Hatem Abou-Senna

Using a traffic simulation model (VISSIM) with an emissions model (MOVES) to predict emissions from vehicles on a limited-access highway

The Intergovernmental Panel on Climate Change (IPCC) estimates that baseline global GHG emissions may increase 25–90% from 2000 to 2030, with carbon dioxide (CO2) emissions growing 40–110% over the same period. On-road vehicles are a major source of CO2 emissions in all the developed countries, and in many of the developing countries in the world. Similarly, several criteria air pollutants are associated with transportation, for example, carbon monoxide (CO), nitrogen oxides (NOx), and particulate matter (PM). Therefore, the need to accurately quantify transportation-related emissions from vehicles is essential. The new U.S. Environmental Protection Agency (EPA) mobile source emissions model, MOVES2010a (MOVES), can estimate vehicle emissions on a second-by-second basis, creating the opportunity to combine a microscopic traffic simulation model (such as VISSIM) with MOVES to obtain accurate results. This paper presents an examination of four different approaches to capture the environmental impacts of vehicular operations on a 10-mile stretch of Interstate 4 (I-4), an urban limited-access highway in Orlando, FL. First (at the most basic level), emissions were estimated for the entire 10-mile section “by hand” using one average traffic volume and average speed. Then three advanced levels of detail were studied using VISSIM/MOVES to analyze smaller links: average speeds and volumes (AVG), second-by-second link drive schedules (LDS), and second-by-second operating mode distributions (OPMODE). This paper analyzes how the various approaches affect predicted emissions of CO, NOx, PM2.5, PM10, and CO2. The results demonstrate that obtaining precise and comprehensive operating mode distributions on a second-by-second basis provides more accurate emission estimates. Specifically, emission rates are highly sensitive to stop-and-go traffic and the associated driving cycles of acceleration, deceleration, and idling. Using the AVG or LDS approach may overestimate or underestimate emissions, respectively, compared to an operating mode distribution approach. Implications: Transportation agencies and researchers in the past have estimated emissions using one average speed and volume on a long stretch of roadway. With MOVES, there is an opportunity for higher precision and accuracy. Integrating a microscopic traffic simulation model (such as VISSIM) with MOVES allows one to obtain precise and accurate emissions estimates. The proposed emission rate estimation process also can be extended to gridded emissions for ozone modeling, or to localized air quality dispersion modeling, where temporal and spatial resolution of emissions is essential to predict the concentration of pollutants near roadways.

Developing a Microscopic Transportation Emissions Model to Estimate Carbon Dioxide Emissions on Limited-Access Highways

This paper presents an optimal design approach for developing a microscopic transportation emissions model (Micro-TEM). The main purpose of Micro-TEM is to achieve an acceptable degree of accuracy as a surrogate model for predicting transportation emissions of carbon dioxide (CO2) on limited-access highways as an alternative to using a traffic model and then integrating those results into an emissions model. Key parameters related to traffic (volume, truck percentage, speed limits), geometry (road grade), and environment (temperature) were selected for detailed evaluation. Estimating vehicle emissions on the basis of second-by-second vehicle operation created the opportunity to integrate a microscopic traffic simulation model, VISSIM, with the latest U.S. Environmental Protection Agency mobile source emissions model, the Motor Vehicle Emission Simulator (MOVES), for higher precision and accuracy. The VISSIM–MOVES integration software, VIMIS, was developed to facilitate running a multilevel factorial experiment on a test-bed prototype of an urban section of I-4, a limited-access highway in Orlando, Florida. The analysis identified the optimal settings for CO2 emissions reduction on the basis of two main parameters, traffic volume and speed. Volume correlation with CO2 emissions rates revealed an exponentially decaying function toward a limiting value expressed in the freeway capacity. Moreover, at speeds between 55 and 60 mph there was a significant reduction in the emissions rate, yet up to 90% of the freeway capacity was maintained. The results demonstrated that active speed management has a significant impact on CO2 emissions provided that a detailed and microscopic analysis of vehicle acceleration and deceleration has been conducted. This approach can provide environmental decision makers with practical guidelines for their decisions on environmental transport policies.

