H old on tight!” shouts my driver Matteo as we accelerate into the chaos of rush-hour Rome . Great advice, except I can’t see exactly what to hold on to. As his Vespa lurches forward, my panic rises. As we slice through lanes of traffic, my body is rigid and I struggle to stay upright. “Grab the bar at your side,” he orders, and, sure enough, I find a small chrome rail circling my seat and grip on for dear life. Navigating a Vespa ride in Rome may not be for the faint-hearted, but if you give in to it, it can be an intoxicating blast. I’m here ahead of the Vespa’s 80th birthday in June, when thousands of Vespa riders will descend on the city’s streets to celebrate the creation of the design classic. I decided to mark the occasion in style by following in the footsteps of Audrey Hepburn in Roman Holiday. When she played a princess who absconds for the night to discover freedom and romance, the iconic status of the Vespa was sealed.…