Safety Evaluation of 2 Lane to 4 Lane Conversions

Granting Agency: Wisconsin Department of Transportation

Researchers: David Noyce (PI), Andrea Bill, Madhav Chitturi

Primary Project Objectives

This research focuses on how the conversion from a two- to four-lane roadway affects safety. Two highways in the Northeastern portion of Wisconsin were converted from two lanes to four lanes. One highway’s safety improved while the other’s safety was negatively affected. There are many factors that can affect road safety and by studying what caused this we can make improvements to increase safety.


The purpose of this research is to examine how the conversion from two- to four-lanes affects roadway safety. There are however, several other factors that affect road safety as well. These include speed, lane width, presence of shoulders or medians, width of shoulders or median, traffic volume, human factors, etc. By analyzing each road segment and determining what factors are present, or changing, we can have a better understanding of the crash frequency when converting a road from two lanes to four. Roadway inventory, traffic and crash data were integrated in a GIS framework for this research.

Highway lane conversion.