Based on our research, the following outcomes have been achieved so far. The papers published on the research conducted at ATLAS are given below:
Authors: Afzal Ahmed, Syeda Ofaq Raza Zaidi, Mir Shabbar Ali, Palwasha Gul
Published in: European Transport
Abstract: This paper analyses the behaviour of university students in their mode selection and their preference towards a proposed bus rapid transit (BRT) line in Karachi, Pakistan. This BRT line, known as Red Line, has a major portion of its route along the University Road. Most of the major higher education institutions of Karachi are located along University Road. A preference survey was conducted from the students to determine individual preferences towards attributes of existing travel modes and the proposed BRT line. The respondents were classified into three categories which included users of private vehicles, public transport, and university shuttle service. The existing literature lacks in behaviour modelling of shuttle service users. This research models the behaviour of shuttle users and compares their behaviour with the commuters of other transport modes. The influencing factors examined in this research included one-way travel time, travel fare, and level of comfort during the travel. The utility model developed in this research shows that students who use private vehicles value travel time more than the other attributes. On the contrary, the commuters of the shuttle service are more sensitive to travel fare. This research shows that the behaviour of shuttle users is significantly different than the other commuters. The multinomial logit (MNL) model was applied to estimate the number of trips expected to transfer to the proposed BRT line. Results show that the shuttle service users will be least influenced by the introduction of BRT, as the shuttle service offers subsidized fares with more convenience. The model developed in this paper can be used by the policymakers to make the BRT more attractive for students and the general public.
Authors: Syed Muzammil Abbas Rizvi, Afzal Ahmed, and Yongjun Shen
Published in: Journal of Advance Transportation.
Abstract: Given the fact that the existing literature lacks the real-time estimation of road capacity and incident location using data from inductance loop detectors, a data-driven framework is proposed in this study for real-time incident detection, as well as road capacity and incident location estimation. The proposed algorithm for incident detection is developed based on the variation in traffic flow parameters acquired from inductance loop detectors. Threshold values of speed and occupancy are determined for incident detection based on the PeMS database. The detection of the incident is followed by the real-time road capacity and incident location estimation using a Cell Transmission Model (CTM) based approach. The data of several incidents were downloaded from PeMS and used for the development of the proposed framework presented in this study. Results show that the developed framework detects the incident and estimates the reduced capacity accurately. The location of the incident is estimated with an overall accuracy of 92.5%. The performance of the proposed framework can be further improved by incorporating the effect of the on-ramps, off-ramps, and high-occupancy lanes, as well as by modeling each lane separately.
Authors: Afzal Ahmed, Fatma Outay, Syeda Ofaq Raza Zaidi, Muhammad Adnan, Dong Ngoduy
Published in: Personal and Ubiquitous Computing
This research presents an in-depth microscopic analysis of heterogeneous and undisciplined traffic at the signalized intersection. Traffic data extracted from the video recorded using an unmanned aerial vehicle (UAV) at an approach of a signalized intersection is analyzed to study the within green time dynamics of traffic flow. Various parameters of Wiedemann 74, Wiedemann 99, and lateral behavior models used in microscopic traffic simulation package, Vissim, are calibrated for the local heterogeneous traffic. This research is aimed at exploring the queue-jumping phenomenon of motorbikes at signalized intersections and its impact on the saturation flow rate, travel time, and delay. The study of within green time flow dynamics shows that the flow of traffic within green time is not uniform. Surprisingly, the results indicate that the traffic flow for the first few seconds of the green time is significantly higher than the remaining period of green time, which shows a contradiction to the fact that traffic flow for the first few seconds is lower due to accelerating vehicles. Mode-wise traffic counted per second shows that this anomaly is attributed to the presence of motorbikes in front of the queue. Consequently, the outputs of simulation results obtained from calibrated Vissim show that the simulated travel time for motorbikes is significantly lower than the field-observed travel times even though the average simulated traffic flow matches accurately with the field-observed traffic flow. The findings of this research highlight the need to incorporate the queue-jumping behavior of motorbikes in the microsimulation packages to enhance their capability to model heterogeneous and undisciplined traffic.
