https://www.vice.com/en_us/article/z3epje/google-and-apples-contact-tracing-api-doesnt-work-on-public-transport-study-finds

Covid-19 contact-tracing apps that rely on an API developed by Apple and Google and bluetooth technology cannot accurately measure the distance between users on public transport, a recently released study from Trinity College Dublin has found. 

The researchers of the study first tested the API on a group of volunteers who switched seats every fifteen minutes in a Dublin tram. They then ran the collected data through the detection rules of the Swiss, German, and Italian contact-tracing apps to see how often they correctly identified contact between users. Based on this, they found that the chance of an accurate detection was “similar to that of triggering notifications by randomly selecting from the participants in our experiments, regardless of proximity.”