Declining revenue is threatening to put the West Virginia Turnpike in default on its bonds.

The state Parkways, Economic Development and Tourism Authority on Thursday approved traffic and engineering studies in anticipation of raising tolls on the 88-mile highway by summer's end.

Senate Majority Leader Truman Chafin of Mingo County and Senate Republican leader Don Caruth of Mercer County hope to avoid increases by diverting federal stimulus money to the turnpike.

But their efforts may be futile. State Transportation Secretary Paul Mattox says toll roads don't qualify.

Parkways authority manager Greg Barr said toll revenues were down nearly $730,000 in January and February from the same period in 2008.

The authority's annual bond payment is $11 million.

Existing tolls were set in 1981.