The speed limit on Kelly Drive near Fountain Green Drive is 35 m.p.h., but the average speed of motorists is nearly 55.
In an attempt to slow everybody down, the city has installed sensors in the roadway that determine the speed of vehicles approaching Fountain Green, about a half-mile north of the Girard Avenue Bridge.
If a vehicle passes the sensor going above the speed limit, the light at Fountain Green turns red.
Previously, the light turned red only if a car was waiting to turn onto Kelly Drive or a pedestrian pushed the crosswalk button.
On Friday, two electronic signs went up on Kelly Drive warning motorists that the light will turn red if they speed.
The $11,050 pilot project was activated at the beginning of October, and that's how the city found out that the average speed of the 25,000 vehicles passing over the sensors daily was 54.8 m.p.h.
"Speeding motorists on Kelly Drive have made that roadway unsafe," acting Streets Commissioner David J. Perri said Monday.
Daily commuters on Kelly Drive know well the frequent traffic jams caused by accidents and the occasional car veering into the Schuylkill.
Richard Montanez, chief traffic and lighting engineer for the Streets Department, said he learned about a similar system in Portugal from a friend who returned from a visit several years ago.
On Kelly Drive, three sensors spaced six feet apart have been embedded in each lane heading north and south near Fountain Green Drive, Montanez said.
Each sensor detects when a vehicle passes over and its speed, Montanez said. An average is determined from the three sensors to make the reading more accurate.
Montanez would not disclose their exact location, but said they are positioned to give drivers time to brake for the red light.
He said it was too early to tell if motorists were slowing down.
If they do, the pilot could be expanded to Lincoln Drive and possibly Roosevelt Boulevard, Perri said.
In another safety measure, the city will add a nonslip surface on Kelly Drive next year to help reduce accidents on rainy days, Perri said.