SHERPA OF RAIL LEVEL CROSSING SYSTEMS

As described in Chapter 2, SHERPA (Embrey 1986) is a human error identification method used to identify the potential errors that could arise during task performance. In the current project, SHERPA was applied to identify the errors that drivers could make at existing rail level crossings in Victoria, Australia. In addition, we were interested in understanding the error tolerance of current rail level crossing designs and to identify initial design ideas for improving behaviour and safety.

Analysis Approach

Initially, one analyst used SHERPA to identify potential errors. This involved taking each bottom-level task step from the HTA, classifying it into one of the five SHERPA behaviours (Action, Check, Retrieval, Communication, Selection) and then using the error mode taxonomy in Figure 5.7 to identify credible errors. For each credible error, a description of the error and its consequences were documented along with any recovery steps (i.e. the point in the HTA at which the error could be recovered), ratings of probability and criticality of the error and potential remedial measures.

Following the initial analysis, two analysts with experience in applying SHERPA reviewed the analysis to check the credibility of the errors and their associated probability and criticality ratings. An extract of the rail level crossing SHERPA is presented in Table 5.4.

SHERPA error mode taxonomy (Embrey, 1986)

FIGURE 5.7 SHERPA error mode taxonomy (Embrey, 1986).

TABLE 5.4

Extract of SHERPA for Driver Behaviour at Rail Level Crossings

Task

Error

Mode

Error Description

Consequence

Recovery P C

Potential Remedial Measures

6.1.1. Look for early warning signage

C5

Driver looks for signage too late

Driver fails to comprehend approaching train

Step 6.2.1 H

In-vehicle reminder system Runway red lights in stop line (in-road studs) Alternating LED image of moving train on active early warning signage (or replace current signs with this) Traffic lights linked to RLX

6.1.2. Detect flashing lights

R1

Driver fails to detect flashing lights

Driver fails to comprehend approaching train

Step 6.3.1 M /

In-vehicle system

Runway red lights in stop line (in-road studs) Alternating LED image of moving train on active early warning signage (or replace current signs with this) Traffic lights linked to RLX

6.1.2. Detect flashing lights

C5

Driver detects flashing lights too late

Driver fails to comprehend approaching train

Step 6.3.1 M /

In-vehicle system

Runway red lights in stop line (in-road studs) Alternating LED image of moving train on active early warning signage (or replace current signs with this) Traffic lights linked to RLX

6.1.3. Interpret flashing lights

R1

Driver fails to interpret flashing lights (LBFTS)

Driver fails to comprehend approaching train

Step 6.3.1 M /

In-vehicle system

Runway red lights in stop line (in-road studs) Alternating LED image of moving train on active early warning signage (or replace current signs with this) Traffic lights linked to RLX

C, criticality; H, high; L, low; M, medium; P, probability; RLX, rail level crossing; LBFTS, looked-but-failed-to-see error.

 
Source
< Prev   CONTENTS   Source   Next >