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Evaluation of ground mounted diagrammatic entrance ramp approach signs : executive summary.
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2000-10-01
[PDF-68.28 KB]
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Edition:Executive summary.
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Abstract:The effectiveness of ground mounted diagrammatic signs in the context of urban
multi-lane arterials leading to a freeway was evaluated. This type of guide sign provides
much needed information well in advance of the interchange entrance, thus giving drivers
more time to change lanes, if needed. Six highway-freeway interchanges were selected
in the Greater Columbus, Ohio, area to determine the effectiveness of ground mounted
diagrammatic signs in the field. Traffic flow video footage was collected at the selected
sites before the diagrammatic signs were installed. The finalized ground mounted
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. The model was tested with data obtained
from additional interchange evaluations with unfamiliar test drivers. This data
corroborated the findings of the theoretical model analysis, in that drivers were able to
execute a needed lane change much earlier when ground mounted diagrammatic signs
were provided. Eye movement recordings were performed at night at the six sites in
order to determine if the presence of these diagrammatic signs was distracting. The
results of the eye movement analysis indicate that ground mounted diagrammatic signs
are not looked at excessively often or excessively long. The overall median first look
distance to these signs was found to be 125m. ODOT/FHWA evaluators visited the six
interchange sites and provided their input and opinions as to the use of ground mounted
diagrammatic signs. The vast majority of the evaluators fully embraced the idea of
ground mounted diagrammatic signs.
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