DC Noodles is not on the 42 bus line, but I have to give them a shout out. I love when a restaurant makes it clear on the menu, or signage what's vegan, what can be made vegan and what isn't vegan. And especially those who back that up with knowledgeable employees.
DC Noodles has always offered vegan-friendly, good food, but on a recent visit I noticed that they had clearly labeled the menu with vegetarian items, even going as far to show which items were made with fish or oyster sauce and broth; often a hidden ingredient. Some dishes are just vegetarian, but not vegan so definitely ask the server your detailed questions. They are happy to accommodate and check with the cooks, etc.
DC Noodles is located at 1410 U Street; quite a walk from the closest 42 bus stop, but you can walk from Adams Morgan easily.