Complex sentence: When not on the guideway buses run on the town's main roads alongside normal traffic, When on the guideway buses are kept on track by small wheels that are angled at 90 degrees to the normal wheels-these run along the kerb edges of the guideway.
Split into simpler sentences: When not on the guideway buses run on the town's main roads alongside normal traffic. Whilst on the guideway, the buses are kept on track by small guide wheels, angled at 90 degrees to the normal road wheels--these run along the kerb edges of the guideway.