Prius truly green?

<div class='quotetop'>QUOTE(Albertus @ Feb 28 2007, 07:23 AM) [snapback]397762[/snapback]</div>

Isn' that Toyota that has a "green" factory? so maybe the factory that the Prius is made in is also green. its nice to dream isn't it?

 

<div class='quotetop'>QUOTE(chogan @ Mar 1 2007, 02:27 PM) [snapback]398706[/snapback]</div>

All the statistics I've seen show that bicycling is safer or as safe per mile as driving whereas motorcycling is much more dangerous than either.

 

<div class='quotetop'>QUOTE(Squint @ Mar 1 2007, 02:48 PM) [snapback]398728[/snapback]</div>

Safer, but perhaps not healtier. Exercising in a polluted environment (most cars throw off more pollution, and not just CO2 than the Prius). The question becomes "Do the improved cardiovascular benefits outweigh the negative affects on your respiratory system?".

I used to cycle a great deal. In the mid-sixties I rode on the average of about 30 miles/day. There was certainly less air pollution where I was doing that then, than there is today in the same location.

Dave M.

 

Even if, or when, a Prius or a PHEV vehicle is in electric mode, or a true ZEV, tires rolling on the ground still generate particulate matter (0.2 micrometers (µm)) and contribute to poor air quality. I make a concerted effort to bicycle, but I wear a face mask, both for protection from sun and particulate matter.

 

This thread is awesome. That is all. =)

 

<div class='quotetop'>QUOTE(Squint @ Mar 1 2007, 05:48 PM) [snapback]398728[/snapback]</div>

Could you point me to some sources? I'll revise my opinion if there's some hard evidence to back that up.

The study I cited above was from Johns Hopkins Snell Institute (you know, the helmet guys), and appeared to be reasonably well done, and suggested a much higher injury and death rate. I assumed that Hopkins would get the data right, but that's not guaranteed.

As I said before, the absolute number of deaths is well-documented, and the rate of injuries requiring hospital treatment is also well documented. All the uncertainty lies in what denominator you use, and how you count that. I'd be interested in seeing some credible studies that take a different approach. I pinged a few internet sites but all I came up with was advocates who were playing fast and loose with the numbers.

I mean, it's an inherently hard number to calculate, and I could believe alternatives, but I'd need to see them. This is complicated by the presence of large numbers of children in the data. The peak per-capita bicycle injury rate is for boys age 10 to 14. No surprise there. Looks like the vast majority of bicycle decedents were not wearing helmets, and that traumatic head injury is the main reason they die. (But you can either say that helmets save lives, or the kind of person who'll wear a helmet is the kind of person less likely to do stupid things.)

On the other hand, most auto deaths are due to stupid behavior as well, so there's nothing unusual about bicycle deaths having a large component of that.

I probably ought to state what number I'd ideally like to see. Adults only? Yeah, I can probably get car dat to match that, and that's what's relevant to my bicycling decision. Then, the right denominator is the question. Risk data for activities are usually calculated per hour unless there's a good reason to do otherwise. But auto data are shown either per-capita (assuming that almost everybody drives or is exposed to drivers) or per mile. Rarely is it shown per trip, and it's never done per driver (so a denominator consisting of bicycle owners would not be acceptable).

I guess the right denominator would depend on your point of view, so there's probably no one right one. If this is bicycle commuting, then the relevant risk is, I suppose, per trip. The fact that it might take you longer to get there is not relevant. But if you are bicycling for pleasure/exercise, and tend to spend a given time at it, then the traditional per-hour is perhaps right. I can't quite conceive of where a per-mile calculation would be useful, but that's traditional in transportation.

Anyway, yeah, I'd like to see some contrary studies, if you have the time to list them. The first things I hit on my google search seemed to be advocacy pieces more than they were research.

Personally, the older I get, the more chicken I get about bicycling. I look back at bicycling in downtown Washington DC and say, I can't believe I did that. So maybe I found the Hopkins/Snell study attractive merely because it matched my perceptions.

Thanks.

 

<div class='quotetop'>QUOTE(Albertus @ Mar 2 2007, 07:30 AM) [snapback]399009[/snapback]</div>

The important thing is to do something. Yes - we are one among hundreds of millions of drivers, but got to start somewhere.

A sig on www.cleanmpg.com I like...

<div class='quotetop'>QUOTE("Gandhi")</div>

 

<div class='quotetop'>QUOTE(Albertus @ Mar 2 2007, 08:30 AM) [snapback]399009[/snapback]</div>

I love bizarre questions like this. I'll take a stab.

