Generic Speed–Flow Models for Basic Freeway Segments on General-Purpose and Managed Lanes in Undersaturated Flow Conditions

Aghdashi, Seyedbehzad; Rouphail, Nagui M.; Hajbabaie, Ali; Schroeder, Bastian J

doi:10.3141/2483-12

Cited by 8 publications

(4 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…f LW = 0 if lane width (ft) x .=12 f LW = 1.9 if lane width (ft) 12 . x .=11 f LW = 6.6 if lane width (ft) x \ 11 Work zone free-flow speeds were estimated using the model presented by Hajbabaie et al (7) as FFS WZ = 9:95 + 33:49f Sr + 0:53f S À 5:60f LCSI À 3:84f Br À 1:…”

Section: Delay Costsmentioning

confidence: 99%

Effects of Pavement Condition on LCCA User Costs

Okte

Al‐Qadi

Özer

2019

Transportation Research Record: Journal of the Transportation R

View full text Add to dashboard Cite

Life cycle cost analysis (LCCA) is one of the well-established methods to determine the cost-effective alternative between different transportation infrastructure projects. Life cycle cost of a roadway alternative consists of agency and user costs over an analysis period appropriately selected. Agency costs include initial construction costs, and maintenance and rehabilitation costs incurred within the analysis period. User costs incur when there is a work zone present and also during normal operating conditions. In traditional LCCA, adopted by many agencies around the United States, it is assumed that the difference in user cost between alternatives mainly arise from work zone costs. The costs that arise during normal operating conditions (mainly vehicle operating costs) are not dependent on project alternatives and thus are traditionally considered to be negligible. This paper introduces a methodology to test the sensitivity of vehicle operating costs to roughness and texture profile quantitatively and evaluate its contribution to LCCA calculations. It was hypothesized that even the slight changes in surface profile between various alternatives may result in different user costs between the alternatives. A case study is presented to illustrate the effect of user costs of normal operating conditions on LCCA analysis results. Case study showed that vehicle operating costs that arise during normal operation may greatly affect the results of LCCA and should be considered, especially for low-volume traffic projects.

show abstract

Section: Delay Costsmentioning

confidence: 99%

Effects of Pavement Condition on LCCA User Costs

Okte

Al‐Qadi

Özer

2019

Transportation Research Record: Journal of the Transportation R

View full text Add to dashboard Cite

show abstract

“…Similarly, several researchers have studied the impact of weather on non-recurring congestion. A change in weather conditions can affect the capacity and the free-flow speed of the freeway, resulting in changes in travel time ( 13 , 19 ). The occurrence of different weather conditions is difficult to predict, but their expectancy could be estimated based on historical averages ( 20 ).…”

Section: Literature Reviewmentioning

confidence: 99%

Validation and Calibration of Freeway Reliability Methodology in the Highway Capacity Manual: Method and Case Studies

Karmakar

Aghdashi

Rouphail

et al. 2018

Transportation Research Record: Journal of the Transportation R

Self Cite

View full text Add to dashboard Cite

Traffic congestion costs drivers an average of $1,200 a year in wasted fuel and time, with most travelers becoming less tolerant of unexpected delays. Substantial efforts have been made to account for the impact of non-recurring sources of congestion on travel time reliability. The 6th edition of the Highway Capacity Manual (HCM) provides a structured guidance on a step-by-step analysis to estimate reliability performance measures on freeway facilities. However, practical implementation of these methods poses its own challenges. Performing these analyses requires assimilation of data scattered in different platforms, and this assimilation is complicated further by the fact that data and data platforms differ from state to state. This paper focuses on practical calibration and validation methods of the core and reliability analyses described in the HCM. The main objective is to provide HCM users with guidance on collecting data for freeway reliability analysis as well as validating the reliability performance measures predictions of the HCM methodology. A real-world case study on three routes on Interstate 40 in the Raleigh-Durham area in North Carolina is used to describe the steps required for conducting this analysis. The travel time index (TTI) distribution, reported by the HCM models, was found to match those from probe-based travel time data closely up to the 80th percentile values. However, because of a mismatch between the actual and HCM estimated incident allocation patterns both spatially and temporally, and the fact that traffic demands in the HCM methods are by default insensitive to the occurrence of major incidents, the HCM approach tended to generate larger travel time values in the upper regions of the travel time distribution.

show abstract

“…Merge Segments As noted earlier, the approach used in this study generates an equivalent merge or diverge segment capacity that would yield speeds equivalent to a basic segment speed. Rouphail et al (14) and Aghdashi et al (15,16) proposed two generic equations to determine the capacity c i and speed S i,t for a basic freeway segment as a function of the free-flow speed S FFS , the breakpoint BP, and the prevailing demand D i,t on segment i in analysis period t:…”

Section: Adjustments For Merge and Diverge Sectionsmentioning

confidence: 99%

Planning-Level Methodology for Freeway Facilities

Hajbabaie

Rouphail

Schroeder³

et al. 2015

Transportation Research Record: Journal of the Transportation R

Self Cite

View full text Add to dashboard Cite

This paper presents a planning-level methodology for the analysis of freeway facilities. The proposed approach is based on and compatible with the operational method of the Highway Capacity Manual 2010 (HCM 2010). The approach is specifically constructed with the intent to minimize input data requirements. The method covers both under- and oversaturated flow conditions and produces estimates of travel time, speed, density, and level of service. The underlying methodology relies on developing a relationship between a basic freeway segment's delay rate per unit distance and its demand-to-capacity ratio. For weaving segments, the study develops capacity adjustment factors on the basis of volume ratio and segment length. With these factors, demand-to-capacity ratios on weave segments were adjusted and the segment was treated similarly to a basic freeway segment. For merge and diverge segments, a novel methodology is proposed to estimate their capacity on the basis of demand level, free-flow speed, and space mean speed. Subsequently, capacity adjustment factors are calculated on those segments and their demand-to-capacity ratios are adjusted accordingly. The proposed approach is applied to two examples in the HCM 2010 and produced very promising results. For undersaturated flow conditions, facility travel time is at most 3.4% and density was at most 1.1% at variance from the results found by applying the HCM 2010 operational methodology. The corresponding differences for oversaturated conditions are 6.7% and 13.0%, respectively.

show abstract

Generic Speed–Flow Models for Basic Freeway Segments on General-Purpose and Managed Lanes in Undersaturated Flow Conditions

Cited by 8 publications

References 6 publications

Effects of Pavement Condition on LCCA User Costs

Effects of Pavement Condition on LCCA User Costs

Validation and Calibration of Freeway Reliability Methodology in the Highway Capacity Manual: Method and Case Studies

Planning-Level Methodology for Freeway Facilities

Contact Info

Product

Resources

About