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    Base Condition & Capacity of Two-Lane Highways

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    Mohd Najmi
    Two-lane highways have one lane in each direction and passing maneuvers can only occur when there are gaps in opposing traffic. As traffic demand increases, opportunities to pass decrease which can create traffic platoons with delayed vehicles. Two-lane highways are classified based on expected travel speeds and the areas they serve. Their base capacity is 3,200 vehicles per hour total for both directions, or 1,700 vehicles per hour for a single direction. Level of service is determined by establishing base conditions, measuring or estimating flow rates and speeds, and calculating service measures.

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    Base Condition & Capacity of Two-Lane Highways

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    Mohd Najmi
    6 views8 pages
    Two-lane highways have one lane in each direction and passing maneuvers can only occur when there are gaps in opposing traffic. As traffic demand increases, opportunities to pass decrease which can create traffic platoons with delayed vehicles. Two-lane highways are classified based on expected travel speeds and the areas they serve. Their base capacity is 3,200 vehicles per hour total for both directions, or 1,700 vehicles per hour for a single direction. Level of service is determined by establishing base conditions, measuring or estimating flow rates and speeds, and calculating service measures.

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    Two-lane highways have one lane in each direction and passing maneuvers can only occur when there are gaps in opposing traffic. As traffic demand increases, opportunities to pass decrease which can create traffic platoons with delayed vehicles. Two-lane highways are classified based on expected travel speeds and the areas they serve. Their base capacity is 3,200 vehicles per hour total for both directions, or 1,700 vehicles per hour for a single direction. Level of service is determined by establishing base conditions, measuring or estimating flow rates and speeds, and calculating service measures.

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    6 views8 pages

    Base Condition & Capacity of Two-Lane Highways

    Uploaded by

    Mohd Najmi
    Two-lane highways have one lane in each direction and passing maneuvers can only occur when there are gaps in opposing traffic. As traffic demand increases, opportunities to pass decrease which can create traffic platoons with delayed vehicles. Two-lane highways are classified based on expected travel speeds and the areas they serve. Their base capacity is 3,200 vehicles per hour total for both directions, or 1,700 vehicles per hour for a single direction. Level of service is determined by establishing base conditions, measuring or estimating flow rates and speeds, and calculating service measures.

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    of 8

    Base Condition & Capacity

    of Two-Lane Highways
    Overview
    • Two-Iane highways have one lane for the use of traffic in each direction

    • Fundamental characteristic that differentiates two-lane highway and uninterrupted-flow facilities


    is the passing maneuvers that can happen from the opposite way
    • Passing maneuvers are limited by the availability of gaps in the opposing traffic stream and by
    the availability of sufficient sight distance for a driver to discern the approach of an opposing
    vehicle safely
    • As demand flows and geometric restrictions increase, opportunities to pass decrease.
    • This creates platoons within the traffic stream, with trailing vehicles subject to additional delay
    because of the inability to pass the Jead vehicles
    Characteristic

    • Serve a number of bicycle trips, particularly recreational trips. Any


    consideration of operating quality criteria must account for these
    disparate functions.
    • Connect major trip generators or serve as primary links in state and
    national highway networks.
    • Serve long-distance commercial and recreational travelers, and long
    sections may pass through rural areas without traffic control
    interruptions.
    • Consistent high-speed operations & infrequent passing delays are
    desirable
    Classification

    • Class I: Two-lane highways are highways where motorists expect to


    travel at relatively high speeds.
    • Class II : Two-lane highways are highways where motorists do not
    necessarily expect to travel at high speeds.
    • Class III two-lane highways serve moderately developed areas. They
    may be portions of a Class I or Class Il highway that pass through small
    towns or deveIoped recreationaI areas.
    Base Conditions

    • Minimum lane widths of 12 ft (3.6 meter)


    • Minimum shoulder widths of 6 ft (1.3 meter)
    • No-passing zones
    • Traffic stream consisting of passenger cars only
    • No direct access points along the roadway
    • No impediments to through traffic due to traffic control or turning
    vehicles
    • Level terrain, with grades no greater than 2%
    • 50/50 directional split of traffic
    Capacity

    • Capacity for a single direction is 1700pc/h


    • Capacity for both directions combined is 3200 pc/h. (Because
    of the interactions between directional flows, when a capacity
    of 1,700 pe/h is reached in one direction, the maximum
    opposing flow is limited to 1,500 pc/h.)
    LOS Determination
    • Establish Base Conditions and Capacity
    • Estimate or Measure Free-Flow Speed
    • Calculate Analysis Flow Rate
    • Calculate Service Measure(s) and Determine LOS

    Source : Highway Capacity Manual, Sixth Edition : A Guide for


    Multimodal Mobility Analysis.
    References

    Transportation Research Board. (2016). Highway Capacity Manual, Sixth


    Edition : A Guide for Multimodal Mobility Analysis. Washington, DC : National
    Academies Press.

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