These guys say half a cubic meter per kilogram of C02, showing the calculation:

http://64.233.167.104/search?q=cache:1ju74...;cd=5&gl=us

This commercial gas source says the same thing: one kg of C02 = .5 cubic meter of gas at standard conditions (atmospheric pressure, room temperature).

http://www.uigi.com/co2_conv.html

So 1000kg of C02 = 500 cubic meters of C02 gas, or, for those of us stuck in English units, a room with an 8-foot ceiling, 40 feet on a side.

 

<div class='quotetop'>QUOTE(donee @ Feb 28 2007, 08:19 PM) [snapback]398196[/snapback]</div>

This post is terrific. Now I am reminded of why I originally liked Prius Chat so much!

 

<div class='quotetop'>QUOTE(dmckinstry @ Mar 1 2007, 08:27 PM) [snapback]398775[/snapback]</div>

Ever seen a picture taken (during the 1960's) of the Los Angeles Basin, representive of most days during the summer? Nasty brown. Even with all the many time more autos (largest polluter) here, 40 years later, the air is MUCH cleaner, due to the increase in quanatity and quality of the smog devices on modern cars. In Montana (where there are WAY less cars), smog devices can be removed, or simply not maintained, with NO State or County's regulating the behavior. The rational is that there are so few cars/people ~ so it doesn't matter & the burocracy to enforce is too expensive. Even so, you get behind many of the autos up there, & you'd swear you had a 1940's model exhaust pipe shoved down your throat. So if the state of WA has decent enforcement of auto smog equipment, you'd probably breath much easier now on a bike.

I guess the moral of the story is that if you have to drive, if we all drove the Prius/cleanest production type car, you wouldn't be smelling unburned gas through the recirculate vent. That being said, and dust to dust studies saying so as well, yes, the Prius is green.

 

<div class='quotetop'>QUOTE(hill @ Mar 2 2007, 09:34 AM) [snapback]399129[/snapback]</div>

Well, I'm talking about near Reno, NV. That's where I was in the mid-60s. The automotive population density there now is many times what it was then. Even in Washington State, when I'm out walking, the smell from school buses bothers me.

It's probably not enough to cause health problems (and I'm not exercising as hard as when I was cycling), but it still isn't pleasant.

Dave M.

 

Estimate of Fatal Risk by Activity

Activity # Fatalities per 1,000,000
exposure hours
------------------------------------------------
Skydiving 128.71
General Aviation 15.58
On-road Motorcycling 8.80
Scuba Diving 1.98
Living (all causes of death) 1.53
Swimming 1.07
Snowmobiling .88
Passenger cars .47
Water skiing .28
Bicycling .26
Flying (scheduled domestic airlines) .15
Hunting .08
Cosmic Radiation from
transcontinental flights .035
Home Living (active) .027
Traveling in a School Bus .022
Passenger Car Post-collision fire .017
Home Living, active & passive (sleeping) .014
Residential Fire .003

Data compiled by Failure Analysis Associates, Inc. (see Design News, 10-4-93




<div class='quotetop'>QUOTE(chogan @ Mar 2 2007, 07:08 AM) [snapback]399023[/snapback]</div>

 

<div class='quotetop'>QUOTE(Squint @ Mar 5 2007, 10:35 AM) [snapback]400297[/snapback]</div>

Aw, cmon, how about a URL so I can see how the numbers were compiled? I know that you can find people who will say bicycling is safer. What I'm after is how they arrived at their numbers, so I can make some reasoned judgement across conflicting sources. I don't think I'm going to be able to find the 1993 issue of Design News to get at the underlying detail.

Might as well do this right if I'm going to screw with it at all.

As I said before, the only issue is the denominator -- how much bicycle use is there. The deaths and injuries data are very well documented.

To do my own homework, I used data from the National Household Travel Survey. This is the best source of information for how Americans get around -- US goverment sponsor, representative of the US population, large sample (26000 households), log-diary survey of one randomly chosen day, random-digit dialing to sample within strata, college student dorms and fraternaties were eligible for sampling. It's the gold standard for measuring how the US population moves from place to place. US armed forces and institutionalized population were excluded. Any means of travel was counted -- car, plane, boat, school bus, bike, foot, horse, etc.

For the NHTS, a "trip" is what you'd normally think of as one leg of a trip. From home to store is a trip, from store to home is another trip.

