Selective State DOT Lane Width Standards and Guidelines to Reduce Speeds and Improve Safety
Abstract
1. Introduction
2. Methods
2.1. Research Context
2.2. Interviews with State Department of Transportation
“According to the standards under what circumstances do you use narrow lanes? What is your default lane width for arterials, both urban and rural?”.
“When you reduce lanes, through reconstructing or resurfacing a road and narrow lanes by foot from 12 to 11. What do you typically do with that extra foot per lane?”.
“Have you done any studies to see how lane narrowing, and maybe the addition of sidewalk and/or a bike lane on each side has affected either speed, or safety, or capacity, or pedestrian traffic or traffic?”.
“Do you have a program for reducing lane width or do you have a practice of reducing lane width? And have you done before and after studies to see how the narrower lanes performed with respect to crash rates and in speeds 85th percentile speeds? Is that something that Florida has done once, twice? Maybe multiple times?”.
2.3. Document Reviews
3. Statewide Roadway Design Standards, Manuals, and Policies for Lane Widths
3.1. Florida Department of Transportation (FDOT)
“The use of narrow lanes (less than 12 feet) alone has a limited impact on operating speeds. However, this effect can be enhanced as traffic volumes increase. Visible lane narrowing can serve as a transitional device to signal a change in context. For example, narrowing two 12-foot lanes to 11-foot or 10-foot lanes by adjusting the lane lines and creating a hatch in the newly formed edge space has proven effective in alerting drivers to changing conditions. To maximize effectiveness, lane narrowing should be combined with other low-speed strategies, such as adding parking, creating medians, or introducing chicanes”.
- The optimal combination of shoulder and lane width to enhance safety.
- Advanced signage indicating changes in lane width.
- The use of sensory tools to delineate lanes.
- Designing safe shoulders and edges for vehicles that may leave the lane.
- Reducing crash severity through safe design on road shoulders.
“One of the things that we’ve recognized in our literature reviews and discussions is that simply changing or reducing the lane width solely, by itself, doesn’t have much effect. We’ve been doing some speed management, where we’ve introduced horizontal or vertical deflection we have more impact on speeds. Vertical deflection has become common as with raised crosswalks on the state highway system. We didn’t used to allow them. But horizontal deflection has been very effective. One of our worst corridors with the highest fatalities in the state, we kind of, if you will, put in every countermeasure. What we found is that doing lane narrowing alone, not coupled with other features, that give that sense of canopy or tightness with the trees doesn’t in itself have a huge effect”.
“What we found is that they (decision makers) embraced the context classifications because they love the idea of being able to do 10-foot lanes downtown somewhere, and where it was supposed to be low speed. And they (decision makers) love the idea that they could say yes to that project downtown but say no to this other 10-foot lane in an urban or rural setting, before they had no way to justify why they were saying yes to one and no to the other. And so, they said no to everything”.
3.2. Vermont Agency of Transportation (VTrans)
- Principal Arterials in Urban and Village Areas: Lane widths may range from 10 to 12 feet, with appropriate curb offsets.
- Highly Restricted Areas with Minimal Truck Traffic: 10-foot lane widths are suitable.
- Urban and Village Principal Arterials: 11-foot lanes are typically used for street designs.
- High-Speed, Free-Flowing Principal Arterials: 12-foot lane widths are recommended.
“Under interrupted-flow conditions at low speeds (up to 45 mph), narrower lane widths are generally adequate and offer certain advantages. Reduced lane widths enable more lanes within restricted right-of-ways and make pedestrian crossings easier due to the reduced crossing distance. They are also more economical to build. An 11-foot lane width is sufficient for through lanes, continuous two-way left-turn lanes, and lanes adjacent to a painted median. A 10-foot width is acceptable for left-turn or combination lanes for parking and traffic during peak hours”.
“9-foot lane widths are suitable for areas with severe space constraints and minimal truck traffic. Conversely, 11-foot lanes are typically applied to higher-speed, free-flowing Collectors”.
- 7 to 8 Feet: These widths are ideal for areas with severe space limitations and minimal vehicular activity.
