Showing papers in "Journal of Transportation Engineering-asce in 2009"

Transit Route Network Design Problem: Review

Abstract: Efficient design of public transportation networks has attracted much interest in the transport literature and practice, with many models and approaches for formulating the associated transit route network design problem (TRNDP) having been developed. The present paper systematically presents and reviews research on the TRNDP based on the three distinctive parts of the TRNDP setup: design objectives, operating environment parameters and solution approach.

Crash Injury Severity Analysis Using Bayesian Ordered Probit Models

Abstract: Understanding the underlying relationship between crash injury severity and factors such as driver's characteristics, vehicle type, and roadway conditions is very important for improving traffic safety. Most previous studies on this topic used traditional statistical models such as ordered probit (OP), multinomial logit, and nested logit models. This research introduces the Bayesian inference and investigates the application of a Bayesian ordered probit (BOP) model in driver's injury severity analysis. The OP and BOP models are compared based on datasets with different sample sizes from the 2003 National Automotive Sampling System General Estimates System (NASSGES). The comparison results show that these two types of models produce similar results for large sample data. When the sample data size is small, with proper prior setting, the BOP model can produce more reasonable parameter estimations and better prediction performance than the OP model. This research also shows that the BOP model provides a flexible framework that can combine information contained in the data with the prior knowledge of the parameters to improve model performance.

Dynamic Tolling Strategies for Managed Lanes

Abstract: This paper proposes two sensible approaches that may be potentially implemented in practice to determine pricing strategies for operating managed toll lanes. The tolls vary dynamically in response to real-time traffic conditions in order to provide a superior free-flow travel service to the users of the toll lanes while maximizing the freeway’s throughput. Simulation experiments are conducted to validate and compare the proposed approaches.

Climate Change Implications for Flexible Pavement Design and Performance in Southern Canada

Abstract: Two types of analysis were conducted to examine the impacts of midcentury scenarios of anthropogenic climate change on flexible pavement infrastructure in southern Canada. An analysis of deterioration-relevant climate indicators at 17 southern Canadian sites revealed that over the next 50 years low temperature cracking will become less problematic, structures will freeze later and thaw earlier with correspondingly shorter freeze season lengths, and higher extreme in-service pavement temperatures will raise the potential for rutting. Pavement performance simulations conducted using the mechanistic-empirical pavement design guide and data from the Canadian long term pavement performance program for six of these sites also suggest that rutting issues will be exacerbated by climate change and that maintenance, rehabilitation, or reconstruction will be required earlier in the design life. While the simulated effect of climate change was found to be modest, both in absolute terms and relative to variability in pavement structure and baseline traffic loads, pavement engineers would benefit by incorporating longer time series of weather and climate in their designs. Although the analysis was conducted for southern Canada, many of the findings and impacts may be similar for the northern United States.

Highway Project Level Life-Cycle Benefit/Cost Analysis under Certainty, Risk, and Uncertainty: Methodology with Case Study

Abstract: One of the key steps in the highway investment decision-making process is to conduct project evaluation. The existing project level life-cycle cost analysis approaches for estimating project benefi...

Highway Work Zone Risk Factors and Their Impact on Crash Severity

Abstract: Numerous factors may contribute to high-severity crashes in highway work zones. Identifying these factors and then alleviating their impact is a challenging task that traffic engineers and researchers have to confront. In this study, the work zone risk factors that could increase the probability of causing fatalities when severe crashes occur were examined using a comprehensive approach. The researchers first identified the significant risk factors based on a screening process that incorporates both statistical analyses and empirical research findings. They then systematically investigated these factors using logistic regression and frequency analysis techniques. The severe crashes including the fatal crashes between 1998 and 2004 and injury crashes between 2003 and 2004 in Kansas highway work zones were used in the study. The assessed risk factors included variables describing driver characteristics, environmental conditions, crash road conditions, and other crash information. The results of this study will help traffic engineers to understand these risk factors and how the factors could increase the likelihood of having fatalities when a severe crash occurs in a work zone. Consequently, effective safety countermeasures may be designed at the work zone planning and installation stages to prevent safety deficiencies.

