California Code, Public Utilities Code - PUC § 7806

The legislative body of any city or city and county may permit two or more lines of street railway to use the same portion of the same street or the same tracks upon such terms as are agreed upon by the companies operating the railways, but no permission shall be granted to one company to use the same tracks or portions of the same street for more than five consecutive blocks, without the consent of the person or company occupying that portion of the street and then only upon payment of an equal portion of the cost of construction of the tracks and appurtenances used by the railways jointly.