Take a look at the map on this page and it might help explain why local officials want to convert the carpool lanes on parts of the 10 and 210 freeways in the San Gabriel Valley to toll lanes.

The map was built using data from the 2000 Census, and it shows the average commuting time for nearly all Southland cities. Notice any patterns?

Nearly all the cities in the valley and the Inland Empire are colored yellow or red, meaning residents there have the longest commutes. I've also built a Google maps version online that allows you to see data for individual cities and zoom in and out on different areas.

With that in mind, let's take a deeper look at the new "congestion pricing" plan . . .

What do the 10 and 210 have to do with all this?

Not coincidentally, Caltrans data show that in the last decade Inland Empire traffic on many freeways has grown considerably -- about 5% in some places -- as bedroom communities have spread.

That's why Caltrans district director Doug Failing has said that some of the most intractable congestion problems in Los Angeles County are on the three east-west routes serving the Inland Empire, the 10, 210 and 60.

If Failing had his way, he'd like to put a toll lane on the 60, too. In the meantime, it's his great hope that even single toll lanes on the 10 and 210 can improve traffic on all the other lanes.

Huh?

"We need to have capacity to sell," Failing told me recently. "The capacity will be created by having enough people on express bus service that it opens up space."

To recap, part of the toll lane deal is that the federal government has agreed to give local transit agencies about 60 high-capacity buses that would use the toll lanes for express service. Some federal funds would also go toward improving Metrolink service in the San Gabriel Valley.

Officials believe that improved mass transit in the Inland Empire may remove some cars from the freeway. That would translate to a quicker commute for those who keep driving -- perhaps beyond where the toll lanes end.

How much time can a toll lane save for motorists?

Officials say it's hard to forecast. This much is known: Caltrans data shows that carpool lanes typically move faster than regular lanes but also suffer from congestion during rush hour.

Of course, you don't need a spreadsheet to tell you that. One recent Thursday, I drove in the 210's regular lanes from Pasadena to Upland between 5 p.m. and 6 p.m. At times, I was going faster than vehicles in the carpool lane, where traffic by my count was averaging about 30 mph before speeding up east of the 57 junction.

This is where the toll comes into play. Officials say the fees (which are yet to be set) would discourage some people from using the carpool lane during rush hour and thus improve speeds to at least an average of 45 mph.

If it works, that would be an improvement from some stretches of the 210. For example, bumping average speeds from 30 mph to 45 mph could translate to a savings of about eight minutes in the 11 miles slated to become toll lanes on the 10 and 210.

That's not counting any time savings that might result if areas beyond the toll lanes are improved. Still, some readers are skeptical.

"I don't see how with this short of a distance they'll prove this is a valid concept," said Kent Clark, 43, of La Crescenta, a 210 regular. "Maybe if it went all the way to the 15 [freeway]. That would be a bold idea. This seems like a half-baked new idea."

It is interesting to note that the distance of toll lanes is about the same in other metro areas where they've been tried, including in Minneapolis, Denver and San Diego. However, in all three cases, there is more than one lane in each direction -- so there's more room to sell.