If they only taxed passenger vehicles you'd have a point, but the cost for trucks is actually higher (up to more than double), which means that in the end it is a tax on essential goods, because those goods have to make it into the city somehow and businesses have to pass that cost on to customers. It's reasonable to be afraid that poor customers will see the largest change as a percent of their budget as prices go up to pay for the tax (though obviously we haven't had time to measure whether that to see for sure).