9 ms·

Kinematics of Reverse Angle Parking

138 points by mourner 7y ago

barrkel 7y ago
Why is the interactive diagram on this page so much slower in Firefox than Chrome?
Bigpet 7y ago
It's interesting how quickly analytically solving this problem gets almost impossible (the problem being 'given a start position and a desired end position, how do you maneuver there). I've had a lecture that was basically just about this class of problems. But it was concerning trucks and how adding additional axes and especially adding even one trailer joint (but especially two) made solving this conventionally impossible. With some funky transformations into other number-spaces there were some analytic solutions for it though.
- mourner 7y ago
  Yep! It can be solved for some specific cases though — e.g. I stumbled upon a few papers that calculate the optimal path for parallel parking using systems of differential equations [1][2] [1] https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7463491 https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7463491 [2] http://www.tsi.lv/sites/default/files/editor/science/Research_journals/Tr_Tel/2012/V4/zadachyn_dorokhov.pdf http://www.tsi.lv/sites/default/files/editor/science/Researc...
deleted 7y ago
[deleted]
_pmf_ 7y ago
That's great.
tom_ 7y ago
I need to sit down and work it out on paper, but as a long standing reverse parking fan - I can't park forwards, as it's too difficult - I don't think the diagram shown here is quite right. When going backwards at low speeds, the fact there are two rear wheels is very important! When reversing when turning fully left, the left rear wheel stays pretty much where it is; when reversing when turning fully right, the right rear wheel behaves that way. OK - well, this is of course not quite true, because the car is moving, and so it's not quite rotating around a fixed point. But it's close enough that you can pretty much start your reverse parking manoeuvre by putting one wheel in the right place, so its contact point is lined up with wherever it ultimately needs to be - but it doesn't really matter which angle, provided it's within 45° or so. Then turn full lock in that direction (left for left wheel, right for right wheel), on the spot, and slowly reverse until the other wheel is lined up too. Now you're done. Straighten the front wheels and go in backwards. It's handy to bear in mind the swept volume, as there will be some overhang, but when going in backwards with this technique you don't typically have to worry about it too much. (Making the wheels turn on the spot is not the best thing, but you can fix this once you're confident with the basic manouevre.)
- doublement 7y ago
  Watch out for bikes and pedestrians please. Few people expect a car (especially on the other side of the street/lane) to drift by a space then reverse into it after passing it by.
  - downerending 7y ago
    I've seen this. In addition, it's much harder to spot pedestrians that might suddenly enter the space (and may not have an easy way to get out).
    - jschwartzi 7y ago
      This is one of many reasons why parking maneuvers should be performed slowly. I once turned into a space to park only to encounter a woman on the other side of her housewife panzer tank. The only reason I didn't hit her was that I was going about 5 miles per hour the entire time, so when she came into view I could just put my foot on the brake and stop gently. Contrast this with drivers I've seen who will haul ass into a parking space at 15 MPH and then brake immediately.
  - Hamuko 7y ago
    You should be expecting it if the car is indicating, which is something you should do when you're about to park.
    - doublement 7y ago
      If a person is walking north, about to walk past a parking space, and a car is heading south and signaling left, it's very surprising to see the car pass the person by, then suddenly reverse and try to enter the space. Once the car is past, most people assume it's signaling to turn farther along, instead of about to go backwards. EDIT: To be clear, I'm describing a perpendicular-parking scenario, where people usually make a right angle turn going forward to occupy the space.
- mourner 7y ago
gugagore 7y ago
This page by the same author is also fantastic: https://observablehq.com/@mourner/non-robust-arithmetic-as-art https://observablehq.com/@mourner/non-robust-arithmetic-as-a...
- mourner 7y ago
