| 1. |
- Ahlberg, Erik, et al.
(författare)
-
"Vi klimatforskare stödjer Greta och skolungdomarna"
- 2019
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Ingår i: Dagens nyheter (DN debatt). - 1101-2447.
-
Tidskriftsartikel (populärvet., debatt m.m.)abstract
- DN DEBATT 15/3. Sedan industrialiseringens början har vi använt omkring fyra femtedelar av den mängd fossilt kol som får förbrännas för att vi ska klara Parisavtalet. Vi har bara en femtedel kvar och det är bråttom att kraftigt reducera utsläppen. Det har Greta Thunberg och de strejkande ungdomarna förstått. Därför stödjer vi deras krav, skriver 270 klimatforskare.
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| 2. |
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| 3. |
- Andersson, Jan, 1965-, et al.
(författare)
-
Bygdeväg : När 2 filer blir 1
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Sundbyberg kommun har genomfört en ombyggnation av en del av Ursviksvägen. En traditionell tvåfilig väg med skyltad hastighet på 30 km/tim byggdes om till en fil för bilar och två cykelfält, en på vardera sida om körfältet för bilar, det vill säga en 2 minus 1-väg. Före ombyggnation och efter ombyggnation tillfrågades boende och passerande individer om deras upplevelser av Ursviksvägen. I synnerhet var det utifrån perspektivet säkerhet och framkomlighet, vilket i sin tur kan kopplas till livskvalitet. Dessutom monterades kameror upp längs sträckan som registrerade trafikarbetet samtidigt som insamlandet av individers upplevelser pågick. Resultaten från enkäten är mycket entydiga. Ombyggnation av delsträckan på Ursviksvägen mottogs väldigt väl. Den upplevda tryggheten, säkerheten och framkomligheten påverkades positivt, i synnerhet för cyklister och fotgängare. Bussresenärers upplevelse var också positiv även om effekten av ombyggnationen inte var lika stark. Dessa resultat erhålls utan att bilisters upplevelse av framkomlighet försämrades. Ytterligare analyser visade att om man var nöjd med säkerheten, tryggheten och framkomligheten i området var man också mera nöjd med området runt Ursviksvägen.En rad analyser genomfördes efter detta huvudresultat för att försöka förstå variationen i svaren bättre. I huvudsak studerades om svaren på frågorna påverkades av om respondenten nyttjade Ursviksvägen som fotgängare, bilist, bussresenär eller cyklist. Dessutom analyserades om ombyggnationen lett till ett förändrat färdmedelsval. Slutligen analyserades om de respondenter som har barn i de skolor som ligger utmed Ursviksvägen har andra upplevelser än de respondenter som inte har barn vid en skola utmed Ursviksvägen. Oavsett hur data analyserades framkom positiva effekter av ombyggnationen. Ett exempel på analys där respondenter med barn i skolor utmed Ursviksvägen jämfördes med respondenter utan barn.Resultatet visade att respondenter med barn i någon av skolorna var signifikant nöjdare med alla de aspekter i trafikmiljö som enkäten berörde men detsamma gällde även de som inte hade några barn i skolorna. Däremot visade resultaten att respondenter med barn i skolorna var mindre nöjda med området innan ombyggnationen vilket innebar att de stod för den största ökningen. Värt att poängtera är också att eftermätningen visade att föräldrar som hade barn som gick eller cyklade till skola var måttligt nöjda med tryggheten och säkerheten för sina barn, då det högsta medelvärdet var drygt 4 på den 7-gradiga skalan.
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| 4. |
- Andersson, Jan, et al.
