A road diet is a technique in transportation planning whereby a road is reduced in number of travel lanes and/or effective width in order to achieve systemic improvements.
One of the most common applications of a road diet is to improve safety in the context of two-way streets with 4-lane sections. In this case, two travel lanes in each direction are converted into a 3-lane section with one travel lane in each direction, and a two-way turn lane in the middle. Bike lanes in both directions can easily be installed in place of the removed travel lane.
Michigan has plenty of roads across the state that were simply built over capacity and without bicyclists in mind. Communities across Michigan, however, do appear to be embracing road diets. In fact, preliminary research indicates that Michigan could be leading the way in this department.
Road diets are excellent retrofit options for accommodating bicyclists. They are relatively inexpensive to do, but there are typically costs associated with grinding off current paint lines and repainting. Some roads may also have to have traffic and air quality studies done to determine if reducing travel lanes will create congestion or air pollution.
Information regarding standards for reducing traffic lane widths and adding bike lanes can be found in Lesson 15, Bicycle Lanes in the AASHTO's Guide for the Development of Bicycle Facilities.
Changes like curb extensions, neck-downs, and bike lanes are all traffic calmers that save lives by sending the signal for drivers to slow down. In this Streetfilm, some exemplary traffic calming projects from cities across the country are highlighted.
The Alliance for Biking and Walking also has an excellent resource section on Traffic Calming that includes a neighborhood traffic calming program guide, traffic calming brochures and maps, how-to manuals for traffic calming, and more.