Comparison of Highway Capacity Estimation Methods

Asgharzadeh, Mohamadamin; Kondyli, Alexandra

doi:10.1177/0361198118777602

Cited by 24 publications

(11 citation statements)

References 8 publications

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“…Further comparison between the optimum volumes and the conventional capacity values indicated that the optimum volume is a reasonable estimator of freeway design capacity. This was also supported by other researchers ( 16 – 18 ).…”

Section: Literature Reviewsupporting

confidence: 88%

Optimum Volume of Freeway Corridors

Shojaat

Geistefeldt

Wolshon

2020

Transportation Research Record: Journal of the Transportation R

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Conventional methods to assess the quality of service on freeways are based on the comparison of a specific peak hour traffic demand to the capacity of the facility, which is usually measured at a single uniform bottleneck section. However, estimating the quality of service of one bottleneck section may not be sufficient to assess the performance of an entire freeway facility. A driver traveling along a freeway corridor may actually encounter multiple flow breakdowns at independent bottleneck sections, which affect the overall quality of service. This paper introduces a comprehensive approach that considers an entire freeway corridor as a system consisting of successive independent bottlenecks with different characteristics, and can be used to estimate the optimum sustainable volume. The methodology is based on the sustained flow index, which is defined as the product of traffic volume and the probability of survival at this volume. Optimum volumes of two real-world corridors are estimated based on the new derivations. The empirical results reveal that the optimum volume and the capacity of an entire corridor is less than those of its most restrictive bottleneck.

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Section: Literature Reviewsupporting

confidence: 88%

Optimum Volume of Freeway Corridors

Shojaat

Geistefeldt

Wolshon

2020

Transportation Research Record: Journal of the Transportation R

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“…The definition of capacity has been studied extensively in the literature (14)(15)(16)(17). Generally, as flow increases, the speed gradually decreases until the breakdown phenomenon occurs.…”

Section: Methodsmentioning

confidence: 99%

Estimation of the Effect of Rain and Incidents on Freeway Capacity and Free-Flow Speed

Alsharari

Asgharzadeh

Kondyli

2020

Transportation Research Record: Journal of the Transportation R

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This research aims to examine the effect of incidents with lane closures and adverse weather conditions (medium to heavy rain intensity) on capacity and free-flow speed (FFS) of freeway segments. Data were collected from multiple freeway segments located in the Kansas City, U.S., metro area from 2014 to 2018. The capacity and FFS were measured for two-lane, three-lane, and four-lane freeways under four conditions: ( 1 ) base conditions, ( 2 ) adverse weather only, ( 3 ) incidents only, and ( 4 ) adverse-weather-and-incidents. Capacity adjustment factors (CAF), and speed adjustment factors (SAF) were established to identify the remaining capacity or the FFS reduction during an incident or adverse weather conditions. The findings indicated that medium to heavy rain resulted in a 5% reduction in FFS at three-lane sites which is consistent with the adjustment factors shown in the Highway Capacity Manual 6th edition (HCM6); however, rain was not found to have a significant impact on freeway capacity. It was also found that incidents leading to one-lane closures reduced capacities by 30%, 17%, and 17% at two-lane, three-lane, and four-lane sites, respectively. Incidents were also found to reduce FFS by approximately 5%–10%, possibly because of “rubbernecking.” Adjustment factors that capture the combined effect of incidents and rain on FFS and capacity are also presented.

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“…Effectively measuring freeway performance requires accurate estimation of capacity. Asgharzadeh and Kondyli ( 3 ) compared well-known capacity estimation methods, listing their advantages and disadvantages: Van Aerde ( 4 ), product limit method ( 5 , 6 ), Sustainable Flow Index ( 7 ) and HCM 6th edition ( 1 ). With the exception of Van Aerde, all methods rely on breakdown identification, which brings the substantial advantage of addressing the stochastic nature of capacity.…”

Section: Literature Reviewmentioning

confidence: 99%

Predicting Lane-by-Lane Flows and Speeds for Freeway Segments

Sasahara

Carvalho

Chowdhury

et al. 2020

Transportation Research Record: Journal of the Transportation R

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The Highway Capacity Manual is a major reference for evaluating the capacity and quality of service of road facilities. However, it holds the assumption that lanes perform equally, which can result in inaccuracies in performance estimation. The main purpose of this research is to develop a series of models for estimating flows and speeds by lane for various types of freeway segments, including basic, merge, and diverge types. These models consider the demand-to-capacity ratio, the presence of trucks, grade, and the presence of upstream and downstream ramps. To predict lane performance effectively, it is critical that capacity and free-flow speeds are also determined for individual lanes. Therefore, this study also investigates the relationship between segment average values and lane values for free-flow speeds and capacities, and proposes a method to estimate these parameters for each lane as a function of the segment average. Observed field data has shown that free-flow speeds and capacities have lowest values on the shoulder lanes and highest values on the median lanes. Speed and flow data were collected from 48 segments throughout the U.S.A., including basic, merge, and diverge segments, to develop flow and speed distribution models. A case example is provided to illustrate the application of the developed model and the predicted speed–flow relationship is compared with field data, with satisfactory results.

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Comparison of Highway Capacity Estimation Methods

Cited by 24 publications

References 8 publications

Optimum Volume of Freeway Corridors

Optimum Volume of Freeway Corridors

Estimation of the Effect of Rain and Incidents on Freeway Capacity and Free-Flow Speed

Predicting Lane-by-Lane Flows and Speeds for Freeway Segments

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