General Knowledge: Space Management
37 questions in the bank cover this topic. Everything below is drawn from the sources those questions cite.
Sources: 49 CFR 392.62, Kinematics: total stopping distance as a sum of time-based and speed-squared terms, MUTCD 11th Ed. Section 2C.25, TC 21-305-20 para 13-18, TC 21-305-20 para 2-14, TC 21-305-20 para 2-18, TC 21-305-20 para 2-19, TC 21-305-20 para 3-46, TC 21-305-20 para 3-65, TC 21-305-20 para 3-66, TC 21-305-20 para 3-67, TC 21-305-20 para 3-68, TC 21-305-20 para 3-73, TC 21-305-20 para 3-74, TC 21-305-20 para 3-75, TC 21-305-20 para 3-76, TC 21-305-20 para 3-78, TC 21-305-20 para 3-80, TC 21-305-20 para 6-34
What you need to know
392.62(c) requires baggage or freight to be stowed and secured so as to assure unrestricted freedom of movement for the driver, unobstructed access to all exits, and protection of occupants from falling or displaced articles.
392.62(c) names all three.
Baggage or freight on the bus is stowed and secured in a manner which assures— (1) Unrestricted freedom of movement to the driver and his proper operation of the bus; (2) Unobstructed access to all exits
(3) Protection of occupants of the bus against injury resulting from the falling or displacement of articles transported in the bus.
49 CFR 392.62
392.62(a) requires all standees to be rearward of the standee line or other means prescribed in 393.90.
All standees on the bus are rearward of the standee line or other means prescribed in § 393.90 of this subchapter.
49 CFR 392.62
Four, not three.
You must notice the hazard, then move your foot, and the vehicle covers ground during both. On air brakes there is then a further lag of roughly half a second while pressure builds and the shoes move, before any slowing begins at all. Only after that does braking distance start. Brake lag is what makes an air-braked vehicle different from a car, so leaving it out understates the real distance.
*Why:* Total stopping distance = v*t_perception + v*t_reaction + v*t_lag + v^2/(2a). The first three terms are each a speed multiplied by a fixed time, so they grow linearly with v. The final term comes from F*d = (1/2)*m*v^2 with F = m*a, giving d = v^2/(2a), which grows with the square of v. Brake lag exists because air must travel the length of the system and build pressure in each chamber before the shoes contact the drum, so it has no equivalent in a hydraulic system.
Degraded grip lengthens everything, so both the time and the space needed to stop grow.
This is why following distance is adjusted to conditions rather than fixed, and why a gap that was adequate when dry is not adequate when wet.
Remember, when weather conditions have affected road conditions, more time and space is required to stop.
TC 21-305-20 para 3-68
The test is whether you can finish, not whether you can start.
A legal passing zone tells you the sight distance is normally adequate; it does not tell you whether it is adequate today, at your weight, behind that vehicle. You must be able to see far enough ahead to be sure of it.
An operator cannot pass safely unless they can see far enough ahead to be sure that they can get back in line before they meet any traffic coming from the opposite direction.
TC 21-305-20 para 3-73
Vehicles entering from a side road or a driveway occupy the lane you intend to return to, and they arrive without warning from a direction you are not watching while passing.
They must also be able to get back into line before meeting any traffic crossing or turning onto the road on which they are driving.
TC 21-305-20 para 3-73
Two feet is the common legal minimum.
On a long combination that gap also has to survive your trailer tracking inside your tractor's path through any curve in the pass.
The law in most localities requires a minimum clearance of two feet.
TC 21-305-20 para 3-74
Closing up first destroys the sight line you need to judge the pass and removes the space you would need if the vehicle ahead braked.
Move out first, then accelerate. If the vehicle ahead slows while you are tucked in behind it, you have nowhere to go.
Start to pass from a safe following distance. Move over to the left and speed up quickly. Do not speed up directly behind a vehicle and then turn out suddenly
TC 21-305-20 para 3-75
Not until you are back and settled.
Treating the pass as finished when you draw level is how drivers cut back in too early and strike the vehicle they have just passed. And settled, not merely clear of the other vehicle.
Passing is not complete until the operator of the passing vehicle has returned safely to their side
TC 21-305-20 para 3-76
Dangerous and often unlawful.
The driver you are passing is not looking for you there, and on a large vehicle your own blind spot on the right is the worst one you have.
