xcessive speed is arguably the most common form of law-breaking behavior. It is a factor in about half of all road fatalities inDenmark. We present preliminary results from a randomizedcontrolled trial on the effects of an online intervention againstspeeding. The online intervention consists of a 24-question test onroad safety issues, risk perceptions, and attitudes. All speedoffenders in Denmark (fall 2021 to fall 2022), n=280,699, receivedan invitation by digital mail, 25,480 completed a baselinequestionnaire and were randomized. Approximately 71 % of thetest group completed the intervention. Based on the intervention,test group participants were divided into three groups: 45% are low-risk drivers, 44% medium-risk and 11% are high-risk of a newspeeding ticket. The high-risk drivers are mostly male, younger,and have many recent speed tickets. Two to three months after theintervention, the test group received a follow-up questionnaireabout the intervention and its potential effect. These self-reportsindicate that 70% are more aware of their driving speed, moremotivated to comply with the speed limit and comply with thespeed limit more often. It is not yet possible to quantify the effect ofthe intervention on the number of speeding tickets based oncriminal register data because the one-year follow-up period endsfall 2023. There are indications, that there may be an effect. Bothgroups received a follow-up questionnaire one year after thebaseline. In this self-report, more test group than control groupparticipants stated that they exceed the speed limit less often (test:58%; control: 51%) and that more participants in the test grouphave changed their behavior to better comply with speed limits(test: 27%; control: 21%) (preliminary results)