I don't mean this as an attack against you, but your response to this is exactly illustrative of why it's a useful interview question.
If you are, then I would go so far as to say you are the type of engineer who ends up creating problems other, more thorough engineers have to solve later on down the road.
Furthermore, sometimes your data is inaccurate, and that means that you have to build in error margins in your estimates. Doing that uses exactly the same skills as making rough estimates based on vague information.
If you have reasonable estimation skills, then by the time you get out to the lot with a tape measure, you will have narrowed the search down to the sedan and the SUV. You don't need to bother measuring the double decker bus because you know that it's around 100 times as large as needed. You don't need to consider using the motorcycle because that is clearly far too small. If you collected data on those options, you'd be wasting time, because in the time it takes to collect the data, you could have already ruled them out.
"OK," you say, "but it doesn't hurt to be thorough." But see, it does hurt to be too thorough. Every second you waste on deciding not to use the bus is a second you could have spent making a better decision between the sedan and the SUV.