Determination if VISSIM and SSAM could estimate pedestrian-vehicle conflicts at signalized intersections

ABSTRACT This article examines the optimum values of postencroachment time (PET) and time-to-collision (TTC) parameters that would define a pedestrian-to-vehicle conflict at signalized intersections using a simulation model (VISSIM) and a surrogate safety assessment model (SSAM). A total of 42 video hours were recorded at seven signalized intersections for field data collection. The observed conflicts from the field were used to calibrate VISSIM and replicate the conflicts. The calibrated and validated VISSIM model generated the pedestrian–vehicle conflicts from SSAM software using the vehicle trajectory data in VISSIM. The mean absolute percent error (MAPE) was used to determine the optimum TTC and PET thresholds for pedestrian–vehicle conflicts and linear regression analysis was used to study the correlation between the observed and simulated conflicts at the established thresholds. The results of the regression analysis indicated the highest correlation between the simulated and observed conflicts when the TTC parameter was set at 2.7 and the PET was set at 8. It was also found that the VISSIM model might underestimate the number of pedestrian–vehicle conflicts at specific intersections that would involve illegal pedestrian behavior such as jay walking or pedestrian signal violation that would occur in the real world.

Assessing the impact of converting roundabouts to traffic signals on vehicle emissions along an urban arterial corridor in Qatar

ABSTRACT The type of control at intersections has a major effect on the operation of any urban corridor. Different predefined procedures are available to calculate some of the main operational characteristics, such as capacity, delay, and level of service, in order to select the best type of control. However, there are other important factors that affect major arterials operational characteristics, factors that are not fully addressed, such as the impact of emissions. In this study, a microscopic simulation approach using VISSIM and MOVES was developed to assess the environmental effect of converting four three-lane roundabouts to signalized intersections along a heavily congested urban corridor in Qatar. A decision was made to switch all roundabouts to traffic signals for better operations. Preliminary results indicated that the signal control outperformed the roundabout in the range of 37% to 43% reduction in emissions. A more detailed analysis revealed that roundabout corridor operations’ effects on emission rates are divergent from those of signalized corridors, particularly upstream and downstream of the intersections. Immediate roundabout upstream approaches are driver behavior dependent, characterized by substantial coasting at lower speeds and subsequent re-accelerating with less idling, described as acceleration events, which resulted in high emission rates, while signalized corridors are signal timing dependent, characterized by ample idling with less coasting and re-acceleration, resulting in reduced emission rates. The results also revealed that there was no significant difference between emission rates in the vicinity of the two types of control. Both recorded nearly the same emission rate. Implications: A microscopic simulation approach using VISSIM and MOVES was developed to assess the environmental effect of converting four three-lane roundabouts to signalized intersections along a heavily congested urban corridor in Doha, Qatar. Intersection geometries along with the control type have significant impact on emission rates and play a major role in assessing environmental impacts. US EPA MOVES was calibrated to Qatar conditions which can be used to estimate emission factors and quantify vehicular emissions along other corridors in the country. The results can also be beneficial for other countries within the region.

Interactive Decision Support System for Predicting Flashing Yellow Arrow Left-Turn Mode by Time of Day

Accommodation of left turns at signalized intersections has been a challenge for traffic engineers seeking a balance between two conflicting goals: capacity and safety. The use of a four-section display for the left-turn lane only with a flashing yellow arrow indication for permissive left turns has been deemed the new standard for signalization. With the advent of this new signal configuration, the opportunity to take the protected–permitted left-turn mode to a new level of operation has been presented. Although numerous studies have developed warrants and guidelines for selecting types of left-turn control, no clear or uniform standards for the implementation of a variable left-turn mode that changes by time of day are currently available. This study developed an interactive decision support system for evaluating left-turn phasing alternatives by time of day by the use of a custom-design approach. The resultant model predicts the number of left turns during the permitted phase under different intersection conditions and assesses the operational and safety aspects warranting a permitted left-turn phase on the basis of specific criteria and thresholds; comparison of the amount of permitted green time given throughout the hour with the number of permitted left turns determines whether the opposing traffic flow is operating near or at saturation. The guidelines that were developed will provide traffic engineers with the tools that they need to use the efficiency of the permitted left-turn phase. Furthermore, the decision support system that was developed will assist traffic management centers with the identification of intersections requiring attention to or modification of the left-turn mode.