Georgia Tech students, working with the Georgia Tech Department of Parking and Transportation, have built a system based on our idea in which each bus contains a tablet computer with GPS and wireless networking capabilities. We conducted live trials for over a year and held a public demonstration on 20 April 2012 that was covered by CNN, PBS, and many others. The system went fully live in mid-August 2013 and has controlled the trolley route since then.
Figure 1: The Tech Trolley route is about 4 miles long round-trip (click for a larger view).
The Georgia Tech Trolley
The Tech Trolley provides service between the Campus Transit Hub and the Midtown MARTA Station, stopping at many locations throughout campus and Midtown along the way. This route carries over 5000 passengers per day and is subject to bunching because there are many sources of variability in bus velocities. One source of variability is the seventeen stops, at which ridership surges just before and after class changes. Other sources of variability include the seventeen traffic lights,
five stop signs, and fourteen pedestrian walkways that buses must cross in circumnavigating the route. Depending on traffic and passenger load it can take anywhere from 20 to 40 minutes for a trolley to traverse the route.
Despite these challenges, our system outperforms the schedule. Passengers like it for the more regular service. Management likes it because the system re-equilibrates spontaneously after disruption, without oversight or intervention. Drivers like it because it removes the constant pressure of schedule adherence (We advise them to forget the schedule and just drive safely with the traffic. Our system will make any necessary corrections at the next checkpoint.)
The Georgia Tech trolleys may be instructed to pause at either of two “checkpoints”, the Student Center Hub (bottom middle of the map in Figure 1) and the MARTA (subway) station (top right). Since these stops are at opposite ends of the route there are rarely passengers riding through and so this is unlikely to inconvenience anyone. Another reason to choose these locations as checkpoints is that the bus can pull aside and not interfere with the flow of traffic.
When you board any of the Tech trolleys you will see a tablet computer mounted beside the driver. It regularly notes its position by GPS and sends this information via cellular network to our server. The server recognizes when a bus arrives at a checkpoint and tells the driver how long to pause before continuing the route.
Managers have access to a web-based console named “NextBUZZ” by which they can monitor the status of all buses in real-time, adjust control parameters, or generate performance reports. (“Buzz” is the name of the Georgia Tech mascot, a yellow jacket wasp.)
Figure 2: A tablet computer mounted beside
the bus driver signals when to go.
Frequently-Asked Questions About the Implementation
- Has this improved performance compared to the schedule?
- Yes. For example, see this comparison that shows headways during one day of fall break when we turned off control and asked the drivers to revert to the schedule, then headways on the following day when we re-instituted control.
- What have been the advantages?
- Better performance with less supervision. No need to revise/publish/manage schedules with every route alteration. The manager can add or remove buses as necessary, without having to synchronize with a schedule.
- How reliable is the software?
- Very. We tested the system for 1.5 years before deployment at Georgia Tech.
- How do you schedule breaks, lunch, end-of-shift, etc. for drivers when there is no bus schedule?
- Because the buses have no schedule under our scheme, the drivers have no schedule either. This means that the drivers must be flexible. (Scheduled services have the same problem because it is impossible in practice to keep to a schedule.) This is not so much a technical problem as one of driver expectations and management. This has not caused any problems on the Georgia Tech route. It might be a problem on routes that require a very long time to circumnavigate.
- If there is no schedule, how is the performance of a driver judged?
- Instead of managing by schedule adherence, we manage by wait-time adherence: Our system reports how well each driver follows instructions about when to depart the control points. (Other expectations, such as safe driving, courtesy, etc. remain the same.)
- Can one bus pass another?
- Yes: Our system does not require buses to remain in sequence.
- What happens if a bus breaks down and must be replaced by another?
- As soon as a driver logs in on the new bus, the new bus will be seen by our system and the other buses will be quickly re-positioned to equalize headways.
- Can’t a driver game the system by traveling as fast as possible so that they get a longer break at the next control point?
- Yes, this is possible (and it is possible under a schedule as well). But under our system, every driver has the same incentive and this can improve overall performance because we do not restrict headways to a schedule or a target.
- What do the drivers think of this?
- Georgia Tech drivers strongly prefer this scheme because it removes the constant pressure of schedule adherence.
- What do passengers think of this?
- We have received only positive comments. The most common one is that they like that the tablet clearly shows how many minutes until the bus will depart.
- How much did this cost?
- We developed and tested the system with personal smart phones (one per bus). For a commercial implementation the costs depend on the degree of ruggedness and security desired:
- One-time costs
- USD 400–1500 per bus for a tablet computer
- USD 100–500 per bus for a lockable mount for each tablet
- Continuing costs
- USD 50 per month per bus for cellular data service (wifi can work too)
- USD 7 per month for a hosted web server (example: Yahoo, Google, Amazon, etc.)
To hear directly from those responsible for daily operations, contact David Williamson, Associate Director for Parking & Transportation Services.