Traffic congestion on freeways at rush hour is not only a headache, it is an expensive nuisance. But some cities are experimenting with a pricing system to allocate scarce space. Tolls are imposed at peak traffic times, speeding home commuters who don't mind paying an extra fee for the convenience.

• Traffic jams in the country's 10 most congested cities cost more than $34 billion a year, according to Texas Transportation Institute data.

• Cities with the worst traffic problems: Los Angeles, Washington, D.C., San Francisco-Oakland, Miami, Chicago, Seattle-Everett, Detroit, San Diego, San Bernardino-Riverside and Atlanta.

• About 30,000 drivers a day choose to pay between 60 cents and $2.95 to take advantage of 10 miles of express lanes that run along the median strip of the Riverside Freeway in Orange County, Calif. -- and the drivers are automatically billed through use of a scanner as they zip along.

• A system in San Diego allows motorists driving alone to use car pool lanes for a fee of $2 to $3 which adjusts every six minutes, depending on the level of traffic.

Highways around Washington, D.C., do not use a peak-pricing system and the result is big traffic jams. The city's subway system does charge extra for rush-hour travel and some analysts think highway authorities would do well to adopt a similar system.

The danger, some observers point out, is that toll fees will be looked upon by government authorities as an additional source of revenue. They should be used instead to reduce and replace some highway taxes.