Wrote my masters thesis in transportation planning on traffic calming. Peer review or it didn't happen. Not that peer review is perfect, but a viral video with an obvious agenda doesn't do it for me.
Generally, worth taking government reports with a grain of salt. I've participated in a few, and the standards are often much lower than peer-reviewed articles. That said, on a quick skim, I don't see anything that strikes me as being obviously wrong / overturned (FHWA was 1997).
But, I also don't see either source providing justification for driving faster. Both reports seem to accept this (in fact, this is about as close to pure physics you'll find in transportation engineering):
From the FHWA's report:
These requests are founded on public knowledge that crash
severity increases with increasing vehicle speed, because in a
collision, the amount of kinetic energy dissipated is
proportional to the square of the velocity. Simply stated, when a
vehicle is involved in a crash, the higher the vehicle speed, the
greater the chance of being seriously injured or killed.
and quoted by the BC report:
A driver’s choice of speed can impose risks on other road
users. Crash severity increases with increasing speeds because in
a collision, the amount of kinetic energy dissipated is
proportional to the square of the velocity.
Now, beyond this, there are some subtleties. Both of these reports state that crashes are more likely to occur when there is a greater delta between fast and slow roadway users. That's fine. They also talk about how speed limits are more likely to be exceeded where the roadway design encourages higher speeds. Emphatically agree.
So, now we are left with a policy question. Surely we agree that habituating people to breaking the law is bad. If people respond to a combination of law and roadway design (perhaps leaning more heavily on the latter), and we want behavior in line with law, what should we do? Ease the law or change the roadway design?
Normatively, for most roadways (especially those containing bicycles and pedestrians), I say we need to move more toward changing the roadway design to discourage higher speeds. On some highways, it might be appropriate to lift speed limits, though even then I'd tend to cast a cautionary gaze toward the Montana experiment that was referenced elsewhere in this thread.
> If people respond to a combination of law and roadway design (perhaps leaning more heavily on the latter), and we want behavior in line with law, what should we do? Ease the law or change the roadway design?
Or change the context in some third way (e.g., enforcement)? The thing with roadway design is that the roadway designs which enourage higher speed are generally the same ones that are safer at any given speed, so changing the design to reduce the incentive for high speed may not improve safety as much as the reduced "natural speed" would seem to suggest -- and may retain the high delta beteween fast drivers and slow drivers that you note is a major factor in accidents, just reducing the median.
But what if through technology we could get enforcement of existing limits to a place where the probability of penalty for violations was higher (even if the penalty range had a lower bottom end)? One problem with law as an factor in behavior right now is that the probability of any given violation (or even a pattern of consistent violations) being punished is so low that the law serves more as a very weak social signal and the source of an inverted lottery of punishment than as a rational utility factor in regular behavior calculations.
With more consistent enforcement, we may be able to reduce the delta between high and low speed drivers (as the high speed end is usually significantly above the legal limit) without changing the law (at least, the speed limits in the law) or the road design significantly.
Enforcement is certainly part of it (planners and civil engineers make jokes about the ever-changing number of "E"s involved in planning--engineering, enforcement, education, encouragement, entomology, et cetera). From my own experience, enforcement is the number one thing people ask for at public meetings, and the very last thing they are willing to pay for. Enforcement is crazy expensive.
Technology, as you point out, more broadly deployable, as well as cheaper and less likely to discriminate. For that reason, I actually kind of like speed / red light cameras. However, they are wildly unpopular to the point of being made illegal in many places. Plus, I think there are legitimate concerns about surveillance aspects of our newly smart cities.
With respect to "safer at any given speed" designs, I think you have to consider that, in order for safety to hold, you need to make some unrealistic assumptions about other factors remaining constant. Also, many of those so-called safer designs really do everything possible to eliminate other kinds of roadway users from the mix.
An automobile monoculture isn't very robust, and it also assumes the wrong units of analysis. Traffic engineers used to measure mobility in vehicle throughput. Amazingly, if you shift your units of analysis to people, monoculture looks less compelling. And that's even before you consider physical activity, environmental externalities, and a raft of other issues.
That's why I'm for average speed traffic cams and ruthless, fully automatic ticketing of speeders. When the probabilty of getting caught and punished reaches almost certainity, people start to "factor it in regular behavior calculations".
But this is going to be a hard sell for both drivers (who feel entitled to their high speed) and law enforcement (which treats ticketing as a revenue source; widespread deployment of such system would dry up the money stream almost immediately).
It would be an easy sell if drivers (such as myself) didn't feel convinced that highway speed limits are arbitrary. 100km/h is a very unlikely number for an engineer to calculate as an upper boundary for a road.
It wouldn't be a tough sell to lower speed limits on some portions, and raise it on others, even on a time-neutral but safety-positive basis, but yet, the powers that be stick to their arbitrary number.
> 100km/h is a very unlikely number for an engineer to calculate as an upper boundary for a road.
I haven't seen any actual calculations used for setting speed limits, but I do remember being taught in school (on physics lessons) that if you want maximum road throughput then after factoring in safe distance (which is proportional to square of velocity) you end up with ~50km/h as a sweet spot. Even if some other factors (like fuel efficiency) alter this calculation, 100km/h feels quite plausible to me.
Also I believe that many consider speed limits as arbitrary because most people seem not to care about safe distances anyway.
