sentences:  The other four toll roads are state-maintained highways that have been converted to toll highways.These are the Sam Houston Tollway (Beltway 8), the Tomball Tollway (Texas State Highway 249), the Katy Managed Lanes, which is a section of Interstate 10 located between Katy and downtown Houston, and the Grand Parkway (Texas State Highway 99) which is under construction.All toll roads are maintained by the Harris County Toll Road Authority, and are marked with a purple and yellow version of the county highway shield.