How can you reduce the appearance of road rash scars?

Moisture. Removing all debris at the time of injury can help in the longterm cosmesis. In general keeping the area gently moist with a handcream can help it heal in a healthy manner. There may be mild improvement with the use of a vit a cream. If the wound becomes raised as a response to the abrasive trauma, a Hydrocortisone cream may have a minimal improvment. Sadly, road rash often has unsightly cosmesis.
Maybe silicone gel. Road rash scars may look better if one uses silicone sheets or silicone gel for a month or two. Avoiding sun exposure on the scars, for many months or a year, can help. If unable to fine silicone gel or sheets over-the-counter, a dermatologist may be able to prescribe some.