Architect Martin Angelov presents this bike facility concept to transport cyclists over busy intersections and other areas where more traditional infrastructure may be cost prohibitive.
You propel your bike by pedaling in a metal track. To keep from falling off and hurtling to your death, something like a chairlift grip mechanism attaches the bike handlebar to a safety cable on either side of the bike. The "grip" isn't really a grip since it doesn't grip the cable, but rolls freely as shown in the animation below.
The idea is to enable bike transportation in areas where space or money is in short supply. Do you need a new bike / pedestrian bridge over Highway 101 in San Mateo but don't have $8 million in the budget? Buy a truckload of gutter, half inch steel cable, a pile of cable grips and supporting structures and you're good to go!
Can you imagine the vertigo and thrill of flying on your bike underneath the Oakland Bay Bridge while 30 mph gusts toss you to and fro with the churning waves of the Bay 200 feet below?
More info at Kolelinia.com. Via Steve in Chicago.