three lane conversions

Urban planners and transportation engineers throughout North America have begun to advocate for the conversion of existing four lane roads to three lanes to create more inviting pedestrian environments, calm traffic, and increase safety.

Three lane roads require less roadway, making more space available for sidewalks and for related pedestrian uses. Their capacity in congested urban settings is not much different from four lane roads, which tend to function as three lanes (because of turning movements) under these circumstances.

They work by separating turning movements from the main flow of traffic into a continuous left turn lane. By doing so, they discourage lane switching and passing, and calm traffic, make traffic speed more consistent, and improve pedestrian safety.

Current practice is now to convert roads carrying up to 30,000 vehicles per day to three lanes. PPS, in their analysis of the Lake Street Reconstruction Project, cite the example of Edgewater Drive, in Florida, with ADT (average daily traffic) counts between 18,681 to 27,684 through its length.

After conversion to three lanes, it was found that the crash rate for the road decreased 34% while the injury rate decreased 68%. Part of this is the result of lower, more uniform speeds made possible by the new road configuration: the percentage of vehicles traveling at speeds greater than 36 mph was reduced from 15.7% to 7.5%. Traffic volumes decreased 9%, while traffic volumes through neighborhood roads also decreased. The big surprise in this case is that pedestrian and bicycle use increased more than 20% each (23% for pedestrians, 30% for bikes). The total increase in travel time for those in cars was 50 seconds.

Although resistance to conversion remains strong at some state and local levels, there is a growing body of evidence attesting to the many benefits three lane roads can bring to urban areas. You can find background information and case studies below:

Four to Three Lane Conversions (253 Kb) - prepared by members of Powderhorn Park Neighborhood Association's Housing and Land Use Committee, this document summarizes the main issues related to conversion of Lake Street to three lanes, including advantages, disadvantages, and the specific conditions on Lake Street that make this a reasonable design option. Also includes a short discussion of traffic forecasting and reviews the performance of prior traffic projections.

The Conversion of Four-Lane Undivided Urban Roadways to Three-Lane Facilities (1.6 Mb) - a summary of issues related to the conversion of urban four lane roadways like Lake Street to three lanes. From a paper presented to AASHTO's Transportation Research Board. AASHTO (the American Association of State and Highway Transportation Officials) sets national engineering and design standards related to highway transportation. Includes an example from the conversion of Rice Street (in St. Paul) from four lanes to three.

Road Diets - Fixing the Big Roads (750 Kb) - presents a summary of experiences in improving roadway efficiency while reducing the number of lanes roads carry. Includes examples from the US and Canada.

The Chicago Bikelane Design Guide (1.2 Mb) - how the city of Chicago manages to fit cars, permanent on-street parking, and bikelanes on 55 ft wide streets (Lake Street is 60 ft wide).