If drivers proceed, following all the directional signs on the floor, they will find the 11 places, parking officials say.
On a tour of the airport garages this week, parking authority spokeswoman Linda Miller agreed that drivers might be stymied. She and Frank Ragozzino, the authority's director of airport operations, said they would look into clarifying signs at the entrance to each garage level, to reflect that the number indicated is a floor count.
"That's something we can adjust, and put additional signage in. We'll do that," Miller said. "The bottom line is about improving customer service and making it easier for the traveler. That was truly our goal."
The new system is accurate about 94 percent of the time, Ragozzino said, adding that it will never be 100 percent.
Some cars park illegally and, therefore, are not counted. Some cars take up two parking spaces, so the computer may indicate that a space is available when it is not. And cars driven in the wrong direction down an aisle are not counted because the overhead sensors track only vehicles traveling the right way.
The parking-guidance system is part of a $12.8 million technology upgrade that includes photographing the license plates of all vehicles entering airport parking and leaving at the cashier's plaza, as well as installing self-service credit card payment lanes at the plaza.
Roy Landes, an engineer from Newtown, Bucks County, said the parking was "a lot better" than it was when the system was first installed last fall.
"This past week when I was there," Landes said, "the sign said four or five available spots in a row. I did find one. It's better, but there's still plenty of room for improvement."
The space-monitoring system features yellow-plastic poles grouped at the beginning and end of the parking rows. They are there to steer cars under the overhead sensors that track the coming and going of vehicles - and that count the open parking spaces.
But the yellow sticks extend into the car lanes, and drivers sometimes run over them, which defeats the purpose of guiding vehicles under the sensors.
Jeannine Morgan, the parking authority's head supervisor of inventory, monitors the parking spaces and replaces the yellow poles drivers have run over. Keeping the posts in place helps tremendously with parking-accuracy counts, she said.
Some customers, though not a lot, have complained about the technology's quirks.
"I've gotten a few" complaints, Morgan said, "not many."
"We can't overstate," Ragozzino said, "what this was like before we had counters. Cars are not hunting like they did."
Added Miller: "Now, if you come to a garage or a floor that says 'full,' you are not going to waste your time."
But not everyone is convinced.
"Is it working better? I don't know," said Mike Dignen, head of sales for a Houston software company. "I continue to see times when the sign says there are no spaces, and the row is empty. Or signs indicate spaces are available when, in fact, there are none," said the senior vice president with US Dataworks Inc. "I've gotten to the point where I just ignore what's on the sign."
Lansdale resident Matt Clayton, who works in sales for a television-equipment manufacturer based in the United Kingdom, said: "When you see a number at the entrance that says there are 600 spots, you take it for granted that means there are some spots.
"You go up to a floor, and the first floor may say, 'Full,' so you go up to the next one, and the sign says '85 spots.' You go down the row, and it says, 'Four spots down here.' But when you go there, it's completely full. To me, the numbers mean absolutely nothing. They don't seem to correlate to anything."
Dignen said he was "delighted" that some cashier lanes now accepted self-service credit card payments, after an upgrade of video cameras that capture all car license plates.
But, he said, those cameras seem to record his license plate only about half the time. The rest of the time, he must wait for an operator to check the camera image and manually enter his plate number.
The problem, Ragozzino said, is that drivers tailgate. Signs posted at the cashier's booths instruct drivers to stop and proceed only when the lane is clear.
Instead, he said, motorists sometimes ignore the signs and line up one car behind the other in the payment lane, which hinders the camera's ability to record the license plate.
Contact staff writer Linda Loyd
at 215-854-2831 or Lloyd@phillynews.com.