| 11. |
- Dahlman, Joakim, et al.
(författare)
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Realtidskartor i kollektivtrafiken : What you see is where you get
- 2020
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Inom ramen för projektet What you see is where you get har upplevda och faktiska nyttor med en så kallad realtidskarta för kollektivtrafik studerats. Projektet undersöker om en realtidskarta kan förenkla och förändra resenärers beslutsfattande vid kollektivt resande. Vi vill ta reda på resenärers informationsbehov, beslut och önskemål med ett sådant verktyg. På senare tid har en mängd tekniska tjänster som förser kollektiv-trafikresenärer med uppgifter om fordons tillgänglighet i form av tid och plats introducerats. Antagandet för projektet är att tillgången till en bra karta i realtid med olika funktioner skulle kunna förändra och eventuellt förenkla resandet. För att besvara frågorna knutna till detta har attityder, önskemål, behov och användning testats hos såväl kollektiv-trafikresenärer som operatörer/kollektivtrafikmyndigheter.Då realtidskartan visades för tre grupper av resenärer i olika åldrar visade resultaten att samtliga var positiva och kunde tänka sig att använda realtidskartan, som ett komplement till den reseplaneringsapplikation de redan använde. Realtidskartan behövde utvecklas för att bli mer hanterbar och kunna fylla fler behov.Då realtidskartan visades på en busshållplats där resenärerna på en skärm kunde se de vanliga tidsangivelserna växelvis med en realtidskarta, visade resultaten ett lågt intresse för kartan. En introduktion eller instruktion skulle behövas. Ett antal resenärer testade realtidskartan under en resa i staden. I projektet intervjuades även resenärer vid hållplatser om de uppmärksammat och använde realtidskartan i reseplaneringsappen.En övergripande slutsats är att man även inom kollektivtrafikbranschen verkar ha svårt att (mer teoretiskt) sätta sig in i det nya koncept som realtidskartor innebär, och att det ännu är få som har använt dem när de reser. En ytterligare slutsats, från jämförelse mellan de individuella enkätsvaren, är att de som faktiskt hade använt realtidskartor när de reser också hade attityder som reflekterade att de både kunde vara mycket nöjda och mycket missnöjda med hur realtidskartan fungerat.
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| 12. |
- Hjort, Mattias, 1972-, et al.
(författare)
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A method for road description based on map data and road measurements : White Paper
- 2016
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Simulation has become a useful tool for vehicle manufacturers in the design and assessment of new vehicles. Using an advanced driving simulator in early design phases may reveal defects in the construction, which otherwise would not be noticed until full scale prototyping, and thereby reduce development time and costs. In most driving simulator studies the road design does not have to conform to an existing road. But for some purposes it may be crucial that the virtual road describes the real road as close as technically possible. Examples are vehicle vibration studies, fuel consumption evaluation with respect to driver behaviour, and comparisons between driving on the virtual and real road. The required level of detail of different road features varies between applications (projects). Parameters like road curvature, inclination, elevation and crossfall, the surrounding terrain as well as road imperfections and unevenness may be of more or less importance and therefore have to be modelled with high or lower accuracy. In the Known Roads project, a real road, the “Gothenburg triangle” (Gothenburg-Borås-Alingsås- Gothenburg), was modelled as realistically as possible. Road curvature, inclination and crossfall as well as the surrounding terrain were considered important. This White Paper is complementary to other deliverables from the Known Roads project. It presents in more detail the method of recreating existing roads in a simulation environment, developed by VTI in the project. The White Paper concerns specifically the difficulties of merging different data sources into a road representation, and describes the problems that were encountered and the solutions that were developed for implementing an existing road in the driving simulator.
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| 13. |
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| 14. |
- Hjort, Mattias, 1972-, et al.
(författare)
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Bus accidents in wintertime
- 2010
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Ingår i: PIARC 2010 XIII International Winter Road Congress, February 8-11, 2010, Quebec, Canada.
