Effect of flaggers and spotters in directing work zone traffic for Illinois expressways and freeways.
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Summary
This research project, conducted by the University of Illinois at Urbana-Champaign for the Illinois Department of Transportation (IDOT), assesses the effectiveness and safety risks of using flaggers and spotters in work zones on Illinois expressways and freeways with posted speed limits exceeding 40 mph. The study was motivated by the need to evaluate current practices, identify potential hazards to workers and motorists, and determine if alternative safety measures could supplement or replace traditional flagging operations to improve work zone safety and mobility. The methodology comprised eight primary tasks: a comprehensive literature review of standards and research; site visits and field studies to evaluate current flagger practices in Illinois; collection and fusion of work zone crash data from 1996 to 2009; analysis of crash frequency, severity, and contributing factors; investigation of alternative safety measures such as intrusion alarms, portable changeable message signs (PCMS), and portable speed monitoring displays (PSMD); and online surveys of resident engineers and construction personnel from IDOT and other state Departments of Transportation. The surveys gathered feedback on the essential roles, benefits, and risks associated with flaggers and spotters. The findings indicate that while flaggers are currently required in many scenarios, their use presents significant risks, including exposure to traffic hazards and the potential to cause rear-end crashes by excessively reducing traffic speed. The analysis of crash data and survey responses highlighted the limitations of flaggers in high-speed environments. The study found that spotters, defined as trained personnel who monitor traffic from safe locations and warn workers of errant drivers using devices like whistles or air horns, offer a viable alternative. Survey respondents indicated that spotters could effectively perform necessary monitoring functions with reduced risk to both workers and traffic flow, provided they are supplemented by additional temporary traffic control devices. Based on these findings, the report provides six key recommendations for IDOT to update its policies. First, it recommends replacing the mandatory requirement for flaggers in all restricted-lane scenarios with a requirement for flaggers or spotters only when intermittent or additional slowing of traffic is necessary. Second, it proposes allowing the use of spotters instead of flaggers, clearly defining their role to monitor traffic from safe locations. Third, it advises minimizing exposure by positioning flaggers and spotters away from traffic when not actively directing it and establishing predetermined escape routes. Fourth, it recommends supplementing spotters with devices such as police patrols, truck-mounted attenuators, PSMDs, and PCMS. Fifth, it calls for training personnel to avoid excessive traffic slowing that causes delays and rear-end crashes. Finally, it suggests implementing trial experiments to verify that these recommendations do not adversely affect safety and mobility before updating specifications.
Key finding
Flaggers and spotters should be used only when necessary for intermittent traffic slowing, and their use should be supplemented or replaced by spotters monitoring from safe locations along with devices like portable speed monitoring displays and truck-mounted attenuators.
Methodology
mixed_methods
Provenance
The full processing record for this entry. Every stage of this paper's journey through the pipeline is logged — what ran, with which tool and model, how many attempts it took, and when it last completed. Discovered via bulk_ingest_rosap on 2026-05-23 (6 acquisition events logged).
| Stage | Outcome | Tool | Model | Prompt | Attempts | Completed |
|---|---|---|---|---|---|---|
| discover | success | rosap | — | — | 2 | 2026-05-23 |
| archive | success | — | — | — | 1 | 2026-05-23 |
| extract | success | cached | — | — | 2 | 2026-06-10 |
| clean | success | — | — | — | 1 | 2026-06-01 |
| chunk | success | — | — | — | 1 | 2026-06-01 |
| embed | success | — | — | — | 1 | 2026-06-02 |
| enrich | success | — | — | — | 1 | 2026-05-23 |
| promote | success | — | — | — | 1 | 2026-05-23 |
| summarize | success | llm | qwen3.6-27b-prismaquant | summ-v5 | 3 | 2026-06-10 |
| tag | success | vector_similarity | — | — | 19 | 2026-06-11 |
| verify | success | — | — | — | 2 | 2026-06-10 |
Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.
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