Browsing by Author "Bastos Silva, Ana"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
- Calibration of the Gipps Car-following Model Using Trajectory DataPublication . Vasconcelos, Luís; Neto, Luís; Santos, Sílvia; Bastos Silva, Ana; Seco, ÁlvaroOne of the most important tasks in the microscopic simulation of traffic flow, assigned to the car following sub-model, is the modelling of the longitudinal movement of vehicles. The calibration of a car-following model is usually done at an aggregated level, using macroscopic traffic stream variables (speed, flow, density). There is an interest in calibration procedures based on disaggregated data. However, obtaining accurate trajectory data is a real challenge. This paper presents a low-cost procedure to calibrate the Gipps car-following model. The trajectory data is collected with a car equipped with a datalogger and a LIDAR rangefinder. The datalogger combines GPS and accelerometers data to provide accurate speed and acceleration measurements. The LIDAR measures the distances to the leading or following vehicle. Two alternative estimation methods were tested: the first follows individual procedures that explicitly account for the physical meaning of each parameter; the second formulates the calibration as an optimization problem: the objective function is defined so as to minimize the differences between the simulated and real inter-vehicle distances; the problem is solved using an automated procedure based on a genetic algorithm. The results show that the optimization approach leads to a very accurate representation of the specific modeled situation but offers poor transferability; on the other hand, the individual estimation provides a satisfactory fit in a wide range of traffic conditions and hence is the recommended method for forecasting purposes.
- Driving around turbo-roundabouts vs. conventional roundabouts: Are there advantages regarding pollutant emissions?Publication . Fernandes, Paulo; Pereira, S. R.; Bandeira, J. M.; Vasconcelos, Luís; Bastos Silva, AnaThis paper addresses the impact of turbo-roundabouts located in urban areas on pollutant emissions using field measurements of vehicle activity data and road congestion levels. The research also compares the emissions of vehicles moving along a turbo-roundabout and a conventional multi-lane roundabout. Based on field measurements taken at turbo-roundabouts without curb dividers located in Grado (Spain) and multi-lane roundabouts in Aveiro (Portugal), three representative speed profiles for each speed trajectory were identified: no stop (I), stop once (II), and multiple stops (III). This study also develops discrete models for turbo-roundabouts and multi-lane roundabouts in which the relative occurrence of those speed profiles is expressed as a function of the entry and conflicting traffic flows. The Vehicle Specific Power (VSP) methodology is then employed to estimate second-by-second pollutant emissions. This study tests the hypotheses that emissions are impacted by the differences in: 1) the characteristics of speed profiles in each movement; 2) the volumes of entry and conflicting flows; 3) the overall saturation level; and 4) the transportation facility considered (turbo-roundabout /multi-lane roundabout). Considering the selected case studies and traffic demands, vehicles at turbo-roundabouts generated more emissions (15-22%, depending on the pollutant) than multi-lane conventional roundabouts, especially under medium and high congested levels. These findings suggest that there are no advantages in implementing turbo-roundabouts from an environmental point of view, even in no saturated conditions.
- Hybrid calibration of microscopic simulation modelsPublication . Vasconcelos, Luís; Seco, Álvaro; Bastos Silva, AnaThis chapter presents a procedure to calibrate the Gipps car-following model based on macroscopic data. The proposed method extends previous approaches in order to account for the effect of driver variability in the speed–flow relationships. The procedure was applied in a real calibration problem for the city of Coimbra, Portugal, as part of a broader calibration framework that also includes a conventional optimization based on a genetic algorithm. The results show that the new methodology is promising in terms of practical applicability.