Pavement Preservation Optimization Considering Multiple Objectives and Budget Variability

Abstract: Pavement preservation programming often involves multiple objective considerations. Traditional single-objective optimization frameworks consider one single objective while imposing competing objectives as constraints in the optimization formulation. This paper proposes an approach for pavement preservation programming that uses multiobjective optimization and chance constraints. This approach can handle multiple incommensurable and conflicting objectives while considering probabilistic constraints related to the available budget over the planning horizon. The implementation of the approach in a case study with two conflicting objectives of: (1) maximizing the network level of service in terms of weighted average state condition; and (2) minimizing the total preservation cost, shows that its application provides a practical and flexible tool to determine optimal allocation of resources for pavement preservation that reflects agency goals, resource limitations, and performance targets.

Evaluating the Cost Effectiveness of Flexible Rehabilitation Treatments Using Different Performance Criteria

Abstract: At a certain point in the life of a flexible pavement, rehabilitation is required to improve pavement condition and to defer reconstruction. Pavement managers seek the best rehabilitation treatment on the basis of cost effectiveness. Using 1994–2002 data from a wet-freeze mid-Western state in the United States, this paper analyzes the cost effectiveness of four flexible pavement rehabilitation treatments: functional hot-mix asphalt (HMA) overlay, structural HMA overlay, resurfacing (partial 3R standards), and mill full-depth and asphaltic concrete overlay. The performance indicator used is the international roughness index and treatment effectiveness is measured in terms of performance jump (short-term), and service life and increase in pavement performance (long-term). The treatment cost is the equivalent uniform annual cost per lane-km incurred by the agency and user; and cost effectiveness is the ratio of effectiveness to cost. The study estimated treatment effectiveness under various combinations of traffic loading and climatic condition, and initial pavement condition. The results suggest that in the short-term, HMA structural overlay is the most effective treatment. For the long-term, the results are equivocal: HMA structural overlay is most effective from the perspective of average performance over the treatment life; resurfacing (partial 3R standards) is the most effective from the perspective of treatment service life. With regard to cost effectiveness, however, the results were consistent: for all three measures of treatment effectiveness, mill full-depth and asphaltic concrete overlay unequivocally appears to be the most cost effective treatment. Finally, the paper recommends that cost effectiveness analysis should be accompanied by a candid deliberation of project constraints, the local environment, and agency practices.

Repeated Creep Behavior of Polypropylene Fiber-Reinforced Bituminous Mixtures

Abstract: In recent years, research has been devoted to the control of permanent deformations in flexible pavements. In order to prevent rutting, fatigue, and low-temperature cracking, different types of polymer modifiers have been utilized. The use of polypropylene (PP) fibers as a modifier in pavement mix that can be found locally and at low cost compared to other modifiers is an attractive option. This paper reports on the Marshall design and the optimum bitumen content for asphalt concrete with the addition of polypropylene fibers. Different types of PP fibers were used in order to determine the optimum bitumen content and the optimal PP fiber dosage. Marshall specimens were tested using the universal testing machine to determine the creep behavior of dense bituminous mixtures under repeated loading. The results from the analysis of the tested specimens show that the addition of polypropylene fibers improves the behavior of the specimens by increasing the life of samples under repeated creep testing.

Multivariate Traffic Forecasting Technique Using Cell Transmission Model and SARIMA Model

Abstract: The paper develops a short-term space-time traffic flow forecasting strategy integrating the empirical-based seasonal autoregressive integrated moving average (SARIMA) time-series forecasting technique with the theoretical-based first-order macroscopic traffic flow model—cell transmission model. A case study in Dublin city center which has serious traffic congestion is performed to test the effectiveness of the proposed multivariate traffic forecasting strategy. The results show that the forecasts at the junctions only deviate around 10% at a maximum from the original observations and seem to indicate that the proposed strategy is one of the effective approaches to predict the real-time traffic flow level in a congested network especially at the locations where no continuous data collection takes place.

Potential Applications of Nanotechnology in Pavement Engineering

Abstract: Nanotechnology is the term used to cover the design, construction, and utilization of structures with at least one dimension measured in nanometers. Compared with typical civil engineering structures, the two fields operate on hugely divergent dimensional scales. Nanotechnology initially developed in the fields of physics and chemistry, and most fundamental developments still occur in these fields. However, for the technology to affect society at large, it needs to be applied in areas such as the engineering field. This paper focuses specifically on current and potential developments in pavement engineering where the unique properties of nanomaterials may be used to deliver a better environment to society, based on identified needs and challenges in the pavement engineering field. It is demonstrated that there are essentially two areas where nanotechnology can complement pavement engineering. These are in the development of improved materials and the use of characterization methods to improve the understanding of materials. Examples of current and planned research in these areas are cited and discussed. Finally, current challenges in exploiting the unique properties of nanomaterials in pavement engineering are indicated and discussed. The paper demonstrates that although the majority of the fundamental developments in nanoscale science and technology are occurring in the fundamental physics, chemistry, and typically electronic engineering fields, the potential for this technology to impact on the quality of life of society at large is huge.

