Endeavour is 122 feet (37 meters) long and 78 feet (24 meters) wide and stands 5 stories tall at the tail - which police said makes it the largest object ever to move through Los Angeles. Its combined weight with the transporter is 80 tons.
Organisers say that only a few inches separate Endeavour's wings from structures along the route, and workers have felled 400 trees along curbs to clear a path. The science center, where Endeavour is heading, will plant more than 1,000 trees to make up for their loss.
Some street lights, traffic signals, power poles and parking meters also are being temporarily removed.
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Poncho is a first aid pro and even listened to his police trainer's chest to check he was still breathing.