SAN FRANCISCO (KCBS) – For years, traffic data compiled by the Metropolitan Transportation Commission showed that the busiest part of the morning commute on the Bay Bridge was between 7 a.m. and 8 a.m.

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But a review requested by KCBS, prompted by the observations of anchor and early morning commuter Stan Bunger, reveals something that startled traffic planners at the MTC.

Spokesman John Goodwin said starting in 2013, the 6 o’clock hour had the most traffic on the Bay Bridge, and by last year, rush hour had creeped up even earlier.

“By the time we got to 2015, the busiest hour was 5 to 6 in the morning,” Goodwin told KCBS. “And that is pretty amazing.”

Goodwin says on the other six state-owned Bay Area bridges, the 6 a.m. or 7 a.m. hour is still the busiest.

But the number of cars crossing the Bay Bridge into San Francisco between 5 and 6 a.m. has gone up 50 percent in the last five years through last Tuesday, even though total daily crossings are only up about 3 percent.

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The mystery, said Goodwin, is why this is happening.

Taxi driver Haron Hayat said he knows: its people coming in to San Francisco from Sacramento and the Central Valley, to spend their day driving for Uber and Lyft.

“Some of them they come from Sacramento, and some of them from Tracy and Manteca,” Hayat said. “And they come and work in here, there are no jobs over there.”

Paul Overton, who works for a software company in San Francisco, doesn’t think there are enough out-of-town Uber drivers to account for the spike. He thinks there are just more people like him, who are starting their day earlier to beat the crowds.

“I go in early to avoid the crush, really. To avoid the crush of the commute in the morning,” he said.

Goodwin said the explanation is probably complex. All he knows is Caltrans has to fire up those metering lights before 6 a.m.

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“Just the reflection of a changing Bay Area economy, and a changing Bay Area commute,” Goodwin said.