By Dom Nozzi, AICP
The Transect
There is an emerging concept in urban design known as a “transect.” The concept essentially posits that there is a place for everything and everything has its place. Dennis McClendon states that it is “a way of classifying different kinds of neighborhoods along a continuum, from rural to suburban to city neighborhood to downtown; things that belong in once zone would be out of place in another.”
In the Smart Code introduction, version 6.5, Andres Duany says that “one of the key concepts of transect planning is the idea of creating what are called immersive environments. Successful immersive environments are based, in part, on the selection and arrangement of all the components that together comprise a particular type of environment. Each environment, or transect zone, is comprised of elements that keep it true to its locational character…planners are able to specify different urban intensities that look and feel appropriate to their locations…a farmhouse would not contribute to the immersive quality of an urban core, whereas a high-rise apartment building would. Wide streets and open swales find a place on the transect in more rural areas while narrow streets and curbs are appropriate for urban areas. Based on local vernacular traditions, most elements of the human habitat can be similarly appropriated in such a way that they contribute to, rather than detract from, the immersive character of a given environment.”
Applying the Transect to Bicycle Facility Planning
Appropriate bicycle travel routes vary based on their location in a community in the following generalized ways:
Walkable Urban Core
In this location, the pedestrian is the design imperative, which means that quality design emphasizes a low-speed street design. This means that there are generally no more than 2 travel lanes (and possibly a turn lane or pocket). Curb radii are modest, and combined with intersection and mid-block bulb-outs, minimize crossing distances for pedestrians.
Further enhancing the safety, comfort and convenience of the pedestrian is on-street motor vehicle parking, sidewalks, and buildings abutting the back of sidewalks.
There is a dense, connected grid of streets with short block lengths.
When designed properly, the modest motor vehicle speeds mean that most all bicyclists are able to safely and comfortably “share the lane” with motor vehicles (that is, ride within the motor vehicle travel lane). Those bicyclists who are not comfortable sharing the lane with vehicles are able to ride on nearby parallel streets.
In walkable urban locations, in-street bicycle lanes should generally be considered a “transect violation,” since their installation usually means that average motor vehicle speeds are increased (due to the perceived increase in street width for the motorist). Bicycle lanes also tend to increase the crossing distance for pedestrians, and are often incompatible with on-street parked cars unless an excessively wide bicycle lane is created.
Note that I do acknowledge that when a walkable, compact urban location contains major (arterial) streets that such streets generally require the installation of in-street bicycle lanes. However, when such major streets require bike lanes, it is a strong indication that the street itself is a transect violation. Ideally, such streets should be re-designed to be compatible (or “immersive”) in the walkable location through such techniques as removing travel lanes, adding on-street parking or other mechanisms that dramatically slow down motorists and obligate more attentiveness in their driving.
Also incompatible in this location are bicycle paths separate from the street. Such paths are not only unaffordable to install in this location, but significantly increase bicyclist danger.
Suburban
In this location, in-street bicycle lanes tend to be most appropriate on major (“arterial”) streets, due to the increased average car speeds. Bicycle lanes should be 4-5 feet wide.
On-street motor vehicle parking tends to be used somewhat less on suburban roads than on walkable urban streets. Building setbacks are larger, as are turning radii.
In general, bicycle lanes are not necessary on intermediate (“collector”) streets, due to low traffic volumes.
Like walkable urban locations, bicycle paths separate from the street are generally incompatible in this location. Such paths significantly increase bicyclist danger, largely due to the number of cross streets, the reduced visibility of the bicyclist, and the false sense of security created for the bicyclist.
Rural
In this location, bicycle paths separate from the road tend to be most appropriate, due to the relatively high speed of motor vehicles here, and the relative lack of crossing roads.
On-street motor vehicle parking tends to not be used on rural roads. Building setbacks are largest in this portion of the transect, as are turning radii.
In-street bicycle lanes are sometimes appropriate here, but are not as appropriate as in suburban locations.
Summary
In sum, bicycle travel routes are increasingly separated from motor vehicles as one moves along the transect from walkable urban to suburban to rural.
Walkable Streets 