Back when this happened, the driver could have been high on something, BUT... In today's times it is unlikely. I don't know what you mean by some legislation to curb truckers taking uppers.... I have driven a truck for over 20 years, managed a company for 12, I take random drug tests, and to be quite frank, there are less truckers using drugs than there are people on the streets using per capita. Truckers not only has to wiz in a cup, they also at times have to blow for alcohol testing. EVERY trucking company is part of a drug consortium and a high percentage of numbers are drawn randomly each quarter, so many are drawn for urine testing, so many are drawn for both urine and breath testing. Truck drivers are more regulated on MANY levels, not just drug testing, they must pass a physical that has higher standards than a airline pilot, they are also computer tracked and logged these days. Some companies have cams In the cab to ensure they are not using their telephone while driving and a front facing cam to record accidents etc. In a few years all trucks will have OBR's or they will not be able to get insurance or be allowed to keep their operating authority and DOT numbers, ALL these things I have talked about including the testing for drugs and alcohol are regulated by the FMCSA. Each company not only files quarterly with the FMSCA but the state DOT comes and looks at their records at will anytime, no advance notice required.
I know these things because when I retired I became certified for reasonable suspicion testing, I freelance as a broker who sets up companies, I properly put their files together and sit in on their DOT audits.
I'll step off my soapbox now, it just irritates me to no end when people assume things they do not understand.