Los Angeles

Imo, it’s kind of a necessary evil. I’m not blind to the fact that rail yards cause a lot of pollution and make things worse for the marginalized groups living near them. The exact same thing is true, however, of truck shipping and highways.

I don't have hard data, but I would imagine the pollution around roads caused by trucking has a lower impact than the pollution around rail yards and railways simply because of the concentration.

Pound for pound, freight rail causes a lot less emissions pollution (IIRC it’s an order of magnitude more efficient than trucks),

I agree, but the use cases are different for where the emissions occur and in what concentration. Idling locomotives can park near homes and idle for upwards of 30 hours (source)

and it’s easier to convert to electric or hydrogen than converting our national truck fleet.

It doesn't matter how easy it is if rail companies don't get off their butts and make the conversions. From the article:

"Train emissions — about 70% of all rail yard pollution — have remained largely unchanged over the past decade, partly because the rail industry has not purchased new locomotives with cleaner engines, according to the air district."

With this regulation in place, it can act as in incentive for rail companies to make the exact changes you're advocating for. Clearly without the regulation, rail companies aren't. Look at the outsized positive impact CARB regulations have had on automobiles with regard to efficiency and emissions nationwide. Because California had a higher bar that companies had to reach to operate in California, the entire nation has benefited. I see as the start of CARB for rail, and that would be a good thing.