High-occupancy Vehicle Research Articles

A Progressive Deployment Strategy for Cooperative Adaptive Cruise Control to Improve Traffic Dynamics

Cooperative adaptive cruise control (CACC) vehicles are intelligent vehicles that use vehicular ad hoc networks (VANETs) to share traffic information in real time. Previous studies have shown that CACC could have an impact on increasing highway capacities at high market penetration. Since reaching a high CACC market penetration level is not occurring in the near future, this study presents a progressive deployment approach that demonstrates to have a great potential of reducing traffic congestions at low CACC penetration levels. Using a previously developed microscopic traffic simulation model of a freeway with an on-ramp — created to induce perturbations and trigger stop-and-go traffic, the CACC system’s effect on the traffic performance is studied. The results show significance and indicate the potential of CACC systems to improve traffic characteristics which can be used to reduce traffic congestion. The study shows that the impact of CACC is positive and not only limited to a high market penetration. By giving CACC vehicles priority access to high-occupancy vehicle (HOV) lanes, the highway capacity could be significantly improved with a CACC penetration as low as 20%.

Collection, Screening, and Evaluation of Vehicle Occupancy Data

In 2008, the Georgia State Road and Tollway Authority and the Georgia Department of Transportation successfully applied to the U.S. Department of Transportation for seed funding under the Congestion Reduction Demonstration Program Grant to convert the congested I-85 high-occupancy-vehicle (HOV) lane to a high-occupancy-toll (HOT) lane. The facility was converted into a HOT lane and opened on October 1, 2011. This paper reports on the collection, processing, and filtering of the vehicle occupancy data and the factors that influenced vehicle occupancy along the I-85 corridor both before and after the conversion. The research effort used regression tree analysis techniques to identify data collector bias and then the effects of different factors such as season, data collection site, morning peak–evening peak, and lane type on vehicle occupancy. The study found that vehicle occupancy data on Monday were different from those data collected on Tuesdays, Wednesdays, and Thursdays. The study identified data collectors and sessions that had statistically different data from other sessions and filtered those data. The research effort then explored the factors affecting vehicle occupancy for the morning peak and the afternoon peak periods separately, given that related travel behavior characteristics were quite different. The research identified lane type (managed or general-purpose) as the most significant factor affecting occupancy, followed by pre- and postconversion of the HOV lane to HOT lane. The study also found that average vehicle occupancy decreased after conversion of the HOV lane. On the basis of the results of this study, the vehicle occupancy data were aggregated into the center stations, north of the GA-316 region and south of the I-285 region. The vehicle occupancy data are currently being applied to evaluate person throughput along the corridor.

I-85 High-Occupancy Toll Lane's Impact on Commuter Bus and Vanpool Occupancy in Atlanta, Georgia

In October 2011, Atlanta, Georgia, opened its first high-occupancy toll (HOT) lanes, which were converted from high-occupancy vehicle (HOV) lanes. In partnership with the Georgia Department of Transportation, the Georgia Institute of Technology established a research team to assess changes in vehicle throughput, vehicle occupancy, and passenger throughput associated with the I-85 HOV-to-HOT lane conversion. For the assessment of these measures, commuter bus ridership, which carries a significant portion of ridership, could not be collected through the applied efforts to collect field data. Moreover, the effects of ridership and vehicle throughput on vanpools, which also use the managed lanes, are unknown. The purpose of this research was to estimate the change in vehicle and person throughput of alternative modes before and after the HOV-to-HOT lane conversion. The results indicate that person throughput remained relatively stable for commuter buses, even with an increase in vehicle throughput. The vehicle throughput of vanpools was not substantial and increased slightly after the conversion. The commuter bus results were unexpected, as ridership was expected to increase because of the related travel time saving and reliability. Behavioral research is needed to understand the underlying effects of ridership to separate the underlying effects from external factors such as gas prices, travel times, employment, and others.

