Page 134 - 360.revista de Alta Velocidad - Nº 5

Grande, Zacarías. Blanco López, Marta. García Tamames, Alberto. Castillo, Enrique.

By distracted we understand a situation in which the driver lacks the necessary attention to
correctly react when an action is required. By attentive we refer to the case in which the
driver is able to react adequately to the required actions with a small probability of error.
Finally, alert refers to the case where the driver is ready to take an action and knows that
he/she has to act immediately (for example, after seeing a warning signal or consulting the
railway driver’s guide, etc.).
The evolution of driver’s attention when driving progresses and different elements along
the line encountered must be considered.
3. S: Speed It refers to the train speed at the corresponding location and can take a discrete
list of values. In the examples considered in this the- sis we have simplified the model using
the following list of values.

4. A: Accident. It refers to the accident occurrence at the actual location or before and can
take the following values: none, minor, medium and severe.
The model assumes that once an accident has occurred at a given location, no accidents can
take place in any other forward location.

5. RS: Rolling Stock. It refers to the rolling stock conditions and includes the damage levels:
none, minor, medium and severe.

6. Inf: infrastructure. With this variable the infrastructure state (rails, sleepers, ballast, plate,
maintenance standards, etc.) is considered, and it includes the following damage levels:
none, minor, medium and severe.
7. T: Terrain. This variable is used to consider the risk associated with falling stones on the
infrastructure or slope sliding in cuttings and embankments and takes values: stable, small
instability, medium instability and high instability.

8. DE: Driver’s decision on speed control. It refers to the decision made when speed is controlled
by the driver, and includes the following levels: correct, error I (speed remains unchanged),
error II (selected speed does not coincides with required speed).

9. DA: Driver’s decision at signal. It refers to the decision made when the train encounters a
signal, and includes the following levels: correct, error (incorrect action of the driver).

10. ATP: Automatic Train Protection System. This variable refers to the supervising or driving
assistance system operating at the considered point of the line. It takes the values:”ERTMS”,
“ERTMS-ASFA”, “ASFA-dig”, “ASFA-AV’’, “ASFA-Conv”, “ASFA- anal”, “SR” (staff responsible).

11. AS: Light signal Decision. It refers to the possible errors at a light signal: none, error I (stop
announcement signal), error II(signal at red).
12. DS: Driver’s decision made at a speed limit signal. It refers to the possible errors made by
the driver at a speed limit signal: none or error I (fail to reduce speed).

13. SS: Light signal state. It refers to the light signal: free, stop announcement, stop.
14. TF: Technical failure. It refers to the possibility of a technical failure: yes or no. For
example, if the driver tries to stop the train and the brakes fail.
2.1.3 Markovian Model

To analyze the driver’s attention, we propose a Markovian model that considers only three
driver’s attention states (distracted, attentive and alert) (see Figure 1). “Distracted” means

132 360.revista de alta velocidad