- 9 to 11 Feet: These widths cater to areas requiring more flexibility and where higher speeds or increased vehicle flow are anticipated.
“So, while there were abilities to go down below 12 or 11 feet, again, that was really focused on speed and traffic volumes to make those types of decisions. One of the reasons our highway safety design engineering instruction was developed to formalize the ability to have more flexibility and ability to recognize the benefits of having more widths for different uses on our roadways”.
“The engineering instruction basically sets our lane width to 11 feet (instead of 12 feet) for the state system. The primary reason was more of a complete street bicyclist accommodation approach, and it was thought to be the flexibility that was allowed within our state standards and now within the Greenbook even more, however wasn’t necessarily being utilized in all cases. And there’s increased demand for the limited footprint that we have to make it accommodating for all users and especially on our rural roads, that was challenging. So, the engineering instruction was more of a systematic type of approach, where if we have a resurfacing job, more of that kind of three R’s (resurfacing, restoration, and rehabilitation) type approach. It allows us to better utilize the space to accommodate bicyclists and traffic without, the larger scale investment of widening”.
3.3. Oregon Department of Transportation (ODOT)
“We suggest flexible cross-sections rather than absolute numbers. While our preferred measurement is 11 feet, the BUD allows for a range of 11 to 12 feet due to discussions with our freight community. We initially excluded 10 feet from the range, although our chief engineer does not oppose it. It requires a design exception based on appropriateness and route needs”.
“The state’s highway design approach differs from local jurisdictions prioritizing their grid and specific needs. The state must consider long-term, extensive mobility. We cannot permit 9-foot road lanes where 25% of the traffic is trucks. Decisions are made based on appropriateness for the specific location, relying on flexibility in project-level decision-making processes”.
3.4. California Department of Transportation (Caltrans)
- Conventional State Highways: For highways with posted speeds of 40 miles per hour or less and average annual daily truck traffic (AADTT) below 250 per lane in urban areas, city or town centers, and rural main streets, the minimum lane width is reduced to 11 feet.
- Right-Turn Channelization: Section 405.3 of the HDM permits the reduction of right-turn lane width to 10 feet in urban, city, or town centers (and rural main streets) where posted speeds are below 40 miles per hour, space is severely constrained, and truck or bus volumes are low.
- Standard Lane Widths and Exceptions (Index 301.1):
- Conventional State Highways: For urban, city, or town centers and rural main streets with speeds ≤ 40 mph and AADTT < 250 per lane, the minimum lane width is 11 feet, while 12 feet is preferred.
- Interchanges: Where a two-lane conventional State highway connects to a freeway within an interchange, the lane width must be 12 feet. The outermost lane in each direction must also be 12 feet for multilane State highways connecting to freeways.
- Curve Radii: For highways, ramps, and roads with curve radii of 300 feet or less, additional width must be considered to accommodate vehicle off-tracking and minimize conflicts with bicycles.
“We created policies to provide additional design flexibility for the lowest speed, lower truck volume to allow the use of 11 feet in the urban and the Town Center. So, the 11 feet provide the flexibility for a bike lane or the other feature so they can have an additional room without widening the way to fit the other feature with the existing roadway; that’s the goal of that”.
“So, where we have slower speeds, even 40 miles per hour and lower, I have absolutely no problem going with 10-foot lanes. We don’t have a lot of 10-foot lanes right now, as I mentioned before, these are projects in the works. We had a conventional highway; it was by Highway 168 but by Fresno State. And there were some right-of-way concerns. And to get bus bays, and dual left turn lanes, we went down from 12-foot lanes down to 10-foot lanes. And this was a conventional highway that had a 40 mile per hour speed limit. So, wherever we had these very long left turn pockets, which were 400 feet long. And this is a very busy roadway 50,000 ADT, but we went down to 10-foot lanes with no issues. I mean, no collision history related to the lanes in this new urban environment; you’re always kind of getting to get the congestion-related crashes, the rear ends. But as far as the Sideswipe experience, None. But we relinquished that facility, gosh, close to 20 years ago”.
3.5. Delaware Department of Transportation (DelDOT)
- 12-Foot Lanes: These are recommended for new construction and reconstruction projects on roadways with 55 mph or higher design speeds.
