TRAFFIC  thundering through the invisible Irish border on the main road between Derry and Letterkenny is relentless. Seconds into the Republic side - noted from a change in speed limits from miles to kilometres - a thriving hub of businesses has sprung up in recent years around the once sleepy village of Bridgend. The old Irish Customs post is now a fireplace showroom. There is no evidence of the once heavily fortified and towering British army checkpoint that once loomed over the Northern Ireland side. Several filling stations do a roaring trade from Derry motorists taking [...]