Despite the wide application of Floating Car Data (FCD) in urban link travel time and congestion estimation, the sparsity of observations from a low penetration rate of GPS-equipped floating cars ...make it difficult to estimate travel time distribution (TTD), especially when the travel times may have multimodal distributions that are associated with the underlying traffic states. In this case, the study develops a Bayesian approach based on particle filter framework for link TTD estimation using real-time and historical travel time observations from FCD. First, link travel times are classified by different traffic states according to the levels of vehicle delays. Then, a state-transition function is represented as a Transition Probability Matrix of the Markov chain between upstream and current links with historical observations. Using the state-transition function, an importance distribution is constructed as the summation of historical link TTDs conditional on states weighted by the current link state probabilities. Further, a sampling strategy is developed to address the sparsity problem of observations by selecting the particles with larger weights in terms of the importance distribution and a Gaussian likelihood function. Finally, the current link TTD can be reconstructed by a generic Markov Chain Monte Carlo algorithm incorporating high weighted particles. The proposed approach is evaluated using real-world FCD. The results indicate that the proposed approach provides good accurate estimations, which are very close to the empirical distributions. In addition, the approach with different percentage of floating cars is tested. The results are encouraging, even when multimodal distributions and very few or no observations exist.
Despite the wide application of floating car data (FCD) in urban link travel time estimation, limited efforts have been made to determine the minimum sample size of floating cars appropriate to the ...requirements for travel time distribution (TTD) estimation. This study develops a framework for seeking the required minimum number of travel time observations generated from FCD for urban link TTD estimation. The basic idea is to test how, with a decreasing the number of observations, the similarities between the distribution of estimated travel time from observations and those from the ground-truth vary. These are measured by employing the Hellinger Distance (HD) and Kolmogorov-Smirnov (KS) tests. Finally, the minimum sample size is determined by the HD value, ensuring that corresponding distribution passes the KS test. The proposed method is validated with the sources of FCD and Radio Frequency Identification Data (RFID) collected from an urban arterial in Nanjing, China. The results indicate that: (1) the average travel times derived from FCD give good estimation accuracy for real-time application; (2) the minimum required sample size range changes with the extent of time-varying fluctuations in traffic flows; (3) the minimum sample size determination is sensitive to whether observations are aggregated near each peak in the multistate distribution; (4) sparse and incomplete observations from FCD in most time periods cannot be used to achieve the minimum sample size. Moreover, this would produce a significant deviation from the ground-truth distributions. Finally, FCD is strongly recommended for better TTD estimation incorporating both historical trends and real-time observations.
•We examine the impacts of in-vehicle navigation information by driving simulator.•We test four information provision design schemes under three traffic flow status.•Lane-changing characteristics are ...analyzed by selecting six indicators.•In-vehicle navigation has positive impact on safety under medium/high density.•More improvement could be gained when the in-vehicle navigation provided earlier.
Lane-changing behaviors frequently occur at upstream of the urban expressway off-ramp, which possibly cause bottleneck or accident. This paper studies how in-vehicle navigation information impacts lane-changing behavior at this urban expressway diverge segments with comparison to the traditional road signs by conducting a series of driving simulator experiments, in consideration of variation of the first provision time point and traffic flow density. Firstly, the driving simulator is validated by comparing data of lane-changing position and merging gap from both field survey and simulator. Then comparison study was performed for twelve scenarios which comprise four information provision design schemes under three different traffic flow density status. Lane-changing characteristics are analyzed by selecting six indicators, which are lane-changing merging gap, lane-changing position, lane change delay, lane-changing steering angle, lane-changing deceleration, and the safe distance of lane-changing. The results show that the impact of in-vehicle navigation information on lane-changing behavior varies with traffic flow density and the time point of the first navigation information provided. The in-vehicle navigation information had significant positive impact on lane-changing safety under medium to high density condition. However, the effect is not significant under light density condition. Moreover, more improvement in operational safety and smooth could be gained when the in-vehicle navigation information is provided earlier within range of 2km upstream of the exit gore.
Route travel time information is essential for better travel planning, traffic guidance and congestion avoidance. An available way of representing such information is the estimation of travel time ...distribution (TTD). However, most methods both in literature and practice prefer to estimate route mean travel times rather than TTDs, especially with less consideration about the spatiotemporal correlations between adjacent links. This study develops a framework of estimating urban route TTD based on Markov chain approach and pair-copula construction with emphasis on capturing the dependence in time and space. The proposed method is validated with Radio Frequency Identification Data collected from an urban arterial in Nanjing, China. The results indicate that the proposed method can dynamically capture the positively correlated, negatively correlated, and uncorrelated relationships between adjacent link travel times. Moreover, the performance of the proposed method produces the least deviation from the route empirical distributions, compared to the considered competing methods.
