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Åretruntdäck är en typ av däck som tidigare inte varit godkända att använda som vinterdäck i Sverige, men som efter en regeländring 2019 nu är tillåtna. I syfte att jämföra väggreppet för denna typ av däck med renodlade vinter- och sommardäck så genomfördes bromstester för 14 olika åretruntdäck på packad snö och is, likväl som på torr och våt asfalt. Åretruntdäcken valdes ut för att vara representativa för de tillgängliga åretruntdäcken på den svenska marknaden, och jämförelsedäcken valdes ut för att vara representativa för respektive däcktyp. Resultaten visar att det är stora skillnader i bromsgrepp mellan olika åretruntdäck. En del åretruntdäck presterar mer likt europeiska dubbfria vinterdäck, och andra mer likt sommardäck, vilket verkar vara ett medvetet val från de olika tillverkarna. I genomsnitt så är åretruntdäckens bromssträcka på snö tydligt längre än för både nordiska och europeiska dubbfria vinterdäck, och även om det finns åretruntdäck som är mer lika europeiska vinterdäck på snö, så finns det andra som är betydligt sämre.

Trafikverket överväger att tillåta längre och tyngre fordon på vägarna förutsatt att de inte påverkar trafiksäkerheten negativt. Syftet med studien var att undersöka säkerhetseffekten av fordonslängd, speciellt med avseende på olycksrisken vid omkörningar. Intervjuade förare av en 30-meters timmerbil hade inte upplevt de farhågor som förare av normallånga lastbilar uttryckt i samband med trånga rondeller och korsningar, men de nämner betydelsen av stödjande åkeri, arbetsmiljö och fordonsutrustning. En simulatorstudie studerade bilförares omkörningar av ett 30- och ett 18,75-metersfordon på en 2+1-väg i situationen då två körfält går ihop till ett. Tidluckan till ett återstående körfält var i genomsnitt 0,2 s (sign.) kortare efter omkörningar av 30-metersfordonet i situationer då bakänden var i samma relativa position som för 18,75-metersfordonet vid början av omkörningen. En fältstudie analyserade videoinspelade omkörningar av en 30- och en 24-meters timmerbil på en 2+1-väg och en tvåfältig väg. Ingen signifikant skillnad i tidluckor kunde påvisas mellan omkörningar av de två fordonen för någon av vägtyperna. Det senare resultatet ska dock tolkas med försiktighet på grund av ojämnt distribuerad data som insamlats under specifika förhållanden. Slutsatserna är att det finns en liten tendens till negativ säkerhetseffekt vid omkörningar av längre fordon, och att fler fältstudier är nödvändiga., The Swedish Road Administration considers permitting longer and heavier trucks on Swedish roads, provided that they do not affect traffic safety. The purpose of the study was to investigate the effect of truck length, particularly accident risk associated with overtaking. Interviewed drivers of 30 meter trucks had not experienced the problems predicted by drivers of ordinary trucks concerning narrow roundabouts and intersections, but mentioned the importance of a supportive truck company, working environment and truck equipment. A simulator study investigated car drivers overtaking trucks 30 m and 18.75 m long on a 2+1 road where two lanes merges to one. The headway time gap was 0.2 sec. (sign.) shorter after overtaking the 30 meter truck in situations where the back was in the same relative position as of the 18.75 meter truck. A field study analysed video-recorded overtakings of a 30 meter and a 24 meter timber truck on a 2+1 road and a two-lane road. No significant differences were found between headway time gaps when overtaking the two trucks, regardless of road type. The latter result should be interpreted with great caution because of unevenly distributed data collected during specific conditions. The conclusions are that longer trucks may have a small negative effect on overtaking situations, and that further field studies are required., Sam-modalitet i praktiken -utveckling och samhällsekonomisk utvärdering av landtransportsystem för långväga transporter

In this study we have investigated how tyres with different road grip affect the stability of passenger cars equipped with Electronic Stability Control (ESC) systems during winter road conditions. The introduction of ESC in passenger cars has been very positive for traffic safety. An ESC system's function is however dependent on forces between road and tyres. Thus, it is not clear how important the tyre road grip performance is for the ESC system to function properly. Field tests on ice with six different drivers were used for assessing how well an ESC system can help the driver in a specific critical situation during slippery road conditions, namely a sudden double lane change. Four different studless winter tyres were used in the study: one studless winter tyre for Nordic conditions, and three studless winter tyres for central European conditions. The specific tyres were chosen to represent a large difference of road grip on ice and snow, and winter tyre tests in the media served as a guide for picking out the tyres.

