Drivers' ed for a Mexican bad air day

It's another day of higher-than-usual air pollution in Mexico City, and the regular driving restrictions have been reinforced, or "doubled," to try to lower the contaminants from cars.

So may you take to the streets with that 1988 Volkswagen or 1995 Chrysler? You might want to consult a Nobel scientist to figure out if it's really your day to drive.

"Today circulate cars with: Hologram 0 and 00; Hologram 1 (except plates 3 and 4); Hologram 2 ending in even numbers (0,2,4,6,8) except with red sticker; permit vehicles; cars with foreign plates except those ending with 3 and 4, irrespective of the model."

Got that? If you're left with any doubts by those instructions, issued by the city's Environmental Secretariat, you can double-check with this additional information:

"Today will not circulate: Hologram 1, red sticker and plates ending in 3 and 4; Hologram 2 with uneven ending (1,3,5,7,9); foreign vehicles ending in 3 and 4."

If you're still unsure, you might throw down the car keys and join the 55,000 confused drivers who called the local telephone information service on the first day of a recent week's air alert for help with the matter; or the hundreds of others who swamped radio stations, newspapers, and - why not? - even the Environmental Secretariat, trying to figure things out.

Mexico City's notorious bad air days used to be a simpler matter. On any given weekday, cars with plates ending in one of two digits - for example, on Wednesdays plates ending in 3 or 4 - stayed home. When ozone levels passed certain predetermined levels, the restrictions were "doubled" by extending them to cars with plates ending in one of two additional numbers, such as 5 and 6.

That was elementary enough. But, like an overused carburetor, things got mucky as the program was amended to cover particulate levels and prescribe various stickers and color codes to designate late-model cars that had passed exhaust tests and could circulate more freely.

Some Mexico City residents think the whole driving-limitation program has little effect and should be dropped. Others would get the hundreds of thousands of smoke-spewing old clunkers off the streets through a public financing program for new private autos. But that is probably just another (exhaust) pipe dream.