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Case Study: Safety Evaluation of Stop-Sign Mounted Beacons

Technical Review:


This study examines the safety implications of stop-sign mounted beacons compared to overhead flashing beacons in Iowa. While overhead flashing beacons have demonstrated effectiveness, concerns over driver confusion prompted the state's Department of Transportation to advocate for stop-sign mounted beacons. A cross-sectional analysis, due to limited installation dates, assessed 40 rural intersections with stop-sign mounted beacons. The study reveals a 5% - 54% reduction in nighttime crashes, particularly a 54% decrease in injury-related nighttime crashes.


1. Introduction:

Rural intersections, constituting 16% of rural fatalities, often involve failure to yield right of way (FTYROW). Various studies link failure to yield to speeding, sight distance issues, and driver inattention. Beacon systems, including overhead flashing and stop-sign mounted beacons, aim to mitigate risks by drawing attention to intersections.


1.1 Studies on Effectiveness of Overhead Flashing Beacons:

Previous studies on overhead flashing beacons reveal mixed results. Srinivasan et al. reported an 11.9% reduction in angle crashes, while Murphy and Hummer found a 12% decrease in total crashes. Concerns about driver confusion exist, especially with multiface flashing beacons.


1.2 Studies on Standard Stop-Sign Beacons:

Stop-sign mounted beacons, evaluated by Srinivasan et al., showed a 58.2% reduction in angle crashes. Brewer and Fitzpatrick found a 43% crash rate reduction with flashing beacons on "STOP AHEAD" signs. These studies indicate the potential of stop-sign mounted beacons.


1.3 Problem Statement:

Iowa's DOT, preferring stop-sign mounted beacons, raised concerns about overhead flashing beacons causing driver confusion and requiring overhead structures. With limited information available, a cross-sectional analysis compared 40 intersections with stop-sign mounted beacons against controls, selecting treatment and control sites based on various characteristics.


2. Data:

Data collection involved identifying intersections with stop-sign mounted beacons, confirming their presence, and selecting control locations based on matching criteria. Propensity scores were used for matching, with 40 control locations selected. Crash data for 2012-2014 were collected within 250 feet of each intersection.


3. Methodology and Results:

A cross-sectional analysis, considering daytime and nighttime crashes, was conducted due to the absence of beacon installation dates. Elasticities for continuous variables and percentages for indicator variables were calculated. Results indicate an increase in daytime crashes at treated sites (3% - 46%) but a substantial reduction in nighttime crashes (5% - 54%), with a notable 54% decrease in injury-related nighttime crashes.


4. Conclusions and Discussions:

Stop-sign mounted beacons show potential for reducing severe crashes, with a 54% reduction in injury nighttime crashes. Results suggest their effectiveness compared to overhead flashing beacons, and the cost-effectiveness of stop-sign mounted beacons is highlighted. The study supports Iowa DOT's transition and expansion of stop-sign mounted beacons, emphasizing their utility in reducing nighttime crashes at rural intersections.



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