Your suggestion is ideal, however it requires widening the bridge over I-26. There isn't enough funding available to widen this bridge at present. The existing configuration wasn't created to facilitate a right turn lane from Harbison onto I-26 West. It was created so that I-26 West traffic exiting onto Harbison could continue onto Harbison without stopping (for right turns). This is helping decrease the amount and length of backups onto I-26 West due to the exiting traffic. A new bridge (or widened bridge) would need to facilitate a total of at least 6 lanes just to serve present needs, however given the growth in the area 8 or 9 lanes will likely be needed unless the interchange is massively reconfigured.