A blog post last week about the Philadelphia Parking Authority's new app MeterUP, which allows parkers to pay through smart phones, prompted a good question from one reader, Brian Rosenwald of Wynnewood.

"Why hasn't the parking authority phased out the remaining meters and gone to kiosks everywhere?" Rosenwald emailed. "Especially with the app debuting (even if it's just in Center City for now) it is even more jaw dropping that the old quarter only meters continue to exist in 2015."

The city has 8,000 parking meters, most of which are outside the city core.

The city's 1,023 kiosks are installed only in Center City and University City. The reason, Martin O'Rourke, an authority spokesman, wrote in an email, is the volume of parking in those areas.

A single kiosk costs about $8,000, O'Rourke wrote, and operating it also includes wireless costs and credit card processing fees.

"To install a kiosk in an area that does not always have a high occupancy rate is not cost productive," he wrote.

Part of the appeal of kiosks when they were installed in 2009 was that, by offering a greater range of payment options, they would better manage the increased cost of Center City parking that went into effect that year, O'Rourke wrote. Meters were inadequate for holding all the coins that would be pumped into them as parking rates grew.

Parking outside the city core, though, is typically $1 an hour.

"To install one (a kiosk) at a $1.00 an hour zone, the costs outweigh the revenue," O'Rourke wrote.

For drivers outside the city core tired of pockets sagging with quarters, there is some relief coming. The authority anticipates MeterUP, currently in a six month trial period, will eventually be available citywide.