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Difficulty: HardAdjusting Margins in Ice and Snow

You are waiting to turn right from an ungritted side road onto a main road covered in compacted snow and ice. Traffic on the main road is travelling at moderate speed. How should you adjust your margin of safety when deciding whether to emerge?

  1. Wait for a much larger gap in traffic than usual, because your vehicle will accelerate much more slowly and approaching vehicles require up to ten times the distance to stop.Answer
  2. B
    Allow double the normal gap in traffic, assuming approaching vehicles can stop within wet-weather braking distances.
  3. C
    Emerge into a standard dry-weather gap, as the reaction time and thinking distance of approaching drivers remain unchanged on icy surfaces.
  4. D
    Emerge into a smaller gap by applying sharp acceleration in first gear to overcome tyre slip and join the traffic flow quickly.

Answer

Wait for a much larger gap in traffic than usual, because your vehicle will accelerate much more slowly and approaching vehicles require up to ten times the distance to stop.
In icy and snowy conditions, tyre grip is severely compromised. A driver pulling out from a junction cannot accelerate quickly without spinning the wheels and risking a skid. Simultaneously, approaching traffic requires up to ten times the standard dry stopping distance to brake safely. Therefore, drivers must wait for a much larger gap in traffic than normal before emerging.

Step-by-Step Solution

1
Assess vehicle acceleration limitations on ice
Recognise that low tyre grip significantly hinders acceleration when emerging from a standstill, increasing the time needed to complete the turn.
Harsh acceleration causes wheelspin on snow and ice, requiring gentle clutch control and a higher gear where possible, which slows down the entry manoeuvre.
2
Evaluate the stopping capabilities of approaching traffic
Acknowledge that approaching vehicles on packed snow and ice may take up to ten times normal distance to stop.
If an approaching driver is forced to react to an emerging vehicle, their braking distance is vastly extended, preventing rapid emergency deceleration.
3
Determine the necessary safety margin
Conclude that a substantially larger gap in traffic is mandatory in both directions before committing to emerge.
The combination of slow vehicle entry speed and severely degraded braking capability of oncoming vehicles requires an expanded buffer zone.

Key Concept

Adjusting junction gap selection to account for severely reduced traction and up to tenfold stopping distances on ice and snow.
Estimated Time:1m 0s
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Adjusting Margins in Ice and Snow

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