Drive over a potholed urban road after the first rains, and you quickly realise that a road is not simply tarmac poured on dirt. Roads are layered structural systems — engineered to transfer wheel loads through successive strata of bound and unbound materials down to the natural subgrade below. Get any layer wrong, and the…

Drive along the Lagos–Ibadan Expressway after a heavy rainstorm and you will see the difference between a road that was designed and one that was merely surfaced. Potholes don’t appear because asphalt is weak. They appear because someone, somewhere, got the layer beneath it wrong — the subgrade, the drainage, the compaction, or the traffic…