Prakash Ranjitkar

Multiple Car-Following Data with Real-Time Kinematic Global Positioning System

The real-time kinematic differential Global Positioning System (GPS) has facilitated a new horizon in traffic engineering. Multiple car-following experiments conducted with a real-time kinematic GPS with 10 vehicles participating in a probing field gave high-quality results in headway, speed, relative speed, and acceleration. The expected accuracies for measuring position and speed were 10 mm and 0.16 km/h, respectively. The vehicles were driven in a loop consisting of two parallel straight sections connected by two semicircular curves. Different driving conditions were induced in the platoon by instructing the leading driver to follow predetermined speed variations. The experiments yielded sets of continuous observations. Headway, speed, and acceleration were measured using conventional equipment for the purpose of comparing accuracy. The accuracy of the data obtained using the GPS was superior to that of the same data obtained using conventional measurements. The variation in driving characteristics down the stream of vehicles was studied using the experimental data. The results showed that the reaction time between a change in relative speed and the corresponding change in acceleration varies during the driving process. The reaction time of individual drivers also changes along the platoon. The good-quality data were able to give high-resolution plots of acceleration and relative speed illustrating that both the reaction time and the functional relationship between acceleration and relative speed do not remain constant.

Stability Analysis Based on Instantaneous Driving Behavior Using Car-Following Data

An attempt is made to analyze the stability of a platoon using experimental data measured by real-time kinematic (RTK) Global Positioning System (GPS) receivers. Car-following experiments were conducted on a test track using 10 passenger cars. Various speed patterns were tested for the lead car, including random, constant, and sinusoidal, giving different driving conditions. The responses of the following drivers were measured by RTK GPS receivers in each car. The stimulus–response car-following concept was examined, assuming that the reaction time might vary over time. A graphical method was modified to estimate the time-variant reaction time more efficiently. A new algorithm was proposed to estimate the sensitivity factor using Lissajou’s diagram between relative speed and acceleration. The statistical analysis showed that intrapersonal variability was higher than interpersonal variability for both reaction time and sensitivity factor. However, the influence of the driver’s position in the platoon and speed patterns was low. It was found that the reaction time was distributed in a lognormal function for most of the drivers. The variations in the estimated values for the sensitivity factor were relatively high. The stability analysis showed that the average responses of drivers were unstable both locally and asymptotically. The influence of speed fluctuation frequency was found insignificant for the stability of the platoon.

Bus Dwell Time Modeling Using Gene Expression Programming

A gene expression programming (GEP)-based approach that shows prospects how to estimate bus dwell time (BDT) more accurately and overcome some of the issues associated with the multiple linear regression (MLR) method is proposed in this article. The model is calibrated and validated using the data collected from 22 bus stops in Auckland and compared against the MLR model based on five different performance measures: mean error, mean absolute error, root mean square error, mean absolute percentage error, and R² value. The restrictions to stick with a predefined model and the need to satisfy assumptions made on multicollinearity, homoscedasticity, and the normality of random error are often difficult to satisfy.

Integrated Approach Combining Ramp Metering and Variable Speed Limits to Improve Motorway Performance

Ramp metering (RM) and variable speed limits (VSLs) are two widely used intelligent transportation system (ITS) means to improve and manage motorway traffic. The former controls the flow of traffic into motorways from on-ramps, and the latter affects the speed of traffic on the motorway main line. An integrated approach to the prudent use of these two ITS measures can help to achieve optimal utilization of motorways. This study proposed a new method to integrate RM with VSL controllers to attain an efficient and equitable motorway system. The proposed method was used to combine a local and a coordinated RM strategy, namely ALINEA and Heuristic Ramp Metering Coordination (HERO), with VSLs. The method developed was assessed with a case study in Auckland, New Zealand. The analysis of the case study was based on a critical bottleneck section of Auckland Motorway by using the AIMSUN microsimulator. The outcome performance was assessed in relation to the efficiency and equity of the motorway system. The efficiency was measured by total vehicle travel time, average number and duration of stops, and emission levels; the equity of the motorway system was measured by the Gini coefficient. The main results were that the modified VSLs and the HERO + VSL control scenarios outperformed all other control scenarios in improving vehicular emissions, total travel time, and the equity measure, respectively. This outcome provides prospects for the developed method.

Virtual Traffic Lights+: A Robust, Practical, and Functionally Safe Intelligent Transportation System

The latest advancements in intelligent transportation systems (ITSs) increasingly rely on wireless vehicle-to-vehicle (VTV) and vehicle-to-infrastructure (VTI) communications to manage traffic flows at intersections dynamically. A prominent example is virtual traffic lights (VTLs), which use only VTV communications and which have been shown to have the potential to increase traffic flows and reduce emissions significantly. Two key issues that can affect the adoption of desirable ITS solutions like VTLs are functional safety and the management of a move from a vehicle fleet not equipped with VTLs to a vehicle fleet completely equipped with VTLs. For the first issue, the first model-driven engineering-based modeling and verification technique for ITSs is proposed. This technique can be used to prove functional safety with 100% coverage. Through the use of this technique, it is shown that although VTLs are safe under normal circumstances, they are very fragile when they face unlikely, but not impossible, exceptional circumstances. For the second issue, an extended algorithm called VTL+ is proposed. VTL+ uses additional VTI communication with the existing infrastructure to enable effective and safe traffic flow during the VTL transition phase. It is also found through static analysis that VTL+ is more robust and more feature rich than VTLs.