  Thank you! A fellow programmer Jacob even printed that viz as a woven textile — floating point errors can be very pretty :) https://twitter.com/jashkenas/status/1191829600214507520 https://twitter.com/jashkenas/status/1191829600214507520
exabrial 7y ago
Given the example show, I would make this a much easier problem by pulling across the center line onto the opposite side of the street, then steering back towards the right hand side. I would time this so I'm parallel with the lines. Now it's a simple back-in job since you're already lined up. This may or may not be a legal traffic maneuver where you live and obviously can only be performed with both lanes clear.
- mourner 7y ago
  There's just one lane here — the thick line at the top is a barrier (a line of bollards).
  - massysett 7y ago
    Even so, the thing to do here is first turn the wheel to the right and pull past the parking space and pull up to the bollards, then back in.
- gowld 7y ago
  That trades one problem -- knowing how far to pull forward and how sharply to turn -- for another: known when and how sharply to turn toward the oncoming traffic lane.
  - archi42 7y ago
    The technique described by GP kind of does, but you don't have to get the first part of the maneuver perfect - it just reduces your angle relative to the parking spot. The backward driving then then fixes bad alignment and having a non-0 angle (but with limited space you might need iterate using back-and-forth moves). Also, for OP: You'll often find that getting into a spot is difficult, but getting out again is trivial. Obviously you could try to just reverse the "leaving movement" as part of your parking maneuver. This can help with finding the perfect spot for starting the parking maneuver.
mhb 7y ago
Control Schemes of Steering System of a Multi-axle All-wheel-steering Robot: https://news.ycombinator.com/item?id=21893476 https://news.ycombinator.com/item?id=21893476
- mourner 7y ago
  Awesome! This paper uses the same model for calculating wheel angles (Ackermann steering geometry).
itronitron 7y ago
I don't think I have ever seen a parking area with reverse-angle parking. Any angled parking usually has signs to make it clear that cars must park forward facing only. Having said that, it would be nice to see this adapted to parallel parking since that is a much more common parking scenario.
- mourner 7y ago
  Observable makes it easy to fork notebooks and make modifications, so I'll be happy to see other parking arrangements! I made the viz for my real-world situation — reverse angle parking is quite common where I live (Ukraine), and it's the type where we got our parking spot (took a long time since all the spots around my apartment complex are sold out). https://en.wikipedia.org/wiki/Back-in_angle_parking https://en.wikipedia.org/wiki/Back-in_angle_parking
jws 7y ago
For those in regions without reverse angle parking (like me)… It's used in areas where you might have roadside parking along a road, either parallel or angled. It has higher linear density than parallel and is easier/faster. Compared to forward angled parking it removes the "backing out into traffic you can't see because your rear pillars and the hausfrauenpanzer next to you have completely blocked view of the oncoming traffic" (so you go slow and figure any drivers coming down the road don't want to die today either). You safe the road by stopping to park, and have road visibility as you back in. Coming out you get better visibility because your upstream neighbors corner is further from the traffic and your eyeballs are also closer. An added bonus is that bicyclists have very little reason to ride in the zone of opening doors, compared to parallel parking. Some places it is popular. Changing to it from forward angled makes people crabby. https://en.wikipedia.org/wiki/Back-in_angle_parking https://en.wikipedia.org/wiki/Back-in_angle_parking
- jessriedel 7y ago
  What's the advantage over back-in perpendicular parking? I don't actually think your eyeballs are closer to the road (since the diagonal to your front corner is longer than the line to your nearest headlight), and you can always force neighboring cars to be further away by just painting the lines wider apart. At first I wondered if the road can be slightly narrower while still allowing one to get into the parking space, but if you look in the OP article at how the orange envelope is shaped by the way the front end swings around, I don't really think that's the case. In general, I'm confused about why angle parking is picked over perpendicular parking. It's significantly less linear density (reduced by the factor cos(theta)), but the square shape of cars means the road width occupied by the parking is hardly less. (The wasted space is the triangular patches between the parked cars and the road/sidewalk.) Parallel parking has even lower linear density, of course, but takes half the road width.
