The carpool lanes on northbound I-5 between CA 55 and CA 57 seem to always be more jammed than the general lanes, probably due to the 55 connector adding a second carpool lane, then shortly later, the Grand Ave exit taking that lane away. This is going to be addressed by keeping the second carpool lane up to the 57 exit. In doing this, the Main St carpool ramps will be removed.
https://www.octa.net/Projects-and-Programs/All-Projects/Freeway-Projects/Santa-Ana-Freeway-(I-5)/I-5-(SR-57-to-SR-55)/?frm=7128
Good news. That always struck me as poorly thought out.
Here's a news article about it:
https://www.ocregister.com/2019/04/08/3-mile-stretch-of-i-5-through-santa-ana-will-gain-a-second-carpool-lane-in-each-direction/
It mentions the barrier separating the carpool lanes will be removed, for continuous access.