Bangkok is a huge city—more than 10 million people with countless more coming in each day from neighboring provinces for work. The result, as you might expect, is a vast sprawl of bumper-to-bumper traffic: street cars, trucks, and motorcycles, sidewalks teeming with pedestrians, even canals full of boats. The Thai capital’s infrastructure is part of the reason for the intense gridlock, since the city grew rapidly, with little land use or transportation planning. Its road surface area accounts for only about 8 percent of the metropolis, compared with 20 to…