Chicago’s growing network of speed cameras so far has issued more than a half-million warnings to lead-footed drivers, but it brought in just a tiny fraction of the money that Mayor Rahm Emanuel’s administration had expected in 2013, according to new numbers released this week.

The city’s Department of Finance says the cameras, situated in so-called “children’s safety zones” near city parks and schools, issued nearly 574,000 warnings through last week.

But a combination of installation delays and lenient enforcement meant to give drivers a break resulted in just 17,901 actual tickets and $337,452 in revenue for City Hall last year, according to numbers obtained by WBEZ through the Freedom of Information Act.

That’s two percent of the roughly $15 million take the city had predicted.

State lawmakers okayed Chicago’s speed camera program back in 2011. But the project faced long installation delays and the first cameras didn’t actually go live until this August.

Aside from the delay, Finance Department spokeswoman Kelley Quinn said the rollout “has been designed to give motorists opportunities to change their behavior.”

Through Jan. 5, the city issued roughly 487,000 warnings during each camera site’s 30-day grace period, designed to give drivers time to slow down. It also generated 86,587 “freebie” warnings, issued once to each driver after a grace period ends. All told, Quinn said that would have generated $17 million worth of tickets so far.

“We wanted to roll the program out in a thoughtful manner that wasn’t tied to revenue, but instead safety,” Quinn said in an email to WBEZ. “Additionally, the program has been implemented to give motorists every opportunity to change behavior.”

The 2013 shortfall from the speed cameras was covered by better-than-expected hotel, sales and personal property replacement tax revenues, Quinn said.

Emanuel is still banking on the new speed cameras to bring in between $65 and $70 million in 2014, despite the dramatically low take last year.

The speed cameras work a lot like the city’s existing network of red light cameras: Speeders who get their car photographed automatically receive a ticket in the mail.

For now, the city has only been issuing fines to the fastest speeders - $35 for those caught going 10 mph to 11 mph over the posted limit, and $100 for those caught cruising faster than that.

The Emanuel administration announced it would go a bit easier on speeders after early speed camera data, first reported by WBEZ, suggested City Hall could be in for a windfall.

The city Department of Transportation says it will eventually lower the speeding threshold so that anyone snapped driving between six and 10 mph over the limit will get the $35 ticket, but it has not publicized a timeline for when it plans to crack down.

Some critics of Emanuel’s speed camera plan, including several Chicago aldermen, have maintained the system is more about making money for a financially strapped city than protecting kids. But the administration and its backers point to a steep drop in speeding at existing sites to say that the cameras are doing their job.

There are currently 48 speed cameras up and running at 22 sites around the city. Of those, 31 cameras are now issuing fines, while 17 are still issuing grace period warnings. Emanuel’s administration has said it’s aiming to install 105 speed cameras at 50 locations early this year.

Alex Keefe is political reporter at WBEZ. You can follow him on Twitter and Google+.