A month after new, super-stringent speed limits were imposed across the town, Oxford seems to have as many notices informing drivers that "it's 20 for a reason" as it has actual signs for the new 20mph limit. I must admit that I'm still looking for it.

It's easy to make a reasoned argument for well-applied 20 zones, and it's not one I would ever stand in the way of. Oxford's problem is the new limit's very universality. Which, at a stroke, has completely removed a 20-zone's ability to emphasise particular dangers or risks.

The nearest 20 road to me has got no houses or driveways on it, and has already been traffic calmed with a pair of 'pinch points' and two humped Zebra crossings capable of stopping a Panzer Tiger in its tracks. Yet it's been slapped with the same 20 limit that protects the narrow residential streets around the local primary school.

The net result, predictably, is that the new limit is being almost universally ignored. Anyone socially responsible enough to try and stick to it is likely to be either overtaken in the belief they're about to stop - or to have their mirrors filled with the flashing headlamps of one of the city's kamikaze minicabs trying to hurry them along. The entirely predictable next stage will be dozens more speed cameras to enforce this slightly ludicrous limit.

A recent trip to the Scottish Highlands suggested a far better idea: part-time 20-limits around schools which are timed to protect kids arriving and leaving, and advised by easy-to-see flashing signs. But I bet that's far too rational an idea for the other local authorities eyeing up Oxford's blanket 20 restriction and looking to impose something similar themselves.