Particularly among experienced cyclists, one will often hear advice about "bike fit" or "improving the engine" when people talk about riding more comfortably, faster, or further. I'll be the first person to say that even as an experienced cyclists whose read and thought about the subject, I am no expert. So instead of rattling off detailed nonsense, I have collected a few sources of bike fit information and categorized them below.
My only advice is to be willing to try different things if the fit isn't perfect. A little experimentation will go a long way towards figuring at a comfortable setup for you.
How to Fit a Bicycle ...
Peter White discusses his method in fine detail.
The Competitive Cyclist has a GUI that maps your body measurements to an optimally sized bike. They also have some verbiage that discusses their methodology on that page.
If you're really new at this, Jim Langley's page is a nice place to start.
For a scientific oriented discussion, the pages at slowtwitch are interesting.
What I chose ...
After reading a few articles and seeing some videos, I became a fan of Dr. Andy Pruitt. A google/youtube search on his name will produce a ton of hits which, unfortunately, seem to be somewhat unstable.
His medical guide for cyclists.
His fitting method and "optimized" components/clothing/shoes sold by Specialized.
A summary from a popular randonneuring site.
Some stuff on saddles ...
A summary from Captain Bike.
Jim Langley's discussion on saddles.
Need to change a stem?
A page that shows extension and rise as a function of stem angle and length.
Jim G's that compares two stems to get the change in rise and extension.
Looking at different (road) handlebars?
Two general discussions on handlebars ...
... by Grant Peterson of Rivendell.
... by Tom Deakins of the Harris Cyclery.
Probably more details than you want, but nonetheless, this is an awesome comparison tool. The rest of the blog has other pages with more handlebars, saddles, and so on.
Monday, March 28, 2011
Sunday, March 20, 2011
Carrying children on your Bike Friday
We often take our kids to local places with our bicycles. Bike Friday bicycles with their low mono tube design -- as opposed to the traditional diamond frame -- and small wheels create a distinct advantage for pulling children via a trailer rather than a child seat but also present an extra challenge.
After picking up a set of long rack braces I tested out a Topeak child seat on the back of my New World Tourist with a 25-pound bag of rice. Setting up the rack, by the way, was straightforward but a quite annoying task. But after an hour of jiggling and fumbling for different adaptors and parts, it was secured to the rear of the bike. After a quick test ride it was clear that riding with the child seat was sub-optimal. On a regular diamond-frame bike there is a top tube that one can use his/her legs to push the bike upright when at a stop.
That is, if the bike begins to tip over, one typically uses a leg to push against the top tube to keep the bike upright.
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| No top tube! |
However, the monotube design of a Bike Friday takes away that point of contact such that one will have to keep the bike upright via leverage on the handlebars or perhaps sliding a leg behind you to lean against the seat mast. My conclusion was to pass on the child seat and only use the trailer when carrying children.
While a child trailer is very stable -- all of them appear to be two-wheel designs -- they generally attach to the rear axle of a bike. Consequently, when mated with the small 20" wheels of the Bike Friday instead of a 700c/27" wheel, the trailer has a noticeable forward tilt. Particularly with small children who have a harder time reaching the floor and pushing back, this would probably cause them to tilt forward against the restraints and eventually contort themselves into some sort of equilibrium. My solution is to flip the Burley trailer mount such that it attaches above the axle instead of below it.
Instead of the attaching to a point an inch or two below the axle, it attaches to a point an inch or two above the axle. Resulting in a much more level trailer and presumably more comfortable kiddies.
Friday, March 11, 2011
If you're interested in a Bike Friday ...
Years and years ago -- pre-children ... hence it seems like forever -- the boss and I became interested in traveling with our bikes. After much thought and research we settled on a pair of custom Bike Friday travel bikes. I have a lot of experience with the bikes: maintenance, club rides, touring, pulling the kiddies, and so on. Given that I get around in the cycling world, I often receive lots of questions about the bikes as well as questions about ordering Bike Fridays. If you're thinking about getting a Bike Friday, then this post is for you.
My picture of the person typically interested in a Bike Friday is someone with some cycling experience and is likely much more dedicated to the sport/activity than the average citizen. I will discuss things in an order that reflects importance and how often a particular question is asked. More generally, realize that a lot of what is written here is simply my anecdotal experience somewhat backed by some real and pseudo experimental evidence. Most of my explanations here are edited for brevity with an eye on who is a likely reader. However, this might be inappropriate for others, so I'll be more than happy to elucidate further in response to either a comment or personal e-mail.
