Graphical Route Information Panel Signs for Southbound I-35 and SH 130 Travel through Austin

Ullman, Gerald L.; Brydia, Robert E.; Nelson, Alicia A.; Higgins, Laura L.; Baker, Richard T.; Geiselbrecht, Tina · 2014 · ROSA P / Texas A&M Transportation Institute

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Summary

This study addresses the design and safety implications of Graphical Route Information Panel (GRIP) signs, a signage approach using text, colors, and maps to convey dynamic roadway conditions such as congestion and travel times. While GRIPs are used internationally, they have not been deployed in the United States. The research was motivated by the Texas Department of Transportation’s interest in installing GRIPs on southbound Interstate 35 (I-35) near Austin, Texas, to help drivers choose between the congested, non-toll I-35 and the toll-based State Highway 130 (SH 130). The primary objective was to determine safe and optimal design features that provide useful information without causing driver information overload or unsafe eye-glance behaviors. The researchers employed a three-phase methodology involving focus groups, laptop-based human factors laboratory studies, and driving simulator studies with eye-tracking technology. Focus groups with local and out-of-town drivers identified key design elements, rejecting simplified subway-style maps due to potential confusion. Laboratory studies evaluated driver comprehension and information loading across various sign orientations and display types. Finally, driving simulator studies assessed eye-glance durations for specific sign designs at three potential locations: Georgetown (I-35/SH 130), Round Rock (I-35/SH 45), and Austin (I-35/US 290). The simulator tests measured whether signs induced glances exceeding the 2-second threshold associated with increased crash risk. Results indicated that north-oriented maps were slightly preferred over track-oriented ones, and 3D perspective views performed poorly. Drivers strongly preferred signs displaying both route congestion and travel times. However, displaying both data types simultaneously increased cognitive load; a distributed signing approach—using a separate text-based travel time sign followed by a GRIP showing congestion—yielded the best comprehension metrics. Simulator data revealed that GRIP signs at the Georgetown location did not induce excessively long glances for through trips, remaining below the 2-second safety threshold. In contrast, signs at Round Rock and Austin locations caused significant numbers of participants to exceed the 2-second glance limit, particularly for trips to the airport or when viewing route-only signs. Consequently, the study recommended deploying GRIPs only at the Georgetown location. The significance of this work lies in providing evidence-based design guidelines for the first potential U.S. deployment of GRIP signs. The study concluded that signs must be large enough to allow at least 6 seconds of viewing time, requiring specific dimensions (e.g., 31 feet high for GRIPs) and legibility standards. It also outlined necessary next steps, including securing experimental permits, designing support structures, and developing software interfaces with TxDOT’s Lonestar system. By identifying safe design parameters and limiting deployment to locations where glance times remain within safety thresholds, the research helps mitigate the risks of information overload and unsafe driving behaviors associated with complex dynamic signage.

Key finding

GRIP signs at the Georgetown location maintained driver glance durations under the two-second safety threshold for through trips, while signs at Round Rock and Austin locations caused excessive glance times for airport-bound drivers.

Methodology

mixed_methods

Sample size: 549

Provenance

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

Topics

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• signage environment