Road design, safety and Vision Zero

[danbrotherston]

I don’t think those stats actually prove that the 400 series highways are safer than backroads, but it’s definitely closer or more likely than I thought.

But that still doesn’t change the point. Dan seems to think trading safety for inconvenience is always wrong and a terrible thing to do.  To the point where some how I’m suppose to pick a family member that will die from some small convenience increase...  

But it’s painfully obvious that people do this all the time. It’s how we live our lives.  Maximizing only for safety would be a terrible way to live and commute.  Hell, there’s a bunch of bike riders and heavy pedestrians in this forum.  You should all give that up and take the bus everywhere because it’ll be a lot safer.

I've explained numerous times.  This is about the fact that engineers design roads that are INTENDED to kill people.  Who should those people be?  No engineer has ever built a plane, bridge, or building which was INTENDED to crash or collapse.  So yes, if you support building roads which are intended to kill people, who should those people be?  Which family members would you pick?  Because it sure is easier when it's other people who are intended to die...

You have made it clear, you refuse to understand this point.

[creative]

Another “perfect Dan post”!

[danbrotherston]

Another “perfect Dan post”!

Object all you want, I speak the truth, our roads are intended to kill people.

[MacBerry]

I don’t think those stats actually prove that the 400 series highways are safer than backroads, but it’s definitely closer or more likely than I thought.

But that still doesn’t change the point. Dan seems to think trading safety for inconvenience is always wrong and a terrible thing to do.  To the point where some how I’m suppose to pick a family member that will die from some small convenience increase...  

But it’s painfully obvious that people do this all the time. It’s how we live our lives.  Maximizing only for safety would be a terrible way to live and commute.  Hell, there’s a bunch of bike riders and heavy pedestrians in this forum.  You should all give that up and take the bus everywhere because it’ll be a lot safer.

I've explained numerous times.  This is about the fact that engineers design roads that are INTENDED to kill people.  Who should those people be?  No engineer has ever built a plane, bridge, or building which was INTENDED to crash or collapse.  So yes, if you support building roads which are intended to kill people, who should those people be?  Which family members would you pick?  Because it sure is easier when it's other people who are intended to die...

You have made it clear, you refuse to understand this point.

 
Your logic isn't logical ,,, it is weird.

[SammyOES]

I would guess that based on AADT the 401 is safer than a lot of smaller roads(for fatal collisions)  The percentage of cars on the road that get in accidents is lower than on a road that carrier 1/10 of the traffic. All traffic going in same direction is similar to why roundabouts are safer (fatality wise) than standard intersections.

I think the measurement that is most relevant is per km driven. I think that’s what the link previous was using and accounts for traffic.

My continued skepticism is that typical 4-lane divided highways in the States don’t really compare that well to the 6 to 24(?) lane, heavily trafficked, higher effective speed highways like the 401 in the Waterloo-to-GTA area. But like I said, it’s definitely closer than I realized and it’s quite likely I was wrong.

[jamincan]

Rural highways should really be compared separately from urban highways. Over long distances, collisions from crossing the yellow line are probably more of a problem (due to fatigue or unsafe passing) and have high risk of fatalities. On multi-lane urban roads with no median (think Steeles between Milton and Mississauga), the risk is probably significantly lower, and the number of collisions from rear-ending or side-swiping other vehicles is likely significantly higher (with lower fatality rates). The nature of collisions is likely similar on the 401 between the same cities, but the fatality rate is probably higher on the 401 versus Steeles due to higher speeds.

[jamincan]

I wonder as well how the higher speed limit may affect highway capacity. Generally speaking the highest throughput per lane is supposed to be at speeds quite a bit lower than this (80kph or so I seem to recall reading?), but I suppose if volumes increase, the speed of traffic would drop down naturally anyway.

[SammyOES]

I wonder as well how the higher speed limit may affect highway capacity. Generally speaking the highest throughput per lane is supposed to be at speeds quite a bit lower than this (80kph or so I seem to recall reading?), but I suppose if volumes increase, the speed of traffic would drop down naturally anyway.

I would have assumed that theoretically the higher the speed limit the higher the capacity. And that in practice you’d see increasing the speed limit increase capacity up until some speed that reflects human abilities (but at which point you’d just stay at that capacity figure). I can’t think of why a lower speed limit would have a higher capacity.

In practice I don’t imagine anything would change. I find increased congestion increases the average speed people go (I think people are willing to speed up to match the flow of traffic but much less willing to slow down) up until some point where average speed falls because of general congestion.