Passing on the right may be dangerous and unlawful.
TC 21-305-20 para 3-80
Space ahead buys you braking; space beside buys you the swerve you need when braking has run out of room.
A driver boxed in on all sides has only one option left. Space beside you buys the escape that space ahead cannot.
Even if it is too late to stop or slow down, an operator may often avoid collisions by swerving to one side.
TC 21-305-20 para 3-46
Out first, then power.
Moving out restores the view ahead that the vehicle in front was blocking, so you accelerate into a space you can actually see.
Move over to the left and speed up quickly.
TC 21-305-20 para 3-75
Time.
Space and time are the same thing at speed, which is why managing space is really managing how long you have to decide. Space and time are the same thing at speed.
A safe operator will position his/her vehicle to ensure that there is ample space surrounding it. This space will give the operator time to think and act if something goes wrong.
TC 21-305-20 para 3-65
Three ways at once: it fills more road, needs more distance to stop and sweeps more room to turn.
Each one shrinks the margin a car driver takes for granted.
Larger vehicles occupy more space and require more space for stopping and turning.
TC 21-305-20 para 3-65
Ahead, because it is the only space you are actively driving into.
It is also the space you control directly, by choosing your following distance.
Of all the space around your vehicle, the area ahead of the vehicle – the space you are driving
TC 21-305-20 para 3-66
Less than 500 feet of visibility.
That is the sight distance you need for the whole maneuver, not just to start it. None of the figures offered is the one the rule gives.
On any curve or hill where visibility is less than 500 feet ahead.
TC 21-305-20 para 3-78
Both, because each is a place where something can enter your path from a direction you are not watching while committed to a pass.
At intersections and railway crossings.
TC 21-305-20 para 3-78
No.
The stopped vehicle is itself the warning, and it is also the thing hiding the pedestrian from you until the moment you draw level.
At crosswalks where a vehicle has stopped to allow a pedestrian to cross
TC 21-305-20 para 3-78
The line on YOUR side governs you.
A double line can be solid on one side and broken on the other, permitting a pass in one direction only.
Whenever there is a single or double solid line between lanes or when driver’s side lane of a double line is solid.
TC 21-305-20 para 3-78
Everything works against you at once: gravity adds speed, the brakes you would use are being saved, and a stop you planned for level ground now needs much more room.
As the vehicle operator approaches a downgrade, they should progressively select a gear that, when combined with the engine retarder, allows them to maintain an engine speed at the recommended RPM.
TC 21-305-20 para 13-18
Less traction means a longer stop from any given speed, so the time cushion that was adequate on dry road is no longer adequate at all.
Snow and ice reduce traction even more than a wet pavement does.
TC 21-305-20 para 6-34
Same direction, so a vehicle drifting across closes on you slowly rather than at combined speed.
That is a different kind of hazard from the one a yellow line warns about.
White lines separate lanes of traffic going in the same direction.
TC 21-305-20 para 2-18
A signal is a scheduled reason for the vehicle ahead to stop hard.
Space going in is what lets you stop with it rather than into it.
No traffic signal is more important than the traffic light
TC 21-305-20 para 2-14
They define the space allotted to you and the conditions for leaving it.
A solid line is a boundary; a broken one is a conditional permission. And the conditions on which you may leave them.
Pavement markings are widely used to control the flow of traffic
TC 21-305-20 para 2-19
It out-brakes you.
Matching its following distance means arriving where it stopped, at speed, with nowhere to go.
Remember, a smaller vehicle can stop faster than a larger vehicle.
TC 21-305-20 para 3-66
4 and 6, one second per 10 feet.
The longer vehicle needs more time for the same speed because more of it has to come to a stop.
For example, the operator of a 40-foot vehicle traveling at a speed below 40 MPH should leave 4 seconds between himself/herself and the vehicle ahead; in a 60-foot vehicle, 6 seconds.
TC 21-305-20 para 3-67
One extra second, flat, regardless of length.
Above 40 mph everything happens far enough faster that the length rule alone no longer leaves enough margin.
If the 40-foot vehicle is moving faster than 40 MPH, 5 seconds would be needed; for the 60-foot vehicle, 7 seconds.
TC 21-305-20 para 3-67
You manage it.
