Center platforms are the inexpensive escalator design
SounderBruce/FlickrDavid Cole has a largely correct takedown of Sound Transit's traditional pound-foolish approach to escalators:
Wherever long escalators are required to travel between the train platform and street level, redundant escalators should be provided. This could have been accomplished with a single bank of at least four escalators, or two banks of at least three escalators, etc. With a bank of four escalators, one escalator being out of service would be a minor inconvenience at worst. Even with half the escalators out of service, access to and from the station could be maintained "
Beyond the number of escalators at each station, there is also the issue of the escalators themselves. Broken escalators have been a near-constant bane to riders using the Capitol Hill and UW stations since their opening in 2016, to the point that Sound Transit is already planning to replace all 13 escalators at UW less than four years after that station's completion.
But Sound Transit apparently felt differently back when planning the Capitol Hill and UW stations. According to a source familiar with the design process who declined to be named for this article, Sound Transit insisted on specifying medium-duty "better" escalators at these stations as a cost-saving measure, and then cobbled together a myriad series of customizations to bring them up to heavy-duty standards. As we now know, the reliability of these Frankenstein escalators hasn't exactly been stellar, and Sound Transit will soon spend a fortune to replace them with more robust, off-the-shelf models. Some old adage comes to mind about how it's better to do something right the first time than to do it over again.
The nicest thing to say here is that the highest levels now appreciate that this is a serious problem, even if the rest of the agency isn't quite ready to take full ownership of it.
The more useful thing to add is that center platforms provide intrinsic redundancy. For the same number of elevators and escalators, any rider has twice as many options for getting to the platform.