Drayage has long been a discrete step in shipping port operations: cargo vessels must be loaded and offloaded in an expedient manner and dedicating vehicles to the task has been standard practice since before there were trucks. Given that diesels are not optimal for the short hops associated with drayage runs, replacing them with other energy sources - natural gas, electric, even hydrogen - represents low-hanging fruit to reduce air pollution, especially particulates.The ports in L.A. used to have a lot of diesel trucks sitting waiting for loads. Now they have to be natural gas or electric to go to the port. This law had an unintended consequence of slowing down pickups and drop offs of loads, however. The companies that didn't want to change out their entire fleet to natural gas decided to buy one natural gas truck to stay by the port and load it with the load from the diesel trucks, then just drive the natural gas truck to the port and back about a mile, skirting the law and making it do nothing to reduce pollution.