(författare)
-
När 2 filer blir 1: Ombyggnation av Ursviksvägen i Sundbyberg
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Sundbyberg kommun har genomfört en ombyggnation av en del av Ursviksvägen. En traditionell tvåfilig väg med skyltad hastighet på 30 km/tim byggdes om till en fil för bilar och två cykelfält, en på vardera sida om körfältet för bilar, det vill säga en 2 minus 1-väg. Före ombyggnation och efter ombyggnation tillfrågades boende och passerande individer om deras upplevelser av Ursviksvägen. I synnerhet var det utifrån perspektivet säkerhet och framkomlighet, vilket i sin tur kan kopplas till livskvalitet. Dessutom monterades kameror upp längs sträckan som registrerade trafikarbetet samtidigt som insamlandet av individers upplevelser pågick. Resultaten från enkäten är mycket entydiga. Ombyggnation av delsträckan på Ursviksvägen mottogs väldigt väl. Den upplevda tryggheten, säkerheten och framkomligheten påverkades positivt, i synnerhet för cyklister och fotgängare. Bussresenärers upplevelse var också positiv även om effekten av ombyggnationen inte var lika stark. Dessa resultat erhålls utan att bilisters upplevelse av framkomlighet försämrades. Ytterligare analyser visade att om man var nöjd med säkerheten, tryggheten och framkomligheten i området var man också mera nöjd med området runt Ursviksvägen.En rad analyser genomfördes efter detta huvudresultat för att försöka förstå variationen i svaren bättre. I huvudsak studerades om svaren på frågorna påverkades av om respondenten nyttjade Ursviksvägen som fotgängare, bilist, bussresenär eller cyklist. Dessutom analyserades om ombyggnationen lett till ett förändrat färdmedelsval. Slutligen analyserades om de respondenter som har barn i de skolor som ligger utmed Ursviksvägen har andra upplevelser än de respondenter som inte har barn vid en skola utmed Ursviksvägen. Oavsett hur data analyserades framkom positiva effekter av ombyggnationen. Ett exempel på analys där respondenter med barn i skolor utmed Ursviksvägen jämfördes med respondenter utan barn.Resultatet visade att respondenter med barn i någon av skolorna var signifikant nöjdare med alla de aspekter i trafikmiljö som enkäten berörde men detsamma gällde även de som inte hade några barn i skolorna. Däremot visade resultaten att respondenter med barn i skolorna var mindre nöjda med området innan ombyggnationen vilket innebar att de stod för den största ökningen. Värt att poängtera är också att eftermätningen visade att föräldrar som hade barn som gick eller cyklade till skola var måttligt nöjda med tryggheten och säkerheten för sina barn, då det högsta medelvärdet var drygt 4 på den 7-gradiga skalan.
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| 5. |
- Andersson, Jan, 1965-, et al.
(författare)
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Two minus one road equals improved quality of life
- 2024
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Ingår i: Transportation Research Interdisciplinary Perspectives. - : Elsevier. - 2590-1982. ; 26
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Tidskriftsartikel (refereegranskat)abstract
- Background: Sundbyberg municipality (part of greater Stockholm) has reconstructed a traditional two-lane road, with an allowed speed limit of 30 km/h, into a road with one car lane and two bicycle lanes, one on either side of the car lane (a “two minus one road”). The aim was to increase traffic safety and accessibility, especially for bicyclists and pedestriansMethod: The design used was a before- an after-study including both subjective and objective measures. To collect subjective data a survey measuring quality of life was used by asking residents and travellers how they experienced the road and their neighbourhood. The collection of objective data was done with the help of video cameras recording traffic conflicts, vehicle speed and position on the roadResults: The reconstruction of the road had positive effects on quality of life in general, specifically safety, security, and accessibility for bicyclists and pedestrians. Something which was achieved without reducing car drivers’ experience of accessibility. Subsequent analyses were conducted to increase the understanding of different ‘sub-groups’. Specifically, analyses assessed: if responses could be linked to modal choice; whether the reconstruction of the road resulted in a modal shift; and whether it was any differences between respondents who had or had not a child attending any of the local schools. Overall, the responses from the ‘sub-groups’ were not significantly different from each other (except for respondents with children). The video analyses on traffic safety showed no differences in conflicts before and after the reconstruction. The only negative result was that car drivers’ speed increased by 3 km/hConclusion: The reconstruction of roads with a traffic intensity, equivalent to the selected road is suitable for a two minus one road. Traffic safety, security, and accessibility will increase, but not at the expense of car drivers’ accessibility.
