Left Turn into a 5.5 m Street with a Mirror at 3.3 m
An 8.7 m medium box truck - width 2.29 m, wheelbase 4.8 m, rear overhang 2.4 m, box top 3.45 m, gross 6.9 t loaded, cargo floor 1.1 m - must turn left from a two-lane road into a 5.5 m residential side street in Kyoto. The corner radius is about 6 m, a guardrail runs along the far side of the side street, and a convex road mirror is mounted on a pole at 3.3 m on the near corner.
A cyclist is stopped in the 路側帯 on the truck's left, slightly behind the cab and outside the driver's direct view. A pedestrian waits on the corner. The road surface is damp and the light is flat and grey. Minimum turning radius at the outer front wheel is 7.4 m.
1. Explain why the rear wheels will track inside the front wheels' path, roughly how far inside, and what that means for the guardrail on this corner.
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This is 内輪差 - off-tracking. The front wheels steer; the rear wheels simply follow the rear axle, cutting the corner. The offset grows with wheelbase and shrinks as the turn radius opens out, approximated by L²/2R.
At the minimum radius here the offset is over 2 m: with a 4.8 m wheelbase the rear inner wheel can pass more than two metres inside the path of the front inner wheel. In this gentler 6 m turn it will still be on the order of 1.5 m. Meanwhile the 2.4 m rear overhang swings its outer corner outward, beyond the front wheel track, by a few tens of centimetres as the turn begins.
The consequence for the guardrail: if she positions the cab close to the corner and turns, the rear body will sweep over the corner and the rear wheels will run the inside line - the guardrail, the kerb, and the pedestrian standing there are exactly in that band. She must start wide, take the turn slowly enough to watch the left mirror throughout, and be ready to stop mid-turn rather than complete it. The rear overhang swinging out is the corresponding risk on the right-hand side of the street.
2. What must she do about the cyclist, and what does the Road Traffic Act require of a medium goods vehicle specifically when turning left?
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The cyclist sits in the classic blind band: beside and slightly behind the cab on the left, invisible from the driving position, and still visible in the left mirror if she looks before committing.
Law. 道路交通法第34条 governs left turns, and its provisions for large and medium goods vehicles require such a vehicle, before turning left, to move as far as practicable to the left edge of the road and to stop immediately before the near-side edge of the intersection to confirm safety before proceeding. Her truck at 6.9 t gross is a 中型貨物自動車, so this stop applies to her. It is not a formality: it forces the mirror check at the moment the cyclist is most likely to arrive alongside.
Practice. Signal early, check the left mirror, then a direct glance through the left door window and the 間接視野装置, stop at the edge, check again, and only then turn - slow enough that if the cyclist does roll forward into the blind area, the truck stops rather than closes the gap. On a damp surface her stopping distance is longer, so the approach speed must be lower to begin with.
3. How should she handle the overhead mirror and the vehicle's height, and what is the safe sequence for the whole turn?
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Height first. The box top is 3.45 m; the mirror is at 3.3 m. There is no clearance - a 150 mm conflict, and posted heights on street furniture are often approximate. Clipping a mirror pole brings the pole and the mirror down onto the cab, the cyclist or the pedestrian. Height is a go/no-go question asked before the turn begins, not during it. She should stop short of the corner, verify the geometry from the cab and, if there is no usable margin, take another route: no amount of steering skill fixes 150 mm.
If clearance is confirmed on another approach, the sequence is: indicate early; move to the left edge; stop before the intersection edge and check the mirror, the left blind area and the corner; take the turn at walking pace, starting wide to allow for 1.5 m of off-tracking and watching the left mirror for the rear body and guardrail; be prepared to stop mid-turn; and keep the rear overhang clear of the right-hand kerb. The damp road shortens nothing - it only lengthens stopping distance.