Vehicle Control and Safety Physics

8. Vehicle Control and Safety Physics

The BTT evaluates the driver’s understanding of the physical limitations of the vehicle under various conditions.

The Two-Second Rule

Application: Used under normal, dry conditions.
Technique: The driver watches the vehicle ahead pass a fixed object (e.g., a lamp post) and counts “One-thousand-one, one-thousand-two.” If the driver passes the object before finishing the count, they are following too closely.
Rationale: This provides sufficient reaction time and braking distance.32

The Four-Second Rule

Application: Used in wet weather or poor visibility.
Rationale: Braking distance doubles on wet roads due to reduced tire friction. Therefore, the safe following gap must also be doubled.33

Stopping Distance is defined as the sum of Reaction Distance and Braking Distance.

Reaction Distance: The distance traveled while the driver perceives the hazard and moves their foot to the brake pedal. This remains relatively constant unless the driver is tired or intoxicated.
Braking Distance: The distance traveled after the brakes are applied. This increases exponentially with speed and is affected by road surface (wet vs. dry).
Assessment Scenario: Question: “What happens to the stopping distance on a wet road?” Answer: “It increases significantly (braking distance doubles).“.32

Singapore has extensive tunnel networks (KPE, MCE, CTE) which require specific safety protocols.18

Lighting: Drivers must turn on dipped headlights (not high beams) to ensure visibility and rear-light activation.
Lane Discipline: Lane changing is generally prohibited in tunnels (indicated by continuous white lines) to prevent side-swipe accidents in enclosed spaces.
Emergencies: In case of breakdown, turn on hazard lights. Do not stay in the vehicle if it is safer to evacuate to a cross-passage.
Prohibitions: Vehicles carrying dangerous goods are prohibited from entering tunnels.