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Hauer E.,University of Toronto | Bonneson J.,Kittelson and Associates Inc. | Council F.,University of North Carolina at Chapel Hill | Srinivasan R.,University of North Carolina at Chapel Hill | Zegeer C.,University of North Carolina at Chapel Hill
Transportation Research Record | Year: 2012

Crash modification factors (CMFs) are listed in the Highway Safety Manual and other authoritative publications. This information does not allow the reader to distinguish between the predictions of safety effect that can be made confidently and are likely to lead to correct decisions and those that can easily be wrong. Nor can it be known how transferable past research results are to decisions about future actions to be implemented under different circumstances. The conceptual framework described in this paper aims to provide guidance for research about CMFs and for meta-analyses. The central claim is that CMFs are random variables and are not universal constants that apply everywhere at all times. The smaller the standard deviation of a CMF, the more confident the related decision making can be. Therefore, the aim of research into CMFs is to reduce their standard deviations. Ways to do so efficiently are indicated. The requisite theory and equations are provided. Source

Li J.-Q.,University of California at Berkeley | Wu G.,University of California at Riverside | Zou N.,Kittelson and Associates Inc.
Transportation Research Part D: Transport and Environment | Year: 2011

This paper investigates the environmental impacts of signal timing on vehicle emissions at a pre-timed signalized intersection. We use a two-stage approach: the first consists of developing optimization models that examine the trade-off between vehicle delays and the number of stops; and, based on the outcomes of the first stage, the second of estimating vehicle emissions using microscopic emission estimation models. A dynamic programming algorithm is developed to solve the optimization problems appearing in the first stage. A vehicle specific power approach is used to estimate the vehicle emissions near the intersection based on the results from the first stage. © 2011 Elsevier Ltd. Source

Sun X.,Nanjing Institute of City and Transport Planning | Urbanik T.,Kittelson and Associates Inc. | Han L.D.,University of Tennessee at Knoxville
Applied Mechanics and Materials | Year: 2013

This paper presents a neurofuzzy signal control system to improve the efficiency at closely-spaced signalized intersections. Building on the conventional actuated-coordinated control system, the neurofuzzy controller establishes a "secondary coordination" between the upstream coordinated phase and the downstream non-coordinated phase based on real-time traffic demand. Under the neurofuzzy signal control, the traffic from the upstream intersection can arrive and join the queue at the downstream left turn lane and be served, and therefore reduce the possibility of being delayed at the downstream intersection. The membership functions in the fuzzy controller are calibrated to further the performance. The simulation results indicate that the neurofuzzy signal control consistently outperformed to the conventional actuated-coordinated controller, in terms of reduction in system-wide average delay and average number of stops per vehicle, under a wide range of traffic volumes, especially under higher demand conditions. © (2013) Trans Tech Publications, Switzerland. Source

Pochowski A.,Georgia Institute of Technology | Myers E.J.,Kittelson and Associates Inc.
Transportation Research Record | Year: 2010

As the modern roundabout continues to grow in popularity in the United States, more states are considering or implementing statewide roundabout programs. To assist states in implementing statewide roundabout programs, a review of four such programs was conducted in Kansas, Maryland, New York, and Wisconsin. The review was completed through an examination of published state roundabout guides and interviews. Results from the review indicate that agency buy-in, public perception, and establishment of a statewide roundabout policy all play crucial roles in the success or failure of a statewide round-about program. It is recommended, therefore, that agencies focus on these areas to ensure success in establishing a roundabout program statewide. Source

Ferguson E.M.,Kittelson and Associates Inc. | Duthie J.,University of Texas at Austin | Unnikrishnan A.,West Virginia University | Waller S.T.,Research Center for Integrated Transport Innovation r 110
Transportation Research Part A: Policy and Practice | Year: 2012

This paper and the proposed formulation contribute to an apparent gap in transit research design by integrating equity considerations into the transit frequency-setting problem. The proposed approach provides a means to design transit service such that equitable access to basic amenities (e.g., employment, supermarkets, medical services) is provided for low-income populations or disadvantaged populations. The overarching purpose is to improve access via transit to basic amenities to: (1) reduce the disproportionate burden faced by transit dependent populations; and (2) create a more feasible transportation option for low-income households as an opportunity to increase financial security by reducing dependence on personal autos. The formulation is applied to data from a mid-sized US metropolitan area. The example application illustrates the formulation successfully increases access to employment opportunities for residents in areas with high percentages of low-income persons, as well as demonstrates the importance of considering uncertainty in the locations of populations and employment. © 2011. Source

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