9.2 The IPDE and SIPDE Processes

9.2 The IPDE and SIPDE Processes

[!IMPORTANT] Know both acronyms. DOL names Drive Right (10th edition) as instructor exam preparation, and Drive Right teaches IPDE. Many state and commercial programmes teach SIPDE, which prefixes an explicit Scan step. They describe the same behaviour; SIPDE simply refuses to let searching be implicit. An instructor should be able to use either and explain the difference.

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The four steps of IPDE

Identify

Detect and name what is present and what is relevant. Identification covers three categories:

• The path of travel - the road surface, its condition, its geometry, and anything on it.
• Other users - vehicles, cyclists, pedestrians, animals, and where they are going.
• The traffic environment - control devices, markings, lighting, weather, and the closure of sight lines.

The commonest identification failure is not blindness but narrow search: the student sees the vehicle ahead and nothing else. Section 9.1's visual search habits are the input to this step.

Predict

Project forward. What is likely to happen next, and what is the worst plausible outcome? A parked van with brake lamps lit and a driver's door ajar predicts a door opening and a pedestrian stepping out. A ball rolling into the road predicts a child.

Prediction is where experience most obviously separates novice from expert, and it is trainable through explicit rehearsal: "what could that do?" is a question a student can be asked hundreds of times in a course.

Decide

Choose a response. Every response is a combination of three basic actions:

Reducing the option set to three families makes decisions faster under pressure, which is the point.

Where two hazards conflict and cannot both be avoided, teach minimising the hazard: choose the option with the least severe consequence, generally in the order of avoiding people first, then objects that will injure, then property damage. Where hazards can be separated in time, teach separating the hazards: adjust speed so you meet them one at a time rather than together.

Execute

Perform the chosen action smoothly and completely. Execution failures in novices are usually of two kinds - too little (a brake application that does not actually slow the vehicle enough) and too abrupt (a steering input that unsettles the vehicle). Section 9.4 covers why abruptness matters in terms of weight transfer and available grip.

SIPDE

S - Scan. Search the environment continuously and systematically: ahead to the 12-to-15-second eye lead, to the sides, to the mirrors on a schedule, and into the blind spots before any lateral movement.

Adding Scan makes a difference in teaching, not in theory. When a student misses a hazard entirely, "you did not identify it" is a conclusion; "your search pattern did not include the right-hand footpath" is a correction.

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How the process compresses

At low speed in light traffic, a driver can run the whole cycle deliberately with time to spare. As speed and complexity rise, the available time shrinks while the number of items to process grows. Two consequences follow.

The eye lead must lengthen with speed. A fixed distance gives less time at higher speed; a fixed time lead gives constant processing room. That is why the eye lead is taught in seconds.

Practised responses execute faster than reasoned ones. Rehearsal moves a response from deliberate decision to trained pattern. This is the justification for practising covering the brake, the emergency stop, and the wheel drop-off recovery in advance rather than explaining them.

When the cycle cannot complete in time, the result is one of the classic novice outcomes: no response at all (freezing), a partial response (braking but not steering), or a response to the wrong hazard.

Diagnosing which step failed

The instructional value of IPDE is diagnostic. When something goes wrong, locate the step.

Sharing that diagnosis with the student is itself instruction. "You identified it late" is far more actionable than "be more careful," and it maps directly onto Instructor Standard 3.7.1, which expects formative assessment to adjust instruction during the lesson.

Building the process across a course

Early lessons. Run IPDE aloud yourself while the student concentrates on vehicle control. The student hears the process modelled before being asked to produce it.

Middle lessons. Hand over one step at a time. Ask the student to identify only, then to identify and predict, then to add the decision.

Later lessons. The student runs the full cycle in commentary, and you intervene only on error.

Assessment. Ask the student to talk through a photograph or a dashcam clip using the four or five steps. This assesses the process without the confound of vehicle control, and it works as a classroom activity satisfying the perception and risk management standard.

[!WARNING] Exam traps in this section

• IPDE = Identify, Predict, Decide, Execute. SIPDE adds Scan at the front.
• Drive Right uses IPDE, and DOL names Drive Right as exam preparation.
• Decisions reduce to three families: change speed, change position, communicate.
• Minimise the hazard when two cannot both be avoided; separate the hazards when they can be met one at a time.
• The eye lead is measured in seconds, not feet, so it scales with speed.