  - brudgers 7y ago
    90 degree parking requires wider drive aisles because more of the forward/reverse turning radius is required...all of it.
  - 7y ago
shkkmo 7y ago
What's missing from this model is a variable rate of turn. You want to turn so that your front bump stays at roughly a fixed distance from the bollard line. As you go, you slowly turn the wheel sharper and sharper until reach your maximum turn radius or you are lined up with your space. You can slightly vary that fixed distance as you go to adjust for minor differences in your initial position. You can also aim for a bit to the right/far side of the space (, and then re-center on the space once you are lined up.
- spectramax 7y ago
  Yea, this whole piece misses the fact that when a human is doing this maneuver, planning for all inputs is dynamic (not pre-cached) using feedback loop. We adjust as necessary (unless hitting a limit) to put the car in place. It is not like we plan the whole process and then close our eyes, execute all inputs and voila! car is now parked!
- mourner 7y ago
  Yeah, the model is definitely contrived and I could try adding a lot more to it, but I still found it very useful just to understand how the path changes with the wheel turn. Also, as a beginner, it's very hard to "feel" how much you're supposed to turn with variable rate — I guess this only comes with a ton of practice. In the driving school, the way we were taught all the parking maneuvers is to reverse straight until you catch some reference point, then immediately turn to the max for the sharpest turn.
Animats 7y ago
Amusingly, I have to solve this problem for a minor game project. Drivers have to back their trucks into a loading dock. Players aren't good enough drivers to do this without assistance, so I have to write an assistance system that yells "Left", "Right", "Straight", "Slow", "Stop", etc. as appropriate.
PhasmaFelis 7y ago
This may be obvious, but for me, reverse parking got a lot easier once I realized that (on my Mini Cooper) if I pull forward until my B-pillar is exactly aligned with the next dividing line past the space I want to enter, then I can reverse into it almost without looking. (Does that make sense? I'm not great at describing visual concepts.) Presumably there's a spot like this on every car; you just have to figure out where it is.
- mourner 7y ago
  That's a great cue! Seems to work on the viz too (if you set x = 6.7m & y = 2.6m). BTW Mini Cooper look like the perfect car for parking conveniently in tight spots.
  - PhasmaFelis 7y ago
    Oh gosh yes, it's the best. I can do a two-point turn in a narrow parking lot lane if I have to. It's actually shorter even than the original Beetle, but has amazing front-seat leg room (a big part of why I chose it) and plenty of trunk space if you fold down one or both rear seats. The rear seats themselves are mostly decorative unless you have very short friends/family. It's not a good car for four people. But for one or two, it's amazing.
- ferongr 7y ago
  You should use the rear axle as a guidline, not the B-pillar, it's more accurate, and it's how a 2-point reverse turn is taught to be done by driving instructors here. Driving exams involve performing a 2-point reverse turn with the rear inside wheel not going further away than 1 meter from the kerb, no more than two stops (except for traffic/safety related reasons), no more than one engine stall, no forward movement and no contact with the kerb itself.
  - PhasmaFelis 7y ago
    > Driving exams involve performing a 2-point reverse turn with the rear inside wheel not going further away than 1 meter from the kerb Which curb? I'm mostly parking in lots with perpendicular parking on both sides of the lane. The only curb involved is the one at the back of the space I'm backing into (unless there's a pull-through from the other side, then not even that).
chrissnell 7y ago
