Mohan Venigalla

A specialized equilibrium assignment algorithm for air quality modeling

Abstract A multiple user class equilibrium assignment algorithm is formulated to determine vehicle trips and the vehicle miles of travel (VMT) in various operating modes on highway links. A heuristic solution algorithm based on the Frank–Wolfe decomposition of the equilibrium assignment problem is presented. The treatment of intrazonal trips, which are very important for emission studies is also discussed. The solution algorithm is implemented in a traffic assignment program for emission studies, referred to as TAPES. The use of the algorithm is demonstrated through a TAPES model case study on a Charlotte, NC network database for 1990 AM peak period. The operating mode mix of VMT in cold transient, hot transient and hot stabilized modes, also known as the mix of cold-starts, hot-starts and stabilized mode trips, is derived on a link by link basis. The results are aggregated by facility type and the location of link segments. It is observed that the operating mode fractions in transient and stabilized modes could vary widely across different facility types geographic locations. The aggregated operating mode fractions derived from the assignment analysis indicates that a lesser proportion of VMT operates in cold and hot transient modes when compared to the operating mode mix derived from the Federal Test Procedure (FTP).

Measuring Impacts of High-Occupancy-Vehicle Lane Operations on Light-Duty-Vehicle Emissions: Experimental Study with Instrumented Vehicles

High-occupancy-vehicle (HOV) lanes on urban highways have long been proved to increase the efficiency of highway operations, as measured by person throughput, vehicle occupancy, travel time, speed, and reliability. Operational measures of effectiveness, such as speed and travel time, for HOV facilities are superior to general purpose (GP) lanes, in which predominantly single-occupancy vehicles operate. Few studies have attempted to study the emissions on HOV facilities vis-a-vis their GP lane counterparts. In this research, differences in vehicle emissions between HOV lane and GP lane facilities were measured with portable emissions sensors. Several hundred miles of on-road emissions data were collected by vehicles instrumented with portable emissions-monitoring systems (PEMSs) operated in HOV and GP lanes during peak hours in the metropolitan Washington, D.C., area. Data were collected at HOV facilities with buffer separation and at HOV facilities with barrier separation (limited-access lanes). Experimen...

Soak Distribution Inputs to Mobile Source Emissions Modeling: Measurement and Transferability

Soak period distribution is a key input for modeling the emissions factors for mobile sources. Methods for deriving soak period distributions from travel survey data are discussed. Data from the 1995 Nationwide Personal Transportation Survey (NPTS) were analyzed to derive soak times. Detailed analyses were conducted to relate soak time variability to geographic, trip-purpose, and time-of-day variables. The findings reinforce the prevailing general guidance on inputs to modeling the emissions from mobile sources. That is, whenever possible, local data should be used to derive soak distribution inputs to the emissions models. Alternatives are offered to accurate but more expensive local surveys as well as to the roughly aggregate and potentially inaccurate national defaults on soak period inputs to emissions factor models such as MOBILE6. On the basis of a detailed statistical analysis, a grouping scheme is devised to consolidate soak distribution inputs by time period. The grouping scheme will enhance the utility of survey data in deriving the soak distributions and reduce the effort in providing soak distribution inputs to MOBILE6. The soak periods derived from the NPTS data also can be used for deriving the operating-mode fractions inputs needed for MOBILE5B and modal emissions models.

Measuring Travel Behavior and Transit Trip Generation Characteristics of Transit-Oriented Developments

Transit-oriented developments (TODs) have been recognized as a promising proposition for policy makers and land developers in meeting the challenges of urban sprawl. The rapid pace with which TODs are being developed across the United States has left policy makers and transportation planners looking for methods aimed at modeling the travel characteristics of TODs. Current ITE trip-generation models are generally based on consolidated survey data from various land uses and are inadequate for serving the planning needs for travel demand parameters necessary to predict trip generation rates, develop trip distribution tables, identify mode choice characteristics, and determine trip assignment of TODs. The primary foci of this research were to understand the trip-making behavior of the TODs and develop a method for determining vehicular trip generation rates. A comparative assessment of TODs vis-à-vis non-TODs in relation to trip rates, transit usage, and primary travel mode was performed. A regression model relating TOD trip ends to gross floor area was developed and validated. Model behavior was consistent with the industry state of the practice; this factor would help transportation practitioners accurately forecast the trip generation rate for TODs. Validation of the regression model was performed by checks for normality, multicollinearity, and heteroscedasticity of the independent variable. The activity-based survey data used for this research were associated with the Washington, D.C., metropolitan area, which provided a wealth of transit-oriented corridors and diverse land use. Use of these data mitigated the loss of computational information frequently caused by aggregate data and therefore provided a more accurate quantitative forecast.

Impact of Electronic Toll Collection and Electronic Screening on Heavy-Duty Vehicle Emissions

The proliferation of electronic toll collection (ETC) mechanisms such as E-ZPass has a positive effect in reducing automobile emissions at toll plazas because of decreased acceleration, deceleration, and idling events. Modeling tools such as the California Modal Emissions Model can be used to measure the emissions impacts of ETC and other electronic screening (e-screening) facilities only on light-duty gasoline-fueled vehicle operations. No such tools exist for modeling of the emissions impacts of ETC and e-screening facilities on heavy-duty vehicle operations. This paper presents a speed profile discretization (SPD) technique for modeling emissions at ETC and e-screening facilities. The SPD technique is based on the MOBILE6.2 method of representing vehicle miles of travel in various speed bins. The technique defines an emissions influence zone within which speed profiles are altered and further determine vehicle emissions. With this technique, the emissions impacts of heavy-duty trucks at the toll collection plaza on the George Washington Bridge in New York City are estimated. The current mix of cash and E-ZPass transactions on the George Washington Bridge are shown to reduce emissions of volatile organic compounds (VOCs), hydrocarbons (HCs), and oxides of nitrogen (NOx) within the emissions influence zone. The degree of reduction is dependent on the speed with which E-ZPass vehicles are processed. If E-ZPass vehicles are processed at no more than 10 mph, reductions in VOC, CO, and NOx emissions are estimated to be 30.8%, 23.5%, and 5.8%, respectively. Results indicate that if E-ZPass allows vehicles to be processed at 20 mph, reductions in VOC emissions due to truck traffic alone could be as high as 50%.

