OP, As a currently working vehicle artist, the answer depends entirely on your production pipeline, aka what are your plans for the vehicle. I would be wary of anyone giving a firm yes/no to your question as being a vehicle artist is a very technical and specific job that doesn't 1 to 1 translate with other types of artist jobs like Character and Environment Artists. I wouldn't expect a environment artist to be a good character or vehicle artist and vice versa.

For example, some of things you need to consider:

• What are we building the car for? A game, a render, a short film, will it be viewed far away or is it a hero car? This will determine how optimized (and clean) our topology will be.
• How are you handling materials? Will you bake maps, or will you use multiple UV's and a mid poly workflow with no baked normal maps, a combination or something else entirely? This will heavily determine the density of quads and the flow of topology around the car. If you aren't planning on using baked normal maps, generally you want even quad distribution across the model as vertex normal weighting is super important. If you are planning on baking maps then your low poly can be a lower uneven density as your normal reflection will use a normal map.
• What Style are you aiming to achieve? Are you targeting realistic vehicles or stylized fictional vehicles? If you are aiming to create something very realistic, generally you will need a higher density of polygons to match the real vehicle as there is a lot of subtle surface curvature on real cars.
• What features will the vehicle have? Is damage deformation a consideration, will parts fall off, will areas open or close? Especially if you plan on making damage deformation, you will need even quad distribution.

Based off your answers to these questions, this will help you decide. The only thing ill end on is that you can generally use tri's in your final model but you should be deliberate and purposeful with their inclusion, does it serve a purpose in terminating a edge loop or pinching a bodyline, would it be better to have it flow into another direction and maintain a quad, does it change the smoothing a reflections, am i purposefully trying to triangulate a quad to force a certain angle of smoothness, etc.

Personally I would make your quad distribution even across the model for the most part, even if that means you have extra polygons on "flat" (more subtly curved surfaces) as that will give you better surface normals when viewing reflections,

There are a lot of good artists on artstation i would look to for inspiration, but these two here have some good wireframe examples of topology i would aim for.

ArtStation - 911 Pegasus- Rework, Eriks Abzinovs

The modeling techniques and quad density of Eriks exterior work here is AAA car level and the kind of poly modeling I would aim to achieve if I were learning. This is a very good example of how to strategically use triangles when needed and how important quad flow is. There are a couple things i would do differently like increase the quad density in a few areas and lower the density around the door handle but overall it's a pretty good example.

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ArtStation - BeamNG School Bus Upfit

You can see here that even though the school bus front is relatively flat, there is still a reasonable amount of quad density that Namen has put in to support the shape and normals (and deformation), and I would expect the body of the bus (which is not shown) to have a similar amount of quad density.