(Photo © J. Maus/BikePortland)
Reader Chris S. came across a story in The Oregonian yesterday that made him do a double-take. In a report about the ‘State of the County’ event held by the Clackamas County commissioners, the topic of bicycles came up. The event allowed citizens to ask commissioners any question they’d like. The Oregonian reporter shared a few of the questions and summarized the answers.
Here’s the first question in the story — and the one that Chris said he “had to read a few times to make sure I read it correctly.”
Q: Bicyclists and studded tire users cause considerable road damage. Why shouldn’t bicyclists and studded tire users be required to pay an annual fee to the county for wear and tear?
And the answer?
Commissioner Jamie Damon: We are currently working on our transportation system plan. As a part of that, we are looking at the funding structure for necessary maintenance and capital improvements. While our bicyclists do add a different element to our transportation system, most of them also own vehicles and they are paying fees through their vehicle use. Looking at a bicycle fee of some sort is something we can explore. As part of our survey for the Canby Ferry, we are looking at a fee for bicyclists.
Commissioner Paul Savas: We’re asking people, “How do we deliver transportation projects or address our problems? What is a fair and equitable way of doing that?”
I’m not sure exactly what Commissioner Damon meant by “bicyclists do add a different element to our transportation system,” but at least she mentioned they pay for the roads just like everyone else. I’m also curious if Clackamas County would really “explore” a bike fee, especially since that county is working very hard to cash in on bicycle tourism.
Elected officials throughout our region have a long history of bungling responses to similar questions from constituents. Back in November 2010, Metro President Tom Hughes responded to a citizen’s question about tolling by saying people who ride bikes should pay some sort of “token registration fee” and added that riders, “need to pay a share of the cost of providing those facilities.”
And who can forget Oregon State Rep. Wayne Krieger’s attempt to pass a mandatory bike registration bill in 2009?
With budgets tighter than ever in counties and cities across the country, you can bet we’ll continue to hear ideas and schemes about getting more money out of us “free-loading bicyclists.” Heck, even people who get it have supported for a bike-related excise tax.
In Clackamas County, citizen activists funded by anti-tax groups like Americans for Prosperity are fired up. They’re out to stop TriMet’s Milwaukie light rail project and they’re the ones behind the county’s inability to pass a $5 vehicle fee to help pay for the Sellwood Bridge project.
Clackamas County is definitely a place to watch closely as this debate heats up.
Thanks for reading.
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Quick reference point: Jamie Damon is a woman. Otherwise, thanks for bringing this to our attention.
Curious as to how bicycles do “considerable damage to roads” ? There was no validation to the argument and no challenge to it. (No, I haven’t read farther than this post.) And to liken it to studded tires??
The person making the statement was either deliberately lying or impossibly mie-informed. I have been using these numbers for the better part of 4 years now, but using the formula from AASHTO’s 2002 paper on road wear and postulating a 350 pound rider/bike (Fat guy on a cruiser bike, or medium loaded cargo bike) as 1 unit of damage, a Smart FourTwo does 1100 Bicycles of damage to a road, an Escalade does 8000 Bicycles of damage, a mid-legal(20 ton) loaded semi does 10000000 Bicycles of damage, and a semi loaded to the USDOT maximum of 40 tons does 160000000 Bicycles of damage.
From my Intro to Civil Engineering class in 1976, the amount of damage bicycles and small motorcycles do to roads is indistinguishable from normal weathering without traffic.
Toby,it’s those road bikes with the skinny wheels. They’re like diamond tipped saw blades cutting into the asphalt as they go by.
I thought you would have known.
How silly of me Joe! I also forgot about the fixie’s with all their skidding and what-not…Also can’t leave out the two days a year that some commuters don studded bike tires. That just increases wear exponentially!! Just crazy
Also, in the response – actually, ALL cyclists also own vehicles, because under Oregon law, a bicycle *IS* a vehicle. I think Commissioner Damon actually meant “motor vehicle”, but that type of mistake should be called out and addressed.
What about those scofflaw pedestrians?! They wear dark clothes at night, walk anywhere they like, are distracted by iPods and cell phones and they are causing tremendous damage to sidewalks… Let’s see a tax on Shoes Now!!! (kidding)
“Bicyclists and studded tire users cause considerable road damage.”
