The GENERAL SPEED LIMIT in the Irish Republic seems to have been reduced on this sign which is older than the County Cavan sigh, I suspect. The <a href='http://en.wikipedia.org/wiki/Road_speed_limits_in_the_Republic_of_Ireland' rel='nofollow'>55mph General Speed Limit in Ireland</a> was introduced in 1979 as a response to the energy crisis, and raised back to 60 mph in 1990-2. Prior to 1969, there had been a top speed limit of 50mph, except for certain built up areas,where 40 or 30 was appropriate. In 1992 also, the General Speed Limit was excepted for motorways, where the maximum was raised to 70mph. Since January 2005, all maxmimum speeds in the Irish Republic are in km/h, viz 120, 100 80 50 and so on.
In some ways, the irish limit paralleled the US <a href='http://en.wikipedia.org/wiki/National_Maximum_Speed_Law' rel='nofollow'>National Maximum Speed Law</a> between 1974 and 1987 of 55mph.
THere was no control of any sort at this border crossing.
A temporary speed limit of 55mph on the M1 during improvement works to junction 45