Four road crossings between the two Punjabs operated at various times after 1947: Attari-Wagah, Hussainiwala-Ganda Singh Wala near Ferozepur, Sadqi near Fazilka, and Dera Baba Nanak.
Hussainiwala and Sadqi were working crossings for goods and passengers into the 1960s and were closed after the 1971 war. Attari remained.
Trade through Attari was substantial when it was open: cement, gypsum, dry fruit and rock salt coming east, cotton, soya and vegetables going west, on trucks that were unloaded and reloaded at the line because the vehicles could not cross.
It was suspended in 2019. Since then almost nothing moves between two provinces that were one economy until 1947.
Indian goods reach Pakistan through Dubai and Pakistani goods reach India the same way, at several times the cost, which is the most straightforwardly wasteful arrangement in South Asian trade and has persisted for decades.
The Kartarpur corridor is the one exception and it carries people, not goods.
Attari is also the rail crossing. The Samjhauta Express began on 22 July 1976 running Amritsar to Lahore, was cut back to Attari and Lahore in 2000 with a separate link train from Delhi, and made its last run on 8 August 2019. The line under it is the first railway ever built in Punjab and it now ends at a platform nobody uses.
The retreat ceremony at Wagah runs every evening, with stands on both sides, a compere and soldiers kicking higher than either army does anywhere else. It is the only part of the border either country encourages its citizens to come and look at, and it is a performance of the closure rather than a crossing of it.
Each closure detached a town from its hinterland. Fazilka's road to Bahawalnagar, Ferozepur's to Kasur and Amritsar's to Lahore were the arteries those towns were built on.