The Transit Authority of River City has received another federal grant to purchase new buses.Most of the news about TARC involves cuts, since the authority's funding is tied to the city occupational tax.But recently, TARC has won grants to replace aging vehicles. The latest award is for $4 million, which is enough to buy a dozen buses that more cleanly burn diesel fuel.Previously, a grant was used to order 27 new buses, eleven of them hybrids.In all, there are 210 buses in TARC's fleet. The new vehicles will be on the street next year.