Roadway Width for Bike Lanes
asked: What is the minimum road width that allows a bike
In other words is a 15 foot lane width or a 12 foot lane width enough to allow a 5 foot bike lane to be incorporated within it?
I’m afraid the answer is not as simple as the question implies and I cannot give a comprehensive answer. Roadway design is complex and dependent on numerous factors, including proximity to urban centers, travel volumes and whether the roadway is new construction or rehabilitation. The following is some information from the FDOT Plans Preparation Manual.
8.4.1 Bicycle Lanes
Where required by Table 8.1.1, provide a bicycle lane for each direction of travel on the roadway. The bicycle lane is defined as the area between the edge of travel lane and the edge of pavement. Bicycle lanes are to be marked in accordance with Design Standards, Index 17347 and the MUTCD. Shared use paths do not meet the requirement for bicycle lanes. For new construction or reconstruction projects, both curbed and flush shoulder roadways, the standard width of a buffered bicycle lane is 7 feet. For high-speed curbed arterials, the standard width of a buffered bicycle lane is 6.5 feet.
For RRR projects, the distribution of available roadway width may require a bicycle lane other than the standard buffered bicycle lane (refer to Section 18.104.22.168 of this Volume). When providing a bicycle lane on a RRR project, the options in the order of priority are:
1. 7-foot buffered bicycle lane
2. 6-foot buffered bicycle lane
3. 5-foot conventional bicycle lane
4. 4-foot conventional bicycle lane
Traffic Lanes are typically 10 to 12 feet wide depending on many factors. A 15-foot wide curb lane is normally shared by many types of vehicles.
27. Traffic Lane/Traveled Way: The designated widths of roadway pavement, exclusive of shoulders and bicycle lanes, marked to separate opposing traffic or vehicles traveling in the same direction. Traffic lanes include through travel lanes, auxiliary lanes, turn lanes, weaving, passing, and climbing lanes. They provide space for passenger cars, trucks, buses, recreational vehicles and, in some cases, bicycles.
You can find more information about bicycle facilities here. You may need to copy and paste into your browser:
The Plans Preparation Manual (PPM) has been superseded by the Florida Design Manual (FDM), but to the best of my recollection there have not been any significant improvements to the minimum standards for bicycle facilities. [1,2] Keep in mind that projects that are already in the pipeline will be governed by the PPM—only new projects need to meet the FDM’s minimum standards.
It should also be noted that the PPM and FDM only govern the design and construction of facilities on state highways—other jurisdictions such as counties and cities are only required to meet the minimum standards published in the Florida Greenbook.  And some jurisdictions also publish their own standards for pedestrian and bicycle facilities in private developments that are open to the public, although the ones I’ve reviewed typically required the owner to comply with the PPM/FDM.
I would be remiss if I did not mention that the federal government (FHWA) has (finally) admitted that standards like FDOT’s are a major reason why so many bicyclists are injured and killed in this country (and why so few people are even willing to consider the bicycle as a viable alternative to motorized vehicles), so it has begun to publish new guidelines. Its “Bicycle Network Planning & Facility Design Approaches in the Netherlands and the United States”  is an eye-opening document because it actually identifies the real culprit of the hazardous design of our nation’s bicycle facilities (pg 2).
FHWA’s “Bikeway Selection Guide”  is a major step in the right direction, although it has serious flaws which, I’m assuming, reflect the influence of those who continue to work behind the scenes to preserve our deadly existing standards. It will be interesting to see how long FDOT will be able to cling to its outdated standards because I know of no mechanism by which FHWA can force DOTs like FDOT to change their standards.
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The most critical element is not the width of the road, but rather the speed, and to a lesser degree the volume, of the vehicular traffic traveling upon it. Extensive research and experience (mostly in other countries) has shown that bicycles and motorized vehicles can share the same facility relatively safely if the speed of motorized traffic is limited to no more than 10 to 15 mph. At higher speeds it becomes critical that the two modes are separated.
A marked bike lane can often provide sufficient separation if motor vehicle speeds do not exceed 25 mph, but at higher speeds only physical separation, such as a barrier or an open space, ensures that bicyclists are adequately protected from life threatening collisions with motor vehicles.
There is nothing magical or mystical about these numbers because they are based on human nature and physics, neither of which are predicted to change any time soon. People will always make mistakes, whether they’re riding a bicycle or driving a motor vehicle, and when they come into conflict, physics dictates the consequences.
What I find shocking is that I have been unable to find a single study which supports the idea that bike lanes next to vehicular traffic traveling at speeds greater than 25 mph is ‘safe’, if ‘safe’ is defined as a high probability the bicyclist will not suffer severe or fatal injuries in a collision with a motor vehicle traveling at the design speed of the highway.
I ride a bike to an from work each and every day that I can given the weather and that my bike doesn’t break down. All the bike lanes that I have come across are only as wide as my bike… only two lousy feet wide!
I have no room to go anywhere if need be and I have people honk at me even though I am in the right. I also only have the option to go straight unless I cut off a car in the turn lane next to me because there isn’t even a diverging point to turn right because there is no shoulder, only a road gutter and sidewalk that I can’t jump the curb.
It is bad that the only safe place to bike is the wide shoulder on a major highway on the way to work and even some sections of that narrows to nothing. Oh, sidewalk use is really frowned upon in my area, so…