My picture of the person typically interested in a Bike Friday is someone with some cycling experience and is likely much more dedicated to the sport/activity than the average citizen. I will discuss things in an order that reflects importance and how often a particular question is asked. More generally, realize that a lot of what is written here is simply my anecdotal experience somewhat backed by some real and pseudo experimental evidence. Most of my explanations here are edited for brevity with an eye on who is a likely reader. However, this might be inappropriate for others, so I'll be more than happy to elucidate further in response to either a comment or personal e-mail.
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| Our bikes with the Burley at a local park |
It rides great. If you're a fast/slow rider on other bikes, you'll be a fast/slow rider on a Bike Friday. For those familiar with bike geometry, the bike will handle like low-trail bikes that were popular in the past and have a growing set of followers today: the bike will be more and less sensitive to steering inputs at the handlebar and body inputs to the bike, respectively. For those of you who could care less about geometry and simply want to ride, the bike will be a little "squirelly" in the beginning but easily accommodated with a little practice. Handling improves considerably with a front load such that I recommend a handlebar bag or something of the sort instead of a saddle bag. What is the effect of the small wheels? In my experience with a variety of wheel sizes -- 16" through 27" -- the small wheels certainly have some effect but that effect is small relative to other determinants of handling and performance. There are pluses and minuses -- see here for a positive spin on them -- but they definitely make a huge improvement on folding, packing, storage, and general portability. More about small tires/wheels. Everyone always asks whether the bike is fast. Really ... it's not about the bike: it's the motor that is important. Looking back at GPS records of some old 60-mile hilly training rides through Northern Virginia with the Bike Friday and my road bike, it is the case that the road bike was about 5 minutes faster. But my Bike Friday is a 26 pound touring bike whereas the road bike is about 6-7 pounds lighter with a more aggressive position. Without doing any fancy calculations, that difference sounds reasonable and I imagine that if instead one purposely built a Bike Friday for aggressive road riding that most if not all of that 5 minutes would disappear.
Much of what I wrote above depends on how well the bike fits you. In my experience, a well-fitting bike is necessary for "the motor", as well as, for the bike to perform well. If you are more performance oriented and expect to get road bars with the swan stem, I highly recommend getting the Bike Friday fit stem for sizing a custom ultralight or adjustable stem. The fit stem allows an incredible amount of adjustment: plus or minus four inches in height and a reach from 50 to 150 mm. I also recommend getting one with a faceplate will let you swap and try out different handlebars on your new bike. A low-trail bike with small wheels is a new experience for a lot of riders. You might find that you want a different amount of weight on the front handlebar or that the relative position of the crank to the saddle results in small changes for the best personal fit. The lack of a top tube might encourage you to use different handlebars with more space for "stuff". I can go on and on; but the point is that I think that you'll discover that having the bike with you will result in a better fit than simply sending your measurements in to Bike Friday. Alternatively, if you plan on using an ahead-type stem, then there is already some sizing flexibility. Remember that Bike Friday can split most aluminum handlebars with a 25.4 or 26.0 mm clamp area. So there is little need to go with the standard bars that Bike Friday offers with their models; although the Bike Friday H-bars and STI-bars are easy to pack and pretty good for recreational riding.
A folding bike for general use and travel is quite useful. In addition to getting the bike into a suitcase, realize that on a lot of trips, you might drive or take a taxi to get from A to B at some point. Since the boss and I can fit both of our bikes into the trunk of a Toyota Echo, just about any ordinary car can take us and our bikes for whatever purpose without a rack. Whenever I do long solo ride, I generally take the Bike Friday since I were ever to bail on the ride or have a big mechanical failure, calling a cab is an easy option. Many public transportation systems have prohibitions against bicycles but allow folding bikes to be carried onboard.
