Assessing the long term benefit of banning the use of hand-held wireless devices while driving

An increasing number of legislative efforts have been undertaken to prohibit the use of hand-held wireless devices while driving. As of July 2012, ten states and the District of Columbia enforce laws banning the use of hand-held cell phones while driving. Thirty-nine states and the District of Columbia have banned text messaging while driving. Recent studies of driver behavior suggest that hand-held wireless device usage negatively impacts driver performance. However few studies at the aggregate level address the plausible link between the use of hand-held wireless devices while driving, increased risk of automobile accidents, and government legislative efforts to reduce such risk. This paper analyzes data at the aggregate level and builds a regression model to estimate the long term accident rate reduction due to a hand-held ban. This model differs from previous studies, which consider short term accident rate reduction, by considering time trends in the accident rate due to the ban. Additionally, counties considered in this analysis are placed into groups based on driver density, defined by the number of licensed drivers per centerline mile of roadway, and a separate analysis is performed within these groups. This approach allows one to better quantify the effect of hand-held bans in counties of different driver densities. Results from this paper suggest that bans on hand-held wireless device use while driving reduce the rate of personal injury accidents in counties with high levels of driver density, but may increase accident rates in counties with low driver density levels. These results can inform transportation policymakers interested in reducing automobile-accident-risk attributable to the use of hand-held wireless devices while driving.     

What is paratransit worth?

Paratransit is a flexible demand-responsive form of public transportation intended for transporting mobility impaired individuals. This is the first study that estimates both demand and cost functions for publicly provided paratransit in the United States and the first to conduct a benefit-cost analysis for this mode. We find that the benefits of paratransit far exceed its associated costs. The results suggest that paratransit riders have few transportation alternatives available to them. We also find that the level of service matters in the demand for paratransit.     

Individual versus mass transportation: feasibility of substitution

This paper is addressed to the question of social costs and social benefits (primarily environmental) which might derive from a large‐scale substitution of so‐called mass‐transit for the present, largely private, system of automotive transportation. Energy consumption and emissions are compared for the two basic alternatives and several variants. Varying degrees of physiological tolerance to pollutants are taken into account, in an attempt to develop comparable weight‐factors for different types of emissions. It is suggested that if automobiles succeed in meeting the 1975/76 emission standards set by the Clean Air Act of 1970, rail rapid transit will probably offer no advantage (in environmental terms) unless electric power is available from virtually non‐polluting sources (e.g., natural gas or nuclear plants). Economic implications of large‐scale substitution are examined, and it is noted that such substitution would involve major restructuring of our society as a whole. However, more intensive use of mass transit in central cities, possibly in conjunction with various measures to discourage the use of private automobiles in very congested areas is feasible and likely.     

Estimation of TKE dissipation rates in dense bottom plumes using a Pulse Coherent Acoustic Doppler Profiler (PC-ADP) — Structure function approach

During a hydrographic survey in January 2006 the spreading of inflowing saline water was observed in the Arkona Basin (Western Baltic Sea). Two bottom mounted ‘pulse coherent’ acoustic Doppler profilers (PC-ADP) were used to measure the near-bottom current field of the dense plume with a high temporal (1 s) and spatial resolution (5 cm). In order to estimate the dissipation rate of turbulent kinetic energy () a structure function approach was applied to the beam velocity data. Simultaneous measurements with a microstructure shear profiler (MSS) and an acoustic Doppler velocimeter (ADV) supplied independent data for the verification of the structure function method. Additional measurements with standard CTD, near-bottom towed and vessel mounted acoustic Doppler current profilers (ADCP) completed the data set.The estimated dissipation rates from the structure function approach fit well with the values derived from the ADV and the MSS probe. It is shown that the structure function approach is a reliable and easily applicable method to derive estimates of TKE dissipation rates from PC-ADP beam velocities. The observed dissipation rates ranged between 5 · 10^− 6 and 1 · 10^− 8 W kg^− 1 depending on the hydrographic conditions. Inside the plume the dissipation rates exceeded that of the overlaying brackish water by two orders of magnitude. Since the noise level of velocity data in pulse coherent mode is considerably lower than in the Doppler mode the PC-ADP can also be used for estimates in marine environments with low turbulence level. Reynolds stresses estimated from the PC-ADP and the ADV agreed well at the same depth level. TKE production derived from PC-ADP measurements compared reasonably well with the dissipation rate of TKE in a varying environment.     

Large-eddy simulation of air entrainment during diesel spray combustion with multi-dimensional CFD

Large-Eddy Simulation (LES) was used to perform computations of air entrainment and mixing during diesel spray combustion. The results of this simulation were compared with those of Reynolds Averaged Navier Stokes (RANS) simulations and an experiment. The effect of LES on non-vaporizing and vaporizing sprays was evaluated. The validity of the grid size used for the LES analysis was confirmed by determining the subgrid-scale (SGS) filter threshold on the turbulent energy spectrum plot, which separates a resolved range from a modeled one. The results showed that more air was entrained into the jet with decreasing ambient gas temperatures. The mass of the evaporated fuel increased with increasing ambient gas temperatures, as did the mixture fraction variance, showing a greater spread in the profile at an ambient gas temperature of 920 K than at 820 K. Flame lift-off length sensitivity was analyzed based on the location of the flame temperature iso-line. The results showed that for the flame temperature iso-line of 2000oC, the computed lift-off length values in RANS matched the experimental values well, whereas in LES, the computed lift-off length was slightly underpredicted. The apparent heat release rate (AHRR) computed by the LES approach showed good agreement with the experiment, and it provided an accurate prediction of the ignition delay; however, the ignition delay computed by the RANS was underpredicted. Finally, the relationships between the entrained air quantity and mixture fraction distribution as well as soot formation in the jet were observed. As more air was entrained into the jet, the amount of air-fuel premixing that occurred prior to the initial combustion zone increased, upstream of the lift-off length, and therefore, the soot formation downstream of the flame decreased.     

