(a) Every common carrier of passengers by motor vehicles shall keep open for public inspection all current tariffs at each location at which an agent is employed. Such tariffs must be produced for inspection upon request at all reasonable times.

The carrier shall post in a prominent location in each vehicle operating on the routes affected, an appropriate notice of any proposed tariff changes in accordance with this subdivision. Such notice shall be of sufficient size as to be easily read and understood and shall state the general nature and amount of the proposed fare change and the effective date thereof, but need not include the complete text of the proposed change. Such notice shall be posted starting at least 20 days prior to the effective date of the proposed change. A copy of such notice, in the form it is to be posted, shall accompany the tariff filing. The department may require evidence of such posting prior to approving the proposed tariff changes.