The TTC will ask City Hall on Thursday to bow out of commitments to purchase 120 hybrid buses for use in 2010.

The TTC stands to save $24 million if the 120 new diesel buses are purchased in place of the hybrid ones currently scheduled to arrive in 2010. Diesel buses average $200,000 less per vehicle than the hybrids manufactured by Daimler-owned Orion Bus Industries.

Hybrid buses first hit Toronto streets in December 2007. The TTC was the first Canadian transit agency to widely embrace the technology.

TTC chair Adam Giambrone says the hybrids, which are partially assembled in Mississauga, have not lived up to expectations.

The buses, which currently make up one-third of the TTC fleet, aren't as fuel efficient as hoped.

Even worse, the buses only reduce greenhouse gas emissions by about 10 per cent. They had been projected to cut such emissions by 20 to 30 per cent.

The batteries that power the buses don't last as long as promised. Most need replacing within the first 18 months of use, not the four to five years as anticipated.

The TTC will honour its commitment to purchase 130 hybrid buses for use in 2009. They'll be equipped with Chrysler's longer-lasting lithium-ion battery instead of the lead-acid batteries powering the existing fleet.

One suggested reason for the fleet's shortcomings is that hybrid technologies tend to perform best in stop-and-go traffic situations. Batteries in most hybrid models are recharged each time the vehicle's brakes are engaged.

Streetcars serve the TTC's most heavily-congested routes, not by the approximately 500 hybrids currently in operation.

Giambrone said the city bought the technology due in large part to federal incentive plans which cover as much as one-third of the hybrid's $750,000 bus price tag.

"You have to remember there would have been no buses because there would have been no funding. We didn't have a choice. It was hybrids or nothing," Giambrone said.

Unfortunately the savings just aren't there when one considers the cost of battery replacements and fuel, he said.

Councillor Michael Walker said the fleet's problems are a sign the TTC has failed taxpayers.

"The members on the TTC commission -- starting with Mr. Giambrone -- should do the honourable thing and resign," Walker said.

With a report from CTV Toronto's Naomi Parness