Authors: Muzammil Abbas, Afzal Ahmed, Mir Shabbar Ali, Dong Ngoduy
Published in: 99th Annual Meeting of Transportation Research Board, At United States of America
The merging and diverging of weaving flow with the through flow to reach the U-turn create a weaving section. The average speed of vehicles along the weaving sections has been studied as a function of through and weaving flow. However, the literature on the effect of the length of weaving sections on the average speed of vehicles along the weaving section is lacking. In this study, the effect of traffic flows and the length of weaving sections on average speed is studied. For this purpose, three U-turns were selected along the existing signal-free corridors in Karachi. The first U-turn has the least length of weaving section while the third U-turn has the highest length among the selected U-turns. Traffic data was collected from the selected U-turns, and the developed model shows that the length of the weaving section has a significant effect on the average travel speed of vehicles. From the coefficients of developed regression model, it was found that weaving vehicles have more effect on the average speed in comparison with through traffic vehicles. This study concludes that such U-turns if required, should be designed with sufficient weaving length as it improves the performance of the weaving section and it is also expected to improve the safety of road users.
Authors: Afzal Ahmed, Mir Shabbar Ali, Toor Ansari , Uresha Mansoor
Published in: Journal of Traffic and Transportation Management
This research calibrates Cell Transmission Model (CTM) for heterogeneous and non-lane disciplined traffic, as observed in Pakistan and some other developing countries by constructing a flow-density fundamental traffic flow diagram. Currently, most of the traffic simulation packages used for such heterogeneous and non-lane-disciplined traffic are not calibrated for local traffic conditions and most of the traffic flow models are developed for comparatively less heterogeneous and lane-disciplined traffic. The flow-density fundamental traffic flow diagram is developed based on extensive field data collected from Karachi, Pakistan. The calibrated CTM model is validated by using actual data from another road and it was concluded that CTM is capable of modelling heterogeneous and non-lane disciplined traffic and performed very reasonably. The calibrated CTM will be a useful input for the application of traffic simulation and optimization packages such as TRANSYT, SIGMIX, DISCO, and CTMSIM.
Authors: Syed Muhammad Noman, Afzal Ahmed, Mir Shabbar Ali
Published in: SN Applied Sciences
This study presents a comparative analysis of selected parameters of existing formal and informal Public Transport (PT) modes being operated on three different types of fuels. The performance of PT modes is analyzed on fuel consumption, capacity, transportation cost, and emissions resulting from these modes. The required data were collected using route-check survey method and conducting a questionnaire-based survey from drivers and operators of these modes. Furthermore, the performance of proposed buses for an under-construction BRT corridor is also evaluated and compared with the existing PT modes. The comparative analysis of the existing PT modes in Karachi shows that CNG operated PT modes are economically more efficient, which caused the conversion of diesel engines of buses and minibuses to CNG fuelled-engines. The study, for the first time, evaluates and compares the performance of informal PT mode (chingchi) with other modes of PT. Results show that the PT modes with less capacity, such as chingchi, should be discouraged due to their comparatively lower performance on the selected parameters. This study can be used by the authorities to analyze the performance of existing modes and prioritize the PT modes for future planning.
Authors: Afzal Ahmed, Mohammed Raza Mehdi, Muzammil Abbas, Tehniat Fatima
Published in: Arabian Journal for Science and Engineering
Traffic streams in most of the urban areas of developing countries are highly heterogeneous with poor lane discipline. Traffic simulation and optimization packages based on microscopic traffic flow models are popular for modeling traffic flow and optimizing traffic controls all around the globe. However, applying microsimulation packages to model undisciplined and heterogeneous traffic streams may not yield perfect results. Whereas, macroscopic models can be easily calibrated for such heterogeneous and undisciplined traffic streams. This research applies the calibrated Cell Transmission Model (CTM) based optimization tool to determine optimal signal plans and to evaluate the potential of reduction in control delay at signalized intersections. Most of the traffic signals in Karachi are the pre-timed with a constant signal plan throughout the day, despite significant changes in traffic dynamics within a day. This study evaluates the performance of existing signal timing plans at two different locations in Karachi. The selected locations include a segment of urban arterial with three consecutive signals in close proximity. The second location was a standalone signalized intersection. 12-hour traffic and delay data on typical working days were collected through video recording technique. The data collected from the field was simulated using CTM-based signal optimization software, DISCO. The optimization results show an improvement of 45% in the existing delay at the selected segment of Khayaban-e-Ittehad. The delay at KDA intersection can be reduced by 29% by optimizing signal plans. The study shows that optimum signal timings based on accurate data can reduce delays and improve traffic network performance.