This is a logically true sentence. The set (“bicyclists” && “studded tire users”) does indeed cause “considerable road damage.” In the same sense that (“a pillowcase full of feathers” && “fifteen elephants”) are “heavy.”
Somehow I don’t think much formal logic went into the formulation of the question in question…
You’ve shown how the sentence can be parsed in a novel way to make it possible to be analyzed as true. As I think we all realize, it’s more reasonably understood to mean, “bicyclists cause considerable road damage” (F) && “studded tire users cause considerable road damage” (T), which evaluates to false.
Hope I didn’t strangle your very clever joke, but I thought it needed to be said!
I found another way it’s true: The damage is “considerable.” It can be considered. You can consider it. Yep, you can. Let’s consider it. Hmm.
I’m not good with the logical whatnots, but in some bastardized Boolean notation that might be:
“bikes cause damage”.AND.”bike damage can be contemplated by humans”.AND.”studded tires cause damage”.AND.”studded tire damage can be contemplated by humans”
NERDIN’ OUT BIGTIME!!!
Just to be sure, is the subject question one that was thought up asked of the Clackamas County Commissioners by a citizen?:
“Q: Bicyclists and studded tire users cause considerable road damage. Why shouldn’t bicyclists and studded tire users be required to pay an annual fee to the county for wear and tear?”
The questioner presumes that bicyclists “…cause considerable road damage. …”, challenging the commissioners to accept or refute the notion, in defiance of common logic finding that bicyclists actually do not cause any damage, let alone considerable damage to roads.
The commissioners should have first dealt with this ambiguity before saying anything further in response to the question.
Who worded and asked the question, and what kind of mushrooms were they eating just before they wrote?
I don’t think it was mushrooms. I believe it was a deliberate confounding maneuver by the questioner to paint bikes in a bad light. To create guilt by association where there is none.
Krieger and others need to go into the history books. Let’s not forget 12 months ago: Rep. Mitch Greenlick. He “said” he was trying to start a dialog when he introduced a law to ban me from having my child under 6 ride on my cargo bike or bike with a baby seat. If I owned an extracycle that would be illegal too.
The bike community has really done a great job recently to stop these attacks based on intent and accident. In both cases we’ve got to be polite, but not back down one inch.
http://bikeportland.org/2011/01/12/oregon-house-bills-would-prohibit-wearing-headphones-carrying-kids-under-six-while-biking-45860
When these lawmakers get caught they lie. Mitch could have called the BTA if he really cared about dialog and safety and wanted to help bikes. What has Mitch done to work with bikes about safety in the last 12 months. Nada.
But somebody has to think of the children!
Bubble wrap ’em an put ’em in a sensory deprivation tank until they are 18 years old then kick them out of the house because they aren’t your problem anymore.
/sarcasm
definitely
right?
What a weird question, its like saying:
Q: Tulips and nuclear weapons kill people. Why shouldn’t kittens and nuclear weapons be subject to a non-proliferation treaty to limit the growth of the number of kitten and nuclear weapons?
Sorry, should have said:
Q: Kittens and nuclear weapons kill people. Why shouldn’t kittens and nuclear weapons be subject to a non-proliferation treaty to limit the growth of the number of kittens and nuclear weapons?
Don’t Panic… the original comment made as much sense as the original question as it was written in the Oregonian.
Do you know where your towel is?
Yeah… it’s got my back…
http://www.flickr.com/photos/ufobike/6866218059/
Wow. You guys are a couple of froods. Tres hoopy.
No strag’s here…
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Here’s the only tangentially logical argument that could support that statement: When bike facilities (like perhaps cycle tracks) are built that remove travel lanes, it moves more motorized traffic to the remaining lanes. If traffic volumes stay the same, then the remaining motor vehicle lanes will receive more wear and damage, while the bicycle infrastructure will be relatively unworn. It may result in more frequent repair of the vehicle travel lanes. So there you have it – bicyclists cause road damage!
(of course, this is still false, as it is the motorized vehicles causing the additional wear…but I tried)
From the article’s comments section…
“Beefbone
The first question originally was a little more complex than quoted in the article. (I’m the person who posed it.) As quoted, it would seem that I was suggesting that bicycles cause road damage.
