It's not mentioned in the article, but Julia was used to solve the huge optimization problem for this project—specifically, the JuMP optimization package [1]. This SIAM article has more technical detail: https://sinews.siam.org/Details-Page/a-school-bus-trip-to-th.... This seems to be a preprint of the paper that may describe the algorithm used in Boston, although it seems to talk more about the well-known New York taxi data set: http://web.mit.edu/~jaillet/www/general/travel-time-18.pdf.

[1] https://github.com/JuliaOpt/JuMP.jl

[2] http://www.nyc.gov/html/tlc/html/about/trip_record_data.shtm...