Traffic Data Collection under Mixed Traffic Conditions Using Video Image Processing

Abstract: Traffic data collection under mixed traffic conditions is one of the major problems faced by researchers as well as traffic regulatory authorities. Study and analysis of traffic behavior is critically dependent on the availability of observed traffic data. For mixed traffic observed in developing countries, no suitable tool is available for this purpose. Keeping in view these necessities and problems in data collection, a novel offline image processing-based data collection system, suitable for mixed traffic conditions, is developed. Its underlying ability to detect, track, and classify vehicles makes it useful in collecting traffic data under varying traffic conditions. This system can automatically analyze traffic videos and provide macroscopic traffic characteristics such as classified vehicle flows, average vehicle speeds and average occupancies, and microscopic characteristics such as individual vehicle trajectories, lateral, and longitudinal spacing. It is observed that this new system is working well even under congested mixed traffic conditions.

Data Envelopment Analysis as a Decision-Making Tool for Transportation Professionals

Abstract: Data envelopment analysis (DEA) is a mathematical method based on production theory and the principles of linear programming It enables one to assess how efficiently a firm, organization, agency, or such other unit uses the resources available (inputs) to generate a set of outputs relative to other units in the data set Recent papers by different writers present different applications of DEA in the transportation engineering domain All of these papers are published in transportation journals These papers are mainly aimed at addressing the transportation-related issues and thus do not focus too much on the DEA concept itself It can be asserted that DEA is very likely to be used more and more in the transportation engineering domain Given this, there is a need for the transportation professionals to fully understand the DEA concept It is essential for such a community to identify cases where the application of this innovative and powerful method can be useful to help the decision-making process, to accurately apply DEA in a particular setting, to derive meaningful conclusions from the obtained results, and to acknowledge the limitations of DEA in certain cases so as to approach the results with caution The purpose of this paper is to illustrate to the civil engineering, more specifically to the transportation engineering community the use of this powerful approach in performing comparative performance measurement Within this context, this paper will address a transportation-related problem by using the DEA approach Different from the other papers containing transportation-related DEA applications (as mentioned above), this paper will discuss, in detail, the steps that need to be taken to generate the DEA model and solve it

Simulation of Dynamic Effects of Vehicles on Pavement Using a 3D Interaction Model

Abstract: The present study formulated a three-dimensional (3D) vehicle-pavement coupled model to simulate the pavement dynamic loads induced by the vehicle-pavement interaction where both the vehicle vibration and pavement deformation were considered. Based on this model, the effects of road surface conditions, vehicle parameters, and driving speed on pavement dynamic loads were analyzed. The impact factor, dynamic load coefficient, and frequency distribution of pavement loads were mainly concerned in this study. The simulated results indicated that under rough road conditions the dynamic loads of vehicles are significantly higher than the static loads. The developed methodology can be used to further study the vehicle-induced pavement response, and the loading information will be useful in analyzing vehicle-induced pavement damage.

Artificial Neural Network Approach to Estimating Stiffness Behavior of Rubberized Asphalt Concrete Containing Reclaimed Asphalt Pavement

Abstract: Accurately predicting the stiffness of asphalt pavements is difficult due to the complex behavior of materials under various loading, pavement structure, and environmental conditions. This study explores the utilization of the artificial neural network (ANN) in predicting the stiffness behavior of rubberized asphalt concrete mixtures with reclaimed asphalt pavement (RAP). A total of 296 asphalt mixture beams were constructed from two different rubber types (ambient and cryogenic), two different RAP sources, and four rubber contents (0, 5, 10, and 15%). All samples were tested at two different testing temperatures of 5 and 20°C. The regression statistical method was used to predict the stiffness behavior of these mixtures via the 7 input variables covering the material engineering properties of the asphalt beams. In addition, the data were organized into 5 independent variables and one dependent variable (the stiffness values of the modified mixture beams) in ANN models. Results showed the ANN techniques to be more effective in predicting the fatigue life of the modified mixture than traditional regression-based prediction models.

