Interstate 5 is the largest and the widest freeway in Seattle. There are traffic back ups available from the north as well as south into Seattle especially during the morning and rush hours.

The freeway covers the major part of the metro region and it goes right through the downtown Tacoma. The highway also passes through one of the major shopping malls. It crosses the beginning of another highway at this point that is Interstate-405.

The freeway also passes the SeaTac International Airport and it continues within the airfield of Boeing. The freeway then moves towards the downtown Seattle:

http://en.wikipedia.org/wiki/Metropolitan_Seattle_Freeways

The Century 21 Exposition and the World's Fair was hosted by Seattle in the year 1962. This was done in order to combat the decline of downtown Seattle due to the economic downturn that was suffered during the war. The fair was hosted with a futuristic theme and several iconic structures were involved as a part of the fair such as Space Needle, Monorail, and the complete Seattle Center.

http://www.seattle.com/explore-seattle-tour/

While the project proved to be a success, revitalizing Seattle's civic center, it had the unforeseen effect of creating a Seattle transportation nightmare as people began to return to the city and the same problem that exists to this day.

http://www.seattle.com/transport