Summer Night City is one of my favourite Abba songs, even better when they sung it live
I think what stopped them getting a number 1 out of it was that it was during the Grease sequence of song releases. Think Travolta, Newton John were higher in the charts with solo offerings with 10CC sitting at the top
On the Radio Rewind site Paul Burnett counts down a relevant chart and expresses his surprise as 'Summer Night City' is pushed back from 7 to 8. Remarkably 3 records in that week's top 4 climbed a combined total of 29 places, two of them from the Grease soundtrack.