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| 6. |
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| 7. |
- Ardö, Håkan, et al.
(författare)
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Reduced Search Space for Rapid Bicycle Detection
- 2013
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Ingår i: [Host publication title missing]. - : SciTePress - Science and and Technology Publications.
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Konferensbidrag (refereegranskat)abstract
- This paper describes a solution to the application of rapid detection of bicycles in low resolution video. In particular, the application addressed is from video recorded in a live environment. The future aim from the results in this paper is to investigate a full year of video data. Hence, processing speed is of great concern. The proposed solution involves the use of an object detector and a search space reduction method based on prior knowledge regarding the application at hand. The method using prior knowledge utilizes random sample consensus, and additional statistical analysis on detection outputs, in order to define a reduced search space. It is experimentally shown that, in the application addressed, it is possible to reduce the full search space by 62% with the proposed methodology. This approach, which employs a full detector in combination with the design of a simple and fast model that can capture prior knowledge for a specific application, leads to a reduced search space and thereby a significantly improved processing speed.
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| 8. |
- Ardö, Håkan, et al.
(författare)
-
Superpixel based road user tracker
- 2014
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Abstract A superpixel based tracker is tested on the two Tracking sequences from PDTV [7], Minsk and Sherbrooke. It detects all vehicles from the Minsk dataset although a few of them are splitted. The pedestrians are too small and thus all missed. The results for the Sherbrooke are not as good, especially in the areas far way from the camera where the intersection s viewed at a low angle. Also the sign in the foreground causes misses.
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| 9. |
- Bjørnskau, Torkel, et al.
(författare)
-
Game over for automated vehicles?
- 2022
-
Konferensbidrag (refereegranskat)abstract
- Trials with automated mini buses (AV shuttles) are going on in many cities. According to game-theoretic reasoning, in mixed traffic normal road users will soon take advantage of the defensive driving style of the AV shuttles, and may eventually totally block their accessibility (Camara et al., 2018; Michieli & Badia, 2018; Millard-Ball, 2018). So far there are few studies on the interaction between AV shuttles and ordinary road users. The present study is probably the first to look at changes in interaction patterns with AV shuttles in real traffic over time, making it possible to empirically test the predictions based on game theory.
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| 10. |
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| 11. |
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| 12. |
- Borsos, Attila, et al.
(författare)
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Are collision and crossing course surrogate safety indicators transferable? A probability based approach using extreme value theory
- 2020
-
Ingår i: Accident Analysis and Prevention. - : Elsevier BV. - 0001-4575. ; 143
-
Tidskriftsartikel (refereegranskat)abstract
- In order to overcome the shortcomings of crash data a number of surrogate measures of safety have been developed and proposed by various researchers. One of the most widely used temporal indicators is time-to-collision (TTC) which requires the road users to be on a collision course. Road users that are strictly speaking not on a collision course actually might behave and take evasive actions as if they were, thus indicating that such near-miss situations might also be relevant for safety analysis. Taking that into account, a more flexible indicator T2, which does not require the two vehicles to be on a collision course, describes the expected time for the second road user to arrive at the conflict point. Recently extreme value theory (EVT) offering two approaches, block maxima (BM) and Peak over Threshold (POT), has been applied in combination with surrogate indicators to estimate crash probabilities. Most of this research has focused on testing BM and POT as well as validating various surrogate safety indicators by comparing model estimates to actual crash frequencies. The comparison of collision course indicators with indicators including crossing course interactions and their performance using EVT has not been investigated yet. In this study we are seeking answers to under what conditions these indicators perform better and whether they are transferable. Using data gathered at a signalized intersection focusing on left-turning and straight moving vehicle interactions our analysis concluded that the two indicators are transferable with stricter threshold values for T2 and that POT gives more reasonable results.
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| 13. |
- Bulla-Cruz, Lenin Alexander, et al.