Asymptotic Stability and Vehicle Safety in Dynamic Car-Following Platoon

A vehicle in a platoon sometimes faces the risk of causing a rear-end collision when it is following a vehicle in front. The stability theory of the well-known General Motors car-following models says that the fluctuations of vehicle speeds and headways will increasingly propagate to the rear vehicle in a platoon if the platoon is asymptotically unstable. However, almost no research has been done to validate this phenomenon with the real car-following platoon data. Therefore, the car-following platoon data, including 10 vehicle trajectories, were used to evaluate asymptotic stability in the platoon. The asymptotic stability in vehicle safety is evaluated on the assumption that the vehicle in the rear position is exposed to riskier conditions than the vehicle positioned in front because of the shorter headways created by increased fluctuations of speeds and headways in a platoon if the asymptotic stability is unstable. Three indicators for safety are defined: potential danger time, impact speed, and expected impact speed. The outcomes in these safety indicators did not show that the car-following platoon was in asymptotically unstable conditions. Therefore, two supplemental indicators were defined to closely observe asymptotic stability: maximum speed amplitude and maximum spacing amplitude. These stability indicators were used to explain that the car-following platoon was under asymptotically unstable conditions. As a result, a hidden aspect of the relationship between asymptotic stability and vehicle safety was discovered in the real car-following platoon.

Modeling Bus Dwell Time with Decision Tree–Based Methods

A large proportion of transit travel time is made up by dwell time for passengers boarding and alighting. More accurate modeling and estimation of bus dwell time (BDT) can enhance the efficiency and reliability of the public transportation system. Multiple linear regression (MLR) has been the most commonly used method in the literature for modeling and estimating BDT. However, the underlying assumptions of the MLR method, such as multicollinearity and normality of random error, cannot always be satisfied for real applications. This study developed and implemented two methods based on decision trees (DTs), namely, classification and regression tree and chi-squared automatic interaction detector, for the first time for BDT modeling and estimation. The models were compared with the traditional MLR model after calibrating and validating the new models against the data collected from four bus stops in Auckland, New Zealand. Various error measurements were used to evaluate the accuracy of the models. The DT-based methods eliminated the limitations of the MLR method and provided reliable and accurate estimation of BDT.

Mixed-Criticality Systems as a Service for Non-critical Tasks

Mixed-Criticality Systems are capable of accommodating tasks of varying criticality. In this paper, these are [life, mission, and non-critical]. Tasks usually have an overestimated execution time to allow for the Worst Case Execution Time (WCET). When these tasks finish execution prior to their allotted execution time due to pessimistic assumptions present in the static analysis of the system. The surplus time is used to accommodate tasks with tolerance for deadline-misses. Non-critical tasks are often treated in a ”best-effort” capacity where no quality of service is considered. When processor utilisation is not overconstrained, all deadlines will be met. However, in cases where not enough processing resources exist to meet all deadlines for non-critical tasks, the allotted time for the non-critical tasks must be rationed between non-critical tasks. This paper proposes a novel method of prioritising non-critical tasks. By treating task execution as a service, non-critical tasks with unbounded deadline miss tolerance are given a Grade of Service for their met deadlines. This Grade of Service is used for the dynamic scheduling of non-critical tasks. Four different scheduling algorithms were tested with the proposed Highest Penalty First algorithm for distributing the effort of task execution amongst non-critical tasks in a proportionate manner and showing superior fairness of task execution compared to all other tested algorithms.

Fairness-Based Measures for Safety-Critical Vehicular Ad-Hoc Networks

Transmission timing and delay between communicating vehicles are two important performance measures for safety-critical applications of Vehicular Ad-Hoc Networks (VANETS). Safety-Critical VANETS are composed of multiple nodes each requiring access to a shared communication medium. This access is controlled by the Medium Access Control (MAC) protocol. Numerous MAC protocols have been proposed for VANETS, each with varying degrees of reliability and fairness. A general measure for fairness is required in order to compare different protocols using the same criteria, however, finding a quantifiable measure for fairness is not a simple task and any developed quantifiable measure is application-specific. In this paper, we investigate different measures of fairness, particularly the Jain Index and the Gini Coefficient. We apply these measures to experimental environments in ns-3 to contrast the different fairnesses of three MAC protocols: CSMA/CA, TDMA, and STDMA. It became evident, after experimentation, that the Gini Coefficients obtained from these experiments would vary between iterations and the limits of these variances were uncertain. Therefore we derive a formula which allows a theoretical limit to be placed on the unfairness of a system based on its upper and lower bounds of delay. This formula is not only relevant to VANETs but to any network. The work in this paper is applicable to any discipline wishing to measure the theoretical worst case fairness of a population.

Evaluating Operational Performance of Intersections using SIDRA

Traffic congestion has significant social, economic and environmental costs associated with it. Efficiency of intersections contributes significantly towards the efficiency of whole urban road networks as they are the main bottlenecks in the system. This paper presents a comparative analysis of the operational efficiency of priority controlled, roundabout and signalised intersections under a range of traffic conditions with different volume and turning ratios using SIDRA software. We used three measures to represent the operational efficiency namely: intersection capacity, average delay and total emissions. The analysis revealed strengths and weaknesses of each intersection types under a range of demand and traffic conditions. At low traffic demand, priority controlled intersections outperformed the other two forms of intersection control. At moderate traffic demand, roundabout performed the best while at high traffic demand, signalised intersections performed the best.