-
Konferensbidrag (refereegranskat)abstract
- Buses in Sweden have a low accident risk. However, statistics from 1996 - 2002 indicate that the number of bus accidents in Sweden with personal injuries have been increasing by 4% yearly. Buses also have a higher percentage of accidents that occur on ice/snow covered roads than other vehicles. In Sweden passenger cars must be equipped with winter tyres during the winter period. There is no such regulation for heavy vehicles, and many buses are using summer tyres all around the year. The present project had the purpose of looking at the bus-winter problem in more detail, with the main focus on tyres. Four different studies were carried out: tyre tests, focus group discussions, driving simulator tests and an accident study. Here is given a short summary concerning methods and conclusions of each sub project.Tyre tests on smooth ice did not show any significant difference between summer tyres and non-studded winter tyres, while studded tyres exhibits a better ice grip than non-studded tyres. Nor did driving simulator tests with driving on ice covered road under the influence of heavy wind from the side show a difference between summer tyres and non-studded winter tyres. Also in these tests studded tyres were superior to non-studded. Accident statistics indicate that buses with summer tyres on the steering axle and winter tyres on the drive axle have the lowest estimated accident risk, which is in accordance with the results in a previous study. The results are however not statistically significant due the low number of accidents. Three focus groups were carried out and the importance of the tyres for traffic safety during winter was discussed. It is however hard from the gathered discussion material to estimate just how important the tyres really are. The results do not warrant a winter tyre regulation for heavy vehicles, and a restriction of the use of studded tyres for buses would probably have negative consequences on traffic safety.
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| 15. |
- Hjort, Mattias, 1972-, et al.
(författare)
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Comprehensive study of the performance of winter tires on ice, snow, and asphalt roads : The influence of tire type and wear
- 2017
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Ingår i: Tire Science and Technology. - : Tire Society Inc.. - 0090-8657 .- 1945-5852. ; 45:3, s. 175-199
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Tidskriftsartikel (refereegranskat)abstract
- This work presents a comprehensive study of the performance of winter tires on snow, ice, and asphalt. A set of 77 different winter tires were carefully selected for the study. Of these, 27 were new and 50 were worn from real traffic use. All three tire types for winter conditions (Nordic, European, and studded) were represented. All tires have been tested using a mobile tire-testing device for snow and asphalt and using a stationary tire-testing facility for ice. Both devices recorded the tire forces and motions, enabling a close to complete stationary characterization of the tires. In addition, 42 of the tires were tested on a passenger car, where brake performance was evaluated for the three different road conditions. This enables a comparative study of performance between tire types and wear for various winter road conditions. The results suggest that the recorded data represent real vehicle performance. Some conclusions from the measurements are that the effect of wear is consistent between the tire groups and that the performance degradation is most noticeable on studded tires on ice and on European tires on snow.
