Bike lanes, generally, are a minimum of 5 feet wide. But a lot of roadways have shoulders that are less than five feet in width, which can be problematic for cyclists when this space is mistaken for bike lanes. Shoulders in the range of 2′ or less are narrow enough that it is pretty clear that they aren’t bike lanes. Shoulders in the 3′-4′ range, however, can be a bit problematic. These shoulders are generally not marked or signed as bike lanes, but they can look a bit like bike lanes, which can lead to confusion and unsafe situations as motorists and bicyclists interact. Not all shoulders 3′-4′ in width are unsafe places to ride a bicycle – there are a number of other factors to consider as well, but it is generally a less than desirable situation.
Minnesota State-Aid design standards require a “curb reaction distance” (a.k.a shoulders) on all new construction roadways. Often, there is minimal difference between what is required by state-aid standards for a roadway without bike lanes and what is required for a roadway with bike lanes.
For example, consider a new construction two-lane undivided Collector roadway without parking with projected ADT of 11,000 and design speed of 35 mph. Let’s presume the agency prefers 12 foot lane widths. State-aid design standards would require 4 foot shoulders whether the agency is constructing bike lanes or not. State-aid bikeway standards would require a 5-6 foot bike lane (the 2007 MnDOT Bikeway Facility Design Manual would recommend 6 feet…). In this hypothetical situation, the agency could choose between the following two construction scenarios:
- construct a 32′ wide roadway (curb face to curb face), which will result in “almost bike lanes”
- construct a 34′-36′ wide roadway (curb face to curb face), which will result in bike lanes consistent with design standards
In a new construction scenario, the difference in cost between a 32′ and 36′ roadway is not negligible, but it is also not substantial. Materials are cheap, labor is expensive – 4′ additional width requires additional materials, but little or no additional labor.
The decision seems pretty clear to me (not surprising given my obvious bias in favor of constructing bike facilities). In new construction scenarios, this is not a hard decision. In reconstruction scenarios there will often be things like trees in the way that make the decision much more difficult, and agencies still need to ask questions about how this hypothetical road fits into the overall transportation network. But I hope agencies are aware that in many cases, they are nearly building bike lanes whether they intend to or not – and that shoulder space is likely to get used by bicyclists wither it meets design standards or not. The additional cost for the 4′ difference in width is worth it – if nothing else for the ability to sign and mark the space as bike lanes that meet design standards (as this is how it is likely to be perceived by roadway users anyway), rather than being stuck with an “almost bike lane” scenario for perpetuity.