R150

R150 / 1c:Mc-1

Ego Vehicle is driving on zero or one Road

Road is being driven by zero or one Ego Vehicle

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At a given point in time, the Ego Vehicle may or may not be on the Road. Our vehicle could be in a parking lot, in a driveway or in the middle of a grassy field. Numerous constraints apply to an Ego Vehicle only when it is, in fact, on a Road somewhere, so we need to recognize and carefully distinguish when this is in fact the case. This frees us up to make different rules to constrain vehicle behavior when the Ego Vehicle is in a non-road environment.

An Ego Vehicle cannot simultaneously drive on multiple Roads. This is largely due to the way that Road is defined. For example, a Road may have multiple map designations. So the fact that we are on “Highway 1”, which is also “CA-1” which is also the “Pacific Coast Highway” constitutes a single Road with multiple designations and not three distinct Roads. What about turning through an Intersection? At some, possibly arbitrary, point in the turn we must decide that the Ego Vehicle has left one Road and entered the other. But at no point in time will we consider the Ego Vehicle to be on both Roads simultaneously. (Note that not all intersection turns involve leaving the current Road!)

A Road may be detected by the Ego Vehicle even though the Ego Vehicle is not driving on it: an intersecting Road up ahead, for example.

It is true that a Road may be simultaneously driven by multiple automated vehicles, but the term “Ego” is critical. By definition, there is only one Ego Vehicle, ourself, and therefore we either are or are not driving on a given Road. Thus, a Road is being driven on at most one Ego Vehicle.

Formalization

On Road Ego Vehicle.Ego -> Ego Vehicle.ID
On Road Ego Vehicle.Road -> Road.ID