Almost Bike Lanes

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.

Bike Lane

Bike Lane

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.


5 thoughts on “Almost Bike Lanes

  1. Janne

    What about compromising, and going for 11 foot traffic lanes and 5 foot shoulders/bike lanes? That makes the difference even smaller, and has plenty of (working) examples in Minneapolis.

  2. Froggie

    IIRC, 4ft is the minimum “standard” for a bike lane…5ft is desirable.

    But in an urban setting, especially with curb-and-gutter, Janne’s suggestion of 11ft travel lanes and 5ft bike lanes makes sense.

    It should also be noted that, while materials are cheap compared to labor, materials costs have jumped considerably in the last 10 years.

  3. Walker

    Great post. I really appreciate learning about things from a traffic engineers and official recommendations standpoint.

    My first thought though is skip the bike lane and construct a segregated bike path or MUP if ROW can be acquired, a cycletrack if not. 35 mph is still quite fast and reality, especially with 12′ lanes, is probably 40 – 45 mph. Most people who want to ride bikes would be nervous about such a bike lane so if we want to get more people riding, then we need segregated facilities.

    Also, if we want people to go 35 mph, I think we need 10.5′ lanes (10′ for 30, 11′ for 40, 11.5′ for 45). Realistically, IIRC, each 6″ reduction only reduces average speed by about 3 mph, but that helps and I don’t believe there is any evidence of increased crash risk. Is this feasible (politically (where it will decrease the revenue spigot) and engineering wise)?

  4. Faith

    Reuben, would you care to opine on why exactly the state aid standards would require a 4′ “curb reaction zone”? Is that consistent with or different from AASHTO or NACTO guidance?

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