Right Turns on Green and Pedestrian Level of Service: Statistical Assessment

Abstract: Traditional pedestrian level of service measures at signalized intersections are based on pedestrian space and pedestrian delay. However, these measures may not adequately reflect the negative impact of right-turning traffic on pedestrians. This paper presents a statistical analysis using a binary logit model that provides new insights into the factors that affect the likelihood that a pedestrian is compromised (delayed, altered their travel path, or altered their travel speed) in response to traffic turning right (on green) during concurrent vehicle/pedestrian signal timing. The statistical analysis indicates that a number of factors affect the likelihood of a pedestrian being compromised including pedestrian direction of travel, right-turn traffic volume, number of pedestrians crossing, whether the pedestrian arrived late and began crossing after the end of the walk interval, and the crosswalk characteristics including location (downtown versus suburban) and one-way/two-way streets.

Optimization Method for Highway Horizontal Alignment Design

Abstract: This research presents an optimization heuristic to solve the horizontal alignment of a highway segment. The iterative heuristic works in two stages. The first stage uses a neighborhood search approach to find a good piecewise linear line that approximates the highway alignment. The second stage further adjusts the alignment so that the external and code requirements are accurately satisfied. Both stages manipulate the piecewise linear line with a neighborhood search heuristic, and use a mixed integer program (MIP) to ensure that the piecewise linear line crosses the control areas and avoids the restricted ones. The optimal objective function value returned by the MIP is used to compare the quality between different piecewise linear lines. The lengths of each line segment are properly constrained in the MIP to ensure that curves can be correctly deployed. Starting from an initial feasible solution the process gradually improves the alignment through iterations. Computational examples are provided.

Capacity Expansion Problem for Large Urban Transportation Networks

Abstract: A traffic network design problem attempts to find optimal network expansion policies under budget constraints. This can be formulated as a bilevel optimization problem: the upper level determines the optimal link capacity expansion vector and the lower level determines the link flows subject to user equilibrium conditions. The upper level is a capacity expansion problem which minimizes the total system cost and can be solved using any optimization algorithm. In the present study, genetic algorithm (GA) is used in the upper level because of its modeling simplicity and ability to handle large problems. The proposed model is first applied to a small sized network and then to a medium sized test network and the results are compared with other existing solution approaches. The sensitivity analysis of the model is performed by designing the networks at different demand levels. The resilience of the solution when demand increases the design demand is also carried out. Finally, the network design for the city of Pune, India was taken as a case study. This is a large sized network having 1,131 links and 370 nodes. The capacity expansion is carried out under various budget scenarios and the results are discussed. This study shows the potential of GA to obtain a high quality solution for large network design problems.

Finite-Element Modeling of Instrumented Flexible Pavements under Stationary Transient Loading

Abstract: Results from a finite-element program developed in the commercial code Plaxis were compared to those from an instrumented thin flexible pavement containing multiple test sections. The model has performed reasonably well under the limited environmental conditions encountered to date. Horizontal strain in the longitudinal direction of the asphalt concrete, vertical pressure in the crushed stone, and vertical pressure in the compacted subgrade were measured for 2,100 passes of loaded single axle dump truck traffic to compare to the values calculated in the model. Necessary inputs were determined using a rigorous laboratory testing program, alongside field data from over 500 drops of a falling weight deflectometer. Key features of the finite-element model include stationary transient loading and nonlinear stress dependent characterization of the compacted subgrade and crushed stone. Highlights of the results include the model moderately overpredicted unbound layer stresses, while overpredicting asphalt strain in some cases and underpredicting it in other cases, Discussion of the full scale test section, project scope, finite-element model development, and the results have been included in the body of the paper.

Load Transfer Characteristics of Dowel Bar System in Jointed Concrete Pavement

Abstract: In a jointed concrete pavement, the dowel bar system and the aggregate interlock are two mechanisms for transferring wheel loads from one panel to the adjacent panel. The aggregate interlocking load transfer mechanism is effective for narrow joints while the dowel bar system works well for both narrow and wider joints. This paper examines the effects of different parameters on load transfer efficiency of a joint with the help of a three-dimensional finite-element model for the analysis of a dowel-jointed concrete pavement. The model was compared using experimental data available in the literature. The group action of the dowel bar system was also examined and useful relationships have been developed for estimation of the relative load shared by the individual dowel bars. These relationships will be useful in the design and evaluation of dowel jointed concrete pavements.

