Evaluation of arrow panel displays for temporary work zones : final report.

Griffith, Andrew S.; Lynde, McGregor · 2001 · ROSA P / Oregon. Dept. of Transportation. Research Section

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Summary

This study, conducted by the Oregon Department of Transportation (ODOT) and the Federal Highway Administration, evaluates the effectiveness of a “sequentially flashing diamond” arrow panel display as an advance warning device in temporary work zones. The research was motivated by the discontinuation of the diamond display by ODOT crews after it was omitted from the 2000 Manual on Uniform Traffic Control Devices (MUTCD), despite its prior reliable performance. The study aimed to compare the diamond display against two MUTCD-compliant caution modes: the “flashing line” and the “flashing four-corner.” The objective was to determine which display most effectively alerts motorists to shoulder work without inducing unnecessary lane changes, thereby enhancing safety for workers and drivers. The research methodology comprised three components: a literature review, a survey of 33 state Departments of Transportation, and field trials combined with a motorist survey. Field trials were conducted at two locations in Oregon: a multi-lane highway (OR Route 22) and a two-lane highway (OR Route 99W). At each site, temporary work zones were established on the shoulder, and each of the three display modes operated for one hour within three separate three-hour test periods (morning, afternoon, and night). Traffic data recorders measured hourly average speeds and 85th percentile speeds, which were compared against a 30-day baseline. Additionally, 274 motorists were surveyed at a highway rest area regarding their perceptions of the displays, which were shown in a parking lot setting. The findings indicate that all three display modes reduced vehicle speeds compared to baseline conditions. However, the diamond display consistently produced the greatest speed reductions from baseline across most test periods. Lane distribution data from the multi-lane site showed that vehicles shifted away from the shoulder lane during testing, with the most significant shifts occurring at night. In the motorist survey, over 70% of respondents identified the diamond display as the most effective at capturing their attention. Despite this preference, 61% of respondents found the displays confusing, particularly the line and four-corner modes, often misinterpreting them as instructions to change lanes. Nevertheless, 80% of respondents expressed a desire to see the diamond display used on Oregon highways. The state DOT survey revealed that while the line and four-corner displays were more widely used, the diamond display received the highest average effectiveness rating (3.50 out of 5) among the few states that rated it. The study concludes that the sequentially flashing diamond display holds considerable potential as an advance warning device for temporary work zones. It effectively reduces speeds and captures driver attention better than the standard line or four-corner displays. The authors recommend that the diamond display be considered for inclusion in future MUTCD guidelines or adopted by state agencies as a viable caution mode. The results suggest that while confusion exists regarding caution displays generally, the diamond pattern is preferred by motorists and performs well in reducing vehicle speeds, supporting its reinstatement for use in static and slow-moving work zone operations.

Key finding

The sequentially flashing diamond arrow panel display produced the greatest speed reductions from baseline compared to flashing line and flashing four-corner modes, and was selected as the most effective attention-getter by over 70% of surveyed motorists.

Methodology

mixed_methods

Sample size: 274

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

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• emergency work zone conspicuity
• work zones
• signage environment