All development adjacent to Interstate 90 shall provide a vegetative and/or topographical buffer adjacent to the freeway right-of-way. Buffers shall be of an adequate width and shall contain adequate vegetation to screen uses from being viewed from the freeway. Buffers for attractive open space areas such as parks, golf courses and open space may contain landscaping that permits filtered views of the open space activity. If existing native vegetation within this buffer is insufficient to provide a visual screen, the city may require supplemental plantings and/or an increase in the width of the buffer.