查看更多>>摘要：For oversaturated traffic conditions, the Highway Capacity Manual (HCM) does not apply a progression adjustment factor to the delay model for signalized intersections when there is an initial queue. This causes counterintuitive results in the calculation of delay; for some cases, delay for a nonzero initial queue condition ends up being less than the delay with zero initial queue conditions. Also, for oversaturated traffic conditions, the delay model in the 2000 edition of HCM yields the same uniform delay values for all arrival types when there is an initial queue. This does not seem reasonable because it ignores the effect of pla-tooning on delay. This paper introduces a new approach for computing uniform delay for oversaturated traffic conditions when progression is poor. This approach directly considers the platooning effects in delay and thus eliminates the need to apply a progression adjustment factor. The proposed model is applicable whether there is an initial queue or not. The approach was validated by a comparison of the control delays obtained from a CORSIM simulation to the delays from the proposed model. Validation procedures were conducted on the basis of zero and nonzero initial queue conditions. The proposed approach resulted in more accurate delay values than the HCM model.
Rui Miguel Batista PauloJiong LinNagui M. RouphailJerome Sacks...
p.95-105页
查看更多>>摘要：Calibration and validation of traffic models are processes that depend on field data that are often limited but are essential for determination of inputs to the model and assessment of its reliability. Quantification and systematization of the calibration and validation process expose statistical issues inherent in the use of such data. Formalization of the calibration and validation process naturally leads to the use of Bayesian methodology for assessment of uncertainties in model predictions that arise from a multiplicity of sources, especially statistical variability in estimation and calibration of the input parameters and model discrepancy. The general problem was elucidated in an earlier paper; this paper carries out the full calibration and validation process in the context of a widely used deterministic traffic model, namely, the Highway Capacity Manual model for control delay at signalized intersection approaches. In particular, the reliability of the model was assessed through quantification of the uncertainty in the estimation of model parameters, predictions of model delay, and predictions obtained by adjusting the data used in the model. While the methods are described in a specific context, they can be used generally but are inhibited at times by computational burdens that must be overcome.
查看更多>>摘要：Macroscopic models that can be used to estimate the delay at signalized intersections caused by downstream traffic disturbances, such as queues in closely spaced settings, are presented. The models use basic traffic flow properties and control parameters at neighboring intersections. The models are applied to a hypothetical two-signal system. The results show that the delay caused by downstream disturbances can be significant and therefore must be included in level-of-service and capacity analyses. The results also show that control parameters, such as offsets and green splits at upstream and downstream approaches, play key roles in reducing delay. Validation by the use of microscopic traffic simulation shows close agreement between the delay estimates from the proposed models and that from the microscopic simulation model.
查看更多>>摘要：The uncertainty analysis of the Highway Capacity Manual (HCM) delay model often assumes parameter variances and distributions. In light of the difficulty in specifying distributions and estimating correlations, the present study investigated (a) the possibility of assumed distributions' major effect on the results and (b) the effects of correlations on the accuracy of delay estimates. Field data from one intersection approach in Hawaii and nine intersection approaches in Illinois were used. All input variables in the delay model except for the analysis period were considered uncertain; the analysis period remained fixed at 15 min for consistency with HCM. The simulation results showed that the confidence intervals of delay can be large even if the variability of each input parameter is small. The degree of saturation (X) has a significant effect on the uncertainty of delay estimates for X values 0.9. The standard deviation of input parameters is the main factor affecting the uncertainty of delay estimates. The probability distributions have a slight effect. Correlations among input parameters are often overlooked, but they have a significant effect on the confidence intervals of delay estimates, especially when the variability of the input parameters is large and the input parameters are highly correlated. The frequency distribution of delay estimates is not normal; the shifted lognormal distribution provides a better statistical fit.
查看更多>>摘要：A peak hour factor (PHF) is used to convert hourly traffic volume into the flow rate that represents the busiest 15 min of the rush hour. Past research indicated that PHF had a strong impact on traffic analysis results. The common practice is to use a default value recommended by national or local guidelines or to use limited field observations. This paper investigates the variability of PHF over time and across locations. The day-to-day variability of PHF was found to be as strong as the site-to-site variability. This finding prompts estimation of the PHF on the basis of multiple field measurements or, when it is not possible to obtain measurements, for the use of a model that returns the average value of PHF. This paper presents such a model, which links PHF with the hourly volume, population, and time of day. The paper demonstrates that a large portion of the variability in the sample of observations either can be explained with the model or can be attributed to the day-to-day fluctuation.
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