[danbrotherston]

I wonder as well how the higher speed limit may affect highway capacity. Generally speaking the highest throughput per lane is supposed to be at speeds quite a bit lower than this (80kph or so I seem to recall reading?), but I suppose if volumes increase, the speed of traffic would drop down naturally anyway.

I would have assumed that theoretically the higher the speed limit the higher the capacity.  And that in practice you’d see increasing the speed limit increase capacity up until some speed that reflects human abilities (but at which point you’d just stay at that capacity figure).  I can’t think of why a lower speed limit would have a higher capacity.

In practice I don’t imagine anything would change.  I find increased congestion increases the average speed people go (I think people are willing to speed up to match the flow of traffic but much less willing to slow down) up until some point where average speed falls because of general congestion.

Higher speeds mean greater separation between vehicles, which counteracts the higher speeds.

How does congestion increase average speeds.  Isn't congestion by definition when there are too many vehicles to fit in the available capacity, which necessarily reduces speeds because of queuing....if you have lots of cars, but all traveling at the normal speed, you don't have congestion, you just have lots of cars.

[SammyOES]

Sure, yes, traffic volume instead of congestion.

I agree about higher speeds meaning more separation. But I would be surprised if the average separation doesn’t increase gradually with speed. I guess though it is possible that the rate of change of separation relative to travelled speed increases in such a way that overall capacity decreases.

[jamincan]

From the WSDOT:

As congestion increases and traffic begins to move slower than 70% of the posted speed limit, overall productivity declines and the highway supports fewer vehicles, as highways are engineered to move specific volumes of vehicles. In addition, highways do not operate at their maximum efficiency when moving at 60 MPH (the most common highway speed limit in Washington State) because of the need for increased spacing between vehicles.

Maximum throughput (optimal flow) speed is not a static number for all highways, and can vary from facility to facility and from segment to segment depending on conditions such as lane width, slope, shoulder width, pavement conditions, traffic composition, and presence or lack of a median barrier for example. It should be noted that, as cars are equipped with more sophisticated devices and become easier to maneuver, maximum throughput speed should increase. Currently, maximum throughput speed on a typical freeway segment in the Central Puget Sound region is about 51 mph(roughly 85% of the posted speed). For surface arterials, maximum throughput speed is even more difficult to determine, as it is heavily influenced by conflicting traffic movements at intersections. Ideally, maximum throughput speeds for each highway segment would be determined through comprehensive traffic studies and validated based on field surveys. Due to resource constraints and for simplicity, 85% of posted speed is used as a surrogate for the true optimal flow speed for the purpose of performance analysis.

[KevinT]

Object all you want, I speak the truth, our roads are intended to kill people.

You're right, the engineers do suck. If I was designing a road to intentionally kill people I could come up with infinitely better designs like spike pits after blind curves or something.

[danbrotherston]

Object all you want, I speak the truth, our roads are intended to kill people.

You're right, the engineers do suck.  If I was designing a road to intentionally kill people I could come up with infinitely better designs like spike pits after blind curves or something.

You're right, I misspoke, our roads are intended to kill exactly a specific number of people, in that aspect, our engineers do fine.  They can in fact predict the death and destruction a piece of infrastructure will see with a fair bit of precision.

Again, this is the ONLY engineering discipline where "fail x% of the time" is acceptable for x > 0.

And just in case anyone doesn't want to reread the previous lengthy exchange and is confused, this is not to say that there are no tolerances, no mistakes, that no bridge ever collapses.  What it says is that when it happens, we consider it a failure, and we investigate why it happened and we stop it happening again--in traffic engineering, it's part of the design, no need to fix anything.

[SammyOES]

It’s such a weird view.  Even if we keep narrowing down what you’re talking about, it’s still easy to show that you’re wrong.  Bridge designers know that there’s some probability that someone will jump off their bridge and kill themselves.  In aggregate, they absolutely know for sure that people are dying from their designs. And yet, we don’t strive to make it impossible* for someone to commit suicide.

It’s the same with road designs.  Any given stretch of road has some probability of a fatality.  In aggregate, it’s a guarantee someone will die.


* note: we almost certainly don’t do as much as we should.  So I’m not saying we shouldn’t do more - even while still saying we should accept we can never totally prevent bridge suicides.

[SammyOES]

And, of course, this idea that road fatalities are just accepted and never investigated is also ridiculous. Just because we don’t have the resources to investigate every accident in detail like we do for major plane accidents doesn’t mean it never happens.

Major accidents (like say the Humboldt Broncos accident) are looked at in depth and recommendations are made to try to prevent similar accidents from ever happening again. Wide scale accident statistics are looked at and acted on. For example, we have concrete barriers for most of our divided highways because we found a common cause of death was crossing over through the ditch into oncoming traffic.