Not every crime/infraction requires mens rea. Many states, for example, don't require malicious intent to charge someone with manslaughter, but rather that the perpetrator acted neligently to cause someone's death. Nearly all traffic violations in the US do not require intent, but instead they only require that the operator of the motor vehicle can be established (not the case in the UK). In WI where OP lives that state has a 3-foot passing law. If he can demonstrate that the pass was too close and can also identify visually what the operator looked like, the citation can stand. I've had similar success riding in KS where I was buzzed and got the driver ticketed despite zero malicious intent.