When it comes to lane width, less is more.
This post explores a state highway section with 9 foot travel lanes, and will demonstrate that in spite of transportation agency misgivings about narrow lanes, Forest Hill Boulevard performs better on crash statistics than FDOT guidance for similar roadways, while offering advantages in the form of reduced construction costs, less negative impacts to adjacent properties, and decreased stormwater runoff, among other positive benefits.
Transportation agencies routinely make arguments against roadways such as Forest Hill Blvd. that are not based on studies or facts, but rather are based on conjecture of what might happen if narrower than standard lane widths were utilized. Since Forest Hill Boulevard is a real road in the real world it provides an opportunity to observe 9′ lanes in practice and not conjecture.
Livable streets advocates often recommend the use of 9′ to 10′ wide travel lanes instead of wider 11′ to 12′ lanes for several reasons, including:
- Lower construction costs
- Less right of way acquisition required
- Decreased stormwater runoff
- Lower maintenance costs
- Lower travel speeds and less injurious crashes
- Smaller footprint which can allow limited right of way to be reallocated to other uses such as on-street parking, bike lanes, or landscaping.
Even with all of the advantages of narrower travel lanes it is often impossible to have transportation agencies allow the implementation of narrower travel lanes. The FHWA summarizes the potential adverse impacts to safety and operations for a design exception for lane width as follows:
- Sideswipe (same direction) crashes
- Reduced free-flow speeds
- Large vehicles off-tracking into adjacent lane or shoulder
Jeff Speck’s article, “Why 12-Foot Traffic Lanes are Disastrous for Safety and Must Be Replaced Now“, provides a strong case for why reduced free-flow speeds are desirous and how narrower lanes help to achieve lower speeds and safer streets:
Forest Hill Boulevard Details
Our case study is the section of Forest Hill Boulevard (SR 882) in West Palm Beach between I-95 and S. Dixie Highway. This section of road has five lanes and is classified as an urban minor arterial with an AADT that varies from 28,000 at the western end near the I-95 interchange to 17,000 at the eastern end near S. Dixie Highway.
In spite of the 17,000 to 28,000 vehicles passing by each day on the road the walk on the sidewalk is relatively pleasant. The trees provide much-needed shade on hot Florida days and also a feeling of safety from errant vehicles.
The sidewalk and a wide tree-lined landscaped buffer frame 48′ of asphalt located between the curbs. As shown in the below section from FDOT, Forest Hill Blvd. was proposed to be resurfaced with 9′ wide lanes and a 9.5 wide center turn lane.
It seemed unbelievable that Forest Hill Blvd. had 9′ lanes so Walkable West Palm Beach field investigators measured the lane widths to verify.
Walkable WPB confirmed the 48′ curb to curb dimension, but, as shown in the below section, there were a few minor variations in the lane and shoulder widths compared to the FDOT drawing. Forest Hill Blvd. has 9′ wide inside travel lanes located between narrow, by highway standards, adjacent lanes.
How do roads such as Forest Hill Boulevard compare from a traffic flow and traffic safety standpoint to a similar 5 lane road with 11′ to 12′ lanes? There isn’t much information on the performance of 9′ lanes, but by reviewing the data on 10′ wide lanes we may be able to glean some insight. In Jeff Speck’s article he states that there are very few studies on the issue of 10′ wide lanes, but the few studies that do exist support the theory that 10′ lanes are as safe or safer than 12′ wide lanes and have the same vehicular capacity.
An analysis of crash data obtained by Walkable WPB from FDOT for Forest Hill Boulevard also supports the theory that narrow lanes are as safe as wider lanes. For the 0.787 mile portion of Forest Hill Boulevard just east of the I-95 interchange to S. Dixie Highway there were 60 crashes from January 1, 2011 to December 31, 2013. From this data a crash rate of 3.094 crashes per Million Vehicle Miles (MVM) is calculated by averaging the 17,000 and 28,000 AADT counts. 60/[(22,500 vehicles per day X 365 days a year X 3 years X 0.787 miles)/1,000,000]
This crash rate is less than the average crash rate provided by FDOT. FDOT provided the following information on average crash rates via email:
The average crash rate for 4-5 lane urban divided roadways with painted/paved median for the 2011-2013 period For FDOT Managing District number 4, which includes Palm Beach, Martin, Indian River, St Lucie and Broward Counties, is 3.719 crashes per MVM.