I learned to reverse into spaces in the military. That's the way that all military vehicles are supposed to be parked. I started doing this in my civilian vehicles and found that once you get the hang of it, it's absolutely the best way to park a car. Once you have the skill--and spatial awareness--you will find that it's much easier to get straight into a space with this method. Leaving the space is obviously easier, too. I drive a large Ram pickup truck and backing in is pretty much the only way that I can park it accurately.
gwbas1c 7y ago
FWIW: A good backup camera helps you visualize this. Both of my cars have lines that curve as I turn the wheel.
- mourner 7y ago
  Yep, mine has it too and it's super helpful! What I have more trouble with is feeling when the right front side is about to collide when the car sways in the other direction — there is some beeping proximity detector but it doesn't seem to work well against bollards.
- Jamwinner 7y ago
  A car with good 360 visibilty is even better, although the virtual top-down is getting close, it lacks the subconsious intergration with the motion perception and people still hit things more. Tldr: please turn your head, and use your mirrors.
csours 7y ago
I was sure this would be related to Matt Parker's recent video on back-in parking: https://www.youtube.com/watch?v=0rxghexCKj8 https://www.youtube.com/watch?v=0rxghexCKj8
- mourner 7y ago
  Nice video! I only saw it a few hours ago when I was about to post my viz on /r/math :)
allovernow 7y ago
Slightly related - when reverse parked and pulling out of a 90 degree parking spot with the wheel turned, is it possible for the rear outside corner of the vehicle to clip an adjacent vehicle? In other words, if you were reverse parked, pulling out turning left, and you plotted the track of the outermost portion of the right rear fender/bumper, would it ever cross the rightmost edges of the wheelbase in the parked position?
- mourner 7y ago
  Good question! Since the model is reversible (you would have the same trajectory when pulling out of the parking lot when reversing the steps), you can see the effect there — seems like it would cross the rightmost edges but very slightly (like 10cm) in my case, but protrusion would be bigger with a car that has a bigger rear overhang (e.g. sedan rather than hatchback). You can try it out by tweaking the constants in the car specs section.
Stratoscope 7y ago
For anyone in the Palo Alto area who wants to try this out in person, the first block of Stanford Avenue next to the Dish trail entrance converted to reverse angle parking a while ago: https://www.google.com/maps/@37.4110349,-122.1605769,294m/data=!3m1!1e3 https://www.google.com/maps/@37.4110349,-122.1605769,294m/da...
war1025 7y ago
The key to reverse parking (parallel parking is a bit more complex) is to make good use of your side mirrors and the fact that if you can see a cap between your car and whatever the object is, then you're on course not to hit the thing. Then it just becomes a matter of course-correcting your way to where you want to be, which is pretty easy after a little practice.
- clarry 7y ago
  Where does the cap come from? I assume you mean gap, but when you start reversing and are not aligned with your parking spot yet, the thing you'll soon see in the rear mirror is the car parked in the next slot. No gap. Idk about other people but I feel like I've got very bad depth vision in general, and telling how far my car's rear is from a wall or another car when looking through the mirror is very difficult.
  - war1025 7y ago
    Yes I meant gap. Just typing too quick and not reading closely enough.
  - war1025 7y ago
    When you are not aligned and you don't see a gap between your car and the thing next to you, that is the signal that you need to turn more in order to get where you want to be. Regarding how far back to go, I find that it's the same problem as parking forward. You just need to figure out how to judge some reference point on your car with whatever is around you. I agree that's one of the trickier things to figure out.
    - clarry 7y ago
      Yeah, the problem with turning is that you don't exactly turn in place, and if you're too far backward, you'll back into the thing you're trying to turn next to.. Forward parking sure has the same issue but for me at least it's much easier to assess depth right in front of me than 2-3 meters behind, through a little mirror. And I mean I can park in front of a wall and leave a 15-20 cm gap between the bumper and wall without much trouble, but it is seriously difficult for me to say whether there's half a meter or one and a half between my rear and the next object. I guess they invented reverse cameras for a reason, I just haven't bought one.

