Though I wish the state of Nevada would close roads for me as well! Built by a couple of Brits using home equity loans! They're aiming for 300mph.
The previous record holder appears to have been powered by AA batteries---do a search and all, but I'm guessing it was a commercial-connection for one of the battery companies. Still, the energy density of batteries that you can get at the store is getting pretty high. Check out how light the lithium primary cells are. I use them in my camera flash and it lightens the whole unit significantly compared to NiCad cells.