Haramain High-Speed Railway

Crossing the Jeddah Tihama coastal plain — sabkha salt-flat terrain required engineered embankments and a 26 km causeway section to bridge unstable subsoil

Engineering a 300 km/h alignment through the Mecca and Medina urban fringes without disturbing the Masjid al-Haram and Al-Masjid an-Nabawi precincts — both stations are placed 4–6 km from the holy precincts

Sustaining 25 kV 60 Hz overhead catenary through 45 °C ambient temperatures (Jeddah, Mecca in July–August) — the 60 Hz system is unusual outside the Western Hemisphere and required Saudi-specific catenary adjustment

Designing wadi-bridge crossings for the Hejaz escarpment margins — at least 4 major wadi bridges over 1 km long between Rabigh and Medina

Coordinating Hajj-period capacity peaks — Dhul-Hijjah sees up to 36 daily trains; timetable is frozen 6 months in advance to align with the Hajj date

Avoiding interference with the existing 1,600 mm Hejaz Railway alignment and archaeology (the historic narrow-gauge Hejaz line ran along a similar corridor 1908–1920)

Maintaining sub-ballast through the flash-flood-prone Wadi Rabigh and Wadi Kura crossings during November rains

Integrating with the Jeddah KAIA underground HHR station — the only underground high-speed station on the Arabian Peninsula

Single-direction dual-track operation along the Hejaz escarpment margin between Rabigh and Medina, where lateral space is constrained by the rocky inland terrain

Maintaining continuous welded rail stability across the Jeddah Tihama where diurnal temperature swings exceed 30 °C in summer