Bicyclists who ride on Pine and Spruce streets in Philadelphia enjoy access to the bike lanes there. But if you've driven a car or ridden a bike in the area, you've seen plenty of cars stopped in the bike lane.

The drivers of those vehicles may not be breaking the law, said Richard Dickson of the Philadelphia Parking Authority.

"There are different blocks that have different regulations depending on traffic demand," he said. "Those blocks that are primarily residential have a "no parking" regulation, and that's posted that way so that people that live there can drop off groceries and things like that and then move their car to a regular parking space."

Dickson said drivers in zones designated as "no stopping" in Center City would immediately receive a $76 ticket from PPA officers. Cars in "no parking" zones receive a $36 ticket if they sit there for more than 20 minutes.

A few months ago, the PPA started encouraging people to use social media to report vehicles blocking bike lanes.

"We have received 50 tweets in that time. About 20 of them related to Spruce and Pine streets," Dickson said. "That information is then sent to our ticketing department so we can ensure that if there are specific areas that are a problem, that we can address our ticketing deployment staff."

The information will help the PPA address problem areas, but likely won't result in an immediate deployment, he said.

"The reality is once we get a tweet and get it out to an enforcement officer, by the time he or she got there the car is likely gone anyway," said Dickson.

Nicholas Mirra of the Bicycle Coalition of Greater Philadelphia said the organization is working to educate people about the rules. The lanes are used so much because they're safe and they're convenient, he said.

"That said, a bike lane filled with parked cars is not a bike lane," Mirra said,

Andrew Stober, chief of staff in the Mayor's Office of Transportation and Utilities, said Philadelphia has narrow streets that have many different demands on them.

"And even before we put the bike lanes in on Spruce and Pine, residents regularly used that lane when it was a car lane, to stop and unload vehicles' groceries and other goods or to let people on and off in front of their homes," he said. "And that's something that we wanted to make sure those communities were still able to do."

Otherwise, Stober said, city officials feared there might not be enough support for installing the bike lanes.