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| 16. |
- Hjort, Mattias, 1972-
(författare)
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Electronic structure studies of carbon based nanomaterials
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with theoretical investigations of the electronic structure of conjugated carbon based materials. Novel materials like the C60 fullerene and the carbon nanotubes, but also the more well known, but closely related, graphite phase of carbon were studied. In addition, low dimensional structures like conjugated polymers and DNA, containing other atoms besides carbon, were investigated.The recently discovered fullerene phase of carbon, especially the C60 molecule has obtained a lot of attention among researchers. It has been observed that C60 under certain conditions can form linear polymeric chains, as well as two-dimensional polymeric structures. In the work presented in this thesis, Hückel model parameters have been developed for describing the intermolecular bonds within single bonded C60 polymers. These parameters were used in simulations to establish a simple rule explaining the phase diagram of the observed single bonded C6o polymer structures, namely that each electron added to a C60 monomer stimulates the creation of one single bond to a neighbouring C60 anion. A similar study on graphite was also performed, yielding Hückel parameters which describe the complicated bonding structuresurrounding an atomic vacancy in the graphite. From calculations on large graphitic sheets containing several vacancies, insight was gained of the electronic properties associated with such defects, leading to a better understanding of Scanning Tunnelling Microscopy images of defected graphite.In one-dimensional materials, disorder is known to have an immense effect on electron localisation, seriously affecting the transport properties of these materials. Conjugated polymers and carbon nanotubes are not perfectly one-dimensional, but are often referred to as quasi one-dimensional. In this thesis, work is presented that deal with electron localisation in disordered quasi one-dimensional materials, studied at the Hückel level. To do this, a new method was developed for obtaining the transfer matrix, from which the localisation length of the electronic wave function can be deduced. This was applied to some conjugated polymers and carbon nanotubes using various kinds of disorder. It was shown that it is meaningful to speak about different dimensionalities for quasi one-dimensional systems, and that this is an important concept for understanding localisation in these materials. Furthermore, disorder induced localisation in metallic carbon nanotubes was shown to be independent on tube chirality. By treating functionalisation of nanotubes as a disorder, it was also concluded that such a process may significantly lower the conductance of the tubes. This effect may be utilised in chemical sensors based on carbon nanotubes.The charge migration process in DNA is subject to a lively debate among researchers at the moment. The possibility to use DNA in molecular electronics has triggered an extensive study of the subject, but contradicting experimental findings exist in literature. In the work presented in this thesis the Landauer formula, combined with a pseudo potential method was used for calculating the current through the synthetic poly(G)-poly(C) form of DNA. These calculations substantiate a recent report which indicates band like conduction for this particular form of DNA. The conductivity results from overlap of the 1r-orbitals along the DNA base stacks. It was also demonstrated that the observed increase of the threshold voltage with temperature in poly(G)-poly(C) DNA is the result of electron localisation due to the structural fluctuations associated with temperature.
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| 17. |
- Hjort, Mattias, 1972-, et al.
(författare)
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Handling of buses on slippery roads during the influence of side wind : A study of the effects of different tyres
- 2010
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Ingår i: Accident Analysis and Prevention. - : Elsevier. - 0001-4575 .- 1879-2057. ; 42:3, s. 972-977
-
Tidskriftsartikel (refereegranskat)abstract
- Accident statistics assembled by the Swedish National Road and Transport Research Institute (VTI) have shown that buses are overrepresented when it comes to accidents on icy and snowy roads. For a better understanding of the problem, the performance of modern summer and winter tyres on winter road conditions had to be assessed. The objective of this work has been to go beyond standard road grip studies, and instead investigate how the driver's possibility to deal with one challenging situation depends on the tyres and tyre configuration. This paper describes a novel methodology where measurements with different tyres on ice in VTI's tyre test facility, enabled a simulator study for evaluating the impact of different tyre characteristics when driving in conditions with strong side wind on a slippery road.The main results of the study are: to deal with strong side wind, good front wheel grip is most important, and while non-studded winter tyres provided little or no improvement over summer tyres, studded winter tyres significantly reduced the risk to run off the road. Furthermore, it is very difficult for the drivers to judge, beforehand, whether a vehicle with a particular tyre configuration will perform good or bad.
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| 18. |
- Hjort, Mattias, 1972-, et al.