138 points by mourner 7y ago

Why is the interactive diagram on this page so much slower in Firefox than Chrome?

It's interesting how quickly analytically solving this problem gets almost impossible (the problem being 'given a start position and a desired end position, how do you maneuver there). I've had a lecture that was basically just about this class of problems. But it was concerning trucks and how adding additional axes and especially adding even one trailer joint (but especially two) made solving this conventionally impossible. With some funky transformations into other number-spaces there were some analytic solutions for it though.

mourner 7y ago
Yep! It can be solved for some specific cases though — e.g. I stumbled upon a few papers that calculate the optimal path for parallel parking using systems of differential equations [1][2] [1] https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7463491 https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=7463491 [2] http://www.tsi.lv/sites/default/files/editor/science/Research_journals/Tr_Tel/2012/V4/zadachyn_dorokhov.pdf http://www.tsi.lv/sites/default/files/editor/science/Researc...

deleted 7y ago

[deleted]

_pmf_ 7y ago

That's great.

tom_ 7y ago

I need to sit down and work it out on paper, but as a long standing reverse parking fan - I can't park forwards, as it's too difficult - I don't think the diagram shown here is quite right. When going backwards at low speeds, the fact there are two rear wheels is very important! When reversing when turning fully left, the left rear wheel stays pretty much where it is; when reversing when turning fully right, the right rear wheel behaves that way. OK - well, this is of course not quite true, because the car is moving, and so it's not quite rotating around a fixed point. But it's close enough that you can pretty much start your reverse parking manoeuvre by putting one wheel in the right place, so its contact point is lined up with wherever it ultimately needs to be - but it doesn't really matter which angle, provided it's within 45° or so. Then turn full lock in that direction (left for left wheel, right for right wheel), on the spot, and slowly reverse until the other wheel is lined up too. Now you're done. Straighten the front wheels and go in backwards. It's handy to bear in mind the swept volume, as there will be some overhang, but when going in backwards with this technique you don't typically have to worry about it too much. (Making the wheels turn on the spot is not the best thing, but you can fix this once you're confident with the basic manouevre.)

doublement 7y ago
Watch out for bikes and pedestrians please. Few people expect a car (especially on the other side of the street/lane) to drift by a space then reverse into it after passing it by.
- downerending 7y ago
  I've seen this. In addition, it's much harder to spot pedestrians that might suddenly enter the space (and may not have an easy way to get out).
  - jschwartzi 7y ago
    This is one of many reasons why parking maneuvers should be performed slowly. I once turned into a space to park only to encounter a woman on the other side of her housewife panzer tank. The only reason I didn't hit her was that I was going about 5 miles per hour the entire time, so when she came into view I could just put my foot on the brake and stop gently. Contrast this with drivers I've seen who will haul ass into a parking space at 15 MPH and then brake immediately.
- Hamuko 7y ago
  You should be expecting it if the car is indicating, which is something you should do when you're about to park.
  - doublement 7y ago
    If a person is walking north, about to walk past a parking space, and a car is heading south and signaling left, it's very surprising to see the car pass the person by, then suddenly reverse and try to enter the space. Once the car is past, most people assume it's signaling to turn farther along, instead of about to go backwards. EDIT: To be clear, I'm describing a perpendicular-parking scenario, where people usually make a right angle turn going forward to occupy the space.
mourner 7y ago

gugagore 7y ago

This page by the same author is also fantastic: https://observablehq.com/@mourner/non-robust-arithmetic-as-art https://observablehq.com/@mourner/non-robust-arithmetic-as-a...

mourner 7y ago
Thank you! A fellow programmer Jacob even printed that viz as a woven textile — floating point errors can be very pretty :) https://twitter.com/jashkenas/status/1191829600214507520 https://twitter.com/jashkenas/status/1191829600214507520

exabrial 7y ago

Given the example show, I would make this a much easier problem by pulling across the center line onto the opposite side of the street, then steering back towards the right hand side. I would time this so I'm parallel with the lines. Now it's a simple back-in job since you're already lined up. This may or may not be a legal traffic maneuver where you live and obviously can only be performed with both lanes clear.

mourner 7y ago
There's just one lane here — the thick line at the top is a barrier (a line of bollards).
- massysett 7y ago
  Even so, the thing to do here is first turn the wheel to the right and pull past the parking space and pull up to the bollards, then back in.
gowld 7y ago
That trades one problem -- knowing how far to pull forward and how sharply to turn -- for another: known when and how sharply to turn toward the oncoming traffic lane.
- archi42 7y ago
  The technique described by GP kind of does, but you don't have to get the first part of the maneuver perfect - it just reduces your angle relative to the parking spot. The backward driving then then fixes bad alignment and having a non-0 angle (but with limited space you might need iterate using back-and-forth moves). Also, for OP: You'll often find that getting into a spot is difficult, but getting out again is trivial. Obviously you could try to just reverse the "leaving movement" as part of your parking maneuver. This can help with finding the perfect spot for starting the parking maneuver.

mhb 7y ago

Control Schemes of Steering System of a Multi-axle All-wheel-steering Robot: https://news.ycombinator.com/item?id=21893476 https://news.ycombinator.com/item?id=21893476

mourner 7y ago
Awesome! This paper uses the same model for calculating wheel angles (Ackermann steering geometry).

itronitron 7y ago

I don't think I have ever seen a parking area with reverse-angle parking. Any angled parking usually has signs to make it clear that cars must park forward facing only. Having said that, it would be nice to see this adapted to parallel parking since that is a much more common parking scenario.