For most riders, ERTO 406 wheels are a far better choice. For the unfamiliar, it turns out that there is more than one rim/tire size that is labeled 20 inches: ERTO 406 and 451. Although ERTO 451 has a longer diameter and with some quality tires, most 451 tires are strictly road tires in narrow sizes and is generally unavailable at anything but a bicycle shop that specializes in recumbents and/or folding bikes. Picking a size whose tires and tubes are scarce is probably not the best choice for a travel bike. ERTO 406 is the popular BMX size. Consequently, tires and tubes are widely available -- even at general stores like WalMart and Target -- whereas high quality 406 tires in all widths are available at good bicycle shops or mail order. Note that all of the good 451 tires are available in 406. Long story short, unless one is absolute positive that one is going to stick with narrow road tires and the slightly larger wheel is appealing, I strongly recommend sticking with 406. Since I almost always recommend 406 wheels and typically these bikes are used for travel, I invariably recommend either the New World Tourist or Pocket Crusoe models according to how much the rider weighs.
Generally, I recommend sticking with the standard derailer drivetrain. Moreover, getting low gears are not a problem with a Bike Friday. Instead, determining how high of a gear you need is the problem. I'm assuming that you have already read this summary by Green Gear Cycling and that you have some cycling experience. The vast majority of people choose between a standard derailer drivertrain or the SRAM Dual Drive since internal hubs with wide gear ranges are much more expensive. Before we begin discussing the choice, we need to understand that the 20" wheels directly leads to a drivetrain with lots of low gears -- gears where it is easy to spin the crank but not move fast. But even recreational hybrids bicycles will still have top gears around 100+ gear inches. Just based on personal observations, few people ever use those high gears with any frequency whereas having a low gear, particularly for touring, is quite helpful for long climbs.
The SRAM Dual Drive has several advantages/disadvantages relative to the derailer drivetrain:
The best derailer drivetrain will depend on the top gear you want. Pick a Shimano Capreo hub/cassette if you want a top gear over 100 gear inches or wish to use index shifting; otherwise stick with a standard hub/cassette. Essentially, the Capreo cassette will let a rider stick with a standard Shimano crank/chainring combination -- or presumably Campagnolo or SRAM -- that will shift really ... really well and be better for packing in a suitcase: a big chainring will get very close to the edges of a suitcase which makes it more likely to get damaged in transit. Of course, going with the Capreo cassette/hub means you are getting something "special" that will be hard to acquire from anyone other than Bike Friday or the Harris Cyclery in a pinch: For a price you can get anything delivered FedEx! To some extent you have some of the same problems as the SRAM Dual Drive. But there is an important difference, the Capreo hub/cassette works the same way as other hubs/cassettes such that a competent mechanic will know what to do and how to fix the problem. From what I observe, Capreo components are actually carried by a few online retailers; but Bike Friday and the Harris Cyclery are the two that I use. The alternative which I strongly recommend if you're comfortable with bar ends and would be happy with a top end around 95 gear inches -- I believe that most people have gearing that is way too high -- then you can get a decent gear range with marginally larger than normal chainrings. Here I propose a chainring/cassette combination with a normal cassette and compare it to a standard Capreo cassette.
Check out Bike Friday's Youtube videos for more information on the folding process. The fold with a single chainring. The fold with multiple chainrings. Now that you have seen the single chainring video, note that you can install Bike Friday's chain retainer to avoid chain drop issues during folds. Note that if you intend on folding/unfolding the bike a lot and in somewhat of a hurry, you might consider the folding stem. Of course, if you want a bike that will be folded a lot and in somewhat of a hurry, the Bike Friday tikit or Brompton might be a better fit for you. But I can imagine some scenarios where one would prefer the bigger and more robust bike that still folds easily.
Get a high-end head set for the Bike Friday. In the past, Bike Friday offered the Chris King headset which by no means is cheap. But considering the extra forces on the headset -- the super long stem mast is a giant lever -- I think it is worth every penny spent. Recently I noticed them carrying the Cane Creek 110 which has a 110-year "no questions asked" warranty. I have no experience with it, but I suspect that it is pretty good too.
Use rims drilled for schraeder-valves and use adapters for presta-valve tubes. Personally, I think presta valve tubes are superior to shraeder valve tubes. But it is the case that most ERTO 406 tubes at common stores will be schraeder. If you're traveling and desperate for a tube, being able to remove the adapter is a great option at a trivial weight cost.
Small wheels are wildly strong. Don't be afraid to use lower spoke counts than you would on a typical touring bike. Just because of hub and rim availability -- especially at lower prices -- one is likely limited to 32 spoke holes. But Bike Friday will often lace 36-hole hubs to 24-hole rims as a cost effective method for low-spoke count wheels.
