You can buy "Bug and Tar Remover" products in most chain stores but the product really is just petroleum based and you can substitute many that do the same thing.
Tar is oil and adding more oil to it will remove it. WD-40 (spray oil in an aerosol can) will do the trick. You can also use paint thinner, NOT paint remover or anything else used to thin paint. Just paint thinner. I use this when I need to remove tuff stuff. You'll need to wash your vehicle afterwards to remove excess oil.
As a detailer years ago this was a trick I picked up and is used in many shops still today. Baked on paint and clear coats are not affected by thinner because the paint is cured and the thinner is not a re-activator at that point.
Methal Hydrate is another option and pretty much works the same as the thinner but has a faster rate of evaporation (you'll use more). Good luck with the tar removal. I didn't get the time to do mine this past summer but I'll be doing mine all over this coming spring.