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Open Access Publications from the University of California

Scholarly Works (10 results)

  • Article
Research Reports (2006)
This report documents work accomplished during Fiscal Year 2005-2005 as a part of a research project entitled “New Approach to Bottleneck Capacity.” This project is developing an alternative to the traditional Highway Capacity Manual approach to capacity analysis in which capacity flow [either pre-queue flow (PQF) or queue discharge flow (QDF)] is related to a set of intervening variables, including the average time gaps in the critical lane (i. e., that with the highest flow rate) and the distribution of flow across the lanes, represented by the critical lane flow ratio (i. e., the flow in the critical lane divided by the average flow per lane). These intervening variables, in turn, are to be related to the geometric characteristics of bottleneck sites, their vehicle populations, and their driver populations. Work to date has included the collection and analysis of data, analysis of traffic data to document flow characteristics at individual study sites, and an analysis of the relationships among the various traffic flow characteristics, including relationships among the intervening variables and between the intervening variables and capacity flows. Major findings to date are that (a) there are significant differences in the mean values of the flow characteristics during different episodes of PQF and QDF at individual sites;(b) means of flow characteristics are significantly different among the sites (with the exception of critical lane average time gaps in PQF); (c) flow variances also differ significantly among the sites;(d) QDF appears to vary by time of dayat some sites; (e) critical lane average time gaps and critical lane flow ratios are not correlated with one another in either PQF or QDF; (f) there is a significant negative correlation between the time gaps and the flow per lane; and (g) there is a very strong negative correlation between flow in the critical lane and critical lane average time gaps; when plotted, this relationship is virtually linear. On the basis of these findings, models relating flow per lane (for PQF and QDF) to critical lane flow ratios and critical lane average time gaps are proposed for use in the next stage of the research, which will focus on relating the flow ratios and time gaps to the geometric, vehicle-population, and driver population characteristics of the study sites.
    Cover page: New Approach to Bottleneck Capacity Analysis: Second Interim Report, Work Accomplished During Fiscal Year 2004-2005
    • Article
    Working Papers (2002)
    This report documents results of work completed at San Diego State University during the first year of a research project intended to validate a behavioral traffic-flow theory recently proposed by Daganzo (1,2). Work on this project completed at the University of California at Berkeley will be documented in a separate interim report.  In the idealized form developed so far, Daganzo’s theory assumes two types of drivers, aggressive (rabbits) and timid (slugs), and two lane groups, shoulder lanes and passing lanes.  In free flow, rabbits travel faster than slugs and the two groups are segregated in what Daganzo terms two-pipe flow, with the slugs all in the shoulder lane and the rabbits all in the passing lane.  In high-volume uncongested flow, rabbits will follow one another with very small headways, so long as they are able to pass, and such drivers are referred to as being motivated because the very small headways are held to be motivated by the desire to pass slower vehicles.  Whenever an event occurs that reduces speed in the passing lane to (or below) vf, the free-flow speed in the shoulder lane, the rabbits change lanes to equalize speeds, lose their “motivation,” and increase their headways.  This results in one-pipe flow.  Because of the difference in the headways, maximum uncongested flow rates in the passing lane exceed the queue discharge rate for this lane. Daganzo provides solutions for a number of cases involving transitions from two-pipe to one-pipe flow and vice versa.  These solutions are presented for the most part in terms of wave speeds and traffic states in, upstream, and downstream of queues.
      Cover page: Validation of Daganzo's Behavioral Theory of Mult-Lane Traffic Flow: Interim Report
      • Article
      Research Reports (2006)
      A capacity analysis approach intended as an alternative to the traditional Highway Capacity Manual (HCM) method was evaluated. One- and two-stage models of pre-queue and queue discharge flow (each of which might be thought of as representing “capacity” in some sense) were developed and compared with one another and the HCM method. Two-stage models related capacity flows to intervening variables, including average time gaps (average time separations between the rear of a vehicle and the front of one following it) in the critical lane (that with the highest flow rate) and the critical lane flow ratio (the flow in the critical lane divided by the average flow per lane), and then related these intervening variables to the geometric, vehicle population, and driver population characteristics of bottleneck sites. One-stage models involved direct relationships between capacity flows and site characteristics. Differences in capacity flow among study sites were primarily the result of differences in average critical lane time gaps; however, critical lane flow ratios were also important. The performance of the one-stage and two-stage models was similar. For the sites used to develop the models, both were better able to predict pre-queue and queue discharge flows than was the HCM method. In particular, the HCM method tended to overestimate actual bottleneck flows, especially in queue discharge. However, neither type of model was successful in explaining variations in capacity flows at additional sites used for verification. Once apparently anomalous data were eliminated, the only significant explanatory variable in the models was the number of lanes. Consequently, it is recommended bottleneck capacity analyses continue to be based on existing HCM methods but that these be supplemented by use of a look-up table based on the means and standard deviations of pre-queue and queue discharge flows for sites with particular numbers of lanes.
        Cover page: New Approach to Bottleneck Capacity Analysis: Final Report
        • Article
        Research Reports (2006)
        This report documents work accomplished during Fiscal Year 2005-2006 as a part of a research project entitled “Evaluation of Portable Automated Data Collection Technologies.” Major activities during this period included a literature survey, surveys of potential users and vendors, preliminary evaluation of portable data collection technologies to select candidate systems for demonstration, and development of demonstration plans. There is demand for portable automated data collection systems for uses related to planning, traffic operations, traffic census, and traffic surveillance functions. Potential users are interested in volume count, speed, occupancy, travel time, vehicle-length classification, and axle-based vehicle classification data. Potential uses require systems to remain installed from a few hours up to several years. Potential users want systems that minimize traffic disruption and exposure of crews to traffic, are “plug-and-play,” have IP-addressable communications capability, can provide data in a variety of formats, and have flexible power supplies. Candidate systems for demonstration are expected to consist of combinations of different sensors with different power supply and mounting system options. Current plans call for nine separate demonstrations. These demonstrations include tests of systems based on EIS microwave radar sensors that are currently underway in Caltrans District 11, demonstrations of other systems based on EIS and Wavetronix microwave radar sensors to be designed by the study team and carried out by District 11, and a demonstration of The Infra-Red Traffic Logger (TIRTL) that is planned by District 7.
          Cover page: Evaluation of Portable Automated Data Collection Technologies: Interim Report, Work Accomplished During Fiscal Year 2005-2006
          • Article
          Research Reports (1997)