Wide, high-quality tires are strongly recommended. Ignoring my conclusion that wider tires are more efficient than most people commonly believe ...
Much of what I wrote above depends on how well the bike fits you. In my experience, a well-fitting bike is necessary for "the motor", as well as, for the bike to perform well. If you are more performance oriented and expect to get road bars with the swan stem, I highly recommend getting the Bike Friday fit stem for sizing a custom ultralight or adjustable stem. The fit stem allows an incredible amount of adjustment: plus or minus four inches in height and a reach from 50 to 150 mm. I also recommend getting one with a faceplate will let you swap and try out different handlebars on your new bike. A low-trail bike with small wheels is a new experience for a lot of riders. You might find that you want a different amount of weight on the front handlebar or that the relative position of the crank to the saddle results in small changes for the best personal fit. The lack of a top tube might encourage you to use different handlebars with more space for "stuff". I can go on and on; but the point is that I think that you'll discover that having the bike with you will result in a better fit than simply sending your measurements in to Bike Friday. Alternatively, if you plan on using an ahead-type stem, then there is already some sizing flexibility. Remember that Bike Friday can split most aluminum handlebars with a 25.4 or 26.0 mm clamp area. So there is little need to go with the standard bars that Bike Friday offers with their models; although the Bike Friday H-bars and STI-bars are easy to pack and pretty good for recreational riding.
A folding bike for general use and travel is quite useful. In addition to getting the bike into a suitcase, realize that on a lot of trips, you might drive or take a taxi to get from A to B at some point. Since the boss and I can fit both of our bikes into the trunk of a Toyota Echo, just about any ordinary car can take us and our bikes for whatever purpose without a rack. Whenever I do long solo ride, I generally take the Bike Friday since I were ever to bail on the ride or have a big mechanical failure, calling a cab is an easy option. Many public transportation systems have prohibitions against bicycles but allow folding bikes to be carried onboard.
For most riders, ERTO 406 wheels are a far better choice. For the unfamiliar, it turns out that there is more than one rim/tire size that is labeled 20 inches: ERTO 406 and 451. Although ERTO 451 has a longer diameter and with some quality tires, most 451 tires are strictly road tires in narrow sizes and is generally unavailable at anything but a bicycle shop that specializes in recumbents and/or folding bikes. Picking a size whose tires and tubes are scarce is probably not the best choice for a travel bike. ERTO 406 is the popular BMX size. Consequently, tires and tubes are widely available -- even at general stores like WalMart and Target -- whereas high quality 406 tires in all widths are available at good bicycle shops or mail order. Note that all of the good 451 tires are available in 406. Long story short, unless one is absolute positive that one is going to stick with narrow road tires and the slightly larger wheel is appealing, I strongly recommend sticking with 406. Since I almost always recommend 406 wheels and typically these bikes are used for travel, I invariably recommend either the New World Tourist or Pocket Crusoe models according to how much the rider weighs.
Generally, I recommend sticking with the standard derailer drivetrain. Moreover, getting low gears are not a problem with a Bike Friday. Instead, determining how high of a gear you need is the problem. I'm assuming that you have already read this summary by Green Gear Cycling and that you have some cycling experience. The vast majority of people choose between a standard derailer drivertrain or the SRAM Dual Drive since internal hubs with wide gear ranges are much more expensive. Before we begin discussing the choice, we need to understand that the 20" wheels directly leads to a drivetrain with lots of low gears -- gears where it is easy to spin the crank but not move fast. But even recreational hybrids bicycles will still have top gears around 100+ gear inches. Just based on personal observations, few people ever use those high gears with any frequency whereas having a low gear, particularly for touring, is quite helpful for long climbs.
The SRAM Dual Drive has several advantages/disadvantages relative to the derailer drivetrain:
- No front derailer that can be damaged ... this is particularly good for folding the bike.
- Lowering or raising the gear range is very easy ... just change the chainring.
- A wide cassette leads to a very wide drivetrain; i.e., lots of low and high gears.
- Three speed internal hubs are a very mature technology and very robust. Although there are anecdotes to the contrary. For instance, there are a few discussions on bentrideronline.com where people tell stories of their failures in various situations. But my take is that three speed hubs have been around forever in a wide variety of uses.
- Internal hub can shift at a standstill.
