Comparing cycling infrastructure design guides — American AASHTO vs. Dutch CROW (part 1)
American transportation planners and traffic engineers looking to expand their cycling infrastructure and policy knowledge beyond the American design guides should check out the Dutch “Design Manual for Bicycle Traffic.”
Known also as the “CROW manual” (available in English), this guide offers American readers an opportunity to learn how cycling facilities are designed and prioritized in the Netherlands. As a traffic engineering student, I thought it may be a worthy exercise to compare portions of the American and Dutch design manuals in a series of short articles. For this first article, I’ll compare what the Dutch CROW manual and AASHTO Green Book+Bicycle Guide say about the basic concept and physics of propelling a bicycle forward and how this is influenced by roadway design.
Dutch CROW manual
The CROW manual dedicates many pages to riding fundamentals. A few notable quotes include:
- “Physical exertion is needed to get a bicycle moving and to maintain momentum. Steep inclines [and] poor surfaces can place excessive strain on cyclists’ physical capabilities.” (page 27)
- “The need to combine tasks is another factor increasing mental stress. Consider in this regard focusing on bumps to avoid hitting them with the bicycle’s wheels and at the same time trying to concentrate on intersecting motorized traffic emerging from a side street.” (pages 27–28)
- “To a large extent, the road safety issues that the bicycle presents relate to its instability. At low speeds in particular (and when standing still) the bicycle is unstable and quick to topple. Crosswinds, slipstream and turbulence caused by lorries, bumps in the road surface and compelled low speeds determine its stability and therefore the requisite room for maneuver.” (page 30)
- “The bicycle has very little suspension. For that reason an even road surface is necessary to satisfy the requirements in terms of cycle-friendliness (an uneven road surface is perhaps not as much trouble to bicycles with suspension, but even then it will require extra energy).” (page 30)
- “The cycle infrastructure ensures that cyclists experience minimal nuisance (vibrations, extra exertion due to height differences, trouble from other traffic) and delay (stops).” (page 32)
- “Bicycles are powered by their rider’s muscular strength. Nevertheless, the power that a cyclist can produce is limited. Any additional resistance must be compensated by extra physical exertion. If this extra physical exertion is not forthcoming, then the consequence of this will be decreased velocity. For that reason it is important for potential energetic losses to be minimized in a cycle-friendly design.” (page 44)
- “Road designers…can influence cyclists’ energy loss to a significant extent. The objective must be to minimize unnecessary energy loss.” (page 46)
The CROW manual proceeds to explain both the “why” and “how” of minimizing rider energy loss and increasing comfort, and discusses measures such as:
- Reducing the number of times that cyclists are required to stop— “A single stop takes up as much energy as cycling 75–100 meters” (equals about 250–325 feet) (page 46)
- Reducing rolling resistance and vibration losses by choosing quality materials and maintaining the evenness of the roadway surface (page 46)
- Providing shelter from wind nuisances such as headwinds and building downdrafts (e.g. street trees) (pages 47 and 56)
- Considering and choosing a segment’s slope (pages 53–55) and curve radius (pages 50–51) to minimize physical exertion and the need to substantially slow down
AASHTO Green Book+Bicycle Guide
I could find no discussion of the basics of bicycle operation in the AASHTO Green Book, and it defers often to its Bicycle Guide except to mention typical bicycle lane widths. This surprises me (but maybe shouldn’t) because the Green Book dedicates entire sections to the operating fundamentals of motor vehicles (12 pages in section 2.2 titled “Driver Performance and Human Factors” and arguably more than 100 pages in Chapter 3’s “Elements of Design”).
The AASHTO Bicycle Guide appears to address the energy topic only in a few instances:
- “The speed at which bicyclists can travel is limited by the relative physical strength and fitness of the operator, the terrain and geometry of the roadway, and the gearing and condition of the individual bike.” (page 4–1)
- “Surface condition and pavement smoothness are important to bicyclist control and comfort.” “There are no bicycle-specific designs or dimensions for shared lanes or roadways, but various design features can make shared lanes more compatible with bicycling, such as good pavement quality…” (page 4–2)
- “Bike lanes should have a smooth riding surface.” (page 4–11)
- “Intersections — Bikeways should be planned to allow for as few stops as practical, as bicycling efficiency is greatly reduced by stops and starts. If bicyclists are required to make frequent stops, for example, along streets with stop signs every block, they may avoid the route or disregard traffic control devices.” (page 2–13)
- “Aesthetics — …Trees can also provide cooler riding conditions in summer and can provide a windbreak.” (page 2–14)
The AASHTO Bicycle Guide dedicates Section 7 to “Maintenance and Operations” but does not describe material selection or details that might provide guidance for planning or constructing comfortable and efficient cycling surfaces. My sense is that this section considers maintenance more from the perspective of safety than comfort.
I had very different feelings after reading the CROW and AASHTO manuals. It seemed to me that the CROW manual authors want readers to consider the “Why” of cycling infrastructure design and how the design choices merge together to impact cyclists’ conscious and subconscious decisions to ride in a particular place. Why does it matter how smooth the ground surface is? Why does it matter how often a rider needs to come to a full stop? Why are headwinds and downdrafts a nuisance? Why does the slope of a path or a turn radius matter to cyclist comfort? Why should I fill a pothole within an intersection used by cyclists? The CROW manual offers pictures, ideas, and answers to these questions.
To me, the AASHTO manuals seem to engage less with the “Why” and that feels like a missed opportunity. Many of the same conclusions are there, sure, but I found it less impactful or educational without the underlying reasons and discussion. Maybe the new version of the AASHTO Bicycle Guide will be different?
I continue to think about how to best summarize the differences between the American and Dutch manuals, but my overall impression is that the AASHTO manuals focus more on the roadway while the CROW manual focuses more on the rider and the cycling experience. A sort of impersonal vs. personal distinction maybe. I’ll write again soon and compare other parts of the manuals, and hope to bring these differences into greater focus.
These articles are inspired by Lior Steinberg’s recent article comparing NACTO and CROW bike lane standards. And thank you to George Liu from the Urban Cycling Institute for putting together a chapter-by-chapter CROW manual discussion playlist on YouTube.
Angelo studies civil engineering at Cleveland State University. Follow him and connect on Twitter.
Bonus for Clevelanders!
The Cleveland Public Library has copies of these design manuals. Below are links to the titles in the online library catalog if you’d like to read more.