Evaluation Framework for Rigorous Exploration of Potential Benefits of Integrated Corridor Management

Highway congestion continues to be a major problem in urban transportation, and the search for feasible mitigation measures continues to evolve with the advancement in technology and a better understanding of traveler behavior. Integrated corridor management (ICM) has recently emerged as a potential mitigation measure; however, for this potential to be fully harnessed, research into the ways to identify ICM strategies that best fit the particular circumstances of a transportation corridor is necessary. This study proposed an ICM evaluation framework that was based on which strategies critical to congestion mitigation in a corridor could be identified. The proposed evaluation framework was demonstrated by using the I-95–I-395 ICM corridor in northern Virginia, where the effectiveness of selected ICM strategies was tested under both incident and nonincident conditions through a microscopic simulation model. An analysis of the simulation results identified variable speed limits, an increase in transit and parking capacities, high-occupancy vehicle–high-occupancy vehicle bypass lanes, and high-occupancy toll lanes as the most beneficial ICM strategies for both incident and nonincident traffic conditions. However, the benefits of ICM determined through the strategies modeled were confirmed to be more significant under incident conditions than nonincident conditions. As a result of the ICM strategies implemented, an average flow increment in the corridor of 6,860 persons per hour (+ 37.8%) was experienced during incident conditions compared with 3,286 persons per hour (+ 14.4%) for nonincident conditions. Improvements were also observed in average travel times and vehicle emissions.

Socioeconomic Assessment

High-occupancy toll (HOT) lanes use dynamic pricing to manage demand for lane use and to maintain acceptable traffic flow and traffic speeds. However, minimum occupancy and toll payment requirements raise potential socioeconomic questions concerning disparate negative effects across demographic groups. The objective of this study was to improve the knowledge about socioeconomic aspects of congestion pricing by using the I-85 high-occupancy vehicle (HOV) to HOT conversion in Atlanta, Georgia, as a case study. To evaluate the effects across user groups, more than 1.5 million license plate records were collected during a 2–year period, 1 year before and 1 year after the conversion. Analyses compared collected records with state motor vehicle registration databases to identify the vehicles and link census block group level and marketing household level socioeconomic attributes. In addition, results of a 2-day travel diary survey conducted by Volpe 6 months before and 6 months after the conversion were assessed. This study used all three sources of data in parallel to undertake a socioeconomic evaluation of the HOV-to-HOT conversion. Whereas previous studies were built on only one data source with significantly smaller sample sizes, the use of three distinctive sources of socioeconomic data and an exceptionally large sample size advanced the understanding of the potential socioeconomic effects of managed lanes. Furthermore, with the noted advantages and disadvantages of these data sources, this study provided valuable insight for general demographic analysts.

Combinatorial Auction to Allocate Traffic

This paper proposes an auction system implemented with vehicle-to-infrastructure devices to toll and to allocate traffic. Vehicles bid for paths before entering the network. By solving an optimization problem, the system assigns vehicles to paths and computes the corresponding toll. A mathematical model of this auction is presented and analyzed. The paper proves that this auction mechanism guarantees truthful reporting and maximizes social utility. The auction is then tested on a network with 5,100 vehicles. The paper also discusses the use of the auction as a toll-setting mechanism for high-occupancy vehicle or high-occupancy toll lanes.

Examination of Paid Travel on I-85 Express Lanes

The implementation of the I-85 express lanes in Atlanta, Georgia, was the first conversion of a high-occupancy vehicle lane to a high-occupancy toll lane that simultaneously increased the occupancy requirement (from two or more persons to three or more persons) and implemented tolls without the creation of additional lanes. This paper presents the findings of an analysis of tolling data collected during the first year of operation as part of the National Evaluation of Urban Partnership Agreement and Congestion Reduction Demonstration programs sponsored by the U.S. Department of Transportation. This analysis found the median willingness to pay for express lane travel time savings to be $19.45 per hour across all time periods and $33.17 per hour for southbound a.m. peak travel. There was little difference in the willingness to pay between frequent and infrequent travelers of the express lanes. This analysis was based on actual tolls paid by travelers and therefore represents the minimum these travelers were willing to pay.

