Medium Transport; Low Wing; 2 Turbojet Eng
Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Communication Breakdown; Confusion
ATC Issue All Types; Deviation / Discrepancy - Procedural Clearance; Ground Incursion Runway
Air Traffic Control Issued Advisory / Alert
Procedure; Human Factors
After pushback at Lafayette Airport; we contacted Ground Control for taxi clearance. The clearance consisted of 'Taxi to Runway 4R' via Bravo and Juliette. After receiving the clearance; and prior to taxi; I confirmed with the First Officer and verified the taxi clearance with the airport diagram. We started moving straight ahead via Bravo and momentarily stopped on 4L to do our normal safety visual clearance (Left and Right) and then; continued taxi toward Juliette. After reaching Juliette; and turning right; we stopped before crossing Runway 11. When we stopped; we received a call from Ground Control with a possible Pilot deviation; and they also gave us a phone number to contact them. After the call; we received clearance to cross Runway 11 and continue Taxi to 4R. At the end of the runway; on the holding short area; I called the Tower. They informed me that we crossed 4L without clearance.We never had the intention to cross any active runway. However; with the clearance that we received (and verified with the airport diagram); we understood that we were clear to taxi all the way to 4R; including crossing the Runways (4L and 11). Apparently; my First Officer misunderstood the taxi clearance because; usually the normal taxi clearance instructions are 'Taxi Runway 4R via Bravo and hold short Runway 4L.' After that; we usually receive further clearance.  In my opinion; since Juliette Taxiway is at the end of Bravo; and prior to Juliette is Runway 4L; when we received the clearance instructions the way we got them; it became confusing and created an involuntary error. Again; we understood; we were cleared to taxi to Runway 4R; via Bravo and Juliette.
An air carrier crew cleared to LFT Runway 4R taxied all the way to the Runway crossing Runway 4L but stopping prior to Runway 11 because they thought the taxi clearance included crossing intervening runways.