It's not science in the traditional sense, but I currently study the application of queueing models to urban traffic networks, using simulation based optimization to address a number of issues, such as traffic management (i.e. signal plans) and calibrating behavioral parameters in microscopic traffic simulations.

I don't think transportation research is particularly important, and I'd be willing to bet that this is reflected in the amount of money in transportation research. I think that my friends who work in fusion research would be a better long term investment - but mostly because I think the issues of transportation are more difficult in practice than in theory. Well, maybe that describes a lot of fields. I don't think that transportation receives the attention or funding that it deserves, but the funding would be more for planning and construction than research. Transportation is incredibly important to society and is seems to be taken for granted in the US. It's unfortunate that the transportation suffers from political problems, whether it be from poor judgment on behalf of policy makers (i.e. Congress), or nepotism in the hiring practices of transit agencies. Transportation researchers (on the policy side) have advocated for things like an increase in the gas tax for years, despite the fact that it is a political impossibility. One of my professors pretty much threw it out as a option for discussion in class for that reason.