A new model for variable speed limit in freeway work zone was presented. Model predictive control was applied to optimizing variable speed limit in freeway work zone. The classic macroscopic traffic ...model METANET was a little modified for simulating the traffic in the work zone, considering the effect of speed limit. One new optimization model for solving the optimal variable speed was proposed, which is a real-time nonlinear controlling model. In the optimization model, the objective function considers efficiency and safety by minimizing the total time spent (TTS) and the speed variation. To solve this optimization model, discretization for time horizon was conducted firstly; on every control time step, SQP algorithm was applied to solve the nonlinear programming in the next; the optimization results were integer conversion for the real speed limit displayed. One example was conducted to prove the efficiency of the proposed model. And some valuable conclusion was obtained.
•We test two groups of drivers having different familiarity on EFL intersections.•We examine drivers’ response to EFL intersections by driving simulator.•Drivers are confused with an EFL intersection ...when confronted for the first time.•The EFL intersection does not cause higher safety risk to unfamiliar drivers.•Drivers gain familiarity from education, traffic signs and guiding vehicles.
With the worsening of urban traffic congestion in large cities around the world, researchers have been looking for unconventional designs and/or controls to squeeze more capacity out of intersections, the most common bottlenecks of the road network. One of these innovative intersection designs, known as the exit-lanes for left-turn (EFL), opens up exit-lanes to be used by left-turn traffic with the help of an additional traffic light installed at the median opening (the pre-signal). This paper studies how drivers respond to EFL intersections with a series of driving simulator experiments. In our experiments, 64 drivers were recruited and divided into two groups. One group is trained to use the EFL while the other group is not. In addition, four scenarios were considered with different sign and marking designs and traffic conditions in the experiments. Results indicate that drivers show certain amount of confusion and hesitation when encountering an EFL intersection for the first time. They can be overcome, however, by increasing exposure through driver education or by cue provided from other vehicles. Moreover, drivers unfamiliar with EFL operation can make a left turn using the conventional left-turn lanes as usual. The EFL operation is not likely to pose any serious safety risk of the intersection in real life operations.
Advanced Traveler Information System (ATIS) is a crucial part of Intelligent Transportation System (ITS) and Pre-trip Traveler Information System is an indispensable component of ATIS. In China, the ...current theoretical research and practical application of Pre-trip Traveler Information System is only at the beginning stage. The research preliminarily investigated the relationship between urban travelers' personal attributes and propensity to utilize Pre-Trip Traveler Information System with data collected from Travel Willingness Survey and Household Travel Survey in Zhongshan, 2009. The extent of impacts of five personal attributes on the propensity to utilize Pre-trip Traveler Information System was determined. The research found out that in China middle-aged (30-50) male travelers commuting by motorized modes with middle or high income have highest propensity to utilize Pre-Trip Traveler Information System. Young (age less than 20) female jobless travelers are least potential users. The findings will enrich the theoretical research of related areas and support the system design and supply strategy of Pre-Trip traveler Information System in China.
Travel efficiency and traffic safety of unsignalized intersections are two main objectives considered in traffic management and control. Stop sign and yield sign are the most common traffic signs to ...display the right of the way for all direction vehicle flows of unsignalized intersections. While in most cities in China, signalized control are always adopted for all intersections without considering level of traffic flow volume. This paper analyzes the difference between the stop sign intersection and yield sign intersection from the aspects of delay analysis. Firstly, intersections are designed in VISSIM software and traffic flow performance is validated via VISSIM. Then average vehicular delay under different traffic volumes is analysed under stop sign and yield sign respectively. Taking the lowest delay as the optimal objective, the critical traffic volume is proposed to set stop sign or yield sign. The results can be used in practice to guide the installation of traffic signs.
When different drivers received the same traffic condition information through VMS (Variable Message Sigh), they may image the real traffic situation differently due to their dissimilar individual ...characteristics. Ignoring this dissimilarity and blindly supplying the same traffic condition information to all travelers cause VMS hard to supply high reliable information. This low reliability would induce travelers more likely to ignore what has been told by VMS. In this paper, a model was established to demonstrate the relationship between traffic-condition-division-speed and information-receivers' individual identities including gender, age, driving years, familiarity with road network and trip purpose. Then with the help of multi-agent simulator-SeSAm, a new model for supplying individual traffic condition information and simulating driverspsila route choice behavior was established. It has been proved that providing individual information can significantly enhance the reliability of traffic condition information which leads to a dynamic flow balance more quickly than before.
Traffic state estimation is a key problem with considerable implications in modern traffic management. A simple, general, and complete approach to the design of urban network traffic state and phase ...estimator has been developed in this paper. A uniform traffic state dynamic estimation method structure is designed which consists of three steps. (1) Floating-car data and radio frequency identification data preprocessing method is proposed to remove the abnormal data and finish the map matching process. (2) Section speed estimation method is proposed based on the degree of confidence. (3) Traffic phase identification method is proposed based on the estimated section speed. A number of simulation and field investigations have been conducted to test the estimator performance. The investigation results indicate that the proposed approach is of high accuracy and smoothness on the section speed estimation and effectively eliminates the influence of abnormal data fluctuations and insufficient data. And the traffic phase identification method can effectively filter out the abnormal distortion of estimated section speed around the threshold value and modify the phase step of traffic status caused by abnormal data.
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