The plans for light rail are for most of it to be in tunnels. Tunnels are expensive. The elevated guideway (tracks) of a monorail costs much less. And then there are other factos that would probably make the monorail cheaper than light rail:

Much of the design is already done. Much of the monorail could utilize the design already done for the Green Line monorail that was cancelled only a few months before construction was to begin.

May avoid the high cost of a second tunnel under downtown Seattle. The light rail from West Seattle to Ballard will require another tunnel under downtown Seattle. The proposed tunnel is also to be used for another route, but it may be possible that if monorail is used for the West Seattle - Ballard route, the new tunnel will no longer be required, probably saving billions of dollars.

Shared cost of a Salmon Bay bridge could save millions of dollars. The monorail should cross Salmon Bay (from Interbay to Ballard) on a high-level bridge to avoid conflict with marine traffic and to make monorail service faster and more reliable. At the same time, the low-level Ballard draw bridge for vehicular traffic is a major problem for traffic. If the City of Seattle can share the cost with the monorail builder, then a high-level bridge can be built that would combine vehicular traffic with a monorail above the opposite directions of traffic.

Most of the monorail can be built with pylons (columns) and concrete guideway (track) built offsite and trucked in to the site of construction and lifted into place by cranes. This would take much less time than building tunnels.

Light rail plans include construction of a second tunnel under downtown Seattle, which would also be used for another route. It is possible that if a monorail is built from West Seattle to Ballard instead of light rail, that the other route proposed to use the new tunnel could use the existing tunnel instead, eliminating the need for the second tunnel. This would not only save potentially billions of dollars, but would also avoid the other inconveniences that come with new construction. The money saved by not building the tunnel could be used to speed construction and/or exptension of other light rail routes and/or extend the monorail beyond West Seattle and Ballard.

Key Arena: There would be a station near the southwest corner of Key Arena that would not only serve Key Arena but also Seattle Center.

Seattle Center: The station near the southwest corner of Key Arena would also serve Seattle Center. If the Seattle Center Monorail is extended to this location, it would then be a transfer point from the West Seattle-Ballard Monorail to the Seattle Center Monorail to go to the other side of Seattle Center and Westlake Center downtown.

Safeco Field: The route of the monorail could be along Occidental Avenue South, with a station at Safeco Field, the home of the Seattle Mariners baseball team and a venue for other events.

CenturyLink Field: The route of the monorail could be along Occidental Avenue South, with a station at CenturyLink Field, the home of the Seattle Seahawks football team and a venue for other events.

Proposed SODO Arena: If the route of the monorail is along Occidental Avenue South, there would be a station at the propsed new SODO arena, a proposed future home of the Seattle Supersonics basketball team and a venue for other events. Because the proposed arena would be built where Occidental Ave. S. is now, the monorail would have to deviate to the east around the arena and the station would be on the east side of the arena.

One of the stations at either Safeco Field or CenturyLink Field would stay open full time because it would also serve the surrounding area. However the other of those two stations, and the station at the proposed new basketball arena, would only be open for an event, otherwise trains would pass through without stopping.

The Seattle Center Monorail, built in 1992 for the Seattle World’s Fair, runs from Westlake Center in Downtown Seattle to a station on the east side of Seattle Center. I propose that this monorail be extended west to a new station near the southwest corner of Key Arena. If a monorail is built from West Seattle to Ballard, a station at Key Arena could be combined with a station for the extended Seattle Center Monorail, providing a transfer point between the two lines.

A station about at Elliott Ave. W. and W. Galer and W. Garfield Streets would be close to the new Expedia headquarters and resolve many of the anticipated traffic problems on Elliott Ave. W. and 15th Ave. W. The same station would be only a few hundred feet from the cruise ship terminal and would provide an exciting way for cruise ship passengers to connect to Downtown.

With money saved from construction of a monorail instead of light rail, it should be possible to extend the monorail line to Crown Hill (the original Green Line route was to terminate at 15th Ave. N.W. and N.W. 85th St.).

Later, the north end of this monorail line could be extended northeastward along N.W. Holman Road and then eastward to North Seattle College, Northgate Mall, and Lake City.

And later on, it could be further extended up Lake City Way N.E. and Bothell Way N.E. to Kenmore and Bothell.

Later, the south end of the route could be extended southward to White Center and Burien.