Pedestrian and Vehicle Flow Calibration in Multimodal Traffic Microsimulation

Abstract: This paper provides a method for including pedestrians in a vehicle microsimulation model, specifically the VISSIM model. VISSIM provides a default mechanism for simulating pedestrian movements; however, this does not adequately replicate pedestrian behavior. We instead define pedestrians as vehicles and calibrate various parameters within VISSIM so that pedestrian behavior is calibrated with pedestrian speed-flow models. We validate and refine these parameters using a real traffic network with high levels of pedestrian traffic crossing at signalized junctions. This work demonstrates the feasibility of modeling vehicle-pedestrian interactions in a realistic manner and provides analysts with a tool for evaluating policies that affect both vehicle and pedestrian flows.

Comparison of Cyclic Triaxial Behavior of Unbound Granular Material under Constant and Variable Confining Pressure

Abstract: Cyclic stresses due to passing wheels impose an accumulation of permanent strains in layers of unbound granular materials (UGMs) of flexible pavements. The hollow cylinder triaxial test would be the most appropriate test to simulate the in situ stress conditions but it is difficult to perform on UGMs due to their large maximum grain size. The simpler axisymmetric cyclic triaxial test does not consider the shear stress components. It can be performed with a constant confining pressure (CCP) or a variable confining pressure (VCP). CCP and VCP tests are commonly assumed to deliver similar residual and resilient strains as long as the average stress is the same. Thus, the simpler CCP test is mostly used in pavement engineering. However, this assumption is based on limited test data in the literature and may not be on the safe side. The present paper documents a comparative study of CCP and VCP tests on UGM. The study is mainly dedicated to the permanent deformations. The results show that only for some special stress paths do both types of tests deliver similar permanent axial or volumetric strains. For some other stress paths the CCP tests may underestimate the permanent axial strain in comparison to the corresponding VCP test.

Improved Flow-Based Travel Time Estimation Method from Point Detector Data for Freeways

Abstract: Travel time is an important parameter in evaluating the operating efficiency of traffic networks, in assessing the performance of traffic management strategies, and as input to many intelligent transportation systems applications such as advanced traveler information systems Travel time can be obtained directly from instrumented test vehicles, license plate matching, probe vehicles etc, or from indirect methods such as inductance loop detectors Because of the widespread deployment of loop detectors, they are one of the most widely used inputs to travel time estimation techniques There are different methods available to calculate the travel time from loop detector data, such as extrapolation of the point speed values, statistical methods, and models based on traffic flow theory However, most of these methods fail during the transition period between the normal and congested flow conditions The present study proposes several modifications to an existing traffic flow theory based model for travel time

Kalman Filter Approach to Speed Estimation Using Single Loop Detector Measurements under Congested Conditions

Abstract: The ability to measure or estimate accurate speed data are of great importance to a large number of transportation system operations applications. Estimating speeds from the widely used single inductive loop sensor has been a difficult, yet important challenge for transportation engineers. Based on empirical evidence observed from sensor data collected in two metropolitan regions in Virginia and California, this research developed a Kalman filter model to perform speed estimation for congested traffic. Taking advantage of the coexistence of dual loop and single loop stations in many freeway management systems, a calibration procedure was developed to seed and initiate the algorithm. Finally, the paper presents an evaluation that illustrates that the proposed algorithm can produce acceptable speed estimates under congested traffic conditions, consistently outperforming the conventional g-factor approach.

Aggregate Fuel Consumption Model of Light-Duty Vehicles for Evaluating Effectiveness of Traffic Management Strategies on Fuels

Abstract: The primary objective of this research is to develop a practical model for evaluating the effects of traffic management on fuel efficiency. The relationships between the real-world driving activities, the vehicle specific power, and the corresponding fuel consumptions are analyzed based on the data of 26 gasoline and liquefied petroleum gas-fueled light-duty vehicles (LDVs). Then, an indicator for evaluating the level of fuel consumption is designed by dividing the normalized fuel consumption by the fuel use in the most economic scenario. An aggregate model is developed following the design of the indicator that features minimal input requirement and meaningful output for LDVs. In the case studies, the proposed model is applied to estimating and comparing the fuel efficiency of several driving cycles, evaluating the fuel efficiency improvement resulting from the electronic toll collection system, and developing temporal variations of fuel efficiency for a road in Beijing by using floating car data. Finally, the merits of the proposed model are discussed, and the limitations and recommendations are provided for further model improvement.

