I’ve suggested using up excess street width with diagonal parking. Below are two photos of 17th Street in midtown, one of the section between N and O, which has parallel parking, and a much-too-wide street width. The second is between O and P, which has diagonal parking on the west side. Since these are right next to where I live, I get a regular chance to observe the behavior of drivers on these two sections. On the parallel parking section, drivers are almost always moving above the speed limit, about 30 mph, particularly since most of them have come from an overly-wide section of 17th north of N Street. On the diagonal parking section, drivers are almost always moving at less that the speed limit, about 20 mph. A more subtle difference is that northbound drivers, from the diagonal parking section, seems more willing to yield to pedestrians at the unmarked crosswalks at the intersection of 17th and O streets, whereas southbound drivers, from the parallel parking section, seems to be less willing to yield. Narrowing streets with diagonal parking really does make a difference!