Particles from road and tire wear have in recent years come to the fore as an important and relatively unexplored contribution to air particulate pollution. Mechanically generated wear particles are relatively coarse (>0.5 microns), but in controlled trials in VTI's road simulator it has been found that an ultra-fine fraction (< 100 nm) of particles is formed from tyre and pavement wear. This project was initiated to identify the source of these nanoparticles. The results show that the nanoparticles of the size 30-50 nm occur only from tests with studded tyres. One of the two tested Nordic unstudded winter tyres produced an even finer particle fraction (<10 nm), while the other unstudded winter tyre type did not give rise to nanoparticles. Tests with summer tyres did not result in the formation of nanoparticles. It is clear that the fine particle fraction contains higher relative concentrations of sulphur, which is present at relatively high levels in both bitumen and tyres. It is unclear whether the ultrafine particles formed from studded tyre wear of road pavement in the road simulator also occur in real traffic. If so, this may affect the assessment of health effects from different traffic related particle sources.

Active safety systems are becoming increasingly common in today's vehicles. Electronic Stability Control (ESC) systems were introduced during the end of the 1990s, and accident statistics show that they have had a huge impact on traffic safety. In the USA, a new legislation has recently been adopted which demands on every new light vehicle that is sold to be equipped with ESC, beginning 2011. New systems require new testing methods, and there is a need expressed by the New Car Assessment Program (NCAP), which at present time only evaluates the passive safety of cars, also to include tests for active safety systems. In a previous VTI work, a literature review regarding methods for the evaluation of traffic safety effects of Antilock Braking Systems (ABS) and ESC was performed. Based on the findings of that review, we have proceeded with defining a test method for evaluating safety aspects of ESC equipped passenger cars. The objective has been to suggest a (prototype) test method that can be used for a more holistic evaluation of the safety effect of ESC in cars, including the driver behaviour perspective. From discussions with leading experts on traffic safety and ESC, possible benefits of ESC systems on traffic safety were identified. In addition to increasing the yaw stability of the vehicle, the following ESC benefit effects were identified: - A warning system for slippery roads. ESC activation indication may act as a warning system to the driver about slippery road conditions. - Reduced collision speed. In a critical situation, ESC activation may reduce the collision speed, which will mitigate the outcome of the collision. - Improved vehicle roll stability. The ESC system may also stabilise the vehicle with respect to untripped rollovers. Most rollovers are however tripped rollovers, which can occur when a vehicle, with some lateral slip, strikes an object or slides off the road. These rollovers also benefit from the ESC system as it aids in keeping the vehicle o

I många länder där dubbdäck är förbjudna är trafikpoleringen ett stort problem och föreskrifter finns bland annat för stenmaterialets poleringsbenägenhet. I Sverige har dubbdäckstrafiken medfört att stenmaterialet på vintern ruggats upp varför låga friktionstal varit ovanliga på inslitna beläggningar. Val av allt slitstarkare stenmaterial, övergång till skelettasfalt samt skonsammare dubbar har dock markant reducerat dubbslitaget. På senare år har problem med låg våtfriktion konstaterats på slitstarka beläggningar under sommarhalvåret, framför allt i utsatta lägen och under eftersommaren och hösten. Mätningar har visat att friktionen snabbt kan reduceras om beläggningen är poleringsbenägen och halkrelaterade olyckor har rapporterats på polerade beläggningar. Denna rapport är en kunskapsöversikt om polering, friktion och i viss mån textur och beläggningsslitage från dubbade fordon. Erfarenheter från friktionsmätningar främst i Stockholm och Göteborg har samlats in. En översyn ges över provningsmetoder och de krav som finns. Kompletterande friktionsmätningar har utförts med flera utrustningar (SAAB Friction Tester och BV12) där mäthastighet, tidpunkt på året, vattenmängd, typ av däck och ringtryck varierats., In many countries, where studded tyres are prohibited, the traffic polishing of the coarse aggregate in the wearing courses is a problem to a rather great extent. In those countries there are often regulations on the aggregate polishing value. In Sweden, where the use of studded tyres is extensive, the micro texture of the aggregate in the surface of the wearing courses increases during the winter season. Therefore, there have been few problems with low wet friction levels in Sweden. However, the increased use of wear resistant aggregates and stone mastic asphalt together with lightweight studs has led to a reduced amount of wear. During later years, a problem with low friction levels has been noticed in wear resistant surface courses during late summer and fall, especially at high trafficked roads with a complicated geometry. Measurements have shown that the friction level can be reduced rather quickly on surfaces with aggregates that are disposed for polishing and low wet friction related accidents have been reported. This report is a knowledge survey covering polishing, friction and to some extent surface texture and wear caused by studded tyres. Experiences from friction measurements mainly in Stockholm and Gothenburg have been compiled in this report. A review of testing methods and existing requirements is also presented in the report. Friction measurements have been carried out with two friction measurement equipments, SAAB Friction Tester and BV12, where the measuring speed, time of the year, the amount of water film thickness, the type of tyre and tyre pressure have been varied.