mourner 7y ago
Observable makes it easy to fork notebooks and make modifications, so I'll be happy to see other parking arrangements! I made the viz for my real-world situation — reverse angle parking is quite common where I live (Ukraine), and it's the type where we got our parking spot (took a long time since all the spots around my apartment complex are sold out). https://en.wikipedia.org/wiki/Back-in_angle_parking https://en.wikipedia.org/wiki/Back-in_angle_parking

jws 7y ago

For those in regions without reverse angle parking (like me)… It's used in areas where you might have roadside parking along a road, either parallel or angled. It has higher linear density than parallel and is easier/faster. Compared to forward angled parking it removes the "backing out into traffic you can't see because your rear pillars and the hausfrauenpanzer next to you have completely blocked view of the oncoming traffic" (so you go slow and figure any drivers coming down the road don't want to die today either). You safe the road by stopping to park, and have road visibility as you back in. Coming out you get better visibility because your upstream neighbors corner is further from the traffic and your eyeballs are also closer. An added bonus is that bicyclists have very little reason to ride in the zone of opening doors, compared to parallel parking. Some places it is popular. Changing to it from forward angled makes people crabby. https://en.wikipedia.org/wiki/Back-in_angle_parking https://en.wikipedia.org/wiki/Back-in_angle_parking

jessriedel 7y ago
What's the advantage over back-in perpendicular parking? I don't actually think your eyeballs are closer to the road (since the diagonal to your front corner is longer than the line to your nearest headlight), and you can always force neighboring cars to be further away by just painting the lines wider apart. At first I wondered if the road can be slightly narrower while still allowing one to get into the parking space, but if you look in the OP article at how the orange envelope is shaped by the way the front end swings around, I don't really think that's the case. In general, I'm confused about why angle parking is picked over perpendicular parking. It's significantly less linear density (reduced by the factor cos(theta)), but the square shape of cars means the road width occupied by the parking is hardly less. (The wasted space is the triangular patches between the parked cars and the road/sidewalk.) Parallel parking has even lower linear density, of course, but takes half the road width.
- brudgers 7y ago
  90 degree parking requires wider drive aisles because more of the forward/reverse turning radius is required...all of it.
- 7y ago

shkkmo 7y ago

What's missing from this model is a variable rate of turn. You want to turn so that your front bump stays at roughly a fixed distance from the bollard line. As you go, you slowly turn the wheel sharper and sharper until reach your maximum turn radius or you are lined up with your space. You can slightly vary that fixed distance as you go to adjust for minor differences in your initial position. You can also aim for a bit to the right/far side of the space (, and then re-center on the space once you are lined up.

spectramax 7y ago
Yea, this whole piece misses the fact that when a human is doing this maneuver, planning for all inputs is dynamic (not pre-cached) using feedback loop. We adjust as necessary (unless hitting a limit) to put the car in place. It is not like we plan the whole process and then close our eyes, execute all inputs and voila! car is now parked!
mourner 7y ago
Yeah, the model is definitely contrived and I could try adding a lot more to it, but I still found it very useful just to understand how the path changes with the wheel turn. Also, as a beginner, it's very hard to "feel" how much you're supposed to turn with variable rate — I guess this only comes with a ton of practice. In the driving school, the way we were taught all the parking maneuvers is to reverse straight until you catch some reference point, then immediately turn to the max for the sharpest turn.

Animats 7y ago

Amusingly, I have to solve this problem for a minor game project. Drivers have to back their trucks into a loading dock. Players aren't good enough drivers to do this without assistance, so I have to write an assistance system that yells "Left", "Right", "Straight", "Slow", "Stop", etc. as appropriate.

