From the standpoint of the Mercury News, a report by a rider is more important and more credible than anything done by "an expert."

According to the story, the rider used a phone app to measure the sound level. I've seen such apps. They're the modern equivalent of the old Radio Shack sound level meter. IOW not calibrated in a way that would allow readings that are repeatable with professional equipment (in the ballpark, but could vary by 6 dB or more from a calibrated device, and frequency response affected in an unknown way by the phone's mic), but still useful for comparisons between readings using the same instrument.

The rider allegedly tried to take readings at the same spot in the new and "older" cars - we don't know *which* older cars but that's kind of a trainspotter's game given that there are several older models in use. I'm not sure if any of the genuinely *OLD* cars from the 1960s (the original ones, "A" and "B" types) are still in use or whether they'd be recognizable as such after several rehabs over the years. We also don't know where in the cars the "same spot" was, where along the line the measurements were taken, and for how long they were averaged.

The published results - that the new cars are only a fraction of a dB quieter than old - suggests that the difference is undetectable to the ear. But a good noise study would go beyond that and try to get a noise frequency spectrum as well as sound pressure level. I strongly suspect that the newest cars are in fact perceptibly quieter, given the plug doors and probably a different drive system, plus the reprofiled wheels (are the rails reprofiled too? not known), which could occur from the SPL being lower, from the frequency spectrum being less annoying, or a combination. Finally, it was also noted in the comments that BART is reprofiling wheels on the older cars as they come due for wheel service to match the new ones - if the rider managed to somehow get an older car with reprofiled wheels, the SPLs should in fact be a close match.

Anyway, it's a news"paper" article, JimBob, not a scientific or engineering paper acknowledging sources of error and the like. I agree that BART, if it were organizationally smart, would organize a decently controlled study of the subject and make all of the data and analysis public. It hasn't, so we get stories like this that raise more questions than they answer (good for clickbait!).