4.2 Common Accidents and Speed on Curves
Key Takeaways
- Bus accidents often happen at intersections; use caution even if a signal or stop sign controls other traffic.
- School and mass-transit buses sometimes scrape off mirrors or hit passing vehicles when pulling out from a stop; remember the clearance the bus needs and watch for poles and tree limbs.
- Know the size of the gap the bus needs to accelerate and merge, wait for that gap to open, and never assume other drivers will brake to give you room when you signal or start to pull out.
- Curve crashes that kill people and destroy buses result from excessive speed, often when rain or snow has made the road slippery; a banked curve's posted speed may be safe for cars but too high for many buses.
- With good traction the bus may roll over; with poor traction it may slide off the curve. If the bus leans toward the outside on a banked curve, you are driving too fast — reduce speed for curves.
4.2 Common Accidents and Speed on Curves
Quick answer: Bus accidents often happen at intersections — use caution even if a signal or stop sign controls other traffic. When you leave a stop, wait for a gap large enough for the bus to accelerate and merge; never assume others will brake because you signaled. Slow for curves. Posted speed on a banked curve may be safe for cars and still too high for a bus. If the coach leans toward the outside, you are driving too fast.
CDL Manual 4.3.3 and 4.3.4 are the on-the-road crash pattern for passenger vehicles: intersections, pull-outs from stops, and curves taken too fast. The P knowledge test uses these as decision rules, not as slogans. A green light does not shrink a 40-foot coach. A blinker does not create a merge gap. An advisory plaque designed around automobile traction does not raise a bus's rollover threshold.
Intersections: the most common bus accident pattern
Bus accidents often happen at intersections. Use caution even if a signal or stop sign controls other traffic. That second sentence is the one riders and new drivers skip. A signal tells you who is supposed to stop. It does not tell you who will stop. Cross traffic still runs lights. Left-turning cars still cut across a bus that looks far away because it is large. A stop sign on the side street does not keep a driver from rolling into your path while looking the other way.
A passenger bus makes the intersection problem worse for three physical reasons:
- Length and overhang. The rear of the coach is still in the intersection after the front has cleared. A "safe" gap for a car can leave your tail in a conflict zone.
- Slow acceleration. You cannot dart through a stale yellow the way a sedan can. If you enter late, you occupy the box longer.
- Sight lines. Other drivers hide beside the bulk of the bus. You have to clear the near-side threat and the far-side threat separately, not with one glance.
Drive the intersection as if the other vehicle might not honor the control. Cover the brake earlier than you would in a car. Do not start a turn until the gap will still exist after the extra seconds a bus needs. Watch pedestrians who step off as if your size meant you could stop on a mark — you cannot.
| Intersection cue | What it does not mean | What you still do |
|---|---|---|
| Green light | Other traffic will hold | Scan left, right, and the crosswalk; be ready to stop |
| Stop sign on the cross street | Side-street drivers will stop | Approach as if someone may roll through |
| Your turn signal | Others have granted the space | Wait until the actual gap exists |
| Empty-looking far lane | The lane will stay empty | Recheck before you commit the length of the bus |
Leaving a bus stop: mirrors, poles, and the merge gap
School and mass transit buses sometimes scrape off mirrors or hit passing vehicles when pulling out from a bus stop. The stop is a tight workspace. Poles, benches, trash cans, and tree limbs sit closer to the curb than highway shoulders do. Mirrors stick out farther than the body. A pull-out that feels "close enough" in the seat can take a mirror off on a signpost or clip a passing car that you assumed would slow.
Remember the clearance the bus needs, and watch for poles and tree limbs at stops. Check the right-side mirror and the front right corner before you move. If a limb hangs into the mirror line, you wait or you inch with a spotter — you do not hope the fiberglass will flex.
Know the size of the gap the bus needs to accelerate and merge. Wait for the gap to open before leaving the stop. A bus does not jump into traffic. If you need several seconds and a long hole to reach lane speed, a hole that would work for a van is not a hole. Starting into a short gap and "asking" traffic to brake is how sideswipes and rear-end collisions happen at stops.
Never assume other drivers will brake to give you room when you signal or start to pull out. A signal is a request for attention, not a legal shove. Some drivers will pass you on the left while you are still on the curb. Some will close the gap because they think a bus always yields. Your job is to stay put until the gap is real.
Pull-out sequence that matches the manual
- Finish boarding so you are not rolling with people in the stepwell.
- Check poles, limbs, and mirror swing on the curb side.
- Check left-side traffic, including the lane you will occupy and the next lane if someone may pass.
- Judge whether the open space is large enough for this bus to accelerate and merge.
- Move only after that gap is actually there — not after you wish it were there.
Speed on curves
Crashes on curves that kill people and destroy buses result from excessive speed, often when rain or snow has made the road slippery. That is the 4.3.4 pattern. The curve does not have to look dramatic. A freeway ramp, a highway sweeper, or a downtown radius taken a little hot is enough when the center of gravity is high and the pavement is wet.
Every banked curve has a safe "design speed." In good weather, the posted speed is safe for cars but it may be too high for many buses. Design speed is an engineering number for a typical automobile on that bank. A loaded motorcoach or a transit bus with standing passengers is not that automobile. Higher center of gravity means the same speed that feels ordinary in a car can put the bus onto the outside wheels.
Two failure modes, one cause:
- Good traction: the tires hold, the bus may roll over.
- Poor traction: the tires let go, the bus might slide off the curve.
Either way, the input you can still control is speed. Reduce speed for curves. Do it before you enter, not after the lean starts. Braking hard in the curve upsets the same traction you are trying to keep.
The lean cue
If your bus leans toward the outside on a banked curve, you are driving too fast. The bank is supposed to help hold you down and in. Lean to the outside means speed has beaten the bank. That is not a comfort complaint from riders. It is a rollover warning. Slow on the next straight, and take the following curves slower still.
Rain, snow, ice, standing water, and polished pavement all lower the speed that was already too high for a bus on a dry day. If the posted number was marginal in the dry, it is not a target in the wet.
| Condition | What excessive speed tends to do | Driver response |
|---|---|---|
| Dry pavement, good traction | Rollover | Enter below the car-oriented posted/design speed |
| Rain or snow, poor traction | Slide off the curve | Reduce speed further before the curve |
| Bus leaning toward the outside of the bank | You are already too fast | Treat it as a speed error, not as normal body roll |
The P test will try to sell you the idea that a posted curve speed is a bus speed, or that a turn signal at a stop buys you a hole, or that a green light means you can treat the intersection like an empty street. None of those is the manual.
Where do bus accidents often happen, and what does that require of a passenger-endorsement driver?
You are pulling a transit or school bus away from a curb stop. Which statement is correct?
Your bus leans toward the outside of a banked curve. What does that tell you?