Well, yesterday's post got a lot of responses! Thank you, everybody!

Some of them are visible in the comments and some were by email. But most of them were from drivers rather older than me who said that my formula would have them driving at 40 on motorways (or something like that).

Now, notice that I did talk about the maximum speed you like driving rather than the maximum speed you would consider driving, but clearly I have more high-velocity octogenarians amongst my readership than I had previously realised, for which I feel duly honoured.

Ian Clark suggested an amendment which was essentially

V_max = 103 - (age * 2 / 3)

which would still suit me and give older readers a few more mph to play with, but I think I'll need an exponential component to get anything reasonable, perhaps something more like:

V_max = 100 - age^0.95

Anyway, there was agreement from several readers that the desire to break the speed limit certainly decreases with age, and Andy Davy observed that toddling along at 50mph is often fine as long as you have an interesting podcast playing; an assertion I can definitely support. In my case, though, it's often an audiobook: we're currently touring France to the accompaniment of The Count of Monte Cristo.

I remember, in my younger days, getting stuck in completely stationary traffic on the M25 while heading for an airport to catch a flight. The minutes ticked by, my anxiety rose, and then I realised that the pumping drumbeat of my music probably wasn't helping. I replaced it with some nice Brahms cello sonatas, and, all of a sudden, my equanimity was restored, my blood pressure declined, and I gazed calmly at the surrounding vehicles (about which I could, in any case, do nothing). And yes, I arrived in plenty of time.