查看更多>>摘要：As agencies place more emphasis on monitoring and managing the roadway network, the concept of traffic monitoring systems based on wireless location technology (WLT) is generating increasing interest. WLT-based monitoring anonymously samples the location of probes or drivers by using wireless devices, such as cellular phones. By using a series of these probe vehicle locations, WLT-based monitoring systems could generate true point-to-point speed estimates with a minimal infrastructure investment. Unfortunately, early deployments of these systems have not been entirely successful in generating the quality of information needed by transportation agencies and the public. When transportation agencies are approached by vendors of WLT-based monitoring systems, they have little information to determine whether the system is likely to be effective. The relationship between the design of a WLT-based monitoring system and the accuracy of speed estimates that it generates is explored. A simulation-based approach was used to define general guidelines for different aspects of system design and roadway network characteristics. The type of map matching used, the frequency between position estimates, the error of position estimates, and roadway network geometry were shown to have a significant impact on generating accurate speed estimates from a WLT-based monitoring system.
查看更多>>摘要：Three elementary cases, with ramp metering used to reduce delay by diverting traffic around bottlenecks, are analyzed. In these cases (a) travel times on an alternate route bypassing the bottleneck are insensitive to flow on the alternate route, (b) the alternate route is undersatu-rated but travel times are sensitive to flow, and (c) the alternate route is oversaturated. Travel time equilibria and traffic assignments are relatively straightforward in all cases provided that equilibria in Cases b and c are assumed to be approximate and traffic assignments are based on drivers' expectations about traffic conditions prevailing at particular times of day. A metering strategy intended to minimize delay is proposed. This strategy is expressed in terms of the order in which metering is initiated at different ramps and is similar to one previously proposed to maximize output to exits upstream of the bottleneck.
查看更多>>摘要：The characteristics of preincident, postincident, and nonincident traffic conditions on freeways are investigated. The characteristics are denned by second-order statistical measures derived from spatiotemporal speed contour maps. Four performance measures are used to quantify properties such as smoothness, homogeneity, and randomness in traffic conditions in a manner similar to texture characterization of digital images. With real-world incident and traffic data sets, statistical analysis was conducted to seek distinctive characteristics of three groups of traffic operating conditions: preincident, postincident, and nonincident. The study results showed that the spatiotemporal characteristics of each of the three groups were not discernible. Although the distributions of performance measures within each group are statistically different, no consistent pattern was detected to imply that certain characteristics could increase the likelihood of incidents or identify precursory conditions to incidents.
查看更多>>摘要：Optimally coordinated freeway traffic control for networks containing bottlenecks with capacity drop and hysteresis behavior is considered. Because of the multitude of traffic jams and the spatial and temporal relationships between control actions and traffic behavior, this problem is not as straightforward as that for local control. The order in which the measures are applied may be relevant, or it may be possible that not all jams can be resolved. In that case the best possible locations of jams should be determined. An approach to address these problems is developed in which a generalized representation of flow-limiting control measures and bottlenecks is used. Whether a certain set of control measures is sufficient to improve network performance is determined. The approach also supplies the necessary sequence of control actions and the necessary relocation of traffic jams to achieve the network state corresponding to the best achievable performance.
查看更多>>摘要：The relationship between time mean speed and space mean speed that was derived by Wardrop and presented in several textbooks is suitable for estimating time mean speeds from space mean speeds. In most cases, however, estimating space mean speed from time mean speed measurements is desired. Consequently, a new formulation utilizes the variance about the time mean speed as opposed to the variance about the space mean speed for the estimation of space mean speeds. It is demonstrated that space mean speeds are estimated within a margin of error from 0% to 1%. Furthermore, a relationship is developed between the space and time mean speed variances and between the space mean speed and the spatial travel time variance.
