The change isn't to the top speed, it's to mis-configured time signals that forced trains to slow to a crawl unnecessarily.

In this article (which you probably also won't be able to read, sorry; try incognito?), the Times explains why some mis-configured time signals are the cause of many delays, with compelling evidence to back up the claim.

https://www.nytimes.com/interactive/2018/05/09/nyregion/subw...