It's changed radically over the decades.
Few movie cars are as instantly recognizable or as iconic as the Batmobile, although there are some notable exceptions. A number of people have made their own versions of the various Batmobiles, some of which have even been road legal. It's a car that people of all ages can recognize, and the car has evolved over the years from a fun and quirky-looking dinky toy of a car to an absolute tank. For the upcoming film The Batman, things are a little more restrained (relatively speaking), with the latest Batmobile apparently based on regular roadgoing cars like the original Dodge Charger. But before that new movie gets here and we can take closer looks at the latest Batmobile, let's see how this evolution from fun to fearsome took place.
Although there have been other Batmobiles in the comics and so forth, we start in 1966 with one of the most recognizable designs. Interestingly, this was based on the Lincoln Futura concept, and you can see that the wild, space-age design of the Batmobile here was both upbeat and comical. That changed a lot in 1989 when Michael Keaton's Batman drove a vehicle that was "less like a product and more like Batman himself with wheels." This design is the one that most would recognize, and is sleek, apparently being inspired by jets. Here, the car starts to look sinister for the first time but remains both fun and purposeful. In 1995, the same sort of design evolves heavily, with a more phallic design that seems to sprout wings wherever possible. The gaping openings in the bodywork point to the vulnerabilities of Batman as an individual, while the bright lights and those massive batwings symbolize the excess of the era.
Next up is the Batmobile of 2005, otherwise known as "The Tumbler". In this design, we see that the Batmobile has evolved from a symbol of humanity and hope into an obsessive, vengeful, angry, purpose-driven machine of war - just like the character that drives it. All that matters is being invulnerable and shutting out anything that can hurt or harm the person or the car. As Stephenson notes, this could be the villain's car, and the line between good and evil is extremely blurred. And as the Joker says, "people are only as good as you allow them to be."
Finally, we get to the upcoming Batmobile that we've only seen some teasers of. Things will get even darker, with a dystopian flavor that implies pain, struggle, and a general lack of hope. Ultimately, as Stephenson notes throughout, each Batmobile symbolizes the era in which it debuted on the silver screen. If Batman films are indeed a social commentary, the future is going to be a very scary place...