- Annoying "clickbox" is at an exposed part of the bike: outside the rear derailer.
- Parts can be hard to obtain.
- It is the standard for bicycles and consequently much easier to repair.
- It is about 1 to 1.5 pounds lighter.
- A maintained derailer drivetrain shifts faster and crisper.
- Supposedly the derailer drivetrain is more efficient; although other than some articles in the Journal of Human Power -- see issues 50 and 51 -- I see little evidence for the statement. But my personal anecdote says that it is true and a lot of high-level technical people seem to believe it.
- Despite being subject to damage from travel and being dropped, derailers are still quite robust in my experience.
- Relative to the SRAM Dual Drive, there are much cheaper derailer options available.
The best derailer drivetrain will depend on the top gear you want. Pick a Shimano Capreo hub/cassette if you want a top gear over 100 gear inches or wish to use index shifting; otherwise stick with a standard hub/cassette. Essentially, the Capreo cassette will let a rider stick with a standard Shimano crank/chainring combination -- or presumably Campagnolo or SRAM -- that will shift really ... really well and be better for packing in a suitcase: a big chainring will get very close to the edges of a suitcase which makes it more likely to get damaged in transit. Of course, going with the Capreo cassette/hub means you are getting something "special" that will be hard to acquire from anyone other than Bike Friday or the Harris Cyclery in a pinch: For a price you can get anything delivered FedEx! To some extent you have some of the same problems as the SRAM Dual Drive. But there is an important difference, the Capreo hub/cassette works the same way as other hubs/cassettes such that a competent mechanic will know what to do and how to fix the problem. From what I observe, Capreo components are actually carried by a few online retailers; but Bike Friday and the Harris Cyclery are the two that I use. The alternative which I strongly recommend if you're comfortable with bar ends and would be happy with a top end around 95 gear inches -- I believe that most people have gearing that is way too high -- then you can get a decent gear range with marginally larger than normal chainrings. Here I propose a chainring/cassette combination with a normal cassette and compare it to a standard Capreo cassette.
Check out Bike Friday's Youtube videos for more information on the folding process. The fold with a single chainring. The fold with multiple chainrings. Now that you have seen the single chainring video, note that you can install Bike Friday's chain retainer to avoid chain drop issues during folds. Note that if you intend on folding/unfolding the bike a lot and in somewhat of a hurry, you might consider the folding stem. Of course, if you want a bike that will be folded a lot and in somewhat of a hurry, the Bike Friday tikit or Brompton might be a better fit for you. But I can imagine some scenarios where one would prefer the bigger and more robust bike that still folds easily.
Get a high-end head set for the Bike Friday. In the past, Bike Friday offered the Chris King headset which by no means is cheap. But considering the extra forces on the headset -- the super long stem mast is a giant lever -- I think it is worth every penny spent. Recently I noticed them carrying the Cane Creek 110 which has a 110-year "no questions asked" warranty. I have no experience with it, but I suspect that it is pretty good too.
Use rims drilled for schraeder-valves and use adapters for presta-valve tubes. Personally, I think presta valve tubes are superior to shraeder valve tubes. But it is the case that most ERTO 406 tubes at common stores will be schraeder. If you're traveling and desperate for a tube, being able to remove the adapter is a great option at a trivial weight cost.
Small wheels are wildly strong. Don't be afraid to use lower spoke counts than you would on a typical touring bike. Just because of hub and rim availability -- especially at lower prices -- one is likely limited to 32 spoke holes. But Bike Friday will often lace 36-hole hubs to 24-hole rims as a cost effective method for low-spoke count wheels.
Wide, high-quality tires are strongly recommended. Ignoring my conclusion that wider tires are more efficient than most people commonly believe ...
- Wide tires can be efficiently ridden at much lower pressures. Consequently, it helps alleviate the additional bumpiness from small wheels.
- Wide tires will also help slow down the steering up front.
Of course they will be heavier, but at least this are small diameter tires and will be less heavy than typical wide tires. Personally speaking, I think life is too short to get crappy tires and most wide tires are low end. But thankfully, there is a good selection of high quality high end tires in ERTO 406. Folding tires are also good for travel bike since they pack better and are somewhat lighter.
Carrying loads on the front wheel is recommended. As I mentioned earlier, since the trail is so low on Bike Friday's, carrying loads on the front wheel helps slow down and improve the steering. Moreover, the front wheel is almost always stronger than the rear wheel. A handlebar bag also gives the rider easier access to "stuff" while riding.
