While the highway was constructed as an entirely new route (except the former Perak State Route A171 section from Gerik to Kuala Rui that formed the pioneer route of the highway), the construction of the second phase involved acquisitions of several roads, namely Kedah State Route K171 (Kampung Sadek–Kampung Hangus), Kedah State Route K173 (Kampung Hangus–Kampung Kuala Kuang), Jalan Kampung Keda Kemangi (Kampung Kuala Kuang–Kampung Keda Kemangi), and Jalan Sungai Petani–Baling FT67 (Kupang–Kuala Pegang and Kuala Pegang–Tawar). As a result, the East–West Highway FT4 overlaps with Kedah State Route K171 (from Kampung Sadek to Kampung Hangus) and Jalan Sungai Petani–Baling FT67.