Countdown timers (CDTs) for pedestrians and cars have been shown to produce various effects, including improved efficiency and decreased safety. This study aimed to explore adaptive behaviours of cyclists towards a CDT to green traffic light, conducted as a before-after study in real traffic. Cyclists adapted to the CDT by searching for and using the information that it provided, mainly in terms of speed adaptation and glance behaviour. Start-up delays were reduced but there is a concern that red light violations could increase. There might be undesirable effects on crucial information intake in cases where the CDT was used not as a complement but as a substitute for the traffic light. The results essentially indicate that cyclists use the information provided by the CDT for their own efficiency, rather than for rule-based safety.

Road-user adaptation is a prerequisite for traffic to run smoothly. By adaptation, the road user aims to ensure a feeling of comfort according to his or her present state and capability. In this thesis, adaptive behaviour of car drivers and cyclists in response to different factors is explored, using the individual perspective of the road user. The research focuses on investigating how adaptation in the road traffic environment can be described, and what adaptations road users make in traffic in response to static and dynamic infrastructure, additional tasks and other road users.

One simulator study and three field studies in real traffic were carried out. The study results implied that the current road-user role and the preconditions for that role, in terms of vehicle and infrastructure, affect adaptive behaviour. The results also showed that in non-complex situations, there is a certain level of visual guidance above which more detailed information does not have any effect on speed adaptation. Detailed information that allows road users to improve their predictions to take action to ensure a feeling of comfort, is however preferred. Under increased situational demands, vehicle speed can be reduced to maintain the safety margins. It was found that there are individual strategies concerning what degree of complexity for interaction with an additional task is acceptable.

A conceptual model of adaptation in relation to the environment and subjective perceptions of safety and a feeling of comfort is proposed and applied to different traffic situations. For future transport system designs it is advised that adaptive behaviours of road users are supported.

Att trafikanterna anpassar sig är en förutsättning för ett välfungerande vägsystem. Genom anpassning försöker trafikanten säkerställa en känsla av komfort med hänsyn till hans eller hennes nuvarande tillstånd och förmåga. I denna avhandling undersöks bilförares och cyklisters anpassningsbeteende i samband med olika faktorer, utifrån ett individuellt trafikantperspektiv. Forskningen är inriktad på att undersöka hur anpassning i vägtrafikmiljön kan beskrivas, samt vilka anpassningar trafikanter gör i relation till statisk och dynamisk vägutrustning, extrauppgifter och andra trafikanter.

En simulatorstudie och tre fältstudier i verklig trafik har genomförts. Studieresultaten antydde att den roll som trafikanten har för tillfället, samt de förutsättningar som den rollen innebär i form av fordon och infrastruktur, påverkar anpassningsbeteendet. Resultaten visade också att om den visuella ledningen är över en viss nivå har inte mer detaljerad visuell information någon effekt på hastighetsanpassningen i icke-komplexa situationer. Trafikanterna föredrar dock mer detaljerad information om den gör det lättare att bedöma hur trafiksituationen kommer att utvecklas. Om komplexiteten ökar kan fordonshastigheten minskas för att bibehålla tillräckligt stora säkerhetsmarginaler. Hur man interagerar med extrauppgifter är individuellt och beror på vilken svårighetsnivå för interaktion som individen själv upplever är acceptabel.

En konceptuell modell för anpassning föreslås som tar hänsyn till trafikmiljön och trafikantens upplevelse av säkerhet och känsla av komfort. Framtida trafiksystem bör utformas för att stödja trafikanternas anpassningsbeteenden.

The aim of the study was to investigate how different delineator post configurations affect driver speed in night-time traffic. In addition, the potential speed effect of introducing a secondary task was investigated. The study was carried out in a car simulator on a road stretch including straight road sections as well as curves with different radii. Fourteen drivers participated in the study and the results show that absence of delineator posts leads to reduced speed. However, provided that there are delineator posts continuously present along the road, the overall driver speed is basically the same, regardless of the spacing between the delineator posts. The results also imply that to reduce driver speed in curves with small radius, using more compact spacing of posts in these curves as compared to in curves with a larger radius, could be a potential strategy. Additionally, the speed reducing effect of a secondary task was only prevailing where the task was initiated.