So, from the NHTS, for the denominators:
Bicyclist trips: 3.2 billion
Bicyclist miles: 6.3 billion
Passenger vehicle trips: 340 billion
Passenger vehicle passenger miles: 3.4 trillion

So much for the denominator.

On the numerator side, we can look at reported deaths and injuries.

For deaths, the fact sheet on automobile deaths in 2005 is here:
http://www-nrd.nhtsa.dot.gov/pdf/nrd-30/NC..._623/810623.htm

In 2005, 43000 people died in motor vehicle accidents, of which 33,000 were car and light truck occupants. The rest were motorcyclists, pedestrians, and bicyclists. In 2005, 784 bicyclists were killed in motor vehicle crashes. That number varies a bit from year to year, with 2005 being on the high side of the average. And, crashes with cars are supposed to reflect only about 92% of all bicylist deaths, which would imply about 850 total bicyclist accidental deaths in 2005. All things considered, I'll use 800 bicyclist deaths as the baseline for my calculation.

For reported injuries in hospital ERs, the statistics for ER visits come from the National Center for Health Statistics, National Hospital Ambulatory Medical Survey. You'd have to download the report for injury-related visits here:
http://www.cdc.gov/nchs/products/pubs/pubd/ad/ad.htm#ad270

And then realize that under the coding system they use, E826 is bicycle accidents that don't involve cars, but bike accidents involving cars are reported under motor vehicle accidents. Anyway, in 2003, there were 4.1 million ER visits related to motor vehicle crashes, and 547,000 related to bicycle crashes that did not involve collision with a motor vehicle. When I look at the underlying data, roughly another 40,000 bicyclists were in crashes that involved a motor vehicle. So, total bicylist ER visits is roughly 490,000.

So, for my numerators:
Bicyclist deaths - 800
Biclist ER visits - 490,000
Passenger vehicle occupant deaths 33,000
Passenger vehicle occupant ER visits 4,100,000

Then the outcomes per million trips or miles look like this:

Outcome_______________Cars_____Bicycles
Deaths per million trips____0.10____0.25
Deaths per million miles___ 0.01____0.13
ER visits per million trips__11.97__154.25
ER visits per million miles_ 1.20____78.38

My deaths per mile for motor vehicles benchmarks OK with pubished data if you assume that published data include total motor-vehicle-related deaths, not just car and light truck passenger deaths (e.g., the published rate includes pedestrians). So, my calculation appears correct (or at least matches published data) for cars.

Based on this information, I'd side with the Snell/Hopkins study: from the standpoint of accident injury, travel by bicycle appears more hazardous than travel by car, on a per-trip or per-mile basis. (This ignores the health benefits of cycling, already noted earlier in the thread.)

Having put this much time into it, I'm not going to redo to eliminate children from numerator and denominator. But published sources suggest that about a third of bicycle deaths are children. Even eliminating the children from the bicycle side (but leaving them in the motor vehicle side), deaths per trip or per mile would still be higher for bicycle travel than for motor vehicle travel.

On a per-hour basis, the NHTS data yield an average speed (per trip, which includes getting into and out of the car or on and off (and locking) the bicycle) of 5 mph for bicycles, and 30 mph for cars. The bike number appears low, but ... its the door-to-door time for what appear typically to be short trips. Taking that at face value (as long times per trip advantage bicycles in this next calculation), I can do a per-hour estimate by multiplying the per-mile data by 30 for cars, and by 5 for bicycles.

________________________Cars____Bicycles
Deaths per million hours_____0.29____0.64
ER visits per million hours___35.90__391.92

On a per-hour basis, I'm in the ballpark of the 1993 numbers you cited (ie, right order of magnitude), but this calculation from the NHTS still does not suggeest that bicycles are safter than cars on a per-hour basis.

Anyway, I come to the same conclusion as Snell/Hopkins: travel by car or light truck is safer than travel by bicycle, in terms of accident rate. If there is some better, more credible source on bicycle use rates than the national household travel survey, I'd revise this. Otherwise, I conclude that Snell/Johns Hopkins got it right.

 

<div class='quotetop'>QUOTE(chogan @ Mar 6 2007, 10:52 AM) [snapback]400881[/snapback]</div>

Notice that they specify 'on-road' motorcycling but don't specify for bicycling.

Lots of 8 year olds bicycling around cul-de-sacs would definitely skew the numbers compared to looking at people actually using bicycles for transport in the real world in co-existance with cars, which is what I believe we're discussing here.

You're absolutely right, gotta watch those assumptions and methodolgies like a hawk.