In the first place, I absolutely dislike the through-route system, though I understand Metro uses it to save money. There are three places I see that use the through-route system: Downtown, University of Washington, and Northgate. Here are some of my opinions on the Downtown through-routes.
I think some of the through-routes are a bit mismatched. For example, Route 124 is through-routed with routes 24 and 33 Monday through Saturday, but since Route 124 runs at a lower Sunday frequency than the combined 24 and 33, Route 33 has to be through-routed with a different route on Sundays only. I think it would be simpler if a route would through-route with the same route all 7 days a week.
Sometimes, two routes are coordinated to provide frequent service along a shared corridor. Sometimes it makes sense, as in the case of routes 3 and 4, but I think it does not make sense with routes 26 and 28, now that they run express along the shared corridor (Aurora Ave). Plus, that corridor already has frequent service from Route 5 and RapidRide E Line.
I also think through-routing does not make sense for long routes. Examples include routes 5, 124, 131, 132. These routes should just terminate in Downtown.
Here is my list of revised through routes. The format is: North Route–South Route. I split some routes that already go straight through Downtown, so I have to renumber some of the portions of these routes. For example, Route 2N will become Route 23, and Route 3N/4N will become Route 34.
*Currently, routes 70 and 36 operate at different frequencies. However, due to the increasing popularity of Route 70, a frequency boost would be nice.