The Oklahoma Department of Transportation is warning drivers of heavy traffic congestion on southbound I-35 near mile marker 47 in the Arbuckle Mountains. North and southbound I-35 is currently narrowed to one lane in each direction for an ongoing bridge project and clean up efforts from an accident Thursday is underway in the median area causing significant traffic back-up. Southbound I-35 drivers are encouraged to use US-177 (exit 55 at Sulphur) to avoid the area.