Chicago's red light camera program was beset by "fundamentally deficient" City Hall management and inconsistent enforcement, according to a limited inspector general review released Friday that failed to solve the mystery of suspicious ticket spikes exposed by the Tribune.

But Inspector General Joseph Ferguson did resolve a more recent red light controversy — disclosing that the Emanuel administration quietly issued a new, shorter yellow light standard this spring that generated 77,000 tickets that would not have been allowed before the rule change.

The administration defended the $7.7 million in $100 tickets as valid but agreed to Ferguson's recommendation to end the new practice of issuing citations with yellow light times below the 3-second city minimum.

In his 25-page report, Ferguson said City Hall's oversight of the decade-long red light program "was insufficient to identify and resolve the types of issues identified in the Tribune report."

Ferguson said city transportation officials identified likely causes for just three of the dozen most dramatic spikes cited in the Tribune's 10-month investigation, putting the blame on faulty equipment and inaccurate camera settings.

Ferguson said his office was unable to find reasons for any of the other anomalies, citing missing or destroyed records and his office's desire to quickly respond to public concerns raised by the Tribune's July report. The inspector general relied heavily on work conducted by the city Transportation Department and longtime camera operator Redflex Traffic Systems Inc., which was fired amid charges top company executives paid up to $2 million in bribes to win the Chicago contract.

While he dismissed the Emanuel administration's earlier contention that the spikes were due to normal changes in traffic flow, Ferguson said it may never be possible to know the extent to which any changes in the camera system's operations were intentional or accidental.

In the report, Ferguson suggested the city had never looked for the kind of surges in ticketing the Tribune found but instead focused on the opposite problem — intersections where ticket numbers were low or cameras weren't functioning.

City transportation "staff saw their role at that time as keeping the systems operational rather than ensuring that the equipment functioned accurately."

Emanuel's transportation chief essentially agreed with the inspector general report while seizing on Ferguson's finding that malfunctioning equipment responsible for one North Side spike meant there should have been more tickets, not fewer.

"These issues demonstrate that the past management of the program was insufficient," Transportation Commissioner Rebekah Scheinfeld wrote in her response. "Although the program has shown dramatic improvements in safety, due to those technical and management deficiencies the program was actually under-enforcing violations."

The administration offered to review about 16,000 tickets from the most dramatic spikes identified by the Tribune and announced earlier this month that only 3,000 drivers caught in spikes had responded to an offer to review their tickets. It said 126 were entitled to refunds.

The administration's ticket review did not consider issues of fairness related to inconsistent enforcement. Ferguson said his office did not examine whether the city's efforts were sufficient.

National traffic experts interviewed by the Tribune argue inconsistent enforcement of traffic laws at automated camera locations is fundamentally unfair to motorists because the purpose of camera systems is not to generate ticket revenue, but to improve safety by training drivers to improve their behavior over time.

A Tribune analysis of more than 4 million tickets issued since 2007 found dozens of suspicious spikes throughout Chicago that the city said it could not explain. The July report focused on 12 of the most dramatic spikes involving more than 13,000 questionable tickets. Experts interviewed said the spikes were likely the result of faulty equipment or human tinkering and suggested that drivers ticketed during the anomalies should get refunds.

While Ferguson's report confirmed the Tribune's findings that faulty equipment or human tinkering are the likely culprits, he stopped short of recommending widespread refunds.

"Sudden changes to enforcement parameters, even unintentional changes, can create the appearance of unfairness and have the potential to erode public confidence in the program," he wrote.

Ferguson's report found answers in only three of the spikes.

At Halsted and 119th streets, where one camera in 2011 tagged more drivers in a 52-day period than it had in the previous year and half combined, Ferguson wrote that a change in the system settings caught 1,618 drivers who would not have been ticketed under the camera's normal settings. He said a lack of records means the drivers ticketed during the spike may never find out the motivation behind the change.

The problem, he wrote, was a dramatic drop in the camera system's trigger speed.

Under the rules, video evidence used to determine whether a ticket is issued must start before the car enters the intersection. So sensors in the roadway measured the speed of approaching cars to predict whether or not they have time to stop at the light. If the car is moving faster than a preset "trigger speed" the camera is activated. According to Ferguson's report, the trigger speed during the spike from April to June of 2011 mysteriously dropped from 15 miles per hour to as low as 5 miles per hour.

"This drop resulted in 1,618 additional citations that would not have been issued had the trigger speed remained at 15 mph," Ferguson wrote. Redflex maintenance records indicate that a technician performed a preventive maintenance check May 17 and noted no issues with the trigger speed, he added.

"The increased violation counts continued for over seven weeks," Ferguson wrote, "and available maintenance records do not document when, why or how the trigger speed was reset to 15 mph, or who, if anyone, at CDOT or Redflex was aware of the issue."

On the North Side, a spike at 800 W. Fullerton , was caused by a damaged traffic light that wasn't visible to drivers at the intersection, Ferguson wrote. That two-day spike tagged 64 drivers at a camera that normally only tagged a few motorists a day.

Despite the traffic light being not visible, Ferguson wrote that another light at the intersection was functioning and visible.

"CDOT stated that the increase in RLC violations at the intersection may have resulted from inattentive drivers ignoring the still-functioning traffic signal and driving through the intersection during a red phase," Ferguson wrote.