Compendium of student papers : 2009 undergraduate transportation engineering fellows program.

Senesi, Christopher; Everett, Stephanie; Easterling, Jordan; Bogonko, George · 2009 · ROSA P / Texas Transportation Institute

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Summary

This report compiles research papers from the 2009 Undergraduate Transportation Scholars Program, a ten-week summer initiative at the Texas Transportation Institute designed to provide undergraduate civil engineering students with hands-on experience in sponsored transportation research. The document presents findings from four distinct studies conducted by students Christopher Senesi, Stephanie Everett, Jordan Easterling, and George Bogonko, each mentored by faculty or researchers. The primary focus of the provided text is Senesi’s study on updating left-turn lane warrants for unsignalized intersections. Senesi’s research addresses the validity of current left-turn lane design guidelines, which rely on M.D. Harmelink’s 1967 assumptions regarding time-to-clear values and critical gaps. The study aimed to determine if these decades-old assumptions remain applicable to modern traffic conditions. Data were collected at 18 unsignalized intersections in Texas and Arizona, selected for varied geometric characteristics such as lane count, presence of existing left-turn lanes, and approach speeds ranging from 25 to 65 mph. Video recordings captured left-turning vehicles making gap decisions, allowing researchers to calculate average and 85th percentile time-to-clear values for both advancing and opposing lanes, as well as critical gaps using Raff’s Method. The results indicated that average time-to-clear values observed in the field were lower than Harmelink’s original assumptions, though the differences were minor and did not drastically alter the resulting left-turn lane warrants. However, the 85th percentile time-to-clear values closely matched Harmelink’s assumptions, suggesting that designing for the 85th percentile rather than the average may be more appropriate for accommodating the majority of drivers. Additionally, the study found no major discrepancy between the observed critical gap values and Harmelink’s original assumptions. Specific comparisons revealed that time-to-clear values for the advancing stream were higher when a left-turn lane was present, likely due to reduced pressure from advancing traffic, while higher approach speeds correlated with lower time-to-clear values for opposing lanes. The significance of this work lies in its contribution to updating the American Association of State Highway and Transportation Officials (AASHTO) Green Book guidelines. By validating or refining Harmelink’s procedure, the research supports more accurate and safe intersection designs. The broader compendium also includes studies on driver behavior at freeway interchanges with horizontal signing, quality assurance in high-speed data collection, and measuring travelers’ willingness-to-pay for time savings, collectively advancing practical knowledge in transportation engineering through student-led inquiry.

Key finding

The 85th percentile time-to-clear values closely matched Harmelink’s original assumptions, and critical gap values showed no major difference from the original estimates.

Methodology

naturalistic

Sample size: 18

Provenance

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

Topics

Ranked by relevance to this paper. Hover a topic for its definition.

• work zones
• traffic density
• perceptual countermeasures
• rail grade crossings
• speed choice
• lane changing

Information type

What kind of knowledge this paper contributes, grouped by family — independent of topic (what it is about) and method (how it was studied).

• Empirical Findings: behavioral performance data, observational prevalence
• Methodological Resource: dataset resource