Authors: Afzal Ahmed, Syed Ahsan Ali Naqvi, David Watling, Dong Ngoduy
Published In: Transportation Research Record (TRR)
The accurate depiction of the existing traffic state on a road network is essential in reducing congestion and delays at signalized intersections. The existing literature in the optimization of signal timings either utilizes prediction of traffic state from traffic flow models or limited real-time measurements available from sensors. Prediction of traffic state based on historic data cannot represent the dynamics of change in traffic demand or network capacity. Similarly, data obtained from limited point sensors in a network provides estimates which contain errors. A reliable estimate of existing traffic state is, therefore, necessary to obtain signal timings which are based on the existing condition of traffic on the network. This research proposes a framework which utilizes estimates of traffic flows and travel times based on real-time estimated traffic state for obtaining optimal signal timings. The prediction of traffic state from the cell transmission model (CTM) and measurements from traffic sensors are combined in the recursive algorithm of extended Kalman filter (EKF) to obtain a reliable estimate of existing traffic state. The estimate of traffic state obtained from the CTM-EKF model is utilized in the optimization of signal timings using genetic algorithm (GA) in the proposed CTM-EKF-GA framework. The proposed framework is applied to a synthetic signalized intersection and the results are compared with a model-based optimal solution and simulated reality. The optimal delay estimated by CTM-EKF-GA framework is only 0.6% higher than the perfect solution, whereas the delay estimated by CTM-GA model is 12.9% higher than the perfect solution.
Authors: Afzal Ahmed, Satish V. Ukkusuri, Shahrukh Raza Mirza, Ausaja Hassan
Published In: Transportation Research Record (TRR)
Traffic streams in many developing countries consist of various modes of transport, with high heterogeneity in driver behavior. Modeling these types of traffic streams, in which traffic rules (speed limit, lane discipline, etc.) are not strictly followed, is a complex task. A review of the existing literature shows that there is a lack of traffic flow models that model the behavior of heterogeneous and undisciplined traffic streams. Like other undisciplined traffic streams, there are no speed limits (hence no speed enforcement) on most of the roads in Karachi, Pakistan. Lane discipline is also not observed by drivers, which results in a varying number of traffic lanes on a road. Therefore, most of the existing traffic flow models/simulation packages developed for disciplined traffic streams cannot appropriately model traffic streams without lane discipline. This research proposes a width-based cell transmission model (WCTM) by developing a fundamental flow-density diagram whose parameters are a function of the road width. Extensive field data have been collected from a selected arterial in Karachi for development of the fundamental traffic flow diagram. The values of the computed parameters are significantly different than the values reported in the literature. The piecewise-linear flow-density relation is developed by optimally estimating the breakpoints. Results show that the quadrilateral and pentagonal-shaped fundamental diagrams fit better with the collected data in comparison with the triangular-shaped fundamental diagram. The proposed WCTM is applied to selected segments of an arterial and results show that the WCTM was able to accurately model different traffic conditions.
Authors: Afzal Ahmed, Mohammed Raza Mehdi, Dong Ngoduy, Muzammil Abbas
Published In: Travel Behavior and Society
Heterogeneous traffic in developing countries consists of motorbikes and cars as private vehicles along with various other modes of transport for public and commercial transport. Motorbikes and cars have distinct travel characteristics, having different travel times and owned by commuters from significantly different socioeconomic backgrounds. This study uses a probe motorbike and probe car to collect travel time data for numerous trips covering a total length of 2040 km, on the various roads of Karachi. This travel time data is used to evaluate the accuracy of the only publically available advanced traveler information tool, ‘Google Live Traffic’ (GLT). Results show that there is a significant difference in the accuracies of the information for these two distinct modes of private transport. The overall accuracy of travel times predicted by GLT is 80% (85% for cars and 71% for motorbikes). Trip parameters such as traffic condition and type of road had a statistically significant correlation with the accuracy of the information provided by GLT. The behavior of commuters towards the awareness and utilization of traveler information provided by GLT was evaluated by performing an econometric analysis of selected socioeconomic and demographic parameters. A detailed stated preference survey was conducted from 1200 randomly selected motorbikes riders and car drivers from various locations of Karachi, a metropolitan city with 14.9 million inhabitants from a variety of socioeconomic background. Econometric analysis shows that age, education, income, vehicle type, and occupation have a significant correlation with awareness among commuters, whereas gender is identified as an insignificant factor.