(författare)
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Event-based road safety assessment : A novel approach towards risk microsimulation in roundabouts
- 2020
-
Ingår i: Measurement: Journal of the International Measurement Confederation. - : Elsevier BV. - 0263-2241. ; 165
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Tidskriftsartikel (refereegranskat)abstract
- Conventional road accident risk is measured by the undesirable events/exposure ratio. Common exposure indicators are activity-based, so event-based exposure is needed to achieve event-based safety assessment. Furthermore, road safety simulation is a growing research field. The influence of some software parameters is still unknown. Besides, the use of simulation for exposure assessment is incipient. This paper aims to validate a preventive event-based risk indicator: traffic conflicts/encounters, extending to risk microsimulation by a novel procedure to identify encounters in VISSIM. We evaluated the safety of a roundabout by three independent methods: [i] Swedish Traffic Conflict Technique using T-Analyst tool, [ii] VISSIM/SSAM conflict analysis, and, [iii] exposure mapping using encounters. Findings show that, once calibrated the safety distance factor of VISSIM conflict areas at 0.5, we got a similar number of observed and simulated conflicts, similar severities and similar number of encounters, resulting in similar observed and simulated risk outcomes.
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| 14. |
- De Ceunynck, Tim, et al.
(författare)
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Interact or counteract? Behavioural observation of interactions between vulnerable road users and autonomous shuttles in Oslo, Norway
- 2022
-
Ingår i: Traffic Safety Research. - : Dept. of Technology & Society, Faculty of Engineering, LTH, Lund University. - 2004-3082. ; 2
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Tidskriftsartikel (refereegranskat)abstract
- The current paper presents the results of behavioural observations in a field experiment with automated shuttles in Oslo, Norway. Video observations were conducted at five fixed locations along a challenging 1.2 km automated shuttle line with varying traffic conditions. Observed interactions between vulnerable road users and automated shuttles were coded using a predefined codebook, which allowed a structured quantitative analysis. The paper identified several potentially risky types of situations in which the automated shuttles did not always behave according to the traffic rules. Generally, the automated shuttles failed to give way to pedestrians at pedestrian crossings in 26%–50% of the interactions. Right-turning shuttles failed to yield to cyclists going straight in 38% of the interactions at observation Site 1 (the only location where the automated shuttle takes a right turn). In majority of same direction interactions between cyclists and automated shuttles, the interactions resulted in the cyclist overtaking the automated shuttle, usually on the left-hand side. Generally, the paper found little evidence of road users trying to bully or otherwise take advantage of the defensive driving style of the automated shuttles and identified only a limited number of interactions in which a vulnerable road user behaved ignorant or aggressive towards the automated shuttles. In addition, the paper found very little indication of temporal effects that suggest changes in the interaction patterns over time.
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| 15. |
- De Ceunynck, Tim, et al.
(författare)
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Sharing is (s)caring? Interactions between buses and bicyclists on bus lanes shared with bicyclists
- 2017
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Ingår i: Transportation Research Part F: Traffic Psychology and Behaviour. - : Elsevier BV. - 1369-8478. ; 46, s. 301-315
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents the results of an observation study of interactions between bicyclists and buses on shared bus lanes. The aim of the paper is to analyse bicyclists' safety on bus lanes shared with bicyclists. Straight sections of two bus lanes shared with bicyclists in Belgium are observed. All interactions between bicyclists and buses over two full weeks are recorded and analysed. Additionally, the lateral position and riding speed of bicyclists that are in interaction with buses are compared with the behaviour of bicyclists that are not in interaction with buses. One of the observed bus lanes is in line with road design guidelines in a number of countries that state that a sufficiently narrow bus lane (<3.5. m) is hypothesised to be safer than a somewhat wider bus lane; the other observed bus lane is deemed too wide according to these guidelines and is hypothesised to lead to close overtaking manoeuvres.The results show that close interactions between bicyclists and buses are relatively frequent on both types of analysed bus lanes. Close overtaking manoeuvres (a bus overtakes a bicyclist with a lateral distance less than 1. m) as well as close bicycle-following situations (a bus drives behind a bicyclist with a time gap less than 2. s) are quite common on both analysed bus lanes. The analyses could not confirm the hypothesis that a sufficiently narrow bus lane is safer than a wider bus lane. On the contrary, close interactions seem even slightly more common on the narrower bus lane. Slightly more close overtaking manoeuvres take place on the narrower bus lane, but the difference is not statistically significant. Additionally, more bicycle-following situations take place on the narrower bus lane because overtaking is more difficult. The results show that buses often maintain a close time gap in these situations. The overtaking speed of the buses is, however, significantly higher on the wider bus lane compared to the narrower one.Moreover, the presence of a bus has an influence on the behaviour of bicyclists. Bicyclists who get overtaken by a bus ride more closely to the edge of the road than bicyclists who are not in interaction with a bus. While the road design guidelines assume that bicyclists take up a width of one meter from the edge on bus lanes shared with bicyclists, the observations show that bicyclists take up much less space while being overtaken. The presence of a bus does not have a significant influence on the standard deviation of the lateral position of the bicyclist. On the narrower bus lane, some findings suggest that bicyclists who are involved in an interaction with a bus ride faster than bicyclists who are not involved in an interaction with a bus.
