Evaluation of speed–flow characteristics on two-lane highways with mixed traffic (original) (raw)
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The most appropriate service measure for a two-lane highway is the combination of average travel speed (ATS) and percent time spent following (PTSF). The local driver behavior and traffic operation characteristics in different countries affect the operational analysis results. The objective of this study is to evaluate the applicability of the HCM procedures on two-lane highways in Iraq. Ten highway segments in northern Iraq were selected, and more than 28,000 vehicles were observed to record traffic characteristics. The results show that for low flow rates, the HCM-2000 procedures tend to overestimate the ATS with an amount of 0.0085VP, while for moderate-to-high flow rates, the HCM procedures tend to underestimate the ATS with an amount of 0.0025VP for the highways considered. Moreover, the HCM procedures tend to overestimate PTSF; as well, ATS decreases as PTSF, density, and follower density increase for the highways under study. Equations are developed for the evaluation of tra...
Evaluation of Performance Measures for Two-Lane Inter-urban Highways under Mixed Traffic Condition
The traffic performance of a highway is expressed in terms of level of service (LOS). It is a major input to important decisions on public fund investments that are made at different stages of the highway life. Because of its unique operational characteristics the evaluation of traffic performance on two-lane highways is not an easy task. The objectives of this research are (a) to examine the applicability of various performance measures for two-lane highways under mixed traffic conditions (b) to assign threshold values for different levels of service based on the best performance measure observed. Graphical and statistical analysis are carried out among the six most popular performance measures and traffic volume. No measure was found reliable for mixed traffic conditions. Therefore, the number of followers (NF) was introduced as a new performance measure. In mixed traffic conditions, followers are defined as vehicles travelling with gap less than 2.5s. Although NF is found to have good correlation with flow rate, it was also not able to reflect the true congestion conditions of a roadway. Therefore, this parameter is further modified to number of followers as a proportion of capacity (NFPC). It demonstrated a very strong correlation with traffic volume. Threshold values are proposed for different LOS based on NFPC for mixed traffic conditions.
Model Development to Predict Free Flow Speed for Multi-Lane Highways
2017
As defined in the Highway Capacity Manual HCM, Free flow speed (FFS) is" an average speed of vehicles on a given segment, measured under low-volume conditions, when drivers are free to travel at their desired speed and are not constrained by the presence of other vehicles or downstream traffic control devices. It is a parameter which has being utilized widely for limit and level-of-service investigation of different highway classifications. This research concerns collections and analyses free-flow data at the midpoints of forty-two multilane rural and suburban highway segments all through Al-Najaf city. Thus in order to predict FFS from corresponding collected values a, an extremely tests create model for evaluating normal free-low speed and for recognizing the appropriation of individual free-flow speeds. The most crucial variables that oversee FFS are vehicle type, space mean speed, and functional classification of highway. The subsequent models encourage the FFS rates of suburban and rural roadways.
Proposal of an Alternative Model for Speed-Flow Relationship in Two-Lane Highways
Procedia - Social and Behavioral Sciences, 2011
A research has been carried out in two-lane highways in the Madrid Region to propose an alternative model for the speed-flow relationship using regular loop data. The model is different in shape and, in some cases, slopes with respect to the contents of Highway Capacity Manual (HCM). A model is proposed for a mountainous area road, something for which the HCM does not provide explicitly a solution. The problem of a mountain road with high flows to access a popular recreational area is discussed, and some solutions are proposed. Up to 7 one-way sections of two-lane highways have been selected, aiming at covering a significant number of different characteristics, to verify the proposed method the different classes of highways on which the Manual classifies them. In order to enunciate the model and to verify the basic variables of these types of roads a high number of data have been used. The counts were collected in the same way that the Madrid Region Highway Agency performs their counts. A total of 1.471 hours have been collected, in periods of 5 minutes. The models have been verified by means of specific statistical test (R2, T-Student, Durbin-Watson, ANOVA, etc.) and with the diagnostics of the contrast of assumptions (normality, linearity, homoscedasticity and independence). The model proposed for this type of highways with base conditions, can explain the different behaviors as traffic volumes increase, and follows a polynomial multiple regression model of order 3, S shaped. As secondary results of this research, the levels of service and the capacities of this road have been measured with the 2000 HCM methodology, and the results discussed.
Speed Factors on Two-Lane Rural Highways in Free-Flow Conditions
Transportation Research Record, 2005
The mean free-flow speed and its variability across drivers are considered important safety factors. Despite a large body of past research on operating speeds, there is still much to learn about the factors of free-flow speeds, especially on tangent segments of two-lane rural highways. The roadway factors of speed dispersion across drivers are largely unknown. Also, the use of the entire free-flow speed distribution suggested by other authors has not been yet addressed. Consequently, the existing models are not aimed to evaluate the speed variability at a site.
Modelling Free Flow Speed on Two-Lane Rural Highways in Bosnia and Herzegovina
PROMET - Traffic&Transportation, 2014
Free flow speed is used as a parameter in transportation planning and capacity analysis models, as well as speed-flow diagrams. Many of these models suggest estimating free flow speed according to measurements from similar highways, which is not a practical method for use in B&H. This paper first discusses problems with using these methodologies in conditions prevailing in B&H and then presents a free flow speed evaluation model developed from a comprehensive field survey conducted on nine homogeneous sections of state and regional roads.
Spatial evaluation of speed-flow-geometry relationship on two-lane rural highways
ARPN journal of engineering and applied sciences, 2016
The mean travel speed of drivers on uninterrupted flow facilities such as two-lane rural highways is deemed as good performance indicator for the subject road class; as the variable relates well with user perception. However, the operating conditions on two-lane roads relating to travel speed is different from those on other types of facilities, as fast moving vehicles in either direction are usually impeded by slower moving ones in the same travel direction and also facing oncoming traffic in the opposing lane. Thus, impeded vehicles may be compelled to travel at lower speeds than desired; particularly, in the absence of sufficient sight distance and permissible gap in the opposing traffic stream, being the appropriate lane used for passing maneuvers. This implies that the operating speed on two-lane highways substantially depends on the level of traffic flow and perhaps, its composition as well as the roadway geometric features. This paper examines the effects of traffic level, co...
Transportation Research Record, 2006
This paper presents an alternative way of using average travel speed and percentage of traffic in platoons [the two measures of effectiveness currently in Highway Capacity Manual (HCM) methodology] to evaluate level of service. The definition of a threshold speed that is acceptable to users is implied. Travelers expect different things of different roads, and in the case of two-lane highways the desire to pass and the stress or mild frustration of being delayed are not a function only of headway or of the difference between actual and desired travel speed. Therefore, simplistic approaches do not accurately reflect the point of view of the roadway user. The procedure can be adapted to various two-lane highway types. It could be used for Types I and II already in HCM procedure and for other types that may be considered in the future.
Measuring Performance on Two-Lane Highways: Empirical Investigation
Transportation Research Record: Journal of the Transportation Research Board, 2017
This paper presents an empirical investigation into several performance measures for operational analysis on two-lane highways. The performance measures investigated are average travel speed, average travel speed to free-flow speed, percent followers, followers flow, followers density, percent impeded, impeded flow, and impeded density. Field data from 16 study sites in the states of Montana, Idaho, Oregon, and North Carolina representing Class 1, Class 2, and Class 3 highways were used in this study. The level of association between performance measures and some of the most important traffic variables was examined with graphical and statistical techniques. The traffic variables investigated in this study included combined flow in both directions of travel; proportion of traffic in the direction of travel, called in this study “traffic split”; percentage of heavy vehicles; and speed variance. Study results suggest that speed-related measures have weak associations with traffic varia...