Time-series model for vehicle speeds

This paper presents a time-series model for the spot speeds of vehicles on a road section. Based on time-series analysis techniques, the model incorporates information on the extent of existing dependency between the speeds of successive vehicles. The model for the data is chosen while relying heavily on the data, and thus emphasis is given to their special characteristics. The advantages of using the model are examined with regard to the relative speed of two successive vehicles along a road section. The results are compared with those obtained by using a model of independent observations; fewer errors are obtained with the time-series model. Therefore, it is concluded that the sequence of speed observations contains valuable information which should be incorporated into speed models.     

Further evidence on the temporal stability of disaggregate travel demand models

Current evidence on the transferability of disaggregate travel demand models is inconclusive. Adding to this body of research, the present analysis focuses upon the temporal characteristics of work trip behavior in the San Francisco Bay Area. Using before and after data sets associated with the BART Impact Travel Study, multinomial logit models of work trip modal choice are estimated. The results indicate that the general form and the coefficient estimates of a pre BART model are transferable in time. Moreover, when updated to reflect BART's presence, the model's predictive success and its implied elasticity measures are generally accurate, relative to those implied by reestimating the entire model on post BART data. Finally, as economic theory would predict, elasticity measures of the service related variables were found to increase over time.     

Public transit subsidies, output effect and total factor productivity

This paper extends previous works on total factor productivity decomposition when firms receive both operating and capital subsidies. It shows that previous works considered either the lump-sum or substitution effects of these subsidies but not together. Using constrained cost minimization as the framework it offers formal proofs to show that cost increases are inevitable if the total effects of the subsidies are considered, and that total factor productivity growth results from increasing amounts of subsidies under economies of scale and in the absence of technical change. Applications of the decomposition equations derived to a sample of transit systems finds near constant returns to scale and negative contributions of these subsidies to total factor productivity growth. Technical change reverses this decline and results in total factor productivity growth. Further, it finds that the lump-sum effects of the subsidies reduce total factor productivity more than does the substitution effect.     

Model-based analysis of the mechanical subsystem of an air brake system

Most commercial vehicles such as buses and trucks use an air brake system, often equipped with an S-cam drum brake, to reduce their speed and/or to stop. With a drum brake system, the clearance between the brake shoe/pad and the brake drum may increase because of various reasons such as wearing of the brake shoe and/or brake drum and drum expansion caused by high heat generation during the braking process. Hence, to ensure proper functioning of the brake system, it is essential that the clearance between the brake shoe and the brake drum is monitored. In this paper, we present a mathematical model for the mechanical subsystem of the air brake system that can be used to monitor this clearance. This mathematical model correlates the push rod stroke transients and the brake chamber pressure transients. A kinematic analysis and a dynamic analysis of the mechanical subsystem of the air brake system were performed, and the results are corroborated with experimental data.     

Optimal synthesis of function generation in steering linkages

This paper presents an approach to optimize planar mechanisms for function generation synthesis. It is applied to the design of different steering linkages used in road vehicles where the Ackermann condition is formulated as the objective function. Four different mechanisms are kinematically defined and synthesized in terms of the proposed method. Limitations of the size of the elements are also considered by means of inequality constraints. Solutions are presented as the difference between desired behaviour, established by Ackermann, and actual generated performance. The results show that the accuracy achieved by the proposed procedure is satisfactory for working conditions in this type of linkages.     

Benthic sediment composition and nutrient cycling in an Intermittently Closed and Open Lake Lagoon

Surfical sediments within Corunna Lake, a moderate size Intermittently Closed and Open Lake Lagoon (ICOLL), were examined for solid phase nutrient concentrations (TN, TP, TOC,) and solute exchange rates between the sediment and water column (O₂, NO₃–N, NH₄–N, FRP, and N₂). The surfical sediments in Corunna Lake contained high concentrations of TN (5 mg/g dry mass), total phosphorus (0.6 mg/g dry mass), and TOC (~ 5% dry mass). The carbon stable isotope ratio (δ¹³C) and TOC:TN ratios (δ¹³C ~ ? 24, TOC:TN ~ 11–14) demonstrated that the composition of the organic matter in the sediment was a mixture derived primarily of degraded planktonic matter. The close association between TP and Fe concentrations highlighted the potential role Fe plays in mediating Filterable Reactive Phosphorus (FRP) concentrations in the water column of Corunna Lake. In situ benthic chamber incubations were used to measure benthic fluxes. Solute exchange rates between the sediment and water column in Corunna Lake were similar to other reported studies (O₂ = ? 469 to ? 1765 µmol m^? 2 h^? 1, NH₄–N = 0.1–63 µmol m^? 2 h^? 1, NO₂/NO₃–N = 0 µmol m^? 2 h^? 1, FRP = ? 4–1.6 µmol m^? 2 h^? 1and N₂ = 12–356 µmol m^? 2 h^? 1). As more carbon was deposited and mineralized the efficiency of the bacterial population to denitrify nitrogen in the sediment decreases. The linkage between land use and benthic biogeochemistry was also explored. A dairy farm exists in the middle catchment of Corunna Lake, and the receiving bay sediment consistently demonstrated the highest oxygen consumption rates in winter and spring (? 1408 µmol m^? 2 h^? 1 in winter, ? 1691 µmol m^? 2 h^? 1 in spring) and lowest denitrification efficiencies during summer (~ 3%). Nitrate/nitrite fluxes were not observed during any of the chamber incubations, with the concentrations of nitrate/nitrite being below detection limits (< 10 μg/L). Seasonal changes influenced the rates of solute exchange between the sediment and water column. Critical measures of solute exchange for NH₄–N and biogenic N₂ indicated that seasonal temperature changes play a significant role in mediating the reaction rates of sedimentary based biogeochemical processes. Measurable FRP fluxes were small but greater in the benthic sediments which received higher carbon inputs. Sediments have a high capacity to adsorb P which is released as sediment oxygen demand increases as a result of increases in labile carbon loads.