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Evaluation of alternative intersections and interchanges: volume 1 -- roundabout capacity and rollover analysis for heavy vehicles.
  • Published Date:
    2015-12-01
  • Language:
    English
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Evaluation of alternative intersections and interchanges: volume 1 -- roundabout capacity and rollover analysis for heavy vehicles.
Details:
  • Report Number:
    FHWA/IN/JTRP-2015/26
  • Resource Type:
  • Format:
  • Description:
    There is a recent trend of building roundabouts on high‐speed roads, often with the considerable presence of heavy vehicles. With

    the increased presence of trucks on roundabouts, the issue of overturning has become a concern. Although some geometric, vehicle,

    and loading factors have been connected to rollover, the safety performance of roundabouts built on high‐speed roads is not well

    understood due to their relative novelty. In addition, other concerns related to geometry, driver behavior, and environmental

    considerations may exist at roundabouts. This study examined roundabout circulatory superelevation, aggressive driver behavior,

    roundabout readability, and nighttime conditions in the context of heavy vehicle rollover. Moreover, the critical and follow‐up headways

    were estimated for trucks and other vehicles at roundabouts located on the low‐ and high–speed roads and during daytime and

    nighttime conditions.

    This research developed a methodology which may be used to examine truck overturning at roundabouts. A generalized rollover

    model suitable for application to heavy vehicles was applied to field‐observed semi‐trailer speeds and paths to estimate their proximity

    to rollover at newly‐built Indiana roundabouts. This was done by introducing delta v ‐ the difference between the critical rollover speed

    determined from the model and the actual speed.

    This report revealed that heavy vehicles increased the critical headway, and in turn reduced the entry capacity of roundabouts.

    Drivers of heavy vehicles, on average, accepted a 1.1 sec longer critical headway than drivers of passenger cars. The effects of

    nighttime/twilight conditions indicated additional capacity reduction caused by a 0.6 sec longer critical headway compared to daylight

    conditions. Likewise, drivers on dual‐lane roundabouts in rural areas accepted a 0.6 sec longer critical headway than drivers on singlelane

    roundabouts in urban areas.

    It was determined that the gap‐acceptance parameters for a single‐lane roundabout on a low‐speed state road were shorter than

    the national values, resulting on average in 30% higher capacity for Indiana conditions. In contrast, the estimated critical headway was

    larger for dual‐lane roundabouts on high‐speed state roads, resulting in 15% reduced capacity for Indiana conditions.

    The findings of this report are based on low and medium traffic volumes presently observed on high‐speed rural and suburban

    roads. Heavy traffic flow may affect driver behavior; therefore, studying such roundabouts in heavier traffic conditions might improve

    the results.

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