheel stops or curbing shall be provided to prevent any vehicle using the loading area from encroachment on the required street yards, side yards, or adjacent property.