Assessing the Impact of Transportation Policies on Fuel Consumption and Greenhouse Gas Emissions Using a Household Vehicle Fleet Simulator

The application of a comprehensive model system of vehicle fleet composition and evolution is described; this model system is capable of taking a base-year vehicle fleet and making it evolve over time in annual time steps through the events of vehicle disposal, replacement, and acquisition. The model system is sensitive to a host of socioeconomic, demographic, built environment, and vehicle technology and price variables; this sensitivity makes it ideally suited for such an application. Coupled with a demographic forecasting model system that causes the population to evolve over time, the vehicle evolution simulator is able to predict changes in vehicle fleet composition, miles of travel, fuel consumption, and greenhouse gas emissions under a wide range of scenarios. On the basis of the findings from this study, future technological innovations (e.g., increase of driving range) and pricing levels (doubling of gas cost) will have greater impacts on vehicle fleet composition, utilization, energy consumption, and greenhouse gas emissions than more incentive-based approaches such as free access to high-occupancy vehicle lanes for alternative-fuel vehicles.

Measuring value of travel time and travel time variability in the presence of managed lanes: results from a pilot stated preference survey on the Capital Beltway

Managed lanes are roadways that have additional requirements placed on their usage in an effort to maintain reliable, uncongested flow. This concept is already gaining use in some parts of the United States where vehicles that do not meet the minimum vehicle occupancy requirements are allowed to use the high occupancy vehicle (HOV) lane with the payment of a fee, leading to the term, high occupancy toll (HOT) lanes. This study collects data on behavioral responses to managed lanes and in particular quantifies a traveler’s value of time in the hypothetical scenario that managed lanes are applied on the Maryland side of the Capital Beltway. The main purpose is to provide a data collection and evaluation framework to assess potential projects. Two stated preference (SP) surveys have been designed and executed. The first analyzes choice across normal lanes, HOT and HOV, proposing different components of travel time. The second is developed in a context of departure time shift and proposes uncertainty as a range. Results show that the second experiment was more successful in recovering work and non-work values of travel time, delivers significant results for the uncertainty coefficients, and reinforces the finding that later departure time is perceived more negatively than earlier departure time.

High Occupancy Vehicle (HOV) Lanes As AMeans Of Transport Demand Management:The Thessaloniki Experience

High Occupancy Vehicle (HOV) Lanes As AMeans Of Transport Demand Management:The Thessaloniki Experience

Research on the Link Travel Time Model for High Occupancy Vehicle Lanes of Freeways

Due to the distinctive characteristics of high occupancy vehicles (HOVs), the existing link travel time models are not suitable for HOV lanes on freeway. The objective of this research is to provide a link travel time model for HOV lanes. Road and traffic data were collected from California Department of Transportation and dealt with using Highway Capacity Manual. By Bureau of Public Roads function, the link travel time model for freeway HOV lanes was established, considering both flow- to-capacity ratios on HOV lane and the adjacent mainline lane. Statistical methods including Pearson, Kendall and Spearman correlations, stepwise method were used for coefficient calibration. Through significance test and error test, the model effectiveness was demonstrated. The model proposed in this research can be applied to speed prediction, traffic assignment and some relevant fields.

Analyzing the Changes in Speed Due to High Occupancy Vehicles Using Median Bus Lane

This study estimated the changes in delays and speeds of vehicles in exclusive bus lane and road when the High Occupancy Vehicles(HOV) use the median bus lane. Synchro simulation tool was used to optimize the traffic signal time on the network and VISSIM was applied to simulate various scenarios. Here, drivers behavior parameters in VISSIM was optimized using Simultaneous Perturbation Stochastic Approximation(SPSA) algorithm in order to represent real traffic condition. Based on the simulation results, the delay in Doan daero was decreased when the volume of HOV in current condition runs on the median bus lane, whereas delay in Doan dongro was increased in all scenarios. The changes in bus speed was not sharply decreased for both study sites, even though the number of HOV increased to 10%. Thus, it could be allowed that the HOV use the median bus lane in Doan dongro and Doan daero. Future research tasks include studying about changes in delay when the HOV use the curb bus lane.

The Effects of Regulation in the Presence of Multiple Unpriced Externalities: Evidence from the Transportation Sector

In transportation systems with unpriced congestion, allowing single-occupant low-emission vehicles in high occupancy vehicle (HOV) lanes to encourage their adoption exacerbates congestion costs for carpoolers. The resulting welfare effects of the policy are negative, with environmental benefits overwhelmingly dominated by the increased congestion costs. Exploiting the introduction of the Clean Air Vehicle Stickers policy in California with a regression discontinuity design, our results imply a best-case cost of $124 per ton of reductions in greenhouse gases, $606,000 dollars per ton of nitrogen oxides reduction, and $505,000 dollars per ton of hydrocarbon reduction, exceeding those of other options readily available to policymakers.