The reference to bicycles was about their owners’ needs being accommodated without the owners contributing to road maintenance and other costs. ”
To that I’d say, I pay taxes, and when I buy gas, I pay 100% of those taxes too.
As a cyclist though, I have to split the 1% that is designated to non-motorized traffic w/pedestrians… and you talk about fair accommodation… Accommodation would have bike lanes and sidewalks on every street, and we’re a long way from that.
Despite his or her’ attempt to explain their question in a comment to the Oregonian story, Beefbone’s question to the commissioner’s is still not supported by anything factual.
The question was an attempt to rationalize that cyclists cause considerable damage to roads through being provided bike specific infrastructure without their…if this can be believed to be true…”…contributing to road maintenance and other costs.”
I don’t think the commenter was attempting to explain the question as quoted in the Oregonian, and again here. It sounded like the commenter was explaining that he/she was misquoted, and did not mean to imply that bikes cause considerable road damage at all.
But even if I don’t drive, I contribute to state and local general funds that do finance driving-only projects.
What is not addressed is that increasing bike and pedestrian usage is a cheap way to “buy” road capacity. The marginal cost ( the cost of the next rather than average) of roads is high. In the same way utilities “buy” capacicty with energy saving programs such as insulation rebates, investing in bicycle infrastructure is a way to buy raod capacity at a much lower cost than building more roads.
Okay, my conclusion here is just speculation, and I’m not willing to take any bets, but I do think there’s some evidence for road wear from bicycles:
Vehicle road damage is relative to the pounds per square inch of force exerted on the road surface. That’s why we see grooves worn in the road that match the width of cars and SUVs, not semis. A 6,000 pound SUV has its weight distributed across just four fairly narrow tires. A semi carries its load on 18 wide, lower pressure tires. (On a related topic–this is a bigger factor in groove creation than studded tires. The pavement isn’t being ripped up, it’s being compressed, then it cracks and fails. It happens in states where studs are banned also.)
A bicycle distributes its load on two very narrow tires, often run at extremely high pressure. With a tiny contact patch, the PSI on the road is significant. While I don’t recommend this experiment, you can roll a car across one of your fingers, and it won’t be pleasant, but you’ll be okay. It would be more painful with a 110 psi, 21mm road tire carrying a couple hundred pounds of bike and rider.
Look at fresh pavement on a hot day for evidence. You can see where bikes cut through, while cars don’t leave as much of an impression.
Does this mean bicycles can do significant damage to a road? I don’t know; call Mythbusters. As an avid mountain biker, I can say that bicycling doesn’t cause near the trail destruction of motorized use, but there are effects.
You won’t need to call Mythbusters. The relevant math here is the Generalized Fourth Power Law (http://wiki.pavementinteractive.org/index.php?title=ESAL#Generalized_Fourth_Power_Law)
The damage to a roadway is a fourth-power function of weight. If it costs 1¢/yr. to maintain a certain piece of roadway for regular use by a 200lb bicycle + rider, then as rule of thumb it will cost about $1600 for a 2 ton car or $40,000 for an 8 ton truck. This is just a rule of thumb but you can fudge the numbers a LOT and they are still damning (seriously: knock away two zeroes and bikes still cause 1/1000th the damage of a small car!) Bike-caused roadway wear isn’t even a rounding error. Moss probably causes more roadway damage than bikes in Clackamas County.
no.
that’s a big red herring.
for breakup of pavement you’re talking about a bunch of forces which cause breakdown of the surface layer. Remember that roads are often asphalt (which is a flexible surface) laid on top of looser base layers. (There are actually other designs such as rigid pavement or continuously reinforced concrete pavement- but for our purposes this will be about flexible pavement)
first and foremost- weather/water/cold. freezing and thawing and cause cracks in asphalt into which water penetrates.
mechanical grinding- studded tires.
horizontal forces- these are more destructive than the supposed “psi”. these are shear forces caused by braking and acceleration.
vertical forces- as stated before- the biggest issue is breakdown of the subsurface layers which removes the support from the upper layer-> which then leads to cracking and water penetration. larger vehicles exert larger forces on the subsurface layer leading to compaction and thus degradation of the areas under tire path.
