Shankar C Subramanian

Travel time is one of the most preferred traffic information by a wide variety of travelers. Travel time information provided through variable message signs at the roadside could be viewed as a traffic management strategy designed to encourage drivers to take an alternate route. At the same time, it could also be viewed as a traveler information service designed to ensure that the driver has the best available information based on which they can make travel decisions. In an Intelligent Transportation Systems (ITS) context, both the Advanced Traveler Information Systems (ATIS) and the Advance Traffic Management Systems (ATMS) rely on accurate travel time prediction along arterials or freeways. In India, currently there is no permanent system of active test vehicles or license plate matching techniques to measure stream travel time in urban arterials. However, the public transit vehicles are being equipped with Global Positioning System (GPS) devices in major metropolitan cities of India for providing the bus arrival time information at bus stops. However, equipping private vehicles with GPS to enable the stream travel time measurement is difficult due to the requirement of public participation. The use of the GPS equipped buses as probe vehicles and estimating the stream travel time is a possible solution to this problem. The use of public transit as probes for travel time estimation offers advantages like frequent trips during peak hours, wide range network coverage, etc. However, the travel time characteristics of public transit buses are influenced by the transit characteristics like frequent acceleration, deceleration and stops due to bus stops besides their physical characteristics. Also, the sample size of public transit is less when compared to the total vehicle population. Thus mapping the bus travel time to stream travel time is a real challenge and this difficulty is more complex in traffic conditions like in India with its heterogeneity and lack of lane discipline. As a pilot study, a model based approach using the Kalman filtering technique to predict stream travel time from public transit is carried out in the present study. Since it is only a pilot study, only twowheeled vehicles have been considered as they constitute a major proportion in the study area. The prediction scheme is corroborated using field data collected by carrying GPS units in two-wheelers traveling along with the buses under consideration. The travel time estimates from the model were compared with the manually observed travel times and the results are encouraging. © 2011 IEEE.

In this paper, a model based estimation scheme has been proposed to estimate density incorporating the heterogeneity and lane indiscipline observed in Indian traffic. In order to incorporate lane indiscipline, the road stretch under study was considered as multiple parallel strips. Time occupancy and composition based weighted vehicle length were used to incorporate heterogeneity. Then, using these, a single state non-continuum macroscopic model was developed with density as the state variable and time occupancy as the output variable. The Kalman filtering technique was used for dynamic estimation of density. The estimator was corroborated using data generated from a microscopic traffic simulation software, VISSIM. Results obtained showed that the proposed approach could provide accurate density estimates and reproduced traffic characteristics better than without considering lane indiscipline.

Hybrid electric vehicles are emerging technologies that are considered as eco-friendly alternative solutions to internal combustion engine–driven vehicles. This paper proposes a modified hybrid electric vehicle powertrain system that addresses the shortcomings of a series hybrid electric vehicle powertrain. The proposed configuration replaces the conventional generator of a series hybrid electric vehicle with an integrated starter generator that supports the traction motor of the vehicle during acceleration and peak torque requirements and maintains the state of charge of the batteries to provide an extended electric range of the vehicle. The work done in this paper can be categorized into two stages. The first stage is the methodical development of the powertrain in terms of initial parameter matching and sizing of the vehicle components by considering the fundamentals of longitudinal vehicle dynamics. The second stage describes the optimization of the proposed configuration to meet the design objective of maximizing fuel economy subjected to a set of vehicle performance constraints. The performance of the proposed powertrain was evaluated and compared with a series hybrid electric vehicle powertrain for an on-road Indian driving cycle using AVL CRUISE, which is a commercially available software for the study and analysis of road vehicle powertrains. Result analysis during initial parameterization showed a reduction in gross vehicle weight of the proposed configuration by 244 kg (1.5%) and an improvement in the average operating efficiency of the traction motor by around 11%, when compared to a series hybrid electric vehicle. Furthermore, the optimization results for the proposed configuration established an improvement in the fuel economy by 21% while meeting vehicle performance requirements.

An urban arterial can be considered a series of intersections, intermediate sections (defined as those that link intersections and mid-block areas), and mid-block sections. The intermediate section is characterized by varying speed characteristics at its entry and exit. A vehicle exiting the intersection and entering the intermediate section would accelerate and gradually attain uniform speed when it leaves the intermediate section (entry to the mid-block). Most of the reported travel time studies considered the delays at intersections and the travel times in mid-blocks to get the network level travel time without paying attention to the variability of speeds and travel time at intermediate sections. The present study concentrates on the travel time estimation of the intermediate section, which is not well-discussed in the literature. A speed estimation scheme was developed for the entry and exit of the intermediate section (characterized by varying speed ranges) using a dynamic model-based estimation scheme that captured the speed variations effectively. Intermediate link travel time was then estimated using a weighted average speed-based method. The effects of heterogeneity and limited lane discipline in the traffic stream of mixed traffic were considered using two model formulations, one that represented the traffic stream in Passenger Car Units (PCU) and the other in different vehicle classes for travel time estimation. The developed estimation schemes can be used as a possible application in Intelligent Transportation Systems (ITS) for real-time estimation of travel time at urban arterials under mixed traffic conditions.

