Study Details

Study Title: Analysis of the Safety Impacts of the Left-In Left-Out Median Opening Treatment at Intersections/Driveways

Authors: Russo et al.

Publication Date:OCT, 2021

Abstract: 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.

Study Citation: Russo, B., D. Smith, S. Taylor, and M. Kayser. "Analysis of the Safety Impacts of the Left-In Left-Out Median Opening Treatment at Intersections/Driveways." City of Scottsdale, Arizona. Scottsdale, AZ. (Oct 2021).

Related Citations: Russo, B., D. Smith, S. Taylor, and M. Kayser. "Analysis of the Safety Impacts of the Left-In Left-Out Median Opening Treatment at Intersections/Driveways.". Presented at the 102nd Annual Meeting of the Transportation Research Board, Paper No. 23-00224, Washington, D.C., (2023).


CMFs Associated With This Study

Category: Access management

Countermeasure: Install left-in left-out (LILO) treatment

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.89910.13 StarsAllAllNot specifiedUrban and suburban
0.66833.23 StarsAngle,Left turnAllNot specifiedUrban and suburban
1.49-493 StarsSideswipeAllNot specifiedUrban and suburban
0.85214.83 StarsAllK,A,B,CNot specifiedUrban and suburban
0.84615.43 StarsAllK,A,BNot specifiedUrban and suburban
0.75253 StarsAllK,ANot specifiedUrban and suburban
0.9352 StarsAllAllNot specifiedUrban and suburban
1.158-15.82 StarsAngle,Left turnAllNot specifiedUrban and suburban
1.427-42.72 StarsSideswipeAllNot specifiedUrban and suburban
0.73526.52 StarsAllK,A,B,CNot specifiedUrban and suburban
0.58641.42 StarsAllK,A,BNot specifiedUrban and suburban
0.59940.12 StarsAllK,ANot specifiedUrban and suburban