36 research outputs found
AN USER-OPTIMAL ROUTE CHOICE MODEL WITH ASYMMETRIC COST FUNCTIONS INCORPORATING INTERSECTION-RELATED TRAVEL TIMES.
No full textThis report describes a traffic assignment model which is innovative in two respects as compared with models conventionally used in practice. First, each turning movement in the street intersections of the network is represented by a travel time-flow relationship; conventional models represent only approach travel times and flows, although turning movements may be accounted for. Second, the travel times for each turning movement are determined as a function of all flows in the intersection as well as the appropriate cycle time and green splits for those flows. Such cost functions are termed asymmetric because of their mathematical properties. In conventional models, each link's travel time depends only on that link's flow. This model is implemented and solved for a small street network for St. Charles, Illinois. To the authors' knowledge, it is the first implementation of such a model with realistic link functions and a real network. The report describes how the link travel time-flow functions were estimated statistically from simulated intersection operations. Then, the experience with the solving model computationally is documented. A lengthy discussion of future research directions concludes the report
IMPLEMENTATION AND EVALUATION OF AN ASYMMETRIC, EQUILIBRIUM ROUTE CHOICE MODEL INCORPORATING INTERSECTION-RELATED TRAVEL TIMES.
No full text
Integrated indicator to evaluate vehicle performance across: Safety, fuel efficiency and green domains
No full textIn general, car manufacturers face trade-offs between safety, efficiency and environmental performance when choosing between mass, length, engine power, and fuel efficiency. Moreover, the information available to the consumers makes difficult to assess all these components at once, especially when aiming to compare vehicles across different categories and/or to compare vehicles in the same category but across different model years. The main objective of this research was to develop an integrated tool able to assess vehicle's performance simultaneously for safety and environmental domains, leading to the research output of a Safety, Fuel Efficiency and Green Emissions (SEG) indicator able to evaluate and rank vehicle's performance across those three domains. For this purpose, crash data was gathered in Porto (Portugal) for the period 2006-2010 (N = 1374). The crash database was analyzed and crash severity prediction models were developed using advanced logistic regression models. Following, the methodology for the SEG indicator was established combining the vehicle's safety and the environmental evaluation into an integrated analysis. The obtained results for the SEG indicator do not show any trade-off between vehicle's safety, fuel consumption and emissions. The best performance was achieved for newer gasoline passenger vehicles (<5year) with a smaller engine size (<1400 cm3). According to the SEG indicator, a vehicle with these characteristics can be recommended for a safety-conscious profile user, as well as for a user more interested in fuel economy and/or in green performance. On the other hand, for larger engine size vehicles (>2000 cm3) the combined score for safety user profile was in average more satisfactory than for vehicles in the smaller engine size group (<1400 cm3), which suggests that in general, larger vehicles may offer extra protection. The achieved results demonstrate that the developed SEG integrated methodology can be a helpful tool for consumers to evaluate their vehicle selection through different domains (safety, fuel efficiency and green emissions). Furthermore, SEG indicator allows the comparison of vehicles across different categories and vehicle model years. Hence, this research is intended to support the decision-making process for transportation policy, safety and sustainable mobility, providing insights not only to policy makers, but also for general public guidance
Evaluation of In-Use Fuel Economy and On-Board Emissions for Hybrid and Regular CyRide Transit Buses, October 2012
No full textThe objective of this project was to evaluate the in-use fuel economy and emission differences between hybrid-electric and conventional transit buses for the Ames, Iowa transit authority, CyRide. These CyRide buses were deployed in the fall of 2010.
Fuel economy was compared for the hybrid and control buses. Several older bus types were also available and were included in the analysis. Hybrid buses had the highest fuel economy for all time periods for all bus types. Hybrid buses had a fuel economy that was 11.8 percent higher than control buses overall, 12.2 percent higher than buses with model years 2007 and newer, 23.4 percent higher than model years 2004 through 2006, 10.2 percent higher than model years 1998 through 2003, 38.1 percent higher than model years 1994 through 1997, 36.8 percent higher than model years 1991 through 1993, and 36.8 percent higher for model years pre-1991. On-road emissions were also compared for three of the hybrid buses and two control buses using a portable emissions monitor. On-average, carbon dioxide, carbon monoxide, and hybrid carbon emissions were much higher for the control buses than for the hybrid buses. However, on average nitrogen oxide emissions were higher for the hybrid buses
Assessing uncertainties in traffic simulation: a key component in model calibration and validation
No full textAny opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF)
Modeling Impact of and Mitigation Measures for Recurring Freeway Bottlenecks
No full textRecurrent congestion is a continually growing problem on urban freeways. Facility expansions cannot keep pace with the growing vehicle demand. Low-cost mitigation measures are one way to alleviate the congestion at recurring bottleneck locations. Low-cost measures typically have a life of approximately 10 years and costs ranging from 2.45 million. While benefits have been realized in field applications, there hasn't been a lot of study regarding the performance of these measures in terms of added capacity. While modeling has long been a tool for planning and analyzing freeway networks, there has been little reported regarding its use for estimating the benefits of low-cost freeway improvements. In this study, the author tested proposed treatments at two sites using both a macroscopic and microscopic model. Because empirical performance information of these measures is not available, a quantitative analysis would not be reasonable since confidence in the values reported would be low. Current bottleneck identification methods typically either predict breakdown in real-time, or analyze detector data off-line. In order to identify bottlenecks from recorded aggregated data in an off-line model, criteria were generated to identify active bottlenecks and analyze the models' performance in an empirical and qualitative manner. Application of the criteria has been shown to provide reliable bottleneck identification to the calibrated pre-treatment case and expected results in the post-treatment cases
Calibrating and Validating Deterministic Traffic Models: Application to the HCM Control Delay at Signalized Intersections”, presented at the 84 th Annual Meeting of TRB
No full textAny opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF)
Calibrating and validating deterministic traffic models: Application to the Highway Capacity Manual control delay at signalized intersections
No full textCalibration 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.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
URBAN TRANSPORTATION IN THE PEOPLE\u27S REPUBLIC OF CHINA
No full textChina\u27s rapid modernization has brought urban traffic problems typical of the world\u27s major cities. The article describes how this has occurred with very little auto traffic. Rigorous applications of traffic systems management are being used, but the conflicts between motorized and nonmotorized transit make alleviation of congestion a near impossible task. This article reviews urban transportation demand characteristics and urban transportation system performance, and gives examples of strategies adopted by different cities to meet local needs. The techniques described are as follows: increase the physical capacity of the road system; improve public transportation performance; expand the role of urban rail systems; improve the flexibility of public and private transportation services to meet the needs of both visitors and residents; improve facilities for cyclists; and increase vehicle operator training and education