“In determining the structural life of a road pavement, the effect of cars and similar vehicles is negligible…. It is therefore the heaviest axles in the stream of commercial vehicles that cause a disproportionately large amount of structural damage to a flexible pavement.””- From Bituminous Mixtures in Road Construction.
“”Typically, a truck will carry 10 times as much weight per axle as a car, and hence that truck will do 1000 times as much damage to the road (per axle). For practical purposes, road damage is done by trucks, not cars.””- Economics of the Wheel: The Costs of Cars and Drivers
“Only medium and large trucks are assigned ESAL [equivalent single axle load] equivalency for design purposes. Automobiles, pickup trucks, and other relatively small vehicles have such small ESAL loadings that they do negligible damage to the pavement structure. An old rule-of-thumb is that pavement structural damage done by the passage of a single large truck is equivalent to that done by about 9,000 automobiles.”- Alaska Flexible Pavement Design Manual
In essence- bikes don’t cause any road wear. We don’t compress the subsurface layer and cyclists certainly don’t cause a lot of shear forces.
If you want to really get geeky do a google search for 394-roads-beam.pdf.
For more information on pavement types visit:
http://onlinemanuals.txdot.gov/txdotmanuals/pdm/pavement_types.htm
Okay, you may be wearing me down. But please note that even multiple use paths, without any cars, suffer damage and degradation over time, and it takes money to maintain them. Yes, I realize these paths usually don’t have anywhere near the subsurface construction as roads, and that most of the damage is caused by nature, not use.
Ultimately I may be killing my point with my poor understanding of engineering, but what I’m trying to point out is that we all share a responsibility for the roads. Right now the gas tax is carrying a big part of the load for maintenance, but I believe most of us hope that won’t be the case in the future. Personally, I hope we can see a petroleum-free future even before we burn up every ounce of the poison.
So I think we would be well-served to ignore the spiteful, mean-spirited nature of the folks who consider us freeloaders on the road, and we should help guide them toward a future when we find ways to pay for this shared resource without the gas tax.
Agreed with countering false information with better knowledge.
Road user fees (gas tax, license and registration, tolls) cover about 60% of interstate highway costs–where bicyclists are relatively uncommon users–but much, much less of local roads which are more frequently used by bikes. For example, they are less than 5 percent of Seattle’s street budget. The rest is paid from various other taxes, all of which are not user-specific. For example, see Table 4 in Todd Litman’s Whose Roads?” Other references for all of those and more are in this thread.
…in this thread.
Well, I wouldn’t say false. All I said was “a big part”, not all, not even most. No doubt, the gas tax argument doesn’t hold water, especially since a road’s real value is in the real estate it occupies, not its maintenance. In that sense, roads are truly collective.
And the reliance on gas tax for maintenance is highly variable by place. I used to write a column on cycling for a small weekly in Utah, and I used national statistics to support the idea that the gas tax didn’t pay for our local road maintenance. The head of the local transportation department wrote me personally (I thought it was quite restrained and polite that he didn’t do it on the op-ed page) to correct me. It turned out (he had the documentation) that all but about $50,000 of his maintenance budget came from the gas tax.
It’s great that some places are already using general revenues for road maintenance. It’s only rational that some of my property tax goes to maintain the roads–because I’ve got to get my bike back to the house.
By “false knowledge” I wasn’t referring to you specifically, Ron, but to the common assertions that bicyclists don’t pay for roads. Sorry for the confusion.
Interesting data point about that Utah DOT. I’ve asked before and am still very curious about a breakdown of Portland’s street budget revenue, and Vancouver’s.
Excellent explanation Kenji. I’m actually a roadway engineer and couldn’t have said it better. And just to clarify from Ron’s original statement….truck tires are not “lower pressure”, they run at much higher pressures than car tires.
Okay, Uncle. I lose on the engineering. I see that a bike can’t cause the kind of deflection necessary to cause much damage to a road designed for heavier vehicles.
But the shared cost of maintaining roads, an important public resource whether you use a car or not, remains a much more complicated question than simply “Who has the most impact on the road surface?”
