Complex sentence: This elevated stretch of motorway above the River Tame is 3½ miles long, which makes it the longest viaduct in Great Britain, being a quarter mile longer than the Second Severn Crossing.
Split into simpler sentences: This elevated stretch of motorway above the River Tame is 3½ miles long, which makes it the longest viaduct in Great Britain. It is a quarter mile longer than the Second Severn Crossing.