Walkable West Palm Beach

Who knew? – FDOT design manual already encourages narrowing lanes to 10′ to add bike lanes



In FDOT’s latest response to our design suggestion they stated that one of the reasons for the proposed 11′ wide lanes is to accommodate Palm Tran buses. Although there are streets where buses successfully operate with 10′ lanes, it is appreciated that FDOT has provided a rational reason for the 11′ wide lanes versus the previous response that 11′ wide lanes are the minimum allowed on state highways.

Here is the original article:

As you may be aware, FDOT has plans to resurface Quadrille Boulevard. At the public open house, several citizens requested that FDOT right size the lanes on Quadrille Boulevard. FDOT subsequently responded that “The Florida Department of Transportation does not allow for travel lanes less than 11’ wide.”  The response letter is shown here:

FDOT response roskowski quadrille blvd 2

FDOT response to citizen requests

This response by FDOT forced the Baron to take on the redesign of Quadrille Boulevard. Well, in the further quest to turn Quadrille Boulevard into Rue de Quadrille the Baron has found even more proof in FDOT’s very own design manuals that 10′ lanes and 9′ left turn lanes are allowed on roads with the urban context of Quadrille. Some of our new readers may be thinking… why would anyone spend their free time reading FDOT design manuals? The reason why is that a decision to require an 11′ lane has real world consequences that lead to perpetuating bad design. Below is the existing (FDOT) and a right sized five lane section for Quadrille from 3rd to Dixie. You can clearly see that a combination of 10.5′ and 10’ wide travel lanes will allow the addition of bike lanes in the five lane section.



Quick note – the bike lanes are actually 5.5 feet wide, The bike lane is a combination of 4′ of  asphalt (shown) plus an additional 1.5′ wide concrete gutter – (not shown).

With 11’ lanes there is no room for the bike lanes. We can opine on the merits of 10′ lanes, as Jeff Speck does so eloquently such as slower speeds, lower crash rates, lower maintenance costs, and less strormwater runoff, but in the case of Quadrille you can’t argue with a tape measure. You want bike lanes for Quadrille, you need to go narrower than 11′ lanes.

Even more amazing is what happens when you utilize 10′ travel lanes and a 9′ left turn lane for the existing three lane section with parallel parking. There is now room for a one-way protected cycle track with a buffer against the door zone.  The one way protected cycle track, with 9′ left turn lane, shown below meets the NATCO minimums and is far superior to the door zone bike lanes. This is a great design in that parallel parked cars protect the cyclists rather than the traditional bike lane design where cyclists protect the parked cars from thru traffic. Again, the tape measure doesn’t lie. Without the 9′ left turn lane the buffer on each side of the road is six inches shorter than the NACTO minimums. The question is simple – who should have the buffer? Wider lanes that protect a car to car collision or a buffer between a car door and a cyclist?


(Note: For this section the 1.5′ gutter pan is included in the 5.5′ bike lane dimension. NACTO minimum dimension for the combined parallel parking with buffer is 11′. Where there is a pavement joint in the bike lane, NACTO only gives credit for one foot of the concrete gutter. Therefore, the effective bike lane is 5′ not the 5.5′ shown, 5′ is the  NACTO minimum.)

Now that we understand what is possible with right sizing lanes, you will see the proof that they are allowed for Quadrille. If you have been around engineers then you know that they love their acronyms. You will often hear highway engineers use the term – “Triple R”. Triple R (RRR) refers to a project whose scope is to Resurface, Restore, and Rehabilitate an existing street or highway. The FDOT Plans Preparation Manual (PPM) has an entire chapter (25) devoted to what should be reviewed with a RRR project and what deficiencies should be corrected or left in place.


Chapter 25 of the FDOT manual states that for every RRR project, FDOT needs to investigate if bike lanes can be added. According to the manual if the road has a design speed of 35 MPH or less and less than 7% trucks and the lanes are being right sized to add bike lanes, then the lanes  may be reduced to 10′ travel lanes and 9′ left turn lanes. I have placed quotes from the manual at the end of the post for those, myself included, who enjoy reading design manuals in their free time. This policy will finally allow us to grab some of the low lying fruit. One major flaw with the FDOT policy is that it only applies to RRR projects. Resurfacing only projects are exempt. In my opinion every resurfacing project needs to be reviewed for right sizing.

As promised here is the proof that you have been waiting for. All the text and tables were copied from the January 1, 2014 edition of the manual. Important parts are in red font and I have added my own editorial commentary in parentheses.

25.4.5 Lane and Shoulder Widths

The minimum widths shown in these tables are to allow existing lanes and shoulders to remain, not to be reduced to these widths unless the purpose is to provide a bicycle lane or increase the width of the outside lane for cyclists. See Section 25.4.19 for further information.

(Therefore, you are allowed to reduce lane width for bike lanes.)


(This means that 10’ lanes are allowed for roads such as Quadrille which has a 30 MPH design speed and per FDOT’s traffic data has a 3% truck factor. Even more interesting is that you can have a 9’ wide left turn lane.)

25.4.19 Pedestrian, Bicyclist and Transit Needs

Whenever a RRR project is undertaken, pedestrian and bicyclist needs must be addressed, and transit needs should be considered. Recommendations by the District Pedestrian/Bicycle Coordinator and the District Modal Development Office shall be obtained; local government and transit agency contact in developing these recommendations is essential. This should be part of the project scoping and programming effort. Bicyclist Needs

  1. Bicycle Lanes, Paved Shoulders, Wide Outside Lanes

For existing sections without bicycle facilities where no widening is planned, consideration shall be given to reducing lane widths to provide bicycle lanes,wide outside lanes or paved shoulders. These facilities shall meet the criteria provided in Chapter 8. Existing thru lane widths on urban multilane roadways and two-lane curb and gutter roadways shall not be reduced to less than 11 feet for design speeds ≥ 40 mph, and to no less than 10 feet for design speeds ≤ 35 mph. See Section 25.4.5 for additional information on lane widths. Coordinate with the District Public Transportation (Modal Development) Office and local transit agency when considering the reduction of lane widths on roadways where public transit routes are present. When bicycle facilities are not provided in accordance with Section 8.1, a Design Variation is required.

(A design variance is a process where FDOT has to justify why they can’t do it.)

2 thoughts on “Who knew? – FDOT design manual already encourages narrowing lanes to 10′ to add bike lanes

  1. this is great work and research, Jesse. I tried unsuccessfully to cut and paste it onto the WPBDNA’s page.


    Liked by 1 person

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