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| 16. |
- Hammad, Samir, et al.
(författare)
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Utvärdering av hastighetssäkrade åtgärder på landsbygdsvägar
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Detta arbete har utvärderat hastighetssäkrade åtgärders effekt på landsbygdsvägar genom att filma totalt 34 olika sådana åtgärder i södra Sverige och studera hastigheten av frigående bilar och tunga fordon när de passerar de olika åtgärderna.Varje plats har filmats med drönare och alla fordon har automatiskt spårats m.h.a. videoanalys. Därefter har frigående fordon identifierats och deras hastighet analyserats.Analysen har gjorts i två huvudsakliga steg: (1) en visualisering av fordonens rörelser genom alla studerade åtgärder har gjorts och hastighetsprofilerna återfinns i Bilaga A, B och C; och (2) en matematisk modell har skapats som beskriver förhållandet mellan ett fordons minsta radie genom en åtgärd och fordonets hastighet i samma punkt.Resultaten visar att de studerade hastighetssäkrade åtgärderna på landsbygdsvägar fungerar generellt bra och sänker hastigheten. Alla platser fungerar dock inte lika bra och det är fortfarande oklart exakt vad som avgör varför vissa platser med liknande åtgärder fungerar olika bra. Generellt så verkar Avsmalningar vara mest hastighetssänkande, Portar resulterar i 16% högre hastighet och Chikaner visar 30% högre hastigheter än avsmalningar.
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| 17. |
- Høye, Alena, et al.
(författare)
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SeeMe at the crosswalk : Before-after study of a pedestrian crosswalk warning system
- 2019
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Ingår i: Transportation Research Part F: Traffic Psychology and Behaviour. - : Elsevier BV. - 1369-8478. ; 60, s. 723-733
-
Tidskriftsartikel (refereegranskat)abstract
- SeeMe is a pedestrian crosswalk warning system with automatic pedestrian detection that is mounted on crosswalk signs. Amber flashing lights are activated when pedestrians are approaching or crossing the crosswalk. The aim is to attract motorists’ attention, to improve yielding behavior and to reduce conflicts. A before-after study with a matched comparison group has been conducted in the Norwegian municipality of Trondheim. Video observations were made at eight crosswalks (four of which were equipped with SeeMe in the after period) of 1825 pedestrian-motorist interactions. On average, yielding rates at SeeMe equipped crosswalks increased by 14% (statistically significant) when changes at the comparison sites are taken into account. However, the results are inconsistent between crosswalks. At two of the crosswalks with SeeMe in the after period, yielding rates increased by 39% (statistically significant), while they decreased by 4% at the other two crosswalks (not statistically significant). There were several differences between crosswalks with increased and unchanged yielding rates: Initial yielding rates (below vs. above 80%), placement of crosswalk signs (immediately at vs. at some distance from the crosswalk) and false alarm rates (30% vs. 57% on average). These factors may have affected the effect of SeeMe on yielding rates, but the number of crosswalks included in the study is too small to generalize the differences between different types of crosswalks. The results do not indicate that SeeMe has negatively affected pedestrian behavior or provoked conflicts. It is concluded that SeeMe may be effective in increasing motorist yielding rates at crosswalks with similar characteristics as in the present study - two-lane roads in residential areas with moderate motor vehicle volumes and speed limits of 50 kph or below - and that high initial yielding rates and high rates of false alarms may limit its effectiveness.