Will you ever fold the bike? If no, strongly consider the Easy Pack Mast. The Easy Pack Mast is not hinged from the frame. As the name implies, it makes it easier to pack into a suitcase. It is also somewhat lighter than the typical folding mast. If you have money to burn or want something even lighter, get the titanium upgrade for the easy pack mast.
Believe it or not, that is about all that I typically recommend in a generic sense on a new (or used) Bike Friday either because I find it hard to broadly support a choice or I have little personal experience with it. Some of the things I barely discuss are the Bike Friday tikit, fenders, suspension, and using racks versus the suitcase/trailer (you can find the Bike Friday description on their FAQ page and a negative review here). I always recommend joining the Bike Friday YAK and talking to others in a local Bike Friday club; if you are in the DC area, you can find us here. Generally, you will find lots of helpful folks more than willing to share their experiences and advice. Shockingly people will disagree with my assessments, but it would be worthwhile for a potential buyer to read/hear alternative reasoning.
Believe it or not, that is about all that I typically recommend in a generic sense on a new (or used) Bike Friday either because I find it hard to broadly support a choice or I have little personal experience with it. Some of the things I barely discuss are the Bike Friday tikit, fenders, suspension, and using racks versus the suitcase/trailer (you can find the Bike Friday description on their FAQ page and a negative review here). I always recommend joining the Bike Friday YAK and talking to others in a local Bike Friday club; if you are in the DC area, you can find us here. Generally, you will find lots of helpful folks more than willing to share their experiences and advice. Shockingly people will disagree with my assessments, but it would be worthwhile for a potential buyer to read/hear alternative reasoning.
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| Say hello if you see us. |
Wednesday, March 2, 2011
The Montreal evidence for cycle track-to-street safety
A recent paper on Montreal cycle tracks has drawn a lot of publicity from the official news sources and blogs without an appropriate amount of skepticism for the results.
Briefly, the authors compare six cycle tracks to reference streets to compare the relative risk of cycling on those streets. Exposure is determined by a two-hour simultaneous count on 2009 on the streets. The number of injuries is tabulated from emergency medical reports (EMR) from 1999 though 2008 during the cycling season; but are subsequently adjusted by estimating the number of intersection injuries from bicycle/vehicle collision police reports. Aggregating over all six cycle tracks they conclude that the relative risk of cycle track streets to the reference streets is approximately 0.72. Moreover their two-hour simultaneous count estimated 2.5 times more cyclists on cycle track streets.
Fundamentally, the relative risk measure is only valid if the cycle track and reference street have similar qualities and would face similar risks if not for the cycle track. Below are person-views -- roughly at the beginning of the focus area -- with maps of the first comparison in Table 1 of the paper.
St. Denis ... the reference street
Brebeuf ... the cycle track street
Personally, I think a picture is worth a thousand words. In the interest of completing the point, a cyclist traveling northbound on St. Denis has to deal with several more lanes of motor vehicle traffic including opposing direction traffic -- left turns into driveways, u-turns, buses and so on -- in a commercial area. Moreover, it is unclear to me what type of injuries are in the EMR data; but if pedestrians collisions are included then the St. Denis cyclist would have people shopping and dining in the area. Wider roads also tend to have faster motor vehicles which increase the likelihood of a serious injury. As one might expect, Table 3 show that the relative risk to motor vehicle occupants is significantly different from 1. In short, to find no statistical difference in relative risk would be far more surprising than their estimate. Identifying any effect from the cycle track is highly unlikely, in my opinion. Just to be clear, I picked this comparison because it was listed first. One could grind through the other cycle track-reference street comparisons to be more thorough but I suspect that the point has already been made. Others have done this precise task. If and when they write up a paper or webpage, I will be sure to link it.
In large, we can probably stop here with regards to raising a serious level of skepticism about the study. However, there are also some serious questions about the data underlying the relative risk metric. The exposure data was collected during a two-hour period on a day with mild weather. That data was used to compute the exposure ratio for the cycle track and reference street during a 10-year period of cycling seasons. Now, if we ignore the huge difference in reference periods, we should consider whether the population of cyclists on the cycle track and reference street are similar enough that this remains a good estimate subject to changes in weather, time of day, and other random perturbations over time. Again a picture is worth a thousand words. Does anyone expect similar cyclists on the two pictured streets above?
