Sponsor: City of Scottsdale
PI: Dr. Brendan Russo
Dates: 01/01/2021-11/30/2021
Project Report:
https://www.scottsdaleaz.gov/Assets/ScottsdaleAZ/Transportation/Analysis+Left+In+Left+Out+-+2021.pdf
Over the past few decades the City of Scottsdale, Arizona has installed left-in/left-out (LILO) median opening treatments at approximately sixty intersections/driveways; typically at three-leg intersections or driveways on arterials with medians where the minor leg is stop-controlled. The treatment is relatively unique and consists of a channelizing island with an acceleration length provided for vehicles turning left out of the minor road (these left-turning vehicles then merge with major road traffic). Although anecdotal evidence suggests the treatment has performed well, a data-driven safety evaluation had not been conducted. As such, this study presents the first comprehensive safety evaluation of the LILO median opening treatment, including development of crash modification factors (CMFs). Crash, traffic, and roadway data from 25 LILO treatment sites and 25 control sites were utilized to assess the overall safety impacts of the LILO treatment using a cross-sectional study design, and an Empirical-Bayes before-after analysis was conducted on a subset of treatment sites based on year of installation. Overall, the LILO median opening treatment was shown to be effective in reducing the frequency of angle and left-turn crash types, as well as the frequency of injury crashes. Additionally, the potential safety impacts of LILO-specific design features (e.g. signage, acceleration length, etc.) were explored.