Does meditation increase sensitivity to sense perceptions and why? Each morning, I meditate for 30 minutes. Within 45 minutes to an hour after, I commute to my university. For the first hour or two that I am at university after meditating, I feel almost overwhelmed by the intensity of external stimuli (car noise, sights, sometimes even internal thoughts and physical feelings). Conversely, on days that I do not meditate, I feel relatively stable and at ease walking onto campus. 

Does meditation increase sensitivity to these stimuli? If so, how, and what is the purpose of this with regard to meditation practice?
The sights and sounds were always there. Since your question is about why it is different when you meditate as opposed to the days you don't, may be you need to understand what happens on those days in order to understand this increased sensitivity ?

Maybe your mind was caught up in worrying about fulfilling commitments, like reaching university on time. Maybe you were daydreaming, or probably just scanning the environment and only noting novel and interesting stimuli.

Probably this doesn't happen on the days you meditate. I don't know about your typical meditation session, so I am assuming you are watching the breath. So you watch the sensations that make up the breath for a period of time. You are not only looking at interesting sensations during this session, you are looking at all the sensations - if you are doing it right. So after this session, when you go out, its only natural that you are not looking at just interesting sensations or worrying about getting somewhere, but looking at all the sensations that make up the external reality.


  If so, how, and what is the purpose of this with regard to meditation practice? 


You need to observe all the sensations of your meditation object for making progress in mindfulness meditation. It is normal to have some spill over effects of practice in normal life. If you can, you can maintain mindfulness while interacting with the world as well. If you can't, that is fine, as it is generally considered to be more difficult. So increased sensitivity is normal, and it is result of being open to all sensations during the meditation practice.