Car Talk Puzzler

Fortunately, I'm not a radio program director... because if I were, and 30 years ago two scruffy guys had walked through my door and said, "hey, we propose to do an hour-long radio show during which listeners call in with questions about their car repair needs for us to answer," I would've bellowed, "get out of my office you @*(%$#;!! knuckleheads with your lame-brained idea, and don't ever waste my precious time again!!"

If there is a person on the planet today who doesn't enjoy NPR's "Car Talk" with Tom and Ray Magliozzi  I don't know who it is. And one of the best parts of their weekly schtick is a "puzzler," that they ask listeners to solve during the next week (sometimes with a mathematical component).

All this is by way of introduction to this simple Friday puzzle which I've adapted from a Car Talk offering of a few weeks back -- admittedly, it's not so much a math puzzle as an elementary thought or logic puzzle that I liked:

In Borneo, there is a bridge connecting two islands, constructed of bamboo, lashed together with hemp, and used for hundreds of years. The bridge is 4 miles long and it has a strict weight limit of exactly 20 tons.
One day, a truck full of sedated pigs pulls up to cross the bridge. The weigh station finds that the truck weighs precisely 20 tons. The bridge is emptied and the driver allowed to drive across.
But as he drives forward, a flying sparrow begins to follow alongside, and just when the truck passes the halfway point, the sparrow lands on the truck!

What does the driver do to keep the truck and sedated pigs from plunging into the abyss below? (Note: jumping out of the cab or tossing articles of clothing out are not options.)

answer below:
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answer: It's a trick question and the driver need not do anything: In driving from the beginning of the bridge to the halfway point a 20-ton truck consumes fuel, and will easily consume an amount of fuel that's greater than the weight of the sparrow, so when the sparrow lands on the truck, nothing happens!