It’s an interesting idea to try wrapping your head around how the government collects and allocates tax monies. As a single home-owner, I pay a property tax each year, a large portion of which goes to fund public schools. I don’t have children, but I still have to pay for education. Even if no money I ever gave to the government pays for the roads, I wouldn’t feel guilty about riding my bike all day on them.
The pay to play mentality seems to be very ingrained in our society’s minds, but public services are just that – open to all member of the public. See if this one doesn’t hurt your brain: people on unemployment have to pay taxes on that income. Isn’t that just the government taking money from one pocket and putting it in another? It’s even less efficient than just paying people less in unemployment.. none of it makes sense, really.
Maybe we should just privatize the roads, that way if you want to leave your house you have to pay something to a private corporation. Of course there’s only one road in front of your house, so you don’t really get to choose either. It’s sort of like how garbage service works.
Thanks k! I actually had to think about this one for a bit.
As a bike commuter and lover, as well as a commercial truck driver, I assure you of a few things about a trucks weight.
105psi in all the tires on my 18 wheeled machine, I don’t know where you get ‘low pressure’ from. For the drive axles (2 axles, 8 tires at ~105 psi) ~34,000 lbs is allowed, the steer axles ~12,000 lbs, that’s 6,000 lbs per steer tire. To license and keep a tractor trailer on the road, not including the fuel cost, is VERY expensive, they most certainly pay ‘their fair share’. They generally stay off quiet side streets and bike blvds too.
“A semi carries its load on 18 wide, lower pressure tires.”
Not in my experience. Semi and large commercial vehicles tend to have tyre pressures of 7.0 kg/cm^2 , or about the same as you would put in your HP road tyres. Autos on the other hand tend to have tyre pressures of 2.1 kg/cm^2.
What percent of municipal road funding comes from gas tax and what comes from property tax? In Seattle it’s something like 95% property tax.
Crack-o-my-ass County
Preparation H
I guffawed at that.
This is how I read it:
Q: Bicyclists annoy me, and studded tire users cause considerable road damage. Why shouldn’t bicyclists and studded tire users be required to pay an annual fee to the county so they might all go away?
This translates to “these weirdos are encroaching the domain of the automobile but they are legally allowed to be here so you’d better get used to it.”
There is nothing posted here that supports that in any way.
Not literally I agree.
In fact if you consider that the words were spoken by a politician in politicalese they were more pro-bike than I’ve come to expect out of non-urban politicos.
The popularity contest that is elected office precludes the correct statement which I’d have phrase like this:
“Look: public roads are are just that – public. Anyone can use them without restriction. Autos are licensed and taxed for 2 reasons: heavy vehicles all types cause expensive road damage and it is very easy to injure or kill another person with an automobile.
There isn’t enough money anywhere to make separate roads for all different types of road users so everyone will just have to buck up and share.”
Frank honesty is not valued by the voting process.
Or just let all the roads deteriorate and we can all get by on mountain bikes 🙂 (kidding)
That was a hilariously loaded question with a pathetic answer.
I’m perfectly happy to pay my fair share, but let’s figure out what that is. A good breakdown of revenue sources and expenditures for state and local transportation would be a good start for that.
I suspect it’s a mix of user fees and general fund money. As a non-driver, the former’s out, but I’m guessing the latter goes into driving-only infrastructure at roughly the same rate that money is applied to bike-only infrastructure.
Pretty sure that the county would owe you money if there was a serious analysis of what you pay in through taxes vs. what you are receiving in benefits.
My guess is that a bicyclists “fair share” is an annual tax rebate paid to each regular commuter for keeping the cost of infrastructure down and reducing the need for addition carbon/pollution mitigation.
In the UK, a purchase of a commuting bike is tax deductible! Here in Oregon buying a more efficient washing machine gets you a tax rebate.
Cheers, Alistair
…Or it might have been a question about a specific project they saw – for example, pavement surfaces can be negatively affected by physically grinding off old lane markings (especially thermoplastic) to accommodate a new lane configuration. This can occur when adding a bike lane, parking lane, right turn lane, etc.
