B-Spec Drivers (Striped Status Bars)

[BKViper]

Each B-Spec driver has 3 green status bars which increase in length the more you use the driver.
I just noticed that on my top two drivers, there is a small area at the end of the green on a couple of the bars that is now white and black striped.
Does anyone know what this means?
The green bars have not yet filled up the available space, so there would still be room to grow.
Is this indicating that my driver is losing ability in that category? I know they are supposed to go down eventually toward the end of their career, but when does that begin?
I assume their career ends when you get them to level 40.
These two drivers are at levels 30 & 31, so it seemed a little early to be losing skill and facing retirement, but I guess it's possible.

 

[the Interceptor]

This means that the career of your driver is coming to an end (see the career bar), and that his talents are going to decrease over time. If I'm not mistaken, the career bar is solely advanced by the number of races the driver participated in, not by XP level or the driven miles. Nothing to do about that other than to drop him and "raise" a new driver.