6.7.1.1 - Provide Vehicle Guidance

This DFD shows the three processes that make up the Provide Vehicle Guidance facility within the Provide On-line Vehicle Guidance function. These processes determine the actual vehicle guidance method, and generate the route and guidance instructions.

The key points about the facility are as follows:

• Guidance type depends on driver’s request and on the availability of in-vehicle equipment;
• Dynamic guidance requires a communications links to a central facility;
• If dynamic guidance fails then autonomous guidance is automatically provided until it is restored;
• Autonomous guidance may use link travel times provided centrally, at the driver’s request.

There are three processes in this DFD:
a)Determine In-vehicle Guidance Method (6.7.1.1.1)
b)Provide Dynamic In-vehicle Guidance (6.7.1.1.2)
c)Provide Autonomous In-vehicle Guidance (6.7.1.1.3)

The process in (a) is responsible for deciding on the type of guidance to be used and setting up the data sent to the chosen route calculation process. This data defines the type of route and the preferences and constraints that are to be applied to the calculation process. These will have been set up by the driver through the interface process in the Provide On-line Vehicle Guidance facility - see DFD 6.7.2, except when the request is for a route involving automatic vehicle operations lanes. In this instance the constraints in particular will be set by process (b) so that this type of lane is used. If these lanes are not available at some point, the route will be specified with the end of the last automated vehicle control lane as a new route calculation point, so that alternative preferences and constraints can be used. If the driver omits data from the guidance request, the option is provided for its direct input, or the use of data from the store of retained data.

If dynamic guidance is selected then process (a) sends the route request to process (b) for the addition of the vehicle location and communication with the Select Vehicle Route facility - see DFD 6.6.2. The data that is returned to process (b) is sent to process (a) and then to the driver interface. If no route can be provided by process (b), then process (a) sends the request to process (c) which provides autonomous guidance. At the driver’s request, this may make use of link journey times provided by the Select Vehicle Route facility. Failure of dynamic guidance will cause process (a) to request autonomous guidance from process (c) starting at the vehicle’s current location.

When providing dynamic guidance, process (b) will continually monitor the vehicle’s location. When the vehicle reaches pre-defined points on the route (way points), it will request a new route from the Select Vehicle Route facility. It will also provide the facility with its location at the end of each route segment so that the facility has a feedback of the actual segment journey times (probe data).

The processes (b) or (c) above may be omitted from any particular implementation or offered as options since they are independent. However if the process in (c) is not included, and the communications link with the source of dynamic guidance data fails, then the vehicle will be left to depend on the last set of dynamic guidance data that it received. This cannot now be updated if the vehicle departs from the originally specified route since no autonomous guidance will be available.

DFD: 6.7.1.1 - Provide Vehicle Guidance

Parent DFD: 6.7.1 - Provide On-line Vehicle Guidance

PSpecs in the DFD:

• Determine In-Vehicle Guidance Method
• Provide Dynamic In-Vehicle Guidance
• Provide Autonomous In-Vehicle Guidance