| 1. |
- Andersson, C., et al.
(författare)
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Fully electric ship propulsion reduces airborne noise but not underwater noise
- 2024
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Ingår i: Ocean Engineering. - Göteborg : Elsevier. - 0029-8018 .- 1873-5258. ; 302
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Tidskriftsartikel (refereegranskat)abstract
- Electrification of ships offers zero-emission travel and is spreading rapidly, but the relation between electric ship propulsion and noise pollution is not generally understood. Here, three different types of diesel-electric hybrid ferries have been measured in two operating modes: running in hybrid mode with the diesel engine powering an electric generator; and running in fully electric battery powered mode. Measurements were performed to simultaneously quantify airborne and underwater radiated noise. Findings are that on-board diesel engines for electricity generation do not contribute a large extent of the underwater radiated noise, whilst a major source of airborne low-frequency radiation.
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| 2. |
- Denby, Bruce Rolstad, et al.
(författare)
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A coupled road dust and surface moisture model to predict non-exhaust road traffic induced particle emissions (NORTRIP). Part 2 : Surface moisture and salt impact modelling
- 2013
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Ingår i: Atmospheric Environment. - : Elsevier. - 1352-2310 .- 1873-2844. ; 81, s. 485-503
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Tidskriftsartikel (refereegranskat)abstract
- Non-exhaust traffic induced emissions are a major source of airborne particulate matter in most European countries. This is particularly important in Nordic and Alpine countries where winter time road traction maintenance occurs, e.g. salting and sanding, and where studded tyres are used. Though the total mass generated by wear sources is a key factor in non-exhaust emissions, these emissions are also strongly controlled by surface moisture conditions. In this paper, Part 2, the road surface moisture submodel of a coupled road dust and surface moisture model (NORTRIP) is described.We present a description of the road surface moisture part of the model and apply the coupled model to seven sites in Stockholm, Oslo, Helsinki and Copenhagen over 18 separate periods, ranging from 3.5 to 24 months. At two sites surface moisture measurements are available and the moisture sub-model is compared directly to these observations. The model predicts the frequency of wet roads well at both sites, with an average fractional bias of -2.6%. The model is found to correctly predict the hourly surface state, wet or dry, 85% of the time. From the 18 periods modelled using the coupled model an average absolute fractional bias of 15% for PM10 concentrations was found. Similarly the model predicts the 90'th daily mean percentiles of PMio with an average absolute bias of 19% and an average correlation (R-2) of 0.49. When surface moisture is not included in the modelling then this average correlation is reduced to 0.16, demonstrating the importance of the surface moisture conditions. Tests have been carried out to assess the sensitivity of the model to model parameters and input data. The model provides a useful tool for air quality management and for improving our understanding of non-exhaust traffic emissions.
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| 3. |
- Denby, B. R., et al.
(författare)
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Road salt emissions : A comparison of measurements and modelling using the NORTRIP road dust emission model
- 2016
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Ingår i: Atmospheric Environment. - : Elsevier Ltd. - 1352-2310 .- 1873-2844. ; 141, s. 508-522
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Tidskriftsartikel (refereegranskat)abstract
- De-icing of road surfaces is necessary in many countries during winter to improve vehicle traction. Large amounts of salt, most often sodium chloride, are applied every year. Most of this salt is removed through drainage or traffic spray processes but a certain amount may be suspended, after drying of the road surface, into the air and will contribute to the concentration of particulate matter. Though some measurements of salt concentrations are available near roads, the link between road maintenance salting activities and observed concentrations of salt in ambient air is yet to be quantified. In this study the NORTRIP road dust emission model, which estimates the emissions of both dust and salt from the road surface, is applied at five sites in four Nordic countries for ten separate winter periods where daily mean ambient air measurements of salt concentrations are available. The model is capable of reproducing many of the salt emission episodes, both in time and intensity, but also fails on other occasions. The observed mean concentration of salt in PM10, over all ten datasets, is 4.2 μg/m3 and the modelled mean is 2.8 μg/m3, giving a fractional bias of −0.38. The RMSE of the mean concentrations, over all 10 datasets, is 2.9 μg/m3 with an average R2 of 0.28. The mean concentration of salt is similar to the mean exhaust contribution during the winter periods of 2.6 μg/m3. The contribution of salt to the kerbside winter mean PM10 concentration is estimated to increase by 4.1 ± 3.4 μg/m3 for every kg/m2 of salt applied on the road surface during the winter season. Additional sensitivity studies showed that the accurate logging of salt applications is a prerequisite for predicting salt emissions, as well as good quality data on precipitation. It also highlights the need for more simultaneous measurements of salt loading together with ambient air concentrations to help improve model parameterisations of salt and moisture removal processes. © 2016 The Authors
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| 5. |
- Smith, Andrew S. J., et al.
(författare)
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Efficiency measurement in the tendering of road surface renewal contracts
- 2023
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Ingår i: Journal of Productivity Analysis. - : Springer Nature. - 0895-562X .- 1573-0441.
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Tidskriftsartikel (refereegranskat)abstract
- The problem of slow productivity growth in the road construction (and wider construction) industry is well known. The present paper suggests a means for efficiency analysis in one part of this industry, namely road surface renewal in Sweden, built upon the application of Stochastic Frontier Analysis (SFA) techniques. The paper is novel in that it focuses on project level rather than firm or contractor level performance and takes the perspective of the inefficiency that may result from the way the contracts are specified by the highway agency’s pavement engineers (client side). We compare 233 renewal contracts tendered over a four-year period via the estimation of a cost frontier, with controls for heterogeneity between projects. Our results produce first estimates that expose substantive differences in the relative efficiency performance of different engineers within the Swedish highways procurement organisation (Trafikverket); with indicative savings of around €40 m out of a total road renewals budget in Sweden of €200 m. We also find substantial economies of scale that could, in principle, point to further cost savings if road renewal projects can be packaged up as larger projects. These client-side savings represent potentially important sources of savings in addition to those that can be achieved through the pressure of competitive tendering on the supplier side. The paper therefore illustrates how disaggregate analysis of project level information can readily be used for revealing important information about how best to frame the procurement process and thus deliver productivity and unit cost improvements over time.
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