(författare)
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Jämförelse av vinter och sommardäck på barmark sommartid : tester, riskanalys och djupstudier
- 2015
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Allt fler bilister har ersatt sina dubbade vinterdäck med dubbfria. Eftersom det inte är olagligt att köra med odubbade vinterdäck på sommaren väljer ett stort antal förare att låta vinterdäcken sitta på även sommartid. Syftet med denna studie har varit att undersöka skillnad i väggrepp mellan vinter- och sommardäck sommartid, samt att uppskatta tänkbara trafiksäkerhetseffekter av att använda vinterdäck sommartid. En fältstudie genomfördes där väggrepp mättes på torr och våt asfalt med olika typer av däck. Resultaten visade att vinterdäcken (odubbade av Nordisk typ) i genomsnitt resulterade i 15–20 procent längre bromssträckor jämfört med sommardäcken. Skaderiskanalyser genomfördes för tre olika typer av trafikolyckor: bakifrånkollision, frontalkollision och påkörning av fotgängare. Studien visade på ökningar av skaderisken vid användning av vinterdäck istället för sommardäck för alla tre olyckstyperna. Vid låga kollisionshastigheter är den absoluta riskökningen liten kanske bara ett fåtal procent, medan den relativa ökningen kan vara stor, ibland upp till en fördubbling av risken. Djupstudier av dödsolyckor sommartid indikerade en riskökning på 3 procent vid användning av vinterdäck sommartid jämfört med sommardäck. Detta resultat är dock inte statistiskt signifikant.
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| 19. |
- Hjort, Mattias, 1972-, et al.
(författare)
-
Kan dubbdäck på cykeln minska singelolyckorna? : friktionstester av cykeldäck i VTI:s stationära däckprovningsanläggning
- 2015
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Syftet med det här projektet har varit att ta fram en metod för att mäta cykeldäcks friktion på is och att genomföra inledande tester. Målet är att med hjälp av den framtagna testmetoden kunna ge oberoende och evidensbaserad information till potentiella vintercyklister om väggreppet på is med ett dubbat cykeldäck i jämförelse med ett odubbat, både vid bromsning respektive i kurvor. I studien har fyra olika dubbdäck för cykel jämförts med två vanliga sommardäck. Mätningarna gjordes i VTI:s stationära däckprovningsanläggning, vilken består av en rörlig bana och en stillastående men vridbar mätrigg. Konstruktionen gör det möjligt att under kontrollerade förhållanden mäta såväl broms- som styrkrafter för ett rullande hjul. För att kunna testa cykeldäck krävdes ombyggnationer av anläggningen som tidigare endast använts för studier av personbils- och lastbilsdäck. Den utvecklade testmetoden visade sig fungera bra för jämförande tester av cykeldäck. Mätningarna visade att dubbade cykeldäck har generellt bättre isgrepp än odubbade, men att det kan vara stora skillnader mellan olika dubbdäck. Fler dubbar behöver inte innebära ett bättre isgrepp. För bromsning med låst hjul uppmättes upp till 2,5 gånger högre friktion med dubbdäck jämfört med ett odubbat däck. Dubbdäcken producerar också generellt större sidkraft vid styrning på is. Vid lutning av cykeln ökar skillnaderna mellan dubbat och odubbat. Generellt uppnås en liten ökning av broms- och sidkrafter vid ett minskat däcktryck, men rätt däcktryck tycks vara viktigt för att få ut optimal prestanda ur ett dubbdäck. Resultaten visar att det är väl värt att rekommendera cyklister att använda dubbdäck vid vinterväglag. Med bättre grepp och bättre bromsstabilitet finns goda möjligheter till säkerhetsvinster vid vintercykling.
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| 20. |
- Hjort, Mattias, 1972-, et al.
(författare)
-
Limit handling in a driving simulator
- 2015
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The purpose of this work has been to investigate how the driving simulator performs at the handling limit of a vehicle and improve its function so that the simulator feels and behaves more like a real vehicle when driving on the limit. Tests were performed with a Volvo S40, the same vehicle model for which the driving simulator vehicle dynamics model is based upon. Based on these test results the vehicle model that is currently used in VTI’s driving simulator III was modified in order to better simulate vehicle characteristics when driving on the handling limit. A method for validation of handling characteristics was developed. The method is based on the double lane change manoeuvre, and comprise a subjective and an objective part. The method was regarded to work well, and the validation tests showed that the modified vehicle model closer captures the understeer and time lag properties of a real Volvo S40 compared to the original model. Still, additional improvements need to be made before the model can be regarded as fully useful for on-the-limit driving situations.
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