Don’t blame this week’s morning fog for traffic trouble downtown.

City of Houston engineers activated a long-studied change to the city’s traffic signal pattern this weekend.

No longer do all the downtown lights switch simultaneously to green in one direction. Now, they stagger forward – so a driver heading through downtown will pass through a sequence of changing lights, never stopping for a red.

At least, that’s how it was supposed to work.

Instead, drivers said the new system has led to gridlock during rush hour.

“It’s not working,” said one driver.

“Once we got into town on Smith everything started to back up,” said Kathie Miller who drives in the area.

Alvin Wright, a spokesperson for the City of Houston Public Works Department, said the trouble is not entirely unexpected.

It’s why the city picked this week – the slow days heading up to Thanksgiving – to test the changes.

Wright said the lights are now timed to allow a driver going 28 to 30 mph to zip through downtown without stopping. When an 11 News crew tried that, we sailed down San Jacinto nearly from one end of downtown to the other.

It’s a different story at rush hour. Drivers said in some cases their commute time through downtown has doubled or tripled.

So, after two days of rush-hour gridlock, the Public Works Department has put a so-called “tweak team” on the streets, making changes to unclog the trouble spots.

Wright said the crew will be “tweaking” the system during Tuesday evening’s rush hour.