As I mention above, the EMR injury data that occurs at intersections is adjusted for the expected number of cyclists originating from the cross street instead of traveling on the streets of interest. The authors estimated the fraction from the cross street based on tabulations of police reports which overlap but do not fully cover the same reference period. But do EMR and police bicycle/motor-vehicle collision reports have the same meaning? Certainly they are correlated, but simply based on anecdotes in the US, when a police report is filed seems to vary considerably and could differ from say whether an ambulance is sent to the scene. For instance, until a recently, an Arlington police report would only be filed if the cyclist in a collision with a motor vehicle went to the emergency room despite emergency personnel being sent to the scene. Note that part of this uncertainty is about my limited understanding of Montreal/Canadian laws and data: It could be the case that the relationship is well understood. But the short blurb in the paper omitted a thorough discussion and cited a paper about New Zealand. Consequently, I couldn't tell whether their conclusion was based on their own tabulations/local knowledge or the New Zealand paper. Nonetheless, besides the potential bias regarding the share of intersection EMRs originating from the cross street, modeling this component also induces a bias in relative risk due to the variance of the estimated shares. At the very least, it would have been prudent to do some robustness estimates by using police report collision data only to compute the relative risk ratios. There are 340 and 191 EMR injuries for cycle track and reference streets using the authors' method. If the overlap is high then one could probably get good estimates to make comparisons.
In the interest of brevity, I want to avoid nit-picking another dozen points on the paper and instead make a few general points relevant to cycling advocacy. One, many discussions about safety conveniently ignore notions of convenience and speed. Pro-facilities people gloss over increased conflicts at intersections and slower travel. Vehicular cyclists (VC) tend to ignore the ability for skilled cyclists to use something like a bike lane to pass motor vehicles stuck in a traffic jam which might be safer than filtering up in an alternative environment. By simply looking at collisions, fatalities, or whatever, we often forget that these things are an imperfect proxy for the true object of interest: getting around quickly and conveniently with a low amount of risk and effort. My point is that as advocates, we need to mentally process the statistics and research into something more appropriate for our goals.
Two, the concerns that AASHTO and many traffic engineers have with cycle tracks ( 1, 2) and similar side paths that have a theoretical and empirical base. And there are certainly lots of anecdotes from experienced cyclists -- not necessarily VC -- that echo the concerns. So when we read that there is research concluding the cycle tracks makes cycling safer in an all-things-equal context -- for contradictory evidence read this paper on Copenhagen -- it deserves a lot of skepticism and/or it needs further consideration with respect to my first point regardless of one's beliefs about the world. Given the strong feelings among certain groups, I want to emphasize that bike lanes, wide-outside lanes, cycle tracks or whatever should still be under consideration for some set of circumstances. Instead, I want to emphasize that one should be much more careful about implementation than the current euphoria over cycle tracks.
Lastly, in the context of building livable neighborhoods, I share many goals with cycling/walking advocates and other "smart growth" people. But part of smart growth means being good scientists, properly evaluating all evidence that either confirms or rejects our priors, and giving it the appropriate weight when making decisions and choosing what to advocate. Most importantly, this includes considering much more difficult topics regarding causality and what we don't know.
P.S. M. Kary, a statistician living in Montreal, wrote a response to the paper here. Thanks to John Allen for pointing out the paper and adapting it for the Internet.
Fundamentally, the relative risk measure is only valid if the cycle track and reference street have similar qualities and would face similar risks if not for the cycle track. Below are person-views -- roughly at the beginning of the focus area -- with maps of the first comparison in Table 1 of the paper.
St. Denis ... the reference street
Brebeuf ... the cycle track street
Personally, I think a picture is worth a thousand words. In the interest of completing the point, a cyclist traveling northbound on St. Denis has to deal with several more lanes of motor vehicle traffic including opposing direction traffic -- left turns into driveways, u-turns, buses and so on -- in a commercial area. Moreover, it is unclear to me what type of injuries are in the EMR data; but if pedestrians collisions are included then the St. Denis cyclist would have people shopping and dining in the area. Wider roads also tend to have faster motor vehicles which increase the likelihood of a serious injury. As one might expect, Table 3 show that the relative risk to motor vehicle occupants is significantly different from 1. In short, to find no statistical difference in relative risk would be far more surprising than their estimate. Identifying any effect from the cycle track is highly unlikely, in my opinion. Just to be clear, I picked this comparison because it was listed first. One could grind through the other cycle track-reference street comparisons to be more thorough but I suspect that the point has already been made. Others have done this precise task. If and when they write up a paper or webpage, I will be sure to link it.