Most of it comes from choices you make early, your speed and lane position, rather than from reacting once somebody has closed on you.
In order to have ample space, the operator must manage space.
TC 21-305-20 para 3-65
It feeds traffic into your escape route.
You are committed to the opposing lane, and the space you planned to return to can be taken while you are in it. A side road feeds traffic into your escape route.
They must also be able to get back into line before meeting any traffic crossing or turning onto the road
TC 21-305-20 para 3-73
Deliberate clearance between the two flanks, not just whatever is left over.
A combination tracks inside its own path in any curve, so the gap you start with is not the gap you keep.
When passing a vehicle, the operator should give themselves sufficient distance between the right side of their vehicle and the left side of the other vehicle.
TC 21-305-20 para 3-74
Through the return and the settling.
Most of the risk sits at the end, where drivers cut back in early because the hard part feels finished.
Passing is not complete until the operator of the passing vehicle has returned safely to their side
TC 21-305-20 para 3-76
It is the space a sudden stop consumes.
Space behind and beside you matters, but neither helps if what is in front arrives sooner than you can shed speed.
the area ahead of the vehicle – the space you are driving into – is most important; in case you must suddenly stop
TC 21-305-20 para 3-66
Everyone, more so for you.
The same gap that is generous in a car is marginal behind 40 tons, because the vehicle needs more of it for everything. The same gap that is generous in a car is marginal behind 40 tons.
While this is true for all operators, it is especially important for those operators operating large vehicles.
TC 21-305-20 para 3-65
2C.25 makes it a Standard, so shall.
The threshold is the greater of 14 ft 6 in or 12 inches above the statutory maximum vehicle height.
The Low Clearance Advance (W12-2) sign (see Figure 2C-6) shall be used to warn road users of vertical clearances less than 14 feet 6 inches
MUTCD 11th Ed. Section 2C.25
Frost heave raises the road surface, which lowers the clearance.
The sign may already carry a reduction of up to 3 inches for it, which is why the posted figure is a floor and not a measurement of today.
in areas that experience changes in temperature causing frost action, a reduction, not exceeding 3 inches, should be used for this condition
MUTCD 11th Ed. Section 2C.25
Repaving adds height to the road, so the gap under the structure shrinks while the sign stays where it was.
The rule tells agencies to re-check after resurfacing, which tells you the sign can be out of date.
Clearances should be evaluated periodically to determine if additional low clearance signing is necessary, particularly when resurfacing operations have occurred
MUTCD 11th Ed. Section 2C.25
Check yourself
- What is required of baggage stowed on your bus?
- Where must standing passengers be positioned on your bus?
- What are the components that make up total stopping distance?
- What should you allow for space when weather affects road conditions?
- What must you be certain of before you start a pass?
- Besides oncoming traffic, what else must you be clear of before completing a pass?
- How much side clearance do most localities require when you pass?
- What should you avoid doing directly behind a vehicle before passing?
- When is a pass complete?
- What is the manual's rule on passing on the right?
- Why does keeping space beside you matter as much as space ahead?
- How do you begin a pass correctly?
- What does the space around your vehicle actually buy you?
- Why does space management matter more in a large vehicle?
- What part of the space around your vehicle matters most?
- Below what forward visibility is passing on a curve or hill always dangerous?
- Where does the manual say passing is always dangerous or unlawful?
- What must you do when a vehicle ahead stops at a crosswalk?
- What do the lane markings tell you about passing?
- Why does space ahead matter more on a downgrade?
- How should your following distance change on snow or ice?
- What does a white line beside your lane tell you about space?
- Why keep extra space approaching a signalled intersection?
- What do markings tell you about the space you may use?
- Why is the car ahead of you a particular problem?
- What following distances do a 40-foot and a 60-foot vehicle need under 40 mph?
- Above 40 mph, how does the following distance rule change?
- Is the space around your vehicle something that happens to you or something you do?
- What have you lost when a vehicle cuts in close ahead of you?
- Why does a side road matter to a pass you have already begun?
- What side clearance should you plan for when passing?
- Where does the space you need extend to during a pass?
- Why is the space ahead the most important of all?
- Does space management matter equally to all drivers?
- Below what height must a Low Clearance Advance sign be posted?
- Why can a posted clearance be lower than the real one?
- What can change a clearance after the sign goes up?
Answers are in the practice test for this topic.