There is an excellent article on the efficiency of transportation systems:
Gleave, J. (2019) Space/Time and Transport Planning, Transport Futures, https://transportfutures.co/space-time-and-transport-planning-1aae891194e5 [Last accessed: February 25, 2019].
It is highly recommended not just for academics (including students) but also for anyone interested in transportation and traffic. It’s like a crash course in transportation engineering with a lot of basic concepts in traffic engineering and traffic flow theory being presented for easy understanding by anyone. Enjoy!