Predicting auto-ignition characteristics of RCCI combustion using a multi-zone model

The objective of new combustion concepts is to meet emission standards by improving fuel air mixing prior to ignition. Since there is no overlap between injection and ignition, combustion is governed mainly by chemical kinetics and it is challenging to control the phasing of ignition. Reactivity Controlled Compression Ignition (RCCI) combustion aims to control combustion phasing by altering the fuel ratios of the high- and low octane fuel and injection timings. In this study the dual fuel blend is prepared with gasoline and diesel fuels. The applied injection timings of the diesel are very early (90 to 60° CA bTDC). In the detailed reaction mechanism, n-heptane and iso-octane represent diesel and gasoline fuel, respectively. A multi-zone model approach is implemented to perform RCCI combustion simulation. Ignition characteristics are analyzed by using CA50 as the main parameter. In the experiments for the early direct injection (DI) timing advancing the injection time results in a later ignition. Qualitatively, the trend effect of the diesel injection timing and the effect of the ratio gasoline/diesel are captured accurately by the multi-zone model.     

Fracture properties of aluminum foam crash box

This study investigates the compression property experiment to examine impact absorption when aluminum foam is applied to crash box in order to absorb impact energy in car crash with low speed. The result of compression property experiment shows that case 6, which involves the buckling that collapses into 5-layer structure, is the best model with regard to impact absorption. This study analyzes impact characteristics according to the structure of crash box which influences such factors as damage and safety of vehicles. As the simulation result can be agreed with experimental graph, all experimental data at this study are verified. These experimental results can be applied into real field effectively. It also proposes the effective design to improve impact performance by analyzing the property of crash box through its compressive test.     

The inherent precision of regression estimated route probabilities

From basic assumptions about independent and consistent driver behaviour, and with data from traffic counts, we derive statistical properties of regression or correlation estimates of route selection probabilities, turning probabilities and travelling times. Our modelling is conditional in a way that avoids most traffic generation problems and permits an asymptotic analysis of the precision under mild assumptions allowing non-stationarity. This allows us to put together non-stationary data from the corresponding time intervals during several days when we aim at high precision estimates.     

Evaluation of low-temperature diesel combustion regimes with n-Heptane fuel in a constant-volume chamber

The concept of Low Temperature Combustion (LTC) has been advancing rapidly because it may reduce emissions of NOx and soot simultaneously. Various LTC regimes that yield specific emissions have been investigated by a great number of experiments. To accelerate the evaluation of the spray combustion characteristics of LTC, to identify the soot formation threshold in LTC, and to implement the LTC concept in real diesel engines, LTC is modeled and simulated. However, since the physics of LTC is rather complex, it has been a challenge to precisely compute LTC regimes by applying the available diesel combustion models and considering all spatial and temporal characteristics as well as local properties of LTC. In this paper, LTC regimes in a constant-volume chamber with n-Heptane fuel were simulated using the ECFM3Z model implemented in a commercial STAR-CD code. The simulations were performed for different ambient gas O₂ concentrations, ambient gas temperatures and injection pressures. The simulation results showed very good agreement with available experimental data, including similar trends in autoignition and flame evolution. In the selected range of ambient temperatures and O₂ concentrations, soot and NOx emissions were simultaneously reduced.     

Nearshore Restoration in Puget Sound: Understanding Stakeholder Values and Potential Coalitions

Restoration of nearshore ecosystems presents many challenges for stakeholder involvement. Using surveys and interviews we examined stakeholder values, preferences, and potential coalitions surrounding nearshore restoration in the Whidbey sub-basin of Puget Sound. Most stakeholders in our study believe that Puget Sound nearshore problems are severe and urgent, and that it is worth investing in restoration. They do not agree on the causes of nearshore degradation, yet support stronger regulatory enforcement and increased public ownership as possible solutions to nearshore problems. Five potential stakeholder coalitions were identified based on shared values. These values reflect a varied spectrum of support for public sector solutions to nearshore problems and were labeled: No Government Intervention, Property Rights, Private Land Stewardship, Protect Undeveloped Areas, and Large Scale Restoration. The potential coalitions identified confirm the Advocacy Coalition Framework hypothesis that coalition members who share values do not necessarily share stakeholder demographics or preferences. This study demonstrates one method for understanding local stakeholders, and will help managers direct project resources, planning, and management, through reliance on both stakeholder and scientific input. In addition, managers can use information about stakeholder values and potential coalitions to more effectively frame communication products and stakeholder involvement activities.