          This report documents research focusing on: 1) analyzing performance measurements for California Department of Transportation (Caltrans) Transportation Management Centers (TMCs); 2) identifying and assessing the feasibility of data collection and management activities required to support TMC performance measurement; and, 3) recommending specific actions by Caltrans and the California PATH program that will facilitate performance measurement.

            Cover page: Traffic Management Systems Performance Measurement: Study Directions And Scope, Proposed Measures Of Effectiveness, And Proposed Action Priorities
            • Article
            Working Papers (1997)
            Traffic Data System Improvement Plans were prepared for Caltrans Districts 1 1 (San Diego) and 12 (Orange County) as part of a research project on performance measurement for traffic management systems. The plans document data system objectives, data requirements, and existing data collection and management systems; evaluate the adequacy of existing systems; identify improvements and resource requirements; and document the districts’ priorities for action. Both districts have similar data systems, although Orange County’s is better developed. Both systems rely heavily on single-loop detectors for traffic surveillance. Both either have or plan to have current- generation data display and management software, complete coverage of urban freeways by loop-detector systems, extensive video surveillance systems, and fiber-optic communication systems. In addition, both provide or will provide computerized incident and equipment-status logging, adequate accident and traffic volume data bases, and automatic data screening capability. Traffic data systems in the two districts appear to be generally adequate to support major performance measures identified in a previous phase of the project. Despite their commitment to providing sophisticated traffic data collection and data management systems, however, the two districts do not necessarily have a clear vision of how to use the data to monitor performance, and lack the organizational structure and staffing to carry out evaluation studies, performance monitoring, and data quality control.
              Cover page: Traffic Management Systems Performance Measurement: Working Paper #2
              • Article
              Research Reports (1997)

              This report documents a study of performance measurement for Transportation Management Centers (TMCs). Performance measurement requirements were analyzed, data collection and management techniques were investigated, and case study traffic data system improvement plans were prepared for two Caltrans districts.

