https://phys.org/news/2018-07-vehicle-ramming-social-virus-media.html

As such, Dr. Miller and Professor Hayward examined a third explanation for the spike in VRAs: that they have spread as a form of 'social virus' irrespective of ideology. This does not mean that Dr. Miller and Professor Hayward are suggesting that ideology, propaganda or psychological issues play no role in these crimes. However, they do suggest the need to recognise the viral or mimetic quality of some forms of violence and that exposure to these actions through, for example, news media and social media can create a momentum that leads to people with different beliefs and motives to repeat the act. For example, they argue that similar to the outbreak of plane hijackings that took place in the 1960s and 1970s, the coverage of VRAs in the media and in online discussion forums on websites has encouraged others, often with wholly different political and religious motives, to engage in VRAs.

As such, the sudden 'wave' of vehicle ramming incidents over the last few years is akin to a virus spread by social contagion, whereby a single action leads to a wave of others, which would otherwise not take place—often more akin to a 'crime of passion' than a well-planned terrorist act.