Active safety is of utmost importance in heavy road vehicles due to the relatively higher number of fatalities encountered in their accidents. Vehicle-to-Vehicle (V2V) technology, which is seen as a future of connected vehicles, can potentially complement onboard sensing to reduce the time taken for detection, and to plan the path with the information available from road side units (RSU). This paper investigates the effect of Iatency in (V2V) communication on a collision avoidance algorithm developed for heavy road vehicles. Experiments performed on a Hardware-in-Loop (HiL) setup were used to evaluate the effect of Iatency for various scenarios. It was found that Iatency had a counterbalancing effect on vehicle spacing and relative longitudinal speed that led to insignificant changes in the final spacing. Further, a sensitivity analysis done at different host vehicle longitudinal speeds demonstrated the need of a variable time headway.

During the braking manoeuvre of a vehicle on a pavement, the mechanics associated with load transfer is complex due to the presence of slip, load shift between the front and rear axles, and development of longitudinal forces. The road profiles, braking intensity, truck mass, and speed during braking play a critical role here. This investigation reports an attempt to collect such data. A unique Hardware-in-Loop set-up was integrated with vehicle dynamics software, TruckMaker, to perform a realistic braking manoeuvre. Three truck loadings were chosen from the axle load survey conducted in the field (unladen, laden, and overloaded). Three ISO road profiles (A, B, C) generated using the power spectral density approach, three initial speeds (30, 50, and 80 km/h), and three braking intensities (Partial (10%), Partial (45%), and Complete (100%)) were chosen for the simulation. In total 81 simulations were performed considering all the above-said factors. From the analysis of wheel slip values, it was identified that the wheels of unladen trucks lock during complete braking, irrespective of the speeds and road profiles. The complete braking manoeuvre for all vehicle types showed more load shift from the rear axle to the front axle compared to partial braking manoeuvres. Also, the unladen trucks were found to transfer more percentage (>50%) of their rear axle load to the front axle during braking. The maximum longitudinal force developed at the tyre-pavement interface was found to be independent of the loading conditions during complete braking.

Fuel Cell Hybrid Electric Vehicles (FCHEVs) have the potential for providing a solution for clean transportation. For FCHEVs to be successful, it is important to improve their fuel economy and acceleration performance. One of the important systems to be worked on to achieve these goals is the vehicle's powertrain. This research work aims at providing a systematic procedure for multi-objective optimum sizing of a FCHEV powertrain, with the objectives of minimizing the fuel consumption and maximizing the acceleration performance. The work was carried out for a fuel cell-battery hybrid heavy road vehicle for Indian driving cycle. The design variables in the component sizing process were chosen to be speed ratio (x) of the traction motor and degree of hybridization (H) of the power sources. The values of objective functions and constraints were evaluated using ADVISOR software for a sample set of design variables. Surrogate modelling technique was adopted for constructing models for objective functions and constraints. Then, the optimization was carried out using multi-objective genetic algorithm approach to find the Pareto optimal solutions for the problem. This study provides a framework for component sizing of FCHEV that considers x and H as design variables.

The phenomenon of platoon dispersion deals with the spreading out of groups of vehicles discharged together from a signal (platoon) as they move along the roadway during normal traffic operations. Understanding and analyzing this behavior is important in efficient traffic operations and management. There are different platoon dispersion models reported in the literature, out of which Robertson's model is one of the oldest and widely used. However, all the existing studies were from homogeneous and lane-based traffic conditions and few studies studied platoon dispersion behavior under traffic conditions such as those existing in India. In this study, data were collected in a typical Indian urban arterial road. To account for the heterogeneous and laneless Indian traffic, Roberston's model was modified and an optimization approach was used to obtain the coefficients. The proposed model's performance was evaluated and compared with the original Robertson's model after calibrating for the specific traffic conditions under consideration. Platoon parameters were also estimated using both proposed and calibrated models and the results were compared, which showed a better performance of the proposed model compared to the calibrated Robertson's model. Though the proposed model was tested for heterogeneous and laneless traffic data, it is in no way constraining and is generic enough to be applied for other traffic conditions.

Quantification of the workability of bituminous mixtures has always been challenging due to the associated complexity during mixing, laying and compaction.The transitory response of the rheological behavior of the binder, the particle size distribution and the quantum of work applied during mixing and compaction are a few of these factors.A few attempts exist in the literature to quantify the workability of bituminous mixtures, and such attempts have computed the torque required indirectly at a constant angular speed and constant temperature. Also, the relationship between workability during mixing and during compaction requires detailed investigation. This study presents initial results ofworkability equipment fabricated in-house at IIT Madras, India. Direct torque measurements recorded for different bituminous mixtures at different temperature conditions are reported and their sensitivity is discussed.

A properly functioning brake system is critical for ensuring the safe operation of any vehicle on roadways. Commercial vehicles such as trucks, tractors-trailers and buses are equipped with an air brake system that uses compressed air as the energy transmitting medium. This paper presents a model-based control scheme for an electropneumatic brake system for use in commercial vehicles. A mathematical model for an electropneumatic brake system was developed and corroborated with experimental data. A control scheme was developed based on this model and was used to regulate the pressure of air inside the brake chamber according to a desired pressure trajectory. This control scheme was implemented on an experimental test bench, and its performance was studied for various values of the controller parameter. The control scheme was tested for various desired pressure trajectories reflecting actual brake operation. © 2010 The Korean Society of Automotive Engineers and Springer-Verlag Berlin Heidelberg.