Experience with Cable Median Barriers in the United States: Design Standards, Policies, and Performance

Abstract: A review of the experience of 23 states on the use and effectiveness of cable median barriers is presented. As of 2007, 23 states have installed more than 4,183 km (2,600 mi) of cable median barriers. Experiences of the pioneering states, such as New York, Missouri, Washington, Oregon, North Carolina and Arizona that initiated the utilization of cable median barrier in the United States are included in this paper. Results of the review show that the use of cable median barriers in depressed medians with moderate slopes had a significant effect on the reduction of cross-median crashes in many states. While these results are encouraging, occasional fatal crossover crashes penetrating the cable barrier still demand attention and improved techniques or procedures for selecting or locating cable median barrier will continue to evolve.

Simulation-Based Investigation on High-Occupancy Toll Lane Operations for Washington State Route 167

Abstract: High-occupancy toll (HOT) lane operation has been implemented in several urban areas in the United States and is regarded as one of the most effective management strategies against freeway congestion. By allowing single occupancy vehicles (SOVs) to pay a toll for using high-occupancy vehicle (HOV) lanes, the excess capacities of HOV lanes can be used and the overall traffic mobility of the roadway section can be improved. However, research on HOT lane operations is still in its early stage. A series of theoretical and practical issues on optimizing HOT lane system performance particularly require immediate attention for better practice. Simulation-based investigation on HOT lane operations provides a cost-effective, risk-free, and prospective means of exploring and addressing these issues. A microscopic traffic simulation tool, VISSIM, is exploited in this study. By overcoming functional constraints with the VISSIM built-in modules and taking advantage of its component object model interface, we develop a new external module to enable HOT lane simulation. This HOT lane module provides additional flexibility to satisfy any specific demands from particular researchers and practitioners. Based on this external module, HOT lane operations can be simulated and evaluated as demonstrated using the Washington State Route (SR) 167 HOT Lane Pilot Project. The SR-167 simulation results not only quantitatively evaluate the overall system performance but also identify potential problems. Significantly different operational performance was illustrated between HOV lane and HOT lane systems using the developed simulation models. The simulation platform used in this study has the potential to be a cost-effective evaluation tool for HOT lane operations.

Finite-Element Modeling and Analysis of Reinforced Concrete Box Culverts

Abstract: There have been several controversies with regard to the true behavior of reinforced concrete box culverts in recent years. To be able to conduct a parametric study to develop design equations, a complete three-dimensional verified finite-element model of culverts is essential. This study presents the development of an analytical program to investigate the shear capacity of precast reinforced concrete box culverts. To simulate the experimental results, complete and detailed three-dimensional finite-element models (FEMs) of the test specimens were developed and analyzed. Three-dimensional shell and solid elements were used to model the culvert systems. The welded wire fabrics were modeled by using the rebar elements placed on the surface elements provided by the ABAQUS software. The contact surface between the outside face of the bottom slab and reaction floor was modeled by using a nonlinear node-to-surface contact analysis procedure. The analysis procedure consisted of an incremental loading history to c...

Desired Time Gap and Time Headway in Steady-State Car-Following on Two-Lane Roads

Abstract: Two continuous statistical distribution models, gamma and lognormal, are proposed for desired time gap ( TX ) and time headway (T) of drivers in a steady car-following state on two-lane roads under mixed traffic conditions. A simulation program was developed for traffic movement on two-lane roads incorporating actual behavior of mixed traffic in terms of speed, placement, arrival pattern, and overtaking behavior. The program was run at 50/50 directional distribution with varying traffic composition and volume level. Headway data obtained from simulation runs are analyzed to develop a relationship between the desired time gap ( TX ) and the speed of the vehicles for five categories of vehicles, namely, car, heavy vehicle, motorized two-wheeler, three-wheeler, and tractor. It is observed that the desired time gap of a two-wheeler is the minimum of all other categories of vehicles. It is due to their better maneuverability, which allows them to maintain shorter gaps. The desired time gap for tractors is the ...