The new policy calls for passenger trains to reduce speeds by 20 mph, with a floor of 40 mph, when the mercury hits 90 on consecutive days or when there is a 40-degree or more swing in daily temperatures, CSX spokesman Gary Seease said.

Thus an Amtrak train permitted for 79-mph operation would be reduced to 59 mph under a heat order. The orders are in effect between 1 and 9 p.m. daily on a subdivision-by-subdivision basis.

Last month, after the wreck of the Capitol Limted outside Washington, D.C.-apparently caused by a sun kink in the rails-CSX imposed a new heat order policy.

It called for passenger trains to operate at freight-train speeds when heat orders were in effect. Freight trains permitted 60 mph dropped to 50 mph under heat orders, and passenger train had to drop to 50 also. But in many cases passenger trains were forced to drop to 40 mph-and operate at roughly half-speed.

CSX said the policy was a necessary safety precaution until it could learn more about what caused the wreck of the Capitol Limited, as well as a similar wreck of the Auto Train in Florida in April.