I note this almost every time I ride 4th, and I ride it eight to twelve times a week, day and night. I've gone so far as to count both the cars and the bikes I see, just to make sure my inclinations aren't distorting my impressions, and the numbers confirm that, bureaucratic classifications aside, 4th Street is functioning as a bicycle boulevard.
This despite its horrible pavement, cracked, ridged, and sown with potholes. The street is just too useful as a direct connection for east/west commuters, and a link between neighborhoods and nearby businesses for locals. It's also pretty, and of course it's considerably more pleasant to ride along it than in the narrow frenzied lanes of busy 3rd Street. Though the occasional cars do almost universally break the speed limit by as much as they can, the street is simply too narrow to be comfortable to most scofflaw motorists.
The LADOT seems to have been scared away from making any improvements to the western segment of the street—ironically, the part that sees the most cyclists—as its graceless attempts at explaining exactly what a "bicycle boulevard" was (although a truer name would be "neighborhood greenway") scared some residents into intransigent opposition.
But LA's cyclists continue to use this serene, tree-shaded route to get themselves to work, to shopping, to visit friends, regardless of LADOT's timidity and ineptness. More bikes than cars...and it was well past rush hour too.