It is interesting that you bring this up. Shifting a lane over by 5 or 6 ft often prevents the need to repave it, as the ruts that cars have worn into the surface or now shifted enough to not create a safety hazard. I have heard of this “road diet lane shifting” as being a cheap alternative to repaving.
Its called Clack-onics
It should be noted that car drivers/owners’ use of the public roadways are heavily subsidized. For instance, general funds from the state or county or city pay for any law enforcement on roadways, as well as sanding the roads in winter.
Once there is a discussion of “who pays for the roads” it becomes clear that car drivers are getting a huge free ride with use of our public roads.
All I know is that Jamie flat out nailed that one out of the park with her response to it.
Remember when a politician says “we’re looking into that,” it means just that. They will “look” at it. And, when they “look” the commissioners will see it is not feasible and move on to the next item.
Seems obvious to me that bicyclists who are also studded tire users (on their cars, that is) cause considerable road damage. That must be the meaning of “and” in the original statement.
Simple solution: A tax (yuck) on tires. All tires. Strollers, wheelchairs, bicycles, tricycles. Cars, trucks, whatever.The bigger the tire, the higher the tax. Thus, a skinny road bike tire tax would be less than a knobby mountain bike tire tax, etc. Small car tire taxes would be less than a big fat Hummer tire tax, etc. A pain, sure. But it would blunt the notion that “we” don’t pay our share. And this tax would directly address the point of contact between the vehicle and the road, where said damage occurs.
You should check out the County’s Transportation System Plan update. http://www.clackamascountytsp.com
There’s an interactive survey you can take that talks about the needs of the system, how to pay for it, and who should pay how much? Go to the “Latest News” link, and read the framework, vision and goals to get a better idea of how bicycling fits into the county’s transportation system.
Good! Bikes SHOULD pay, they use the roads as well. A lot of bikes DO cause accidents because they don’t stop at stop signs and they feel they own damn road. Good for you Clack. Co!!
Oh how embarrassing, your ignorance is showing!
What do collisions have to do with paying for road maintenance? Motorists effectively own the roads, anyway. Cyclists don’t want to be squeezed to the very edge of the roadway, and we need some breathing/safety room.
Yes, because we freeloading cyclists do not pay income, property or gasoline taxes. Brilliant observation. Wow.
I can see one instance where you can lay cause of damage to the bike lanes.
Take two lanes of roadway and reduce it to one lane with a bike lane.
You now have the same amount of traffic rolling over a single lane of roadway. The damage to that lane of traffic does accelerate due to the increase in vehicles traveling over it.
The question poses a high level of ignorance about transportation. First of all, freight trucks pose 1000’s of times more damage on roadways and cause the cost of road construction and maintenance to be so high. The wider the roadway, the more roadway has to be constructed at the higher standard required to accommodate trucks. More cars driving requires wider roads. It doesn’t matter much how many cars are driving on these roads once they’re built as they’ve often been built to truck standards. Bike lanes get the shoulder of the roadway that would have been designed into the roadway from the beginning due to the road engineers. It’s not very safe, but it’s their way of at least designating a small piece of the roadway for bikes, officially. Bike lanes only get damaged where buses pull in to make stops. I can confidently say that bikes cause zero damage. Cars cause some damage, but not much. Trucks and buses cause enormous amounts of damage. Studded tires on cars do cause an increase level of damage that requires more maintenance. Bottom line, most of these people who complain don’t have a clue.
This sounds like something out of conservative talk radio. Among the other pearls of wisdom my friends who listen to that radio: bicycle lanes eat up 75% of our transportation dollars, and the classic: bicyclists are not allowed in cross walks (even ones related to a MUP like Springwater Corridor crossing a road!). I get yelled at by a motorist at least once a month when I am crossing the road in a crosswalk either related to the Springwater Corridor or the I-205 bike path. Most recently, one motorist, while flipping me off and cutting me off in the middle of a cross walk in which I had the walk sign, screamed that “cars have the right of way, you moron”.
Thanks, Lars!
Cycling facilities may cost money, but they cost less than providing for other road users. Charging us a user fee for the roadways is absurd, when we actually SAVE taxpayers money!
Bicyclists DO do damage to roads. I’ll explain.
