Operational lifespan of 60's and 70's trucks

Dennis Javelin:
I’ve just driven from Devon to Glasgow and (the things you do on a boring motorway journey) I took a mental note of the ages of the trucks that were using the motorways. I struck me how many trucks were over 5 years old with quite a few 12 years old. There was even an ERF on a N plate pulling a 40’ trailer. Now the first time I ever did this journey was when I was based at Plymouth dockyard in 1976 so it got me thinking - when I did this journey in 1976 how many trucks over 5 years old would I have seen. Would it have been around the same % as today?

So my question is, what was the average lifespan of trucks built in the 60’s and 70’s?

Just as a gut feeling and nothing more than that I would say lorries were kept for longer years ago, lots of the bigger operators have a renewal policy, 2 years, 3, 4 etc whereas years ago vehicles were pretty much run until they were scrapped or virtually worthless, I also think they were easier to maintain years ago, far less technical stuff and more just mechanical. My dad was a HGV Mechanic but I have no idea how he would’ve coped with all the technology nowadays. We live in a throwaway society nowadays.