Everyone in Stockholm seemed to have set his alarm clock to sound off be fore dawn. By 4 a.m., cars, motor scooters and flower-decked taxis that had been hired months before streamed downtown to the Kungsgatan, the city's main street. There they waited through a solemn radio countdown. At the stroke of five, loudspeakers blared: "Now is the time to change over." In a brief but monumental traffic jam, Sweden switched to the right side of the road.
The big change was a long time coming. For decades, while the rest of Europe standardized driving on the right, Sweden, like Britain,...