Safety Effects of Using Narrow Lanes and Shoulder-Use Lanes to Increase the Capacity of Urban Freeways

Source: Federal Highway Administration

"The goal of the study was to examine the effects of the [lane narrowing] treatment on three measures of effectiveness:

  • Total accidents (fatal, injury, and property-damage-only (PDO) accidents, including both towaway and non-towaway accidents).
  • Fatal, injury, and PDO towaway accidents (excluding PDO non-towaway accidents).
  • Fatal and injury accidents (excluding all PDO accidents).

"In addition to examining changes in these three measures for all four- to five-lane conversions combined and all five- to six-lane conversions combined, the authors also attempted to examine the effects of different "bundle" types, different crash types (e.g., sideswipe crashes), and the number of interchange ramps in a section. They also studied possible upstream effects of changes in flow and downstream effects of "accident migration" when the new lane was dropped."

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