But Ebrard, who began his six-year term Tuesday, stopped short of ruling out a fare hike in 2008, when a new expansion phase is scheduled to begin.

He also hinted that other public transport modes in the capital, notably microbuses and taxis, could cost users more soon. "These are impacted more by the federal government´s decision to raise gasoline prices, which I think was a mistake," Ebrard said.

The mayor said a favorable fiscal situation left behind by his predecessors precluded any need for a 2007 raise in Metro fares, despite an ambitious renovation project already underway for the year.

Parts of the system have noticeably deteriorated in recent years, and the city plans to spend 4.4 billion pesos to upgrade lines and stations. Details on which sections are slated for makeovers will be released in a matter of days, Ebrard said.

Work started Monday along the southern leg of Line 2, the longest and busiest route that runs from the Taxqueña transportation center in the southern part of the city north and west to Cuatro Caminos on the border with the State of Mexico.

The construction will take place at night, with the stations from San Antonio Abad southward closing early at 10:30 p.m. The Line 2 work is scheduled to continue into September of 2007.

New Metro routes or extensions of existing lines were eschewed during the previous term (2000-2006) in favor of modernizing sections of the Periférico, the principal freeway that rings the city.

The first dedicated-lane bus line - the Metrobus that runs along most of the length of Insurgentes, the capital´s major north-south artery - was also inaugurated in 2005. Ebrard has said he plans to create 10 more Metrobus routes on key arteries, known as ejes, throughout the city.

But his major transportation project will be an expansion of the Metro system beginning in 2008. Overseeing the project will be Francisco Bojórquez, a veteran city transportation engineer who was introduced Thursday as the new director general of the Federal District´s Metro system.

One possible new route, running from the Constitución de 1917 station at the south end of Line 8 to the Mixcoac station on Line 7, has been planned for several years. Known as Line 12, it would be the first east-west line in the southern part of the city.

But Ebrard said Line 12 will be "reviewed," though not necessarily scrapped. "This project is several years old now," he said. "We have to update the origin-destination study that was the original basis for a route that would essentially connect the Benito Juarez Precinct with Iztapalapa."

In fact, the mayor said, commuting patterns have changed significantly in recent years so that existing mass transit expansion studies are obsolete.

"In the entire Valley of Mexico we´re experiencing huge numbers of people traveling greater and greater distances every day," he said. "We need updated studies in order to determine what kind of investment we need to make in the amplification of the Metro lines."

Much of the research will be done in cooperation with the State of Mexico, in whose territory more than half the population of the greater Mexico City area resides.

To date, only two existing Metro lines operate in both the Federal District and the State of Mexico. Line A runs from Pantitlán southeast to the La Paz station, and Line B takes passengers from the Buenavista station in the heart of the city northwest through Cd. Neza to Cd. Azteca, both in the State of Mexico.

Ebrard did not commit himself Thursday to new Metro routes connecting the two entities, but did say that more and better transportation links are needed. That could mean routes longer than typical Metro lines, such as the 27-kilometer fixed-rail "Tren Suburbano" that will run along a pre-existing right-of-way from Buenavista through the Azcapotzalco Precinct to the State of Mexico cities of Tlalnepantla and Cuautitlán.

That project is now targeted for completion by the end of 2007. Two more suburban train routes have been agreed to in principle by Ebrard and State of Mexico Governor Enrique Peña Nieto.