When 3-lane streets are narrowed to 2-lane streets, street width is recovered for other uses. Traffic lanes are commonly 12 feet wide, though they can be as narrow as 9 feet and as wide as 14 feet or more. Most streets in the downtown/midtown area that I’ve recommended for narrowing are really five lanes wide, three traffic lanes plus two parking lanes. Eight ways in which this recovered right-of-way width can be used:

1. Widen sidewalks: In some areas, sidewalks are too narrow to carry the number of walkers using them. For example, on 16th Street between P Street and O Street, the sidewalk is much too narrow to handle the foot traffic. There are six businesses on the east side of the street: Pronto by Paesano’s and the associated Uncle Vito’s Pizza, Super Cuts, Nishki Sushi, and Starbucks, plus a storefront that is being refurbished to be Thai Canteen. These generate a lot of customers on foot and on bike, and the narrow sidewalk is frequently crowded.
2. Add sidewalk buffers: In cases where the sidewalk is immediately adjacent to the street, or a there is a buffer but it is too narrow, width can be devoted to these buffers. Sidewalks with buffers are called detached sidewalks. These may not appropriate in commercial areas because the isolated high-turnover parking from the sidewalk, but are completely appropriate in residential areas and may be in mixed areas.
3. Add bicycle lanes: Bicycle lanes take up five feet of width if adjacent to the curb, and six feet if adjacent to parking. (AASHTO standards are a minimum of four and five, but these widths are unsafe.) Normally a street will have bike lanes on both side, so two bike lanes will take about the same space as one traffic lane. If we were to otherwise leave the street system as it is, with high speed one-way streets, the protection of bike lanes is critical to making downtown/midtown more bikeable. However, if the recommendations I have made were implemented, streets would move more slowly with lower volumes of traffic, and bike lanes would be less necessary.
4. Add protected bike lanes: A protected bike lane (cycle track) is a protected bike way, with some sort of physical protection from motor vehicle traffic. The protection can be a painted no-vehicle area, hit posts, curbs, parked cars, or a surface raised to a level between the roadway and the sidewalk. Because the protection takes up space, in many situations only a single protected bike lane can be gained from the removal on one traffic lane.
5. Add dedicated transit lanes: Bus routes on streets with heavy traffic are often slowed by congestion and by turning vehicles. Both bus and light rail can be sped up by removing some of the conflict with dedicated transit lanes. Long distance dedicated lanes can be used to create bus rapid transit routes, but short segments of lanes can be useful for solving spot congestion problems. If light rail and buses run more freely, transit times are reduced and people will be more likely to choose transit over privately owned vehicles. It is not clear to me at the moment whether any of the 3-lane streets are logical locations for dedicated transit lanes, but I will look at this in the future.
6. Create wide medians: Medians can be created along the middle of the street, separating the two travel directions. These medians can have plantings, artwork, rainwater basins, sitting areas, and a number of other amenities that may be absent along the street. These parkways or boulevards are probably not appropriate in commercial areas, but would be in residential or mixed areas.
7. Convert from parallel to diagonal parking: Conversion from parallel parking to diagonal parking (60 degree reverse angled parking) uses up about 8 feet of street width, and roughly doubles the amount of parking. Because parking takes more of the street width, it is even more important to consider curb extensions (bulbouts) to increase pedestrian – driver visibility at intersections and mid-block crossings.
8. Create center turn lanes: If the street is also being converted from one-way to two-way, the center lane can become a turn lane. I think that this is the least useful of the solutions because it serves a single and not very common need, left turns, with an entire dedicated lane. If the traffic on a street is so heavy that it is difficult to make left turns, a left turn pocket or a block-long center turn lane can be provided every four to eight blocks, but having a continuous lane is just a waste of precious right-of-way.

Certainly not every solution is right for every situation, and each roadway segment should be analyzed to determine the best overall use of the width recovered from 3-lane to 2-lane conversion.