The "trolley trucks" scheme addresses local air toxics more than traditional criteria pollutants. For (lack of) planning reasons, the LA ports and their railroad/other connections are not separated well (at all, really) from very sensitive populations, so the localized truck (and railroad) diesel particulate matter issue is very hot. Remember, for toxics, the allowable pollutant concentration is zero. There is no standard, because there is a health effect from well below the point where you can detect it in the air. Diesel particulate matter is an official toxic air contaminant in California; EPA hasn't yet declared it that officially, but treats it that way in most studies and environmental comments.

The ports and their shippers are already using some battery-electric tractors for on- & near-dock drayage; they don't work well (laughably short range per charge), but they work, and they reduce by a very small increment the amount of diesel exhaust in the area. The trolley trucks are supposed to expand that to work at longer distances, such as drayage up to Hobart. Personally, I suspect that better near-dock transfers (Hobart is more than 10 miles up the freeway) and more localized rail electrification might work better. But this is LA ... at one time they were talking a maglev freight-transfer system from the ports to industrial/warehouse areas all over the Basin. Call it the Disney approach (Tomorrowland for containers!).

Yes, electrics are remote-emission vehicles. But that means the emissions (which exist - California's power mix is much cleaner than the national average but more than 80% of it still comes from burning something somewhere) are someplace else, not at the docks, intermodal yards, streets, and freeways next to all those impacted populations. In theory, it's easier to control emissions at those other places.