Hello ComradeTaco,
I was in almost the same situation as you just a year ago. First, of all, like Takeruk said, quality is more important than quality. Don't try to do as much as possible, but rather get deeply involved in a few activities/research that you find interesting. If you're sure to want to continue in Transportation Engineering at Berkeley, then I can hopefully help you by presenting you with my personal experience.
In my case, I applied this year and got accepted into UC Berkeley for the Master of Civil Engineering in Transportation. Just a heads up, the master's program at Berkeley for transportation is an MEng and not MS, meaning it's more industry oriented rather than research oriented, and it's also considered a terminal degree (which seems to align with with your desire not to pursue a PhD. It's also only 1 year long). The only transportation research I did was my Final Year project in undergrad, and I did one summer internship at a construction company (completely unrelated to transportation). However, I've been working for the past year and a half on a huge prestigious project, so I suppose that gave me an edge when applying.
My GRE scores are good but not outstanding, and I have a good (again, not outstanding) GPA. I'm writing this to tell you that the most important factor for getting in is (according to my experience) the SOP and LORs. You said the LORs should glow like a nuclear reactor. You're right, they should, and your SOP should shine just as bright if not brighter. This has been said many times in this forum, but I feel compelled to repeat it: Fit. You must show them in your SOP that their program has been created specifically for you, and that you were born specifically for this program. Everything that you have done in your life has led to this program, and you getting in is your destiny. (I'm exaggerating, but you get the point).
You seem to have a strong profile (for the MEng at Berkeley, I have no idea about MIT), but that doesn't mean you're guaranteed an acceptance and should stop working on your application. As Takeruk said, seek the most enriching research (or work if possible) experience for you and don't be afraid to try something outside of transportation. Finally, when it's application season, apply everywhere, even if everybody tells you that you're just wasting your time. As long as you focus on your strengths and fit, you increase your chances of getting in.
Good Luck!