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| 18. |
- Johansson, Maria, et al.
(författare)
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Metodutveckling för att studera allmänhetens respons på energieffektiv utomhusbelysning
- 2017
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Artificial outdoor lighting for pedestrians should provide for a safe and secure outdoor environment after dark. Pedestrian lighting thereby has implications for active transportation and sustainable mobility. Installations of new energy efficient lighting applications should be evaluated in terms of pedestrian’s perception, evaluation and behaviour in the lit environment. Today there is a lack of methods to assess such pedestrian responses, in particular pedestrian behaviour. In a multidisciplinary context this project aimed to develop two methods to capture pedestrians’ behavioural responses possible to employ in urban outdoor spaces and among different user groups: Random Environmental Walking (REW) and Video Analysis of Pedestrian Movement (VAPM). Development of REW and VAPM was carried out in a series of empirical studies. In the final studies the new methods were combined with established methods in environmental psychology. It is proposed that REW and VAPM could complement lighting standards and energy measures to obtain optimal solutions for outdoor lighting. At present REW and VAPM work well in a research context, but further refinement of the procedures and analyses will be necessary for large scale implementation. VAPM constitutes a special case as the mounting of cameras in public spaces increasingly requires special permit, at least in Sweden. The development of REW aimed to obtain pedestrians’ behavioural preference of outdoor lighting applications. The REW was tested in a within-subject design with 80 participants who evaluated four lighting applications placed close to each other in an urban park: Application 1 was a clear Ceramic Metal Halide (CMH), Lighting Application 2 was a frosted CMH, Lighting Application 3 was Light-Emitting Diode (LED), Lighting Application 4 was a LED. The results of REW showed that the participants walked most frequently to Application 3, indicating that this was the behaviorally preferred lighting application. This result agreed well with participants’ self-report ratings of their visual experience of the lit environment and perceived lighting qualities. In this respect, REW was shown to be a viable technique for use in the field. The VAPM aimed to provide detailed data on pedestrians’ microscopic movement. VAPM was tested in a between-subject design with 62 participants who evaluated two lighting applications along a 130 meter traffic-separated walking and cycle path. Twenty-nine participants walked the path with Application I (Philips SGS203 50 Watt SON-T, mounted at lamp-posts with a distance of 33 meters), thirtythree participants walked the path with Application II (Philips P17 Master City White CDO/ET 50W/828, mounted at lamp-posts with a distance of 16.5 meters). In Application II the illuminance on the path was considerable increased. The results of VAPM revealed that participants walked systematically closer to the centre-line of the path in Application II as compared to Application I. Participants assessed Application II to provide better conditions to see along the path but the surroundings where considered too dark, indicating that the brighter and more focused light created a visual tunnel. The VAPM showed a great potential in capturing pedestrian behaviour under different lighting applications. The research project has been situated at Lund University and carried out in close collaboration with Malmö City and Axis Communications.
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| 19. |
- Johansson, Maria, et al.
(författare)
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Video analysis of pedestrian movement (VAPM) under different lighting conditions—method exploration
- 2020
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Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 13:6
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Tidskriftsartikel (refereegranskat)abstract
- When daylight hours are limited, pedestrians are dependent on appropriate outdoor lighting. Although new city lighting applications must consider both energy usage and pedestrian responses, current methods used to capture pedestrian walking behaviour during dark conditions in real settings are limited. This study reports on the development and evaluation of a video-based method that analyses pedestrians’ microscopic movements (VAPM—video analysis of pedestrian movements), including placement and speed, in an artificially lit outdoor environment. In a field study utilising between-subjects design, 62 pedestrians walked along the same path under two different lighting applications. VAPM accurately discriminated pedestrians’ microscopic movements in the two lighting applications. By incorporating methodological triangulation, VAPM successfully complemented observer-based assessments of pedestrians’ perceptions and evaluations of the two lighting applications. It is suggested that in evaluations of pedestrian responses to city lighting applications, observer-based assessments could be successfully combined with an analysis of actual pedestrian movement while walking in the lit environment. However, prior to employing a large-scale application of VAPM, the methodology needs to be further adapted for use with drones and integration into smart city lighting systems.
