J.B. Hunt Transport Inc. and Atchison, Topeka & Santa Fe Railway are expanding their Quantum intermodal joint venture only three months after it started.

The two companies made their plans known here at last week's International Intermodal Expo.Quantum, which now serves a Chicago-Los Angeles corridor, will be extended to northern California and Kansas City will be added, both effective July 1.

Chicago-based Santa Fe, which provides the Quantum trailers leased from Xtra Inc., is adding 100 more to the original 150. An undetermined number will be added when operations begin over the three new lanes.

Dan Koehler, Quantum's director of marketing for the western region, said about one-third of the trailers are in transit at any one time and one-third are at each end moving to and from shippers and consignees.

The service now is delivering loads in three days between points as far east as Ohio and southern California. J.B. Hunt, considered one of the industry's leading high-service truckload carriers, handles Quantum marketing.

The Lowell, Ark.-based motor carrier's trucks pick up the ship- ments and schedule deliveries even before the vehicles are placed aboard the Santa Fe high-speed intermodal trains.

Because the two carriers have linked their computer systems, J.B. Hunt tracks the trains and stages its drivers at the destination ramp so trailers can be on their way to consignees within a half hour of the train's arrival.

Mr. Koehler pointed out that J.B. Hunt is the responsible party in dealings with shippers. Shippers thus have one point of contact, the same as if they were dealing with a trucking company.

To date, there have been no claims by shippers.

Santa Fe has been a leader in intermodal development in the railroad industry. Other carriers also are developing similar premium services. Consolidated Rail Corp., for example, has its Mercury service, which also provides advance scheduling of deliveries and expedited movement through the system.

Quantum service is targeted at traffic now moving in long-haul truck service. It is prices above conventional rail intermodal and is competitive with other truckload carriers. Mr. Koehler said, "We don't want traffic that Santa fe already has and we aren't trying to divert traffic that Hunt already has."

"The response from customers has been enthusiastic," said Michael Haverty, Santa Fe's president. "We've got the product and we're ready to expand. Shippers that have tried us are coming back. We're opening new lanes of opportunity based on the support we have received after only three months of operation."

Paul Bergant, J.B. Hunt's executive vice president, told a news conference at the Expo: "I think we surprised some customers with the speed and quality of service. The balanced operation optimizes equipment utilization with a total 12-day turnaround from origin to destination to origin."