Earlier studies have shown that buses are overrepresented at accidents during winter road conditions compared to other vehicle types. Hence, the traffic safety of buses during the wintertime has been studied in more detail. The study comprised the following parts: - Gripping power studies on ice in VTI's tyre test facility. - Accident study and a survey of the use of tyre. - Focus group to gain knowledge about dangerous situations. - Driving simulator study to test the importance of the tyres during problematic situations. Tests in VTI's tyre test facility on smooth ice did not show any significant difference between summer tyres and non-studded winter tyres, while studded tyres exhibit a better ice grip than non-studded tyres. Nor did driving simulator tests when 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 the studded tyres were superior to the non-studded. If studded tyres are used only on one axle, the driving simulator study showed that during side wind the ability to steer is important. The accident study showed that the buses that have summer tyres on the steering axle and winter tyres on the drivé axle has the lowest estimated accident risk, although it is not statistically significant. The buses equipped with studded tyres on both axles could not be statistically analysed since only 2 accidents occurred on bare roadways, and none on icy/snowy roadways, while at the same time the buses in this category drive a lot on icy/snowy roadways. This probably makes these buses the safest on winter roadways. From the focus groups it was clear that the time table has a great influence on the creating of stress and the demands on the drivers to keep the speed even during slippery roadways. Many bus drivers experience large problems with bad snow clearance, or other winter maintenance. At the same time there is a large consciousness among the drivers th

In today's vehicles, active safety systems are introduced addressing a large variety of safety issues such as providing optimal stability control, braking effect, preventing spin and rollover, as well as collision avoidance, to mention just a few. In this study a literature review was performed in order to establish how the traffic safety performances of active safety systems with focus on Antilock Braking System (ABS) and Electronic Stability Control (ESC) are assessed. The areas covered were statistical evaluation, testing and driver behaviour. The literature review showed that in particular statistical methods, based on odds ratios, had been used in order to evaluate the traffic safety effect. In order to evaluate the effect of ESC in physical testing there are several test methods described in this report. Estimations of driver behaviour effects have been carried out by surveys among vehicle owners. Experiments performed in field or in simulator have also been found in the literature. From EU projects a variety of measures and test methods are available for assessment of driver behavioural effects.

Choice of winter tyres has, from mainly being a matter of safety and economic costs for wearing of road pavements, during later years also become a matter of inhalable particles formed during pavement wear from studded tyres and their negative effects on public health. Further, the tyres' effects on environment and noise have been illustrated in several studies. The issue is also complicated by the fact that tyre choice effects on traffic safety have several components, including such diverging parameters as friction and behaviour. Finally all aspects have to be evaluated from a socioeconomic point of view for society to be able to decide which kind of distribution of tyre types that is the most profitable. This report is a summary of current knowledge in this complex research field., Valet av vinterdäck har, från att i huvudsak varit en fråga om trafiksäkerhet och slitage av vägar under senare år även kommit att handla om negativa effekter av de inandningsbara partiklar som bildas då dubbdäck sliter på vägbanan och de effekter på befolkningens hälsa som dessa partiklar har. Vidare har vägslitagets inverkan på miljön genom spridning av bl.a. tungmetaller belysts liksom däckvalets betydelse för bullerproblematiken. Frågan kompliceras ytterligare av att däckvalets betydelse för trafiksäkerheten har många beståndsdelar inkluderande såväl tekniska parametrar, t.ex. friktion, som beteendevetenskapliga aspekter. I slutändan måste alla dessa aspekter vägas samman samhälls-ekonomiskt för att den för samhället mest lönsamma däckanvändningen skall kunna uppnås. Denna rapport belyser kunskapsläget inom detta komplexa problemområde.