Concerned reader Bob Fitzgerald has submitted the attached photograph, taken recently near a village in Kerry, and invites the Diary to comment.
My first instinct when I saw it was to blame Brussels. There has been a lot of loose talk there about a two-speed Europe. This, I thought, must be one of the pilot projects.
Presumably those who want to move more quickly towards integration could drive on the right (coincidentally the Franco-German side of the road), while those reluctant to embrace change could stay in the slow lane on the left. The obvious weakness in the system is that this appears to be a two-way road, which would put federalists and Eurosceptics on a collision course.
When Mr Fitzgerald informed me that the picture was taken between Tralee and Dingle, an alternative possibility arose: namely, that Éamon Ó Cuív had something to do with it. Could it be that the sign on the left is in Irish, and that anglophone locals erected the other one in protest? If so, this is unfairly confusing for tourists. An obvious compromise would be to put the Irish and English speed limits on the same sign, one on top of the other.
My correspondent adds that the signs occur near a spot where, in 1893, "a runaway train with many wagons of pigs from the Dingle Fair jumped the rails at a very bad bend". This provokes the separate question as to whether, regardless of language differences, there should be a 100km speed limit on any part of the Dingle peninsula. Although drivers going from Tralee to Dingle these days would be extremely unlucky to meet a train coming the other way, the road is more than enough of a challenge on its own.
Mr Fitzgerald doubts that the speed limit confusion is the work of vandals who turned one of the signs around. So do I. This is more likely an initiative by concerned locals suggesting that while the figure on the right may be the legal limit, sane drivers submit voluntarily to the one on the left.
Either that, or the signs are a public art installation of the kind on which road builders now have to spend a percentage of their project cost. If this is the explanation, I think what the artist is saying here is that measurements are inherently unreliable. Especially in Ireland.
Our ambivalence towards value systems is hardly surprising, since for centuries we had competing concepts of what even a "mile" meant. There was the miserable "statute" mile of 1,760 yards, introduced by Elizabeth I. And then there was the magnificent Irish mile, almost 500 yards longer.
Anecdotal evidence suggests that an Irish mile was longer again in rural areas, especially if you were walking. Come to think of it, maybe this explains the apparent contradiction in the speed limits. Is it possible that the "km" referred to on the left-hand sign is "Kerry miles"? Maybe the county council would clarify.
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The Wicklow 400 is not a speed limit, mercifully, although you might be forgiven for thinking otherwise on the Arklow bypass. No. The Wicklow 400 is a year of celebration marking the anniversary of the youngest county in Ireland, which took its current form only in 1606.
Before then, Wicklow was "O'Byrne country", a place feared and avoided by residents of the Pale, with good reason. As late as 1599, an English army was attacked there and panicked, "possessed with such a fear that they cast away their arms and would not strike one blow for their lives".
Half were slaughtered; while for the survivors, the supreme English commander, Lord Essex, revived an old Roman military punishment of executing one in 10 as an example. Terrible as this example was, it remains valuable, if only as a means of educating people about the correct use of the word "decimate".
With the defeat of Gaelic Ireland at Kinsale, however, the game was up even for the O'Byrnes, and Wicklow was finally shired. As this year's celebrations show, few English impositions have been as successful as the county system. And it is one of the ironies of Irish history that this is largely thanks to the GAA.
GAA colours now mark the borders of neighbouring counties in a way that would have warmed the heart of Elizabeth I, even as she was short-changing us with her miles. So the Wicklow 400 has been aptly marked this week by the arrival of football supremo Mick O'Dwyer. Having already reinforced the territorial identities of Kildare and Laois, he now faces his ultimate challenge: putting Wicklow on the map.
This is not the week's only celebration, however. On Friday, locals including the Minister for the Environment will gather in the Roundwood Inn for a 1606-style dinner in period dress. Tickets are still available from Joe McNally (no relation) at 087-2516950; and if wild boar and other delicacies doesn't tempt you, the prospect of seeing Dick Roche in doublet and hose surely must.
A week later, on Saturday 21st, Roundwood Historical Society hosts a day-long seminar on the county. There will be separate lectures on monastic Wicklow, the Vikings, and Diarmuid MacMurrough. The event will conclude with a talk covering the history both of the native Irish and the coming of the Normans: given - rather sportingly in the circumstances - by a man named Emmet O'Byrne.