In large, we can probably stop here with regards to raising a serious level of skepticism about the study. However, there are also some serious questions about the data underlying the relative risk metric. The exposure data was collected during a two-hour period on a day with mild weather. That data was used to compute the exposure ratio for the cycle track and reference street during a 10-year period of cycling seasons. Now, if we ignore the huge difference in reference periods, we should consider whether the population of cyclists on the cycle track and reference street are similar enough that this remains a good estimate subject to changes in weather, time of day, and other random perturbations over time. Again a picture is worth a thousand words. Does anyone expect similar cyclists on the two pictured streets above?
As I mention above, the EMR injury data that occurs at intersections is adjusted for the expected number of cyclists originating from the cross street instead of traveling on the streets of interest. The authors estimated the fraction from the cross street based on tabulations of police reports which overlap but do not fully cover the same reference period. But do EMR and police bicycle/motor-vehicle collision reports have the same meaning? Certainly they are correlated, but simply based on anecdotes in the US, when a police report is filed seems to vary considerably and could differ from say whether an ambulance is sent to the scene. For instance, until a recently, an Arlington police report would only be filed if the cyclist in a collision with a motor vehicle went to the emergency room despite emergency personnel being sent to the scene. Note that part of this uncertainty is about my limited understanding of Montreal/Canadian laws and data: It could be the case that the relationship is well understood. But the short blurb in the paper omitted a thorough discussion and cited a paper about New Zealand. Consequently, I couldn't tell whether their conclusion was based on their own tabulations/local knowledge or the New Zealand paper. Nonetheless, besides the potential bias regarding the share of intersection EMRs originating from the cross street, modeling this component also induces a bias in relative risk due to the variance of the estimated shares. At the very least, it would have been prudent to do some robustness estimates by using police report collision data only to compute the relative risk ratios. There are 340 and 191 EMR injuries for cycle track and reference streets using the authors' method. If the overlap is high then one could probably get good estimates to make comparisons.
In the interest of brevity, I want to avoid nit-picking another dozen points on the paper and instead make a few general points relevant to cycling advocacy. One, many discussions about safety conveniently ignore notions of convenience and speed. Pro-facilities people gloss over increased conflicts at intersections and slower travel. Vehicular cyclists (VC) tend to ignore the ability for skilled cyclists to use something like a bike lane to pass motor vehicles stuck in a traffic jam which might be safer than filtering up in an alternative environment. By simply looking at collisions, fatalities, or whatever, we often forget that these things are an imperfect proxy for the true object of interest: getting around quickly and conveniently with a low amount of risk and effort. My point is that as advocates, we need to mentally process the statistics and research into something more appropriate for our goals.
Two, the concerns that AASHTO and many traffic engineers have with cycle tracks ( 1, 2) and similar side paths that have a theoretical and empirical base. And there are certainly lots of anecdotes from experienced cyclists -- not necessarily VC -- that echo the concerns. So when we read that there is research concluding the cycle tracks makes cycling safer in an all-things-equal context -- for contradictory evidence read this paper on Copenhagen -- it deserves a lot of skepticism and/or it needs further consideration with respect to my first point regardless of one's beliefs about the world. Given the strong feelings among certain groups, I want to emphasize that bike lanes, wide-outside lanes, cycle tracks or whatever should still be under consideration for some set of circumstances. Instead, I want to emphasize that one should be much more careful about implementation than the current euphoria over cycle tracks.
Lastly, in the context of building livable neighborhoods, I share many goals with cycling/walking advocates and other "smart growth" people. But part of smart growth means being good scientists, properly evaluating all evidence that either confirms or rejects our priors, and giving it the appropriate weight when making decisions and choosing what to advocate. Most importantly, this includes considering much more difficult topics regarding causality and what we don't know.
P.S. M. Kary, a statistician living in Montreal, wrote a response to the paper here. Thanks to John Allen for pointing out the paper and adapting it for the Internet.
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