It's just after noon on a recent Wednesday in San Francisco, and Dan Witz is driving a rental car on Highway 101 north, approaching the Vermont Street exit that leads to Potrero Hill. Just before the turnoff, he suddenly pulls over to the right-side embankment. Minutes later, he has walked to his trunk and put on a blue hard hat and green reflector vest, which gives him the appearance of an official Caltrans worker. The... More >>>