                Cover page: Traffic Management Systems Performance Measurement: Final Report
                • Article
                Research Reports (1997)

                The Smart Call Box Field Operational Test evaluated the feasibility and cost-effectiveness of using smart call boxes for five data processing and transmission tasks: traffic census, incident detection, hazardous weather reporting, changeable message sign control, and video surveillance. Evaluation focused on assessing the cost-effectiveness of smart call boxes as compared with a baseline system using hardwire telephone communications. The evaluation was primarily based on functional adequacy and capital costs.

                  Cover page: Smart Call Box Field Operation Test Evaluation: Summary Report (revised Draft 5-1-97)
                  • Article
                  Research Reports (2003)

                  A study was conducted to verify C. F. Daganzo's behavioral theory of multi-lane traffic flow (1, 2). This study was conducted by teams from San Diego State University and the University of California at Berkeley who worked independently on a series of case studies to test predictions derived from the theory. The results of the study suggest that some of the phenomena predicted by Daganzo do occur, but not at all locations, and that the underlying behavioral assumptions are oversimplified. Specifically, the types of flow- density (or flow-occupancy) relationship assumed by Daganzo were found to occur at some sites but not others; semi-congested states and fast waves between semi-congested and fully-congested states, as predicted by Daganzo were observed at one site; an increase in average time gaps indicating a "loss of motivation" assumed by Daganzo was observed at one site but not at others; speeds were found not to be equalized among lanes in congested flow, contrary to Daganzo.s assumption and most past literature; redistribution of flow among lanes was observed at flow breakdown despite the absence of speed equalization, contrary to Daganzo's behavioral assumptions; and distinct capacity and discharge flow states predicted by Daganzo were not observed downstream from queues. Observations not directly related to the test of Daganzo.s theory included details of lane-by-lane speed behavior in congested flow, a case in which the location of the point of maximum density upstream from a bottleneck may have influenced its capacity, and observations of general characteristics of incident recovery flow.

                    Cover page: Validation of Daganzo's Behavioral Theory of Multi-Lane Traffic Flow: Final Report
                    • Article
                    • Peer Reviewed
                    UCLA Previously Published Works (2020)
                    Brown adipose tissue (BAT) is composed of thermogenic cells that convert chemical energy into heat to maintain a constant body temperature and counteract metabolic disease. The metabolic adaptations required for thermogenesis are not fully understood. Here, we explore how steady state levels of metabolic intermediates are altered in brown adipose tissue in response to cold exposure. Transcriptome and metabolome analysis revealed changes in pathways involved in amino acid, glucose, and TCA cycle metabolism. Using isotopic labeling experiments, we found that activated brown adipocytes increased labeling of pyruvate and TCA cycle intermediates from U13C-glucose. Although glucose oxidation has been implicated as being essential for thermogenesis, its requirement for efficient thermogenesis has not been directly tested. We show that mitochondrial pyruvate uptake is essential for optimal thermogenesis, as conditional deletion of Mpc1 in brown adipocytes leads to impaired cold adaptation. Isotopic labeling experiments using U13C-glucose showed that loss of MPC1 led to impaired labeling of TCA cycle intermediates. Loss of MPC1 in BAT increased 3-hydroxybutyrate levels in blood and BAT in response to the cold, suggesting that ketogenesis provides an alternative fuel source to compensate. Collectively, these studies highlight that complete glucose oxidation is essential for optimal brown fat thermogenesis.
                      Cover page: Mitochondrial pyruvate carrier is required for optimal brown fat thermogenesis
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