查看更多>>摘要：To improve freeway modeling and operations, it is important to understand how traffic conditions evolve in both time and space. The widespread availability of freeway sensor data makes detailed operational analysis possible in ways that were not available in the past. This study, inspired by several other studies of a 6-mi segment of Interstate 405 in Orange County, California, describes the evolution of traffic conditions over one morning peak period by using inductive loop detector data, including vehicle count and lane occupancy measured at 30-s intervals. With cumulative curves of vehicle count and occupancy, transformed in ways that enhanced their resolution, 10 bottleneck activations were identified in time and space over one morning peak period. At bottleneck activation, queue propagation was observed in generally predictable ways. Bottleneck outflows were carefully measured only while the bottlenecks were active, that is, while queued conditions persisted upstream and unqueued (freely flowing) conditions prevailed downstream. When bottlenecks were activated immediately following freely flowing conditions, outflow reductions were observed at queue formation. These reductions were consistent with those in previous studies. The study was limited in that only one day's data were analyzed and ramp data were not available on the day analyzed. Future research will include further analysis of the same site by using more recent data now that ramp counts are available in the California Performance Measurement System database. Understanding the mechanisms that lead to bottleneck activation is a critical step toward improving the understanding of how freeways function and is necessary for addressing operational issues. This clear understanding provides a foundation for determining ramp metering rates and addressing the freeway characteristics that cause bottlenecks to form.
查看更多>>摘要：A new test bed for automatic incident detection (AID) systems uses realtime traffic video and data feeds from the Ontario, Canada, Ministry of Transportation COMPASS advanced traffic management system. This new test bed, called the AID comparison and analysis tool (AID CAAT), consists largely of a data warehouse storing a significant amount of traffic video, the corresponding traffic data, and an accurate log of incident start and end times. Also presented is a proof-of-concept field evaluation whereby the AID CAAT is used to calibrate and then analyze the performance of three AID algorithms: California Algorithm 8, the McMaster algorithm, and the genetic adaptive incident detection algorithm. In the calibration and testing process, nuisance rate and false normal rate are introduced as two new performance measures to supplement the three traditional measures (detection rate, false alarm rate, and mean time to detection). Further, the pilot evaluation shows the considerable advantages of AID CAAT in its ability to investigate the impact of freeway geometry, traffic flow rate, and traffic sensor spacing on the performance of the three AID algorithms. This work represents the first stage in a series of further tests to develop a set of AID algorithm deployment guidelines.
查看更多>>摘要：Implementing minor geometric and operational improvements on existing freeways to remove bottlenecks has the potential of achieving high benefits, yet it is not routinely done. Four case studies of bottleneck removal projects in Texas are presented in some detail with before-and-after evaluations of speeds, volumes, and crash histories. The case is made that many benefits may be realized for little cost. In addition, evaluations of nine other bottleneck removal projects are included in summary tables. Benefit-cost ratios as high as 400:1 have been found, with the lowest ratio being 9:1; costs ranged from $8,000 to $2.45 million. Injury crash rates were substantially lower after the bottleneck removal in almost all cases (average reduction of approximately 35%); however, an increase in crash rate was noted in one of the 13 cases.
查看更多>>摘要：The study evaluates lane management strategies along one of the most highly traveled sections of Interstate 81 in the state of Virginia by using the INTEGRATION traffic simulation software. The lane management strategies considered include the separation of heavy-duty trucks from light-duty traffic, the restriction of trucks to specific lanes, and the construction of climbing lanes at strategic locations. Overall, the results demonstrate that a physical separation of heavy-duty trucks from the regular traffic offers the maximum benefits and that restricting trucks from the use of the leftmost lane offers the second-highest benefits in terms of efficiency, energy, and environmental impacts.
Adinarayana BeegalaJohn HourdakisPanos G. Michalopoulos
p.87-98页
查看更多>>摘要：Freeway ramp control has been successfully implemented since the mid-1960s as an efficient and viable freeway management strategy. However, the effectiveness of any ramp control strategy is largely dependent on site-specific customization and calibration, preferably before its deployment. A general methodology for such performance optimization of ramp control strategies is proposed in a microscopic simulation environment as an alternative to trial-and-error field experimentation. The applicability of the methodology is demonstrated by implementation on Minnesota's new stratified zone metering (SZM). Further, the effect of external factors, such as traffic demand variation and incidents, on SZM control and optimization results was also studied. Results show that the optimization methodology is highly effective depending on the optimization objective, test site characteristics, and demand levels.
NETL
NSTL