With the proliferation of school busses we have, no high school student should be allowed to drive a car to school. I don't care if their parents think that it's inconvenient to be forced to drive their kids to functions. College students should not be allowed to have cars on campus before their Junior year. A method of removing hydrocarbons from urban air could consist of absorption from air being pumped through a concrete pipe containing activated carbon in removable cartridges. The concrete pipe is the core of the concrete divider in the middle of the expressway.
Air is pulled through the pipe by a flat black chimney heated by the sun.
The carbon cartridges are removed in sequence and either regenerated by thermal desorption distilling the hydrocarbons recovering them for use as a fuel. An alternative is to use the saturated carbon cartridges as fuel in a coal-fired power plant. Cool urban areas to reduce ozone produced during summer months and to reduce the air-conditioning load. Add a pigment to asphalt to make it more reflective. Use concrete paving rather than asphalt.