文档介绍：Pawlovich, Li, Carriquiry, and Welch 1
3rd Urban Street Symposium
June 24-27, 2007 Seattle, Washington
IOWA’S EXPERIENCE WITH 2-LANE TO 3-LANE CONVERSIONS
AUTHORS:
Michael D. Pawlovich, ., . Wen Li, .
Iowa Department of Transportation, Iowa State University,
Office of Traffic and Safety (TAS) Department of Statistics
800 Lincoln Way 102 Snedecor Hall
Ames, Iowa 50010 Ames, Iowa 50011
Michael.******@ ******@
Alicia Carriquiry, . Tom Welch, .
Iowa State University, Iowa Department of Transportation/TAS
Department of Statistics 800 Lincoln Way
102 Snedecor Hall Ames, Iowa 50010
Ames, Iowa 50011 Tom.******@
******@
ABSTRACT
Over the past couple decades, Iowa has converted several 2-lane urban roadways to 3-lane
sections. Most of these have been on low volume roads in munities. However, no
evaluation of the effectiveness of these conversions had been attempted. However, Iowa has
recently evaluated the safety impacts of these conversions using a Bayesian approach. Within
this paper, initial, tentative results of the analyses are explored, with emphases on the data,
results, and possible future applications of these conversions. Relative to total crash history,
results are mixed, with some sites indicating a reduction and others indicating an increase in both
crash frequency per mile and crash rate.
Pawlovich, Li, Carriquiry, and Welch 2
IOWA’S EXPERIENCE WITH 2-LANE TO 3-LANE CONVERSIONS
By Michael Pawlovich, Wen Li, Alicia Carriquiry, and Tom Welch
INTRODUCTION
A “road diet”, converting a roadway from two lanes to three lanes (one through lane in
each direction and a two-way, continuous left-turn lane), has been suggested as a solution to left-
turn related crashes on undivided two-lane roadways. Over the past couple decades, Iowa has
converted several 2-lane urban roadways to 3-lane sections. Most of the