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| 20. |
- Johnsson, Carl, et al.
(författare)
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A relative approach to the validation of surrogate measures of safety
- 2021
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Ingår i: Accident Analysis and Prevention. - : Elsevier BV. - 1879-2057 .- 0001-4575. ; 161
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Tidskriftsartikel (refereegranskat)abstract
- Surrogate measures of safety (SMoS) are meant to be an alternative/complement to crash data that enables a proactive approach to traffic safety. Validity is a fundamental property of SMoS that describes how well they reflect the quality of interest – traffic safety. However, typical validation studies are extremely resource demanding. Therefore, the aim of this study was to explore a relative approach to validity that uses fewer resources and does not rely on crash records from the observed locations. The core idea of a relative approach tothe validation of SMoS is that while SMoS might not accurately estimate the expected number of crashes, they still work well for comparisons between different sites or between conditions at the same site. Based on thisconcept, we propose a method in which a ground truth based on literature can be used as a baseline that can then be compared to the safety analysis of an SMoS study. Using the proposed method, a case study of six intersectionsin northern Europe was conducted, focusing on bicycle infrastructure. The results indicate that the minimum time-to-collision indicator is in line with the ground truth, whereas the post-encroachment time indicator is not.
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| 21. |
- Johnsson, Carl, et al.
(författare)
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Identification of evasive manoeuvres in traffic interactions and conflicts
- 2022
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Ingår i: Traffic Safety Research. - : Dept. of Technology & Society, Faculty of Engineering, LTH, Lund University. - 2004-3082. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- The study presents a simple and easy to implement method for detection of the evasive action start in traffic interactions. The method is based on comparison of the studied trajectory with a reference set of ‘unhindered’ trajectories, interpreting the start of evasive action as the moment when no more similarities can be found. The suggested algorithm performs well for primary interactions when road users arrive in an unhindered state. It fails, however, in case of secondary interactions. Explorative application of the method on a large dataset of normal and conflict traffic situations concludes that traffic conflicts occur more frequently in secondary interactions, presumably due to higher cognitive load on the involved road users. Despite the limitations, the method can be used both for the safety studies based on traffic conflicts and for more general quantification and visualisation of the road user behaviour.
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| 22. |
- Johnsson, Carl, et al.
(författare)
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In search of surrogate safety indicators for vulnerable road users : a review of surrogate safety indicators
- 2018
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Ingår i: Transport Reviews. - : Informa UK Limited. - 0144-1647 .- 1464-5327. ; 38:6, s. 765-785
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Tidskriftsartikel (refereegranskat)abstract
- Surrogate indicators are meant to be alternatives or complements of safety analyses based on accident records. These indicators are used to study critical traffic events that occur more frequently, making such incidents easier to analyse. This article provides an overview of existing surrogate indicators and specifically focuses on their merit for the analyses of vulnerable road users and the extent to which they have been validated by previous research. Each indicator is evaluated based on its ability to consider the collision risk, which can be further divided into the initial conditions of an event, the magnitude of any evasive action and the injury risk in any traffic event. The results show that various indicators and their combinations can reflect different aspects of any traffic event. However, no existing indicator seems to capture all aspects. Various studies have also focused on the validity of different indicators. However, due to the use of diverse approaches to validation, the large difference in how many locations were investigated and variations in the duration of observation at each location, it is difficult to compare and discuss the validity of the different surrogate safety indicators. Since no current indicator can properly reflect all the important aspects underlined in this article, the authors suggest that the choice of a suitable indicator in future surrogate safety studies should be made with considerations of the context-dependent suitability of the respective indicator.
