Limiting range for live load

I am modeling the span between 4 trusses, trying to get the DF for the trusses based on a truck moving load.

The model I have has three beams framing into 4 trusses as a continuous simply supported beam w/ 3-rollers. My problem is  limiting the range where my load can go:

LOAD GENERATION 700

TYPE 1 0 0 0 XINC 0.05 XRA 8.30 54.65
PERFORM ANALYSIS PRINT STATICS CHECK
FINISH

I thought that XRA would allow me to limit the load from going on the curb on both sides of the truss... but I'm having an issue with the program syntax. Is it because the XRA should be given in terms of nodes not distance along the member or am I missing on something else here?

Help?

Thanks :)

Ana