Effectiveness of Experimental Left-Turn Sign Usage in Terms of Crashes and Analyzing Severity of Left Turn Crashes in Alaska

Abaza, Osama A.; Chowdhury, Tanay Datta · 2018 · Crossref

DOI: 10.2174/1874447801812010021

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Summary

This study evaluates the effectiveness of experimental Dual Left-Turn Lane (DLTL) signs and standard left-turn signs in reducing crash frequency and analyzing crash severity at six signalized intersections in Anchorage, Alaska. The research was motivated by the high prevalence of left-turn crashes, which account for approximately 27% of intersection crashes in the U.S. and 33% of crashes in Alaska. In cold regions like Alaska, pavement markings are often obscured by snow and ice, rendering them ineffective for guiding drivers. Consequently, the Alaska Department of Transportation and Public Facilities experimented with specific signage to improve safety and driver compliance. The methodology involved a before-and-after analysis comparing crash data from 1994–1998 (before sign installation) and 2005–2012 (after installation). Crash frequency was normalized by Annual Average Daily Traffic (AADT) to calculate crashes per 1,000 entering vehicles. Driver compliance was assessed through video analysis using pole-mounted cameras over a one-month period, observing vehicles entering left-turn lanes. Additionally, Binary Logistic Regression (BLR) was employed to analyze factors contributing to Property Damage Only (PDO) crashes, which constituted the majority of incidents. The model considered variables such as time of day, road surface conditions, lighting, and causes of accidents, with multicollinearity and goodness-of-fit tests performed to validate the statistical model. Results indicated that left-turn crashes decreased at four of the six studied intersections when measured per 1,000 entering vehicles. Annual crash data showed a significant decline in left-turn crashes at five intersections after 2009, suggesting an adaptation period for drivers following sign installation. Compliance rates ranged from 89.5% to 100%, with the highest compliance observed at intersections with freshly painted pavement markings. The study found a strong correlation between high compliance rates and low crash rates. The logistic regression analysis identified improper turn and lane usage, careless driving, and angle-type collisions as the most significant factors contributing to PDO crashes. Dry pavement conditions and times other than the evening peak or off-peak periods also significantly influenced PDO crash likelihood. The study concludes that left-turn signs are effective in reducing crashes, particularly when combined with visible pavement markings. The findings highlight the critical role of maintaining road markings in cold climates to ensure signage effectiveness. Furthermore, addressing driver behaviors such as improper lane usage and careless driving is essential for further improving safety. The research supports the use of experimental DLTL signs as a viable countermeasure for intersections with multiple left-turn lanes, provided that complementary infrastructure maintenance and driver awareness campaigns are implemented.

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Topics

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• signage environment
• signaling behavior

Information type

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• Empirical Findings: crash risk outcomes