IMPLICATIONS OF TRANSIENT MODE DURATION FOR SPATIALLY DISAGGREGATED HIGH-RESOLUTION EMISSION INVENTORY STUDIES

High resolution emission inventory studies, such as urban air-shed modeling, often use spatially disaggregated emission parameters in the form of link-specific emissions. A key input variable that influences operating mode mix on highway links is the transient mode duration (TMD) in which start-related emissions occur. The TMD variable also establishes the emission rates to be embedded in emission factor models. The basic emission rates built into the MOBILE model are based on a TMD of 505 seconds, which was based on the federal test procedure (FTP). For newer vehicles, it is indicated that the TMD is much less than 505 seconds. This study examines the effects of variations in TMD on the distribution of cold and hot transient VMT on network links, as well as their effect on overall emissions. A network assignment model developed to track operating modes of vehicles on network links was used on a large California city network. The MOBILE model was used to derive bag-specific emission rates. The experiment includes a series of traffic assignment runs with varying TMD and postprocessing of the assignment output. Link-specific distribution of operating mode mix and total emissions were derived. It is indicated that TMD significantly influences the distribution of operating modes, as well as total emissions. The results indicate that as the TMD decreases, the share of cold transient VMT from freeways diminishes, while that of the local roads increases. It was indicated that total emissions on various link groups may fall within a range of 90 to 300 percent of the total emissions derived from the present FTP duration of 505 seconds. It is recommended that the transient mode duration variable be reexamined for deriving emission rates to be embedded in the future versions of emission factor models.

Psychology of Route Choice in Familiar Networks: Minimizing Turns and Embracing Signals

AbstractIt is widely accepted that path choice of a trip is dependent on trip characteristics, network attributes, and a traveler’s personal characteristics. The best-known network variables that influence route choice are travel distance and travel time. This research attempts to study the influence of other network variables, namely signals, turns, and roadway classification on route choice. Real-world trip data from path trajectories tracked by a global positioning system (GPS) in an urban area are used to isolate nearly 5,700 unique real paths. Procedures to compute the theoretical shortest time path (STP) and shortest distance path (SDP) based on travel time and distance as impedance variables, respectively, are developed. Street network data are augmented with data on signalized intersections. Procedures to identify turns and road classes along the real and theoretical paths, and methods to quantify turn penalties are developed. The real paths are compared to their STP and SDP counterparts to identi...

A Quick-Response Discrete Transit-Share Model for Transit-Oriented Developments

Various studies have highlighted an apparent lack of analyses associated with the modal choice characteristics of transit-oriented developments (TODs) and emphasized the need for quick response models for estimating transit share in TOD areas. In this paper, a methodology for developing transit-share model for TOD’s using travel activity data is presented. A transit-share model is formulated as an innovative combination of the direct generation, urban travel factor (UTF), and logit models. This model determines transit usage in TODs based on household auto ownership as the primary input and the transit system variables as secondary inputs. Validation of the model indicates a close agreement with observed data. Since the input requirements to the TOD transit-share model are minimal, this model structure is expected to be very useful for sketch analysis of many TOD project alternatives.

Global positioning systems data for performance evaluation of HOV and GP lanes on I-66 and I-395/I-95

In this study an empirical analysis is conducted for assessing the performance of high occupancy vehicle (HOV) lanes using Global Positioning System (GPS). Second by second speed, time, and location data were obtained from GPS equipped probe vehicles on HOV lanes with exclusive right of way as well as on HOV lanes that share the right of way with general purpose (GP) lanes. Peak-hour operations of HOV facilities on I-66 and I-395/I-95 corridors in the Washington DC area were used as test beds. Parameters for the performance measures such as travel time, mean journey speed, delay, proportion of stopped time and congestion index were developed and compared for HOV and GP lanes. The data were also used to identify location and the extent of congestion along the study routes. The results of the analysis showed travel times saving, higher journey speeds, less delay, and lower congestion incurred by the probe vehicles on the HOV lanes as compared to the probe vehicles traveling simultaneously on non-HOV lanes

OPERATING MODE FRACTIONS ON URBAN ROADS DERIVED BY TRAFFIC ASSIGNMENT

The federal test procedure for vehicle emissions measurement treats the first 505 sec of engine operation as the transient mode. Using this definition as the basis, a special technique was developed and used to trace the elapsed time of vehicles from trip origins during the traffic assignment of zone-to-zone trips on a highway network and to determine the proportions of transient and stabilized operating modes on every link of the network. The travel models of the Sacramento (California) urban area were used to apply this technique and derive operating mode fractions for this urban area. The data from the Nationwide Personal Transportation Survey were used to distinguish between cold transient and hot transient modes. The operating mode fractions were stratified by functional class of roadways and the location within the urban area. The time of day of travel also was used for further stratification. The results show wide variations in the operating mode fractions among the different categories of roadway, location, and time of day.