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| 23. |
- Johnsson, Carl, et al.
(författare)
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The ‘safety in density’ effect for cyclists and motor vehicles in Scandinavia: An observational study
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Ingår i: IATSS Research. - 0386-1112.
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Tidskriftsartikel (refereegranskat)abstract
- Safety in density (SID) potentially explains the safety in numbers (SIN) phenomenon by positing that ‘the SIN effect can be reproduced simply through encouraging behaviour that leads to the formation of higher-density cyclist groups’. The study further explores this hypothesis using event-based exposure, queues and groups of road users. Using three different definitions of encounters between road users, these were manually counted at signalized intersections, and their relationship to traffic volume was assessed. Based only on the frontmost motor vehicle in a queue and one cyclist among the several passing in front of that vehicle, the results show a less than linear relationship between meetings and trafficvolume. An in-crease in the number of cyclists entails a general increase in cyclists passing in front of each motor vehicle, and an increase in motor vehicles increases queue lengths. However, crash data from the Swedish accident database (STRADA) show that it is exceedingly rare for multiple cyclists to be injured in the same crash. Together with results from a crash-encounter model, this suggests that the SID hypothesis may help to ex-plain SIN
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| 24. |
- Johnsson, Carl, et al.
(författare)
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Validation of surrogate measures of safety with a focus on bicyclist–motor vehicle interactions
- 2021
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Ingår i: Accident Analysis and Prevention. - : Elsevier BV. - 0001-4575. ; 153
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Tidskriftsartikel (refereegranskat)abstract
- Surrogate measures of safety (SMoS) can enable quick, pro-active, and detailed safety evaluations by studying near-crashes. A critical concern regarding SMoS is their validity. This study focused on the validity of two commonly used SMoS indicators—minimum time to collision and post-encroachment time—with a specific focus on bicyclist–motor vehicle interactions. The study was divided into two main parts; the first part focused on observations at intersections in Scandinavia, and the second part focused on developing a crash model using data from 166 similar intersections. Nine signalised intersections in Scandinavia were observed for at least 24 h. During this time, each interaction between a bicyclist and a right- or left-turning motor vehicle was identified and trajectories for the road users were created. The corresponding SMoS values were then calculated. Three main results were found when comparing the results of the crash model with the SMoS analysis. First, there is a significant relationship between the expected number of crashes and both indicators. However, the results also suggest that this correlation might originate from the inherent connection between the indicators and the number of interactions between the studied road users. Finally, when the number of interactions is considered, the results show that the minimum time to collision with a threshold of 3–4 s produces the best results.
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| 25. |
- Kamaluddin, Noor Azreena, et al.
(författare)
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Modelling of motorcyclists' risky behaviour at an urban T-junction using generalised linear model : An exploratory study
- 2023
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Ingår i: IATSS Research. - : Elsevier BV. - 0386-1112. ; 47:1, s. 94-104
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Tidskriftsartikel (refereegranskat)abstract
- Motorcyclists represent the greatest share of recorded traffic crashes and fatalities in Malaysia. The association between motorcyclists' behaviour and traffic conflict occurrence was assessed at a typical stop-regulated T-Junction in an urban area of Kuala Lumpur, Malaysia. Traffic activities were filmed over four months and the behaviour of motorcyclists entering the main road from the minor road was observed from recorded video sequences. Situations ending in a traffic conflict were compared to similar interactive situations not ending with a conflict. In total, 447 sets of interactions of motorcyclists and other motorists at the T-Junction were analysed where 242 interactions ended in conflicts (three of them ended with traffic crashes). The generalised linear model with a binomial response and link logit was adopted to assess the association of motorcyclists' behavioural variables with the probability of conflict occurrence. The significant behavioural variables were classified into categories according to the statistical variation of the value they can assume in the dataset. The motorcyclist's entering angle was the most significant contributory factor in the probability of traffic conflict. The findings can be helpful in deciding on road safety countermeasures. The results could feed into the decisions of policymakers to structure the education and licensing process.
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