Left-Turning Car at 90 Feet
At 40 mph, Ken is approaching a signalized intersection on a green light. A car in the opposing left-turn lane suddenly turns left across his path, about 90 feet ahead. The pavement is dry except for a painted crosswalk and a patch of sand just before it. Ken’s bike has no ABS. He has been riding for six months. His right hand is already covering the front brake, and he has about one second of reaction time before he must act. A box truck is in the lane to his right, slightly behind him. His rear brake pedal has a lot of travel before it bites. The car’s driver is looking left, not at Ken.
1. Ken has 90 feet and one second of reaction time at 40 mph. Roughly how much distance is left for braking, and what does that mean for his options?
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At 40 mph the bike covers about 59 feet per second, so one second of reaction uses about 59 feet and leaves roughly 31 feet. A skilled stop from 40 mph on clean, dry pavement takes far more than 31 feet, even with good brakes. That means braking alone cannot be counted on to stop before the car. Ken should squeeze the front brake progressively and use the rear brake, reducing speed as much as possible, while looking for an escape path. The right lane is occupied by the truck slightly behind him, so a blind swerve right is dangerous. He should not fixate on the car. If a gap opens, he can release some brake and swerve; if not, maximum braking to reduce impact speed is the best remaining choice.
2. What should Ken do if the rear wheel locks during braking?
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If the rear wheel locks, he should keep it locked and concentrate on the front brake and steering. Releasing a locked rear brake while the bike is sideways can cause a sudden high-side fall. A locked rear tire also gives little steering control, so he should not add lean. If the front wheel locks, that is different: he should release the front brake immediately and reapply it smoothly, because a locked front tire causes an immediate loss of steering and balance. The rear brake pedal’s long travel means it may need a firm push to do anything, so he should not assume the rear brake is helping. Smooth, progressive front-brake pressure is the priority.
3. Why are the painted crosswalk and the sand significant, and how should Ken adjust his braking?
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Painted road markings and sand have less grip than dry asphalt, especially when the tires are leaned or the brakes are applied hard. The crosswalk is a smooth painted band, and the sand is loose material that can slide under the front tire. Ken should do most of his braking before he reaches them, cross them as upright as possible, and avoid adding lean or a sudden brake increase on the paint or sand. If he must brake on the sand, he should use less front brake and more rear brake, or release the brakes briefly and reapply after the slippery patch. The lack of ABS means he cannot rely on the bike to prevent lockup, so his hand and foot must do that job.