Marijuana and cellphone use have been implicated in the crash and derailment of two Canadian Pacific Railway trains in southeastern B.C.

A report from the Transportation Safety Board found the engineer of an eastbound train had traces of marijuana in his system after his freight overran a stop signal and rammed the side of a westbound train near Golden on March 3, 2010.

The TSB report also said the crew of the eastbound freight may have been distracted by numerous cellphone calls, with the last one ending about 60 seconds before the collision.

An engineer and a conductor have been fired.

"Railway rules and company policy establish strict protocols for the use of personal electronic devices by employees in safety sensitive positions while on duty," the report said.

"Despite the existence of rules and protocols regarding the use of personal electronic devices, not all railway employees working in safety sensitive and safety critical positions understand and accept the risks associated with such distractions, increasing the risk of unsafe train operations."

No one was seriously hurt, but three locomotives and 26 boxcars were tossed off the track, more than 11,000 litres of diesel spilled and several homes and businesses had to be evacuated when a track-side propane tank was punctured.

The investigation also found the eastbound engineer needed lifesaving treatment when he collapsed after drinking about 10 litres of water in hopes of flushing any traces of marijuana from his system.

"The ingestion of water and the delay in alcohol and drug testing likely affected the usefulness of the tests," the board concluded.

"Without a requirement to conduct timely post accident testing for drug and alcohol use (when warranted), there is an increased risk of inconclusive test results."

In response, Canadian Pacific has tightened its prohibition of personal electronic devices while on the job and also plans to introduce saliva testing in January, as part of the company's battery of drug and alcohol-detecting measures.

CP spokesman Ed Greenberg said a "detailed safety investigation" was undertaken by the company.

It "reinforced that CP should continue with a number of initiatives already underway to reduce in-cab distraction, enhance communication and focus attention on critical tasks to maintain train safety during operation," Greenberg said.

"It's a very serious incident and we didn't take it lightly."