Some rather angry comment on bilingual motorway signs from The Economist, 25 June 1977.
As you barrel along the M4 motorway, heading towards Newport with the Severn Bridge at your back, a giant road sign leaps out from the verge and screams … what? At 70 mph, with the children fighting in the back seat, you search the lines of bold lettering for a clue. There is none, until farther along the road an equally large sign – in English – reveals that the first one instructed Welsh-speaking drivers of heavy lorries to keep to the crawler lane.
How many drivers of heavy lorries speak Welsh? The question of numbers is irrelevant and that of road safety nearly so. The government is spending £10m to cover Wales with bilingual traffic signs, having decided that the opportunity to give the Welsh language a place of importance and dignity in national life is worth it, even though the language may be on its way to extinction by the year 2000 and the signs may keep drivers’ eyes off the road for longer than is strictly necessary.
Martin Johnes 
Nice blog (followed link here from your tweet with #NoTeamGB hash tag).
This might be of interest to you – a post has on ytwll.com has some screen shots from a government report when considering the introduction of billingual road signs.