Originally Posted by
RobertHurst
Jacobsen's paper wasn't all about time-series analysis. He also looked at many different cities in CA and compared census commuter figures to overall accident counts. Not surprisingly, cities with lots of bike commuters had the lower overall accident rates. You see what he did there? He erroneously equated total accident count with commuter accident count, without any sort of acknowledgment that there were other types of cyclists in those communities. (In the cities without commuters, the ratio of kid cyclists and drunks to "competent" adult cyclists would be very high; in Davis, with lots of commuters, the ratio would be relatively small.)
....
Pardon me, it doesn't really seem like the Safety in Numbers people are interested in getting to the truth of the matter. They seem much more interested in pushing their fundamentally bogus analysis.
I'm fairly certain that Jacobsen's regression analysis was biased towards zero. I downloaded much of the data, but have not had a chance to look at it.
I think SIN-supporters from the same bias as the rest of the population. Everyone believes the observation/research that supports their position and denies contrary research. By far, people simply don't ask themselves questions like those below.
Originally Posted by
RobertHurst
In San Francisco, ridership went up, and the number of crashes went up even more. How come Safety in Numbers didn't work there?
How come Safety in Numbers didn't work for motorcyclists?
Originally Posted by
sggoodri
I try to stay open minded about possibility of a safety in numbers correlation, but I insist on learning what the actual causal mechanisms are. It's quite possible that those mechanisms can be exploited in areas where numbers don't increase.
I personally don't believe that small increases in cyclists are likely to do much to increase motorist vigilance and care - at least not directly. However, I wonder what affects that increased numbers of cyclists have on the government and on other cyclists' behavior. Does having more active cyclists increase the government's willingness to build important roads with fewer lanes and lower speed limits? Does it provide more political support for effective traffic law enforcement campaigns? Does it improve support for public education campaigns about safe and lawful cycling? Does it increase cyclists' sense of entitlement to the roadway, reduce the percentage of cyclists on the sidewalk or riding against traffic, and improve awareness of the importance of lights at night?
There is a pretty strong correlation via simple aggregate statistics and there probably is some direct effect from pure numbers, IMO. I just think that it is considerably smaller than the aggregate correlation suggests. Here in the US, I think that the big effect is going to be more "safer cyclists" riding along the lines of Robert's statement about adults and kids.
Of course, given that ILTB is back, another issue we should consider is what do we mean by safe and whether other components of cycling/transportation are kept constant (i.e., speed? convenience? pleasure/utility?).