TxDOT used to have field splices on all plate girder jobs; now I believe they give the contractor bolted & welded options.
TxDOT's construction specs are at ftp://ftp.dot.state.tx.us/pub/txdot-info/des/specs/specbook.pdf
(It's a big file, 6MB, so you probably don't want to try it on a slow connection.)
Item 448 is field welding.
Hg