- 11-Foot Lanes: These are advised for roadways with design speeds ranging from 35 to 50 mph, particularly when adjacent to bike lanes.
- 10-Foot Lanes: These should be used for roadways with design speeds below 35 mph but should be avoided on transit routes and roads with heavy truck traffic.
- Pavement Rehabilitation Projects: Extra space gained from lane width reduction is often allocated to broader shoulders or bike lanes.
- Urban Road Diets: In urban areas, the additional space might be utilized for parking or other purposes.
- Intersection Improvements: Reducing lane widths can help create additional turn lanes, enhancing roadway capacity.
“We’ve had a lot of projects where we’ve gone from 12-foot lanes down to 11-foot lanes just to squeeze it in, and I’ve never heard one person say these lanes are too narrow. I’ve never seen like we were having negative effects from an operational or safety perspective”.
“I think it depends on the context of the project. In a pavement rehab type of environment, it’s either just going to a wider shoulder or a bike lane…. sometimes we’ll even do the road diets where we can reduce the number of travel lanes, and we have to figure out what to do with that excess space. There are some urban areas where it would go to maybe parking but often, it’s going to shoulder or bike lane”.
3.6. Summary
4. Before and after Studies
4.1. Powerline Road Project (Fort Lauderdale, Florida)
4.2. State Route 63 Redesign (Mooney Blvd, California)
5. Discussion and Conclusions
Author Contributions
Funding
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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State DOT | Design Manual | Suggested Lane Width | Context | Conditional Factors |
---|---|---|---|---|
FDOT | Florida Design Manual | 10–12 feet | Urban/suburban |
|
11–12 feet | Rural | |||
VTrans | Vermont State Design Standards | 10–12 feet | Urban/Rural Principal Arterials |
|
11 feet | Urban/Rural Principal Streets | |||
12 feet | High-speed, free-flowing Principal Arterials | |||
11–12 feet | Rural Principal Arterials, Rural Minor Arterials | |||
9–11 feet | Urban/Rural Collectors | |||
9–11 feet | Rural Collectors | |||
7–11 feet | Rural Local Streets | |||
ODOT | Blueprint for Urban Design (BUD) | 11 feet | Urban Traditional downtown/CBD |
|
11–12 feet | Urban Mix, Commercial corridor, Residential corridor | |||
11–12 feet | Rural community, suburban fringe | |||
Caltrans | Highway Design Manual | 11–12 feet | Urban, city, or town centers |
|
11 feet | Rural main streets | |||
10 feet | Urban, city, or town centers, rural main streets |
| ||
DelDOT | Delaware Road Design Manual | 12 feet | Design speeds ≥ 55 mph |
|
11 feet | Design speeds 35–50 mph | |||
10 feet | Design speeds < 35 mph | |||
11 feet | Adjacent to bike lanes |
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Share and Cite
Ewing, R.; Yang, W.; Promy, N.S.; Kaniewska, J.; Tabassum, N. Selective State DOT Lane Width Standards and Guidelines to Reduce Speeds and Improve Safety. Infrastructures 2024, 9, 141. https://doi.org/10.3390/infrastructures9090141
Ewing R, Yang W, Promy NS, Kaniewska J, Tabassum N. Selective State DOT Lane Width Standards and Guidelines to Reduce Speeds and Improve Safety. Infrastructures. 2024; 9(9):141. https://doi.org/10.3390/infrastructures9090141
Chicago/Turabian StyleEwing, Reid, Wookjae Yang, Noshin Siara Promy, Justyna Kaniewska, and Nawshin Tabassum. 2024. "Selective State DOT Lane Width Standards and Guidelines to Reduce Speeds and Improve Safety" Infrastructures 9, no. 9: 141. https://doi.org/10.3390/infrastructures9090141
APA StyleEwing, R., Yang, W., Promy, N. S., Kaniewska, J., & Tabassum, N. (2024). Selective State DOT Lane Width Standards and Guidelines to Reduce Speeds and Improve Safety. Infrastructures, 9(9), 141. https://doi.org/10.3390/infrastructures9090141