Research in different domains has shown that people categorize oneself and others as ingroup (“us”) and outgroup (“them”) members, resulting in group-based stereotyping and attribution errors that may adversely affect social behaviour. To determine whether such patterns also exist in road traffic, we conducted an experimental web-based survey using scenarios of unregulated traffic settings in which the type of other road user was varied (cyclist vs. car driver). We investigated whether road users who described themselves predominantly as either a car driver (N = 330) or a cyclist (N = 315) would (1) report having more in common with members of their respective ingroups than outgroups, (2) be more negative about their respective outgroup than ingroup in terms of their expectations about other road users, (3) make more dispositional and less circumstantial attributions about an outgroup member who failed to yield right of way than about an ingroup member, and (4) show more willingness to raise traffic fines for the outgroup than for the ingroup. Results showed both self-described car drivers and cyclists reported having more in common with their ingroup than with their outgroup. Self-described car drivers were also least inclined to expect to be given right of way by cyclists as compared to car drivers, while self-described cyclists were less inclined than self-described car drivers to expect car drivers to yield right of way. Self-described car drivers were more inclined to make dispositional attributions about cyclists’ rule breaking behaviour and less inclined to attribute these to circumstances compared to rule breaking on the part of car drivers, and were most inclined to disadvantage their outgroup compared to their ingroup in terms of raising traffic fines. Since dispositional attributions are more likely to lead people to behave aggressively, our findings suggest that cyclists, who are arguably among those most dependent on the goodwill and forgivingness of drivers of motorised vehicles, may be less likely to receive it. This means that although both self-described cyclists and car drivers may distinguish between ingroups and outgroups in traffic, this distinction may have much more complicated implications than the simple terms “us” and “them” might imply.