Category: AVL

Assignment functionality takes location data and turns it into information by linking that location to scheduled piece of work (e.g. a transit trip or a delivery itinerary). It is a crucial, yet opaque component of an AVL system. Each AVL product will have a different take on the problem, with different requirements from input data and operator/supervisor interaction.

Assignment sits on a continuum between Explicit and Implicit or Inferred. Explicit assignments are made by an operator or system that assigns a piece of work to a vehicle. Assignments are often provided by a vehicle operator entering their assignment into a device on the vehicle, or a dispatch system with prior knowledge of which vehicle(s) will perform which assignment. Inferred assignments are made by a process that analyzes the vehicle’s recent behavior to guess what piece of work it is serving. Inferring assignments are more complicated in dense networks, where multiple assignments can be likely.

If you are procuring an CAD/AVL/RTPI system, questions to ask about its assignment system are:

What is the interaction that operators are expected to have with the system? Do they have to interact with a new device? What does that interface look like? Specifically, how many new keys do they have to press? Will there be labor relations issues as a result?

Does the system rely on assignment data from an external system (e.g dispatcher entry)?

What validation is done against operator or dispatcher entered data? Can an operator enter incorrect data?

 

What level of intelligence is on the vehicle? Most “computer-on-a-bus” solutions download the entire schedule to the bus and can store data for later transmission when losing connectivity. More simple on-board systems do not store any information on the vehicle; they send only the information they have. How/when are are data on vehicles synchronized?

 

How flexible can the system be when deviating from expectations? For example, how does it handle detours? What about extra unscheduled service?

What does the assignment system it telling you? Does it ever display expected (rather than actual) information? Does it tell you the difference between the two?

Communication is the most “magical” of an AVL system’s components– it carries information over the ether from vehicle to server, and when it works, it just works. It is also the most well understood of these components, so this post will focus solely on things to watch out for.

Cellular:
Most AVL systems are now using cellular communications. Hardware is easy to acquire, costs are somewhat reasonable, and speeds are more than enough for low bandwidth applications.

One thing to watch out for is the the “sunsetting” of 2G and 3G networks. In the US, wireless carriers will be shutting down 2G and 3G networks as soon as 2016 (AT&T), and possibly as late as 2020-21 (Verizon). At this point, solutions that provide no upgrade path to 4G should not be considered for the long run.

Private/Packet Radio:
Packet radio is what has traditionally powered AVL communication. Older AVL-over-radio systems suffer from very long update intervals– often 5-10 minutes between position updates. Most new systems have much shorter intervals, but it is crucial that you know what the update interval is, regardless of technology or age. Some unscrupulous vendors are still selling systems of a previous generation.

Mesh
Long touted as the next big thing, mesh networking has never taken off commercially. The industry has not given up hope =iIt is still seeing new research. Be wary if it is proposed; the supplier better have a good testing and backup plan.