I've pondered the idea of building a "Ton Bike", the opposite of the 12-lb wonders currently being designed. Use car tires, keep the weight low for proper handling.
On the 1,000 lb + hill idea- I recall reading several years ago of a case where a pedicab was going downhill, couldn't get stopped at a redlight, ran it, and got somebody killed. IE, there is a potential safety hazard to be dealt with in addition to the strong legs & low gear requirements.
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"be careful this rando stuff is addictive and dan's the 'pusher'."