Robert, we have not tested MJPEG vs H.264 in some years since MJPEG has been in decline and increasingly camera manufacturers are even dropping support for MJPEG. However, see: H.264 vs MJPEG - Quality and Bandwidth Tested
In your scenario of low frame rate and high scene activity, I would expect the bandwidth savings of H.264 to be modest - 25% or less. So if you really want to use MJPEG, you won't suffer a significant bandwidth penalty by doing so in these conditions.
That said, if there are times of day where the train station has low activity (perhaps in the middle of the night), that's where H.264 will deliver significantly higher savings (especially conjoined with newer smart codecs).