The article was talking about 55 mph speed limits on freeways -- highways restricted to vehicular traffic only. Roads likely to be used by pedestrians or cyclists will have a limit of 25 to 45 mph.
To try to counteract this, those signs that tell you your speed were put up that blink when you are going over the limit. They were promptly ignored.
So really I'm just trying to reiterate that what the article says is absolutely true - people will drive what they feel comfortable going, not what the posted speed limit says. In practice, the risks are there, but nowadays everyone knows to avoid main street for pedestrian crossing because its approaching highway speeds now. But on very congested roads like our main street (this being a 250 year old town, where there is no traffic shaping planned, so all through traffic goes down the road that also has the most foot traffic) you aren't going to have an easy answer, because slowing down traffic can be just as dangerous when its bumper to bumper for the ~5 mile long road through town and drivers will go mad being forced back to 25mph combined with the immense traffic bottleneck it would reintroduce (the main reason they fast tracked paving the road in the first place - traffic would back up onto the nearby highway offramp because of how bad main street traffic is).
I think the reality is that busy streets are just never safe for pedestrians (or bikes, etc). That is why you invest in crosswalks meant to funnel people across them all at once, in centralized places, where traffic is already forced to stop. And if you really care, you get the cars out of downtown entirely.
I have cycled routinely on roads with speed limits greater than this. The first that comes to mind is Madison Ave in Sacramento (often 50mph+). For that matter I used to have a commute that took me on a brief stretch of I-5 in San Diego - that was hair-raising, to say the least. It's legal there due to lack of other options.
However, a modern mid-sized car with an efficient engine gets 40 MPG or more at 75 MPH, while a gas guzzler won't get such mileage at any speed.