What about Crashtests so you have to design a Save Car with Airbags and that stuff?
Player will need to take safety into consideration in later game years - by putting safety equipment.
Take in mind there will be no visualisations of crashtests, as it would be pretty hard to make car crashes look good and realistic.
don’t forget that physics engines are mostly a massive pain, so plain numbers and stuff should do i guess 
If you ever think about adding crash test (visual crash) This link may interest you youtube.com/watch?v=9JPDtDfxf6w
The compagny is Beamng and they are working on an awsome crash physics called soft body physics.
You have to take a look. its awsome! i dont think you can implant it to you game because of the home made car but. wow. if its possible, its the best looking crash ever!
Although I agree that adding a complete crash test modeling to the game would be really painful for the team, I suggest not leaving just some plain and cold numbers to show how safe (or unsafe) our car is.
I have an idea, like giving a global safety scale (just like Euro-Ncap does) which is calculated by summing some parameters like: driver’s safety, front passenger safety and back passenger’s safety at front, side, pol and roll over crashes. Also, child and pedestrian protection, as well as fire prevention systems could finish the figure.
The parameters to calculate these can be: chassis stiffness, presence of crumple zones (and size of them), active safety features (airbags, 2/3 point seatbelts, pretensions…), battery and fuel tank position and construction…
In this way I think that safety can be a more complex and interesting issue than by giving a plain number which only relies on the chassis stiffness and safety features installed.
Finally, I don’t know how costs associated to the development of the car will be calculated, but I think that crash tests should increase them but can give our engineers ideas to improve the overall safety (i.e. tuning the airbags timing), so you can in the end balance costs vs. results.