And verily, they were right on the highroad.
meaning that the city of Sodom, which was physically and spiritually turned upside down, and pelted with stones until it became a foul smelling lake (the Dead Sea), is on a route that is easily accessible until the present day.
This is like the Ayah,
وَإِنَّكُمْ لَّتَمُرُّونَ عَلَيْهِمْ مُّصْبِحِينَ
وَبِالَّيْلِ أَفَلَ تَعْقِلُونَ
Verily, you pass by them in the morning, and at night. Will you not then reflect! (37:137-138)
إِنَّ فِي ذَلِكَ لايَةً لِّلْمُومِنِينَ