Now vents are built into the dashboards of cars so you can have the windows closed if you want

But, in the 1950s and before vents into the car through the engine compartment were rare. Often you ONLY had wind wings to cool down and nothing else. However, gasoline was 17 cents a gallon still by 1969 and so car efficiency "mileage" was not an issue then until the Arab Oil embargo gasoline shortage in the 1970s which made gas cost about 5 times as much as before and caused recessions and inflation more constantly after that. But, before this staying cool mostly was through wind wings and of course all cars and trucks had heaters then too because of snow and cold in winters. However, people were more expected to endure temperatures of 100 to 120 degrees or more in the western states without air conditioners in the 1950s and before. To get some perspective 17 cents a gallon was the same time that the minimum wage was around 1 dollar an hour. So, even if you only made the minimum wage you could buy 5 gallons of gasoline for every hour you worked then. And at 16 in 1964 I was making part time 3 dollars an hour often because they needed young people to fill all the jobs then so there was a general shortage of workers then for jobs. I was even able to easily get jobs making things in a factory setting part time at age 15 too then (even though the equipment wasn't always safe to use either in making things). However, I was trained to be very efficient as an electrician by my father so I wouldn't put up with working in conditions that weren't safe enough either because of incidents while working with my father where I almost didn't make it. So, the methodical methods of staying alive as an electrician helped me survive all the other jobs when i was young that I took for short periods especially while going to High School and college along the way. Safety was a real issue in companies where you worked with your hands back then more than now. People were always getting injured more than now too back then. People were just considered more expendable before about the 1970s and after when people began to be more safety conscious. I think the stupidity of the Viet Nam War and all the American boys that died for nothing changed how everyone behaved and made them much more safety conscious after that throughout American society on all levels.

But, if it wasn't cold out windows were almost always open in cars so you were more comfortable in the 1950s and before. This was also true to some degree in the 1960s and 1970s as well as air conditioners became more affordable and also popular in cars and eventually trucks too.  But, mostly vents were relatively unusual (at least that worked very well) because even if you had dashboard vents there usually weren't fans to blow the air through into the car too.  So, opening windows was one of the only ways to stay cool then.