Cars are frequently used in fiction and real life to represent male/female sexuality. The connection between cars and masculinity is particularly strong. In fact, many men consider owning a car as proof of their virility or manhood. This association has been around since early automobile manufacturing.
Henry Ford famously said "any customer can have a car painted any color that he wants so long as it's black." Many people think this was because the paint required for different colors was more expensive than black, but others suggest it may have reflected Ford's view that women were not important in the purchase decision. Certainly, most early ads focused on the appeal of cars to men. Today, however, there are numerous automotive products aimed specifically at women and some even explicitly associated with sex. Car companies make sports cars, convertibles, hatchbacks, SUVs, luxury sedans, etc. all designed to excite female desire, although they do not necessarily always advertise this fact.
A common trope in literature is that of the eroticized vehicle. Whether due to its sleek design, power under the hood, or simply the thrill of driving, many characters find themselves attracted to vehicles. Sometimes this attraction goes beyond just admiration and leads to actual arousal, masturbation, or intercourse. One famous example is the film Christine by Stephen King, which involves an evil car that possesses its owner, eventually leading him into a violent relationship with it. Another example comes from the television show Mad Men, where Don Draper is frequently seen ogling his cars and having affairs with them. These examples highlight how powerful our sexual fantasies can be when it comes to objects we associate with masculinity or femininity.
More generally, there is a connection between psychology and cars. People tend to associate certain qualities with certain types of vehicles.
Small sports cars are often associated with youthfulness and agility, while large SUVs with strength and power. This is why some people choose particular makes and models based on their personality or lifestyle.
It's also possible for one's personality or landscape context to influence the way they view and relate to different automobiles.
Someone living in a rural area may feel more drawn to trucks than city-dwellers who prefer compact cars. This could lead to confusion over what kinds of cars represent them as individuals and what kind of people they might want to date based on their vehicle choice.
However, most people seem to agree that there is something inherently sexy about cars, whether because of their aesthetics, performance, or simply because they're so much part of modern life.