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Evaluation of ground mounted diagrammatic entrance ramp approach signs : final report, October 2000.
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Evaluation of ground mounted diagrammatic entrance ramp approach signs : final report, October 2000.
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    Final report.
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  • Abstract:
    Highway-freeway interchanges can be a source of confusion to unfamiliar drivers. Typically, freeway entrance ramp

    information is provided by means of trailblazer assemblies (interstate or highway shield, cardinal direction, and a small

    white arrow on a blue shield). Trailblazer assemblies are generally located right at the interchange location, giving

    unfamiliar drivers very little advance notification as to the proper lane choice needed to gain access to the freeway entrance.

    Advance located ground mounted diagrammatic guide signs provide this much needed information well in advance of the

    interchange entrance, thus giving drivers more time to change lanes, if needed. Diagrammatic signs have been used in

    Europe for many years with great success. The present study investigated the effectiveness of ground mounted diagrammatic

    signs in the context of urban multi-lane arterials leading to a freeway. The diagrammatic sign layout was designed as part of

    this project in collaboration with ODOT. Six highway-freeway interchanges were selected in the Greater Columbus, Ohio,

    area to determine the effectiveness of the diagrammatic signs in the field. Traffic flow video footage was collected at the

    selected sites before the diagrammatic signs were installed. The finalized diagrammatic sign designs were then installed and

    the traffic flow videotaping was repeated. The collected video footage was automatically analyzed with Mobilizer PC. The

    resulting vehicle count, speed, and headway data was used as input to a closed form analytical model to determine the

    probability that drivers could successfully change lanes as needed, prior to reaching the gore of the freeway entrance. The

    theoretical analysis indicated a much higher probability that an unfamiliar driver could execute a required lane change when

    diagrammatic signs are used. ODOT/FHWA evaluators visited the six interchange sites and provided their input and

    opinions as to the use of diagrammatic signs. The vast majority of the evaluators fully embraced the idea of diagrammatic

    signs. Eye movement recordings were performed at night at the six sites in order to determine if the presence of the

    diagrammatic signs was distracting. The results of the eye movement analysis indicate that the diagrammatic signs are not

    looked at excessively often or excessively long. The overall median first look distance to the diagrammatic signs was found

    to be 125m. An evaluation with unfamiliar test drivers corroborated the findings of the theoretical model analysis, in that

    drivers were able to execute a needed lane change much earlier when diagrammatic signs were provided. A set of application

    guidelines for diagrammatic signs is provided.

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