Complex sentence: It is one of the four major highways of Thailand, the other three being Phahonyothin highway (National Highway 1), Mittraphap Highway (National Highway 2) and Phetkasem highway (National Highway 4).
Split into simpler sentences: It is one of the four major highways of Thailand. The other three are Phahonyothin highway (National Highway 1), Mittraphap Highway (National Highway 2) and Phetkasem highway (National Highway 4).