Average vehicle (car) weighs about 4000 pounds.
Average tire contact patch is 35-40 square inches – x4 tires.
Divided out that that’s roughly 20-28 PSI (pounds per square inch) laid on the pavement by a car.
Average bicyclist/bicycle weight – 200+ pounds. (person, gear, bicycle)
Average tire contact patch is about 1-1.5 square inches.
Divided out that’s roughly 66-100 PSI laid down on the pavement.
Based on weight/contact patch ratios, bicycles do MORE damage to pavement than cars.
Bwahahahahahahahahahaha
Of course, that assumes that it is primarily downward gravitational pressure that causes the damage vs. the lateral pressures of acceleration and braking. I’m not an expert so I can’t say one way or another, but I think that the momentum/inertial effects could be a contributing factor. Would the size of the contact patch make much difference in distributing those pressures?
All true statements up until the last sentence.
You’re making a very large assumption in this argument, that road damage is purely a function of pressure, and does not depend at all on gross weight. If you have a reference that supports, please let us know.
In the meantime, anecdotal evidence suggests otherwise: look at the pavement in front of any heavily used bus stop in the city (E Burnside at 12th, for example). The extensive damage you’ll see was caused by vehicles with extremely large tires which produce pressures far less than those developed by the bicycle in your example.
I’ll agree that the contact patch is higher pressure for a bike. However, i don’t believe that translates directly to pavement damage. For example, I could take my mtn bike with 80 psi knobby tires and do a lot less damage over the same fire road than a 4×4 with 32 psi tire pressure.
There are other factors involved such as tire tread (spiked, knobby, groved, smooth), accelration rates (ever romped hard on the gas pedal on your car?), and total vehicle mass. Not to mention the weather factors (think of those potholes that appear in the roadways after in rains and freezes…not many of those on dedicated bike paths).
To make a direct comparison we’d need to normalize the data set based on a standard number of vehicle trips (be they cars or bikes) and measured pavement dergedation rates for the two sets of vehicles.
“…Based on weight/contact patch ratios, bicycles do MORE damage to pavement than cars.” RJ
Based on you calculations, bicycles apply more weight to a given square inch of roadway. From those simple calculations, you’ve proceeded to suggest that sheer weight applied to pavement is the singular contributing factor to pavement damage from vehicles. Maybe that’s true, maybe it’s not. Set up a test and prove it.
By the way, have you determined how much damage a car of the weight you’ve based your calculations on, actually does cause to the roadway?
Ten seconds of googling proves you wrong: http://facweb.knowlton.ohio-state.edu/pviton/courses2/crp776/776-roads-handout.pdf
Most road damage is caused by heavy transport vehicles, namely trucks. The amount of damage trucks cause is exponentially higher; a heavy transport truck does about 665x the damage of a car, yet is not 665x heavier.
In case the other comments hadn’t already clarified: road wear is not a simple function of tire pressure and weight.
RJ,
Interesting hypothesis RJ. Let’s test it.
Let’s both lay on the pavement. I’ll let a bike roll over me, and you let a car roll over you. Let’s see who incurs the greater damage.
whoa whoa whoa. You can’t just jump into an experiment like that with so many variables.
Do you and RJ have the same body fat %? If he has more “padding” then the car may do less damage.
Similar, but slightly different; are you both the same height lying down? We don’t want the bike to have to “jump” onto you. That may hurt…
Also, aren’t we assuming that all four wheels of the car are rolling over things? How will this be accomplished?
Lots of things up in the air on this experiment, but if RJ is right we will make sure to have an ambulance nearby to help you after the massive pressure of the bike rolls over you.
Joe, Good point. My proposed experiment has introduced far too many additional variables. Maybe it’s best for both the car and bike to roll over RJ and compare the damage between the two.
Wish I didn’t have to say it, but I do. This is obviously all in jest. Just trying to point out that some hypotheticals can be easily disproved through a thought experiment.
LOL. I know I haven’t had a Physics lesson in well over a decade but I’m pretty sure that if this were the model we used to compute road damage, then we’d also have to assume a world where cars (and bikes) are unable to accelerate since the only force we are considering in this model is PERPENDICULAR to plane of acceleration/deceleration.