A 2014 report from the Federal Highway Administration lays out some of the pros and cons of road diets:

Pros

• Improved safety for drivers by eliminating speed differentials between lanes traveling in the same direction and eliminating weaving between lanes.

• Increased mobility, safety and comfort levels for cyclists with the addition of bike lanes.

• Pedestrian crossings are easier and less complex with a reduction of travel lanes.

• Travel lanes often can be made wider.

• Two-way left-turn lanes make efficient use of limited roadway space and increase safety by eliminating the need for turning vehicles to stop in the left travel lane.

Cons

• Mail trucks and buses can block traffic when stopped.

• Road diets have the potential to reduce the capacity of roads.

• Two-way left-turn lanes could be difficult to access for drivers if demand for left turns is high.

Source: Federal Highway Administration (tinyurl.com/roaddietproscons)