ARLINGTON, Va. — On a recent snowy morning, Michael Ellis prepared his mail truck for the daily route he has run here for the last decade, through a neighborhood in the Washington suburbs.

White, boxy mail trucks are a staple of neighborhoods across the country. But the aging vehicles — many date to the late 1980s — were built for a different era. They have no anti-lock brakes, airbags or even air-conditioning, and more important, the mail trucks simply are too cramped to carry the increasing number of packages postal carriers deliver.

“It’s been a good vehicle for me, but it just can’t keep up anymore with what we need,” Mr. Ellis said, pointing to the stacks of boxes in the back of his truck.

Mr. Ellis, a mail carrier for nearly 29 years, remembers when the post office here received its first batch of the Grumman-bodied trucks around 1990. Back then, he said, they were a dream compared with the Ford Pinto he had been using.