Ventra card

The new Ventra card. (Zbigniew Bzdak, Chicago Tribune / August 25, 2013)

The CTA and its Ventra contractor said Thursday they still could not trace the source of a widespread computer problem during the previous evening’s rush period that knocked out 165 Ventra fare card readers at 60 rail stations, although no new malfunctions were reported.

The mysterious hardware or software problems Wednesday evening, which the CTA attributed to a “Ventra back-office server,” resulted in an estimated 15,000 free rides for customers who were waved through the gates after showing station attendants their Ventra cards, the transit agency said.

The disruption did not affect fare collection on CTA Chicago Cards or CTA magnetic stripe cards, the CTA said. Customers using those fare cards were required to pay to ride, CTA spokeswoman Tammy Chase said.

CTA officials emphatically said the agency will bill the Ventra contractor, Cubic Transportation Systems, Inc., for the lost fare revenue. The tab would be up to $33,750, assuming all rides were based on the $2.25 full fare.

“In the case of Wednesday night’s failure, there was no ambiguity. Each of those 15,000 free rides was the result of Cubic error,’’ Chase said.

“The vendor is still determining the cause of the server failure,” Chase added. The outage, which caused Ventra fare readers to be out of service for 15 minutes to about an hour, was fixed by rebooting the system, Chase said.

The CTA’s speed in pointing the finger at Cubic was a first in the two and a half months since Ventra was introduced.

Up until this week, CTA officials had said it was difficult to pinpoint the problems that led to Ventra readers on buses and at rail stations sometimes not registering fares, because the agency is relying on both Ventra equipment and the CTA’s soon-to-be-retired legacy system.

That uncertainty played out last week, when CTA President Forrest Claypool said, “it will be up to the lawyers” to determine whether the CTA could recoup any money from uncollected fares due to Ventra malfunctions.

The full transition to Ventra, originally set for Dec. 15, has been postponed indefinitely until the glitches are worked out, Claypool said.

Claypool also said the CTA hasn’t paid Cubic any money on the $454 million contract signed in late 2011 for the company to build and manage the new fare-payment system.

He said the CTA won’t write a check until three conditions are met: wait times on Ventra's customer hotline are under five minutes to speak with an operator; Ventra fare readers on buses and at rail turnstiles process transactions in 2.5 seconds or less 99 percent of the time; and 99 percent of Ventra equipment is functioning.

jhilkevitch@tribune.com

Twitter @jhilkevitch