The FDOT crash data for Forest Hill Boulevard is available for download here.
Buses are cited as a reason to not utilize lanes narrower than 11′. Forest Hill Boulevard has bus service.
A few feet reduction in lane width can have a huge change in appearance of a road. Below is a photo of a five lane road in Palm Beach County that meets the standards.
…contrasted with our study section of Forest Hill Boulevard
The first photo of the standard five lane road provides a 3′ shoulder, 11′ lanes, and 12′ center turn lanes for a total of 62′ of asphalt. Note, the lack of trees because there isn’t room for them. Forest Hill Boulevard only requires 48′ of asphalt for the same five lanes of traffic. The difference between the two roads is dramatic.
On which of these would you rather take a walk or own a home?
The Forest Hill Boulevard section is more nuanced and contextually sensitive to the area where it is located. Designing a street section for an urban environment involves tradeoffs. We must avoid the tyranny of specialists who demand that we design roads to optimize only one outcome for one mode of transportation at the expense of other modes. The “standard” five lane road shown with 62′ of asphalt optimizes auto comfort at the expense of higher maintenance costs, greater stormwater runoff, less comfort for pedestrians, and lower property values. A question that engineers and the public should be asking is if the benefits that wider lanes provide for automobiles outweigh the costs. Does the design make sense for the context in which it is located?
Many of the improvements recommended in the Jeff Speck West Palm Beach Walkability study require that FDOT roads in West Palm Beach have their lanes reduced to a 10′ width. While FDOT has switched from 12′ to 11′ lanes in urban areas there is still significant resistance to adopting lanes narrower than 11′ in width. For those that are frustrated at the continued reluctance to utilize 10′ lanes a quote by the German philosopher, Arthur Schopenhauer, may provide some comfort:
All truth passes through three stages. First, it is ridiculed. Second, it is violently opposed. Third, it is accepted as being self-evident.
Given the Forest Hill precedent that 9′ lanes work in an urban environment then what logical argument is left to deny the use of 10′ lanes in low speed urban roads? Even the Federal Highway Administration is endorsing context sensitive design on streets designed for speeds less than 50 mph. From Streetsblog:
The one-size-fits-all approach to street design has been propagated, in part, by federal standards that apply to a surprisingly large number of urban streets. But not for much longer. In what appears to be a major breakthrough, yesterday the Federal Highway Administration proposed rule changes that will allow cities and towns to more easily design streets in a way that’s consistent with an urban setting.
Bill Schultheiss, an engineer with the Toole Design Group, said the changes are welcome news.
“We need to move away from cookie cutter, cut-and-paste designs and allow engineers to be the creative problem solvers that most of us naturally are,” he said. “This is a tremendous change of direction by FHWA that needs our support.”
It’s worth noting this is a relatively busy minor arterial, according to its FDOT classification. Of course, low volume neighborhood streets can be even skinnier still.
Big Asphalt and the Bigger Takeaway
The American transportation model operates under the belief that if some asphalt is good, more is even better. Wider roads drive positive economic indicators, so the theory goes: More asphalt = more growth, more jobs, more tax base.
Forest Hill Boulevard demonstrates there is a point of diminishing returns to this approach and at some point roadway expansions do not increase our prosperity, but rather decrease it (I highly recommend watching Urban3’s analysis of Palm Beach County property tax productivity for the evidence). Our national obsession with short term growth manifests itself in public malinvestment in highways; repeat this same scenario one million times over and you start to find some answers for why we’re having trouble paying for basic infrastructure maintenance despite decades of robust economic growth post WWII.
If you’re interested in changing things, Strong Towns is an organization working hard to get us back on a path of a fiscally sound development pattern and sustainable transportation funding. Here’s a great place to start the conversation.
Urban3 tax productivity analysis of Palm Beach County