Predicting Operating Speeds on Low-Speed Urban Streets: Regression and Panel Analysis Approaches

Tarris, J P; Poe, C M; Mason, J M; Goulias, Konstadinos G.

doi:10.3141/1523-06

Cited by 24 publications

(8 citation statements)

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“…It is possible that a road with a high mean speed and low speed variability has the same 85 th speed percentile as a road with a much lower mean speed but higher speed variability. Modeling the entire free-flow speed distribution, suggested by Tarris et al (1996) and Fitzpatrick et al (2003), might rectify this problem. The mean free-flow speed and its variability across drivers are considered important safety factors.…”

Section: Available Predicting Models and Research Methodologiesmentioning

confidence: 99%

“…Several countries have incorporated the use of the expected operating speed on the highway as a basis for selecting design speeds or specific geometric components, such as the superelevation rate and the stopping sight distance, or for detecting design inconsistencies (Polus et al, 1995 (Polus et al, 1995;Bonneson, 2001). The use of the entire speed distribution has been also recommended (Tarris et al, 1996;Fitzpatrick et al, 2003) to develop speed models instead of focusing on a particular percentile as do the existing models.…”

Section: Research Problem Statementmentioning

confidence: 99%

“…Fitzpatrick et al (1997) The use of other percentiles (Polus et al, 1995;Schurr et al, 2002) and the use of the entire freeflow speed distribution (Tarris et al, 1996;Fitzpatrick et al, 2003) have been proposed to find better estimators of the highway operating speed.…”

Section: Practices Of Selection Of Design Speeds and Speed Limitsmentioning

confidence: 99%

“…The use of the entire speed distribution has been also recommended (Tarris et al, 1996;Fitzpatrick et al, 2003) to develop speed models instead of focusing on a particular percentile as do the existing models.…”

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confidence: 99%

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Reconciling Speed Limits with Design Speeds

Medina¹,

Tarko²

2004

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IntroductionThe INDOT Design Manual recommends that a design speed is selected based on the functional classification, urban vs. rural environment, terrain, traffic volumes and project scope of work. The design speed should be equal or greater than the legal or anticipated speed limit. According to AASHTO, a design speed should be consistent with the speed a driver is likely to expect on the highway.By using design speeds, highways are designed in a conservative manner to facilitate the safe motion of vehicles even in adverse but reasonable conditions. Consequently, the 85 th percentile of actual freeflow speeds may exceed the design speed. This situation does not have to cause excessive hazard because the majority of drivers adequately perceive the risk.Some Indiana road sections designed and built in the past do not meet the current design standards. INDOT makes a continuous effort to modernize these sections. Due to prohibitive costs, reduced design speeds and design exceptions are considered. Guidance is needed to help reduce the discrepancy between the economically justifiable design solutions and the design standards expected by the motorists. Predicting the 85 th percentile speed on modernized sections would help designers in finding solutions that meet both the motorists' expectations and the current design standards to the possible extent.The objective of the research was the development of a tool for predicting the actual speeds on modernized twoand four-lane roads in Indiana. FindingsThe mean free-flow speed and its variability across drivers are considered important safety factors. The existing speed-predicting models combine the mean speed impacts with the speed dispersion impacts, which make identification of the speed factors and interpretation of the results difficult. Furthermore, the existing models are specialized to selected percentiles and are not able to estimate the entire range of the speed variability at a site. This report presents an advanced method of modeling free-flow speeds that overcomes the limitations of the existing models.This has been accomplished by representing the percentile speed as a linear combination of the mean and the standard deviation.Free-flow speeds and highway geometry characteristics collected on two-lane rural highways and four-lane suburban and rural highways were used to develop the models. The crash experience on the studied highways was considered to eliminate segments where a high number of crashes indicated that the driver perception of the risk might be incorrect. The models demonstrated their efficiency in identifying relationships between speed and diverse road geometry characteristics, e.g. crosssection dimensions, horizontal curve elements, intersection and driveway densities and median type. The developed speed models were included in a prototype software tool to help highway designers implement the models. The tool generates a profile of the mean speed and any specified percentile speed for the entire project length based on the preliminary highwa...

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Section: Available Predicting Models and Research Methodologiesmentioning

confidence: 99%

Section: Research Problem Statementmentioning

confidence: 99%

Section: Practices Of Selection Of Design Speeds and Speed Limitsmentioning

confidence: 99%

mentioning

confidence: 99%

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Reconciling Speed Limits with Design Speeds

Medina¹,

Tarko²

2004

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“…Tarris et al (1996) referred that the loss of information due to speed data aggregation reduces the total variability and the nature of the variability associated with the regression function, which may bias the effects of road geometrics, proposing that modeling the entire free-flow speed distribution may help to overcome the problem. The only existing models Despite also using the entire free-flow speed distribution, the authors' approach to percentile speed modeling (Lobo et al 2014) is based on stochastic frontier models usually applied in the field of econometrics (Aigner et al 1977;Meeusen and van der Broeck 1977).…”

Section: Literature Frameworkmentioning

confidence: 99%

Flexible Stochastic Frontier Approach to Predict Spot Speed in Two-Lane Highways

2016

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The approach to spot speed prediction in two-lane highways followed in this study aims to evaluate the effects of a comprehensive set of speed factors, with a special focus on the geometric characteristics of the road segment to which the element belongs. Two flexible models were developed for different types of roads based on a stochastic frontier formulation in which the maximum operating speed is estimated as a function of road geometrics and the one-sided disturbance accounts for diversity in driving behavior and vehicle characteristics, allowing the estimation of any percentile speed. The models are applicable to horizontal curves and tangents and consider both on-site characteristics and aggregated variables characterizing the road segment. The results show a clear influence of segment features on different percentile spot speeds, revealing that recent driving experience and expectations about the quality of the geometric design influence the way a driver approaches a specific road element. Additionally, this study contributes to addressing some of the limitations of existing speed models identified in 2 the literature.

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A Fuzzy Logic Modeling Approach to Assess the Speed Limit Suitability in Urban Street Networks

Hawas

Khan

2013

Communications in Computer and Information Science

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Predicting Operating Speeds on Low-Speed Urban Streets: Regression and Panel Analysis Approaches

Cited by 24 publications

References 0 publications

Reconciling Speed Limits with Design Speeds

Reconciling Speed Limits with Design Speeds

Flexible Stochastic Frontier Approach to Predict Spot Speed in Two-Lane Highways

A Fuzzy Logic Modeling Approach to Assess the Speed Limit Suitability in Urban Street Networks

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