Empirical Study of Lane-Changing Behavior along Different Types of High-Occupancy Vehicle Facilities in California

Lane changing is one important aspect of vehicle maneuvers that has significant impacts on freeway operation. Most of the previous research on lane changing has focused on the microscopic modeling of lane change movements. Very few studies have investigated lane-changing behavior along high-occupancy vehicle (HOV) facilities, especially in the context of comparing different access types. This paper describes work that extracted lane change data with high resolution in both time and space from videos and investigated lane-changing behavior on freeways with different types of HOV access configurations. Furthermore, the extracted lane change data were correlated with lane-by-lane flow and occupancy data from the California Freeway Performance Measurement System. Compared with continuous-access HOV facilities, limited-access HOV facilities were found to have a higher number of lane changes per unit distance and a shorter time gap when the subject vehicle moved out of the HOV lane. Also, most of the lane changes on limited-access HOV facilities occurred within the first half of ingress–egress areas. The insights provided by these results on lane-changing maneuvers along HOV facilities can be used to support traffic operation analyses, calibrate driver behavioral logic in traffic simulation models, and inform the design of lane configurations and access control measures for managed lanes.

Vehicle Reidentification with the Inductive Loop Signature Technology

This study proposed a real-time inductive loop signature based vehicle reidentification approach, RTREID-2M, which improved the previously developed RTREID-2 algorithm on two aspects: (1) Develop a cubic spline data imputation approach to replace the existing linear data imputation approach in order to improve the raw signature data quality; (2) Improve the time window setting for vehicles on High-Occupancy Vehicle (HOV) lanes so that vehicles on HOV lanes traveling with free flow speeds would be considered when generating candidate vehicle sets even during congestion time periods. In addition, a stratified-random sampling method was developed to effectively perform ground-truthing task for evaluating the performance of the proposed RTREID-2M. The evaluation results showed desired performance for vehicle reidentification and travel time estimation under both free-flow and congested flow traffic conditions. The future research will focus on the potential applications and arterial vehicle reidentification utilizing the inductive loop signature technologies.

Evaluation of Wide-Area Traffic Monitoring Technologies for Travel Time Studies

Road agencies typically collect travel time information from their network to identify traffic bottlenecks and to quantify the effects of road improvement investments in terms of travel time improvements. Road agencies can benefit from newly emerging automated data collection technologies that acquire travel time information for a large geographical area at lower costs. The objective of the study presented in this paper was to evaluate travel time data obtained from three technologies (i.e., Bluetooth, in-vehicle navigation systems, and mobile phone probes) compared with travel time obtained from probe vehicles equipped with Global Positioning Systems (GPSs). Traffic data were obtained for road types (e.g., freeways, arterials, ramps) in the study area from commercial data providers for a relatively large study area in the Province of Ontario, Canada. A multicriteria methodology was developed to evaluate data from each data provider on the basis of accuracy, coverage, number of observations, and capability to provide data for special facilities such as high occupancy vehicle lanes. The findings of this research suggested that all three technologies could replace traditional, GPS-equipped probe vehicles. This paper offers several recommendations on the use of travel time data from different data providers.

Impacts to Transit from Variably Priced Toll Lanes

This paper describes the impacts on transit performance from three separate conversions of high-occupancy vehicle lanes into variably priced high-occupancy toll (HOT) lanes in Miami, Florida; Minneapolis, Minnesota; and Atlanta, Georgia. The data showed that the conversions had no negative impact on bus performance. In all three cities, the buses experienced travel time savings after the conversion: 17 min in Miami, 4.5 min in Minneapolis, and 5 min in Atlanta. Similarly, the HOT conversions did not negatively affect bus ridership. Ridership increased over the baseline by 57% in Miami and 13% in Minneapolis. In Atlanta, ridership increased by 11%, and this increase began before the conversion. Bus riders’ overall perception of the HOT lanes has been positive. In surveys, the bus riders from Miami and Minneapolis gave high ratings for travel times and reliability in the HOT lane corridors. Riders in Atlanta rated the bus service as very good but were not as positive about the tolls. Riders disagreed that the HOT conversion had improved their travel or been good for the Atlanta region. These negative responses may be attributable in part to widespread disgruntlement with the HOT concept that existed even before implementation.

