Just skimmed the article, seems like they just reduced the speed limit - and then, predictably, cars really didn't slow down on average.

Drivers will drive at the speed the road is designed for, not the speed printed on a sign. If your road goes from 40 MPH to 25 and nothing about the road changes, people are not going to slow down. As an example, Montgomery Ave does this out in the suburbs. I've driven on that road many, many times - people don't slow down when the speed limit drops through Bala Cynwyd, Narberth, and Ardmore. Why would they? Nothing about the road design makes it clear that you should!

There are things that can be done to actually slow cars down. You have to align incentives - people in cars don't give a shit about anyone outside of their car, but they do give a shit if their car gets scratched! So one way to get them to slow down is to narrow streets so that they have to be careful if they don't want to damage their vehicle.

I've seen a good implementation of traffic calming in Olean, NY (a small town just north of PA but pretty far west). They used to have the issue of cars flying unsafely down their main street. They replaced the signalled intersections on that street with roundabouts and turned two lanes in each direction into one. Now the traffic moves at a much slower pace but there isn't stop and go traffic either, so it isn't even that annoying to drivers! Plus, you don't have to turn left out of parking lots - turn right and go around the next circle!

I am not saying any of the above should be implemented in Philly - I am absolutely not qualified to make judgements about what should be implemented where. But I do know that better design is possible, and that changing speed limit signs does nothing unless you have cops that actually can and do enforce it sitting there all the time.