First, I'd like to note that I don't know if this idea will help or well received. That being said, I think this idea is cost effective.
I know a lack of accommodating roadways for a high and growing volume of drivers are big factors in traffic congestion, but I once read that drivers not leaving enough space between them and the car in front of them is also a factor. The Los Angeles, California area utilizes stop lights on the highway access ramps, and that could be applied to this idea, but the idea itself calls for using these stop lights on the freeway. Putting such stop lights at points on the freeway where congestion is known to begin could essentially buffer, granting driver further passage in intervals. The lights wouldn't have to be in constant use, only during times of known congestion, and yellow flashing lights and signs could be install a head of the red stop lights to indicate to drivers to begin slowing down. I dont think this idea will eliminate traffic congestion, i dont even think bigger roads would do that but, i think it has the potential to alleviate it.