Influence of Quieter Pavement and Absorptive Barriers on US-101 in Marin County, California

A highway-widening project was completed on US-101 near San Rafael in Northern California with the addition of a high-occupancy vehicle lane in each direction, relocation of the southbound existing sound wall, and the addition of a multipurpose path. Because there was an existing sound wall in the northbound direction, additional conventional noise abatement was not considered feasible under California Department of Transportation and FHWA policies for this Type 1 project. However, two elements were included to improve aspects of existing noise environment. The elements included overlaying all lanes of the completed project area with quieter, open-graded asphalt and applying absorptive treatments to the traffic side of both barriers. To document the potential benefit of these features, the Transit Authority of Marin commissioned a study of preproject and postproject noise levels. Included were measurements of wayside noise levels above and behind the northbound sound wall and of tire–pavement noise using the onboard sound intensity method. Measurements indicated that 6- to 7-dB reductions in wayside noise levels both above and behind the barrier could be accounted for by reduction in tire–pavement noise. Effectiveness of added absorption could not be directly isolated in the measurements, so the benefit of this feature was assessed through acoustic modeling. Results indicated that additional reductions of 3 to 5 dB could occur for receptors elevated above the roadway, shielded from ongoing traffic but with a view of the opposing sound wall, and at distances of 500 ft or more. Near the highway, reduction provided by absorptive treatment was 1 to 1½ dB or less.

Valuation of travel time reliability from a GPS-based experimental design

In the Minneapolis–St. Paul region (Twin Cities), the Minnesota Department of Transportation (MnDOT) converted the Interstate 394 High Occupancy Vehicle (HOV) lanes to High Occupancy Toll (HOT) lanes (or MnPASS Express Lanes). These lanes allow single occupancy vehicles (SOVs) to access the HOV lanes by paying a fee. This fee is adjusted according to a dynamic pricing system that varies with the current demand. This paper estimates the value placed by the travelers on the HOT lanes because of improvements in travel time reliability. This value depends on how the travelers regard a route with predictable travel times (or small travel time variability) in comparison to another with unpredictable travel times (or high travel time variability). For this purpose, commuters are recruited and equipped with Global Positioning System (GPS) devices and instructed to commute for two weeks on each of three plausible alternatives between their home in the western suburbs of Minneapolis eastbound to work in downtown or the University of Minnesota: I-394 HOT lanes, I-394 General Purpose lanes (untolled), and signalized arterials close to the I-394 corridor. They are then given the opportunity to travel on their preferred route after experiencing each alternative. This revealed preference data is then analyzed using discrete choice models of route. Three measures of reliability are explored and incorporated in the estimation of the models: standard deviation (a classical measure in the research literature); shortened right range (typically found in departure time choice models); and interquartile range (75th–25th percentile). Each of these measures represents distinct ways about how travelers deal with different sections of reliability. In all the models, it was found that reliability was valued highly (and statistically significantly), but differently according to how it was defined. The estimated value of reliability in each of the models indicates that commuters are willing to pay a fee for a reliable route depending on how they value their reliability savings.

A Car-following Model Based on Discrete Choice Theory

In the car-following model proposed in this paper, the acceleration and deceleration are incorporated into seven alternatives, and alternative-specific parameters are adopted to capture different attractiveness of each alternative. To avoid interferences from lane-changing behavior, the model is estimated and validated by trajectory data in the high occupancy vehicle (HOV) lane. From the estimation results, most estimated parameters are significantly different from zero at 95% confidence level, which indicates that the chosen variables and the classification of alternatives are effective and reasonable. In addition, according to the proposed model, the changing tendencies of choosing different alternatives at different speeds and gaps are completely consistent with common driving behaviors. The validation results show that, for the chosen alternatives, the percentages of predicted probabilities that are larger than 1/7 (the average probability of choosing each alternative) are more than 87% in the used data sets. From the shares of observations point of view, there are only minor differences between the observed and predicted results. Finally, this model is applied to simulate the 30-min single lane traffic conditions. Through simulation results, it can be found that the proposed model can accurately represent the real traffic conditions on the macroscopic level, while, on the microscopic level, there are some defects needed to be further improved.