2 days ago, I asked if coasters are infection machines. Later, I saw this video:
"Empty middle seats on planes won't stop the coronavirus". They were surprised how far the virus spread. Dr. Chen's models show how empty seats do not provide enough distance to avoid spread. He says the only improvement is limiting passenger density. Nevertheless he says he would ride on a plane if masks also were used.
In the case of a large coaster train at high speed, particles from the front row would reach the back row within 2 seconds. However, within another 2 seconds, the entire train would be largely flushed. Some particles would stick to surfaces and a very small amount inhaled. Based on a model that any virus can cause infection, this is terrible. However, if there is a threshold amount, it is possibly very good, and far better than airplanes. In this case also, empty seats do not provide enough distance to avoid spread, only limiting passenger density. Even masks do not limit the distance, only the amount, but that may be more than sufficient also.
By this model, shields might actually make the problem worse. Testing and modeling should be done before more-or-less ruining rides with such devices, indeed before opening rides at all, or fearing them.