“The yellow school bus has remained largely unchanged since it first debuted in 1939,” writes Route Fifty (Aug. 12, 2019). But while the buses look the same, their routes have grown infinitely more complex in the past 80 years, as the number of students, schools, and road systems grow and change. Drawing bus routes for Boston Public Schools (BPS) involves challenges unique to the city, which allows parents to select their child’s school from a list of 10 options. The resulting bus routes can be meandering and complicated.
In 2017, the district was facing serious challenges. On a per-pupil basis, BPS had the highest transportation costs in the country, $2,000 per student per year, representing 10% of the district’s budget. The schools dealt with rising costs each year, despite declining ridership. The on-time performance rate of their buses was also well below that of other large districts.
Quirks can create millions of decision variables that affect any solution. These include varying road widths, differing bus infrastructures, students who require the same bus driver every year, students who have monitors, and students who have been in fights and, therefore, need to be on different buses.
The MIT team selected to tackle the problem replaced what had before been an incredibly laborious process, one that took 10 school system routers thousands of hours to create custom routes for each child and school. In 30 minutes, the new algorithm created a system-level route map that was 20% more efficient than the ones done by hand. And the longer the algorithm runs, the better solution it produces, until it cannot be improved. Running the algorithm in 2017 allowed BPS to eliminate 50 buses, an 8% drop in the fleet that was the largest Boston had seen in a single year. Buses drove 1 million fewer miles that year and cut 20,000 pounds of carbon dioxide emissions per day. The district reinvested the $5 million saved back into classroom initiatives.
Classroom discussion questions:
- Why is scheduling buses so complex?
- How does this differ from scheduling a fleet of airplanes?