PhasmaFelis 7y ago

This may be obvious, but for me, reverse parking got a lot easier once I realized that (on my Mini Cooper) if I pull forward until my B-pillar is exactly aligned with the next dividing line past the space I want to enter, then I can reverse into it almost without looking. (Does that make sense? I'm not great at describing visual concepts.) Presumably there's a spot like this on every car; you just have to figure out where it is.

mourner 7y ago
That's a great cue! Seems to work on the viz too (if you set x = 6.7m & y = 2.6m). BTW Mini Cooper look like the perfect car for parking conveniently in tight spots.
- PhasmaFelis 7y ago
  Oh gosh yes, it's the best. I can do a two-point turn in a narrow parking lot lane if I have to. It's actually shorter even than the original Beetle, but has amazing front-seat leg room (a big part of why I chose it) and plenty of trunk space if you fold down one or both rear seats. The rear seats themselves are mostly decorative unless you have very short friends/family. It's not a good car for four people. But for one or two, it's amazing.
ferongr 7y ago
You should use the rear axle as a guidline, not the B-pillar, it's more accurate, and it's how a 2-point reverse turn is taught to be done by driving instructors here. Driving exams involve performing a 2-point reverse turn with the rear inside wheel not going further away than 1 meter from the kerb, no more than two stops (except for traffic/safety related reasons), no more than one engine stall, no forward movement and no contact with the kerb itself.
- PhasmaFelis 7y ago
  > Driving exams involve performing a 2-point reverse turn with the rear inside wheel not going further away than 1 meter from the kerb Which curb? I'm mostly parking in lots with perpendicular parking on both sides of the lane. The only curb involved is the one at the back of the space I'm backing into (unless there's a pull-through from the other side, then not even that).

chrissnell 7y ago

I learned to reverse into spaces in the military. That's the way that all military vehicles are supposed to be parked. I started doing this in my civilian vehicles and found that once you get the hang of it, it's absolutely the best way to park a car. Once you have the skill--and spatial awareness--you will find that it's much easier to get straight into a space with this method. Leaving the space is obviously easier, too. I drive a large Ram pickup truck and backing in is pretty much the only way that I can park it accurately.

gwbas1c 7y ago

FWIW: A good backup camera helps you visualize this. Both of my cars have lines that curve as I turn the wheel.

mourner 7y ago
Yep, mine has it too and it's super helpful! What I have more trouble with is feeling when the right front side is about to collide when the car sways in the other direction — there is some beeping proximity detector but it doesn't seem to work well against bollards.
Jamwinner 7y ago
A car with good 360 visibilty is even better, although the virtual top-down is getting close, it lacks the subconsious intergration with the motion perception and people still hit things more. Tldr: please turn your head, and use your mirrors.

csours 7y ago

I was sure this would be related to Matt Parker's recent video on back-in parking: https://www.youtube.com/watch?v=0rxghexCKj8 https://www.youtube.com/watch?v=0rxghexCKj8

mourner 7y ago
Nice video! I only saw it a few hours ago when I was about to post my viz on /r/math :)

allovernow 7y ago

Slightly related - when reverse parked and pulling out of a 90 degree parking spot with the wheel turned, is it possible for the rear outside corner of the vehicle to clip an adjacent vehicle? In other words, if you were reverse parked, pulling out turning left, and you plotted the track of the outermost portion of the right rear fender/bumper, would it ever cross the rightmost edges of the wheelbase in the parked position?

mourner 7y ago
Good question! Since the model is reversible (you would have the same trajectory when pulling out of the parking lot when reversing the steps), you can see the effect there — seems like it would cross the rightmost edges but very slightly (like 10cm) in my case, but protrusion would be bigger with a car that has a bigger rear overhang (e.g. sedan rather than hatchback). You can try it out by tweaking the constants in the car specs section.

Stratoscope 7y ago

For anyone in the Palo Alto area who wants to try this out in person, the first block of Stanford Avenue next to the Dish trail entrance converted to reverse angle parking a while ago: https://www.google.com/maps/@37.4110349,-122.1605769,294m/data=!3m1!1e3 https://www.google.com/maps/@37.4110349,-122.1605769,294m/da...

war1025 7y ago

The key to reverse parking (parallel parking is a bit more complex) is to make good use of your side mirrors and the fact that if you can see a cap between your car and whatever the object is, then you're on course not to hit the thing. Then it just becomes a matter of course-correcting your way to where you want to be, which is pretty easy after a little practice.

clarry 7y ago
Where does the cap come from? I assume you mean gap, but when you start reversing and are not aligned with your parking spot yet, the thing you'll soon see in the rear mirror is the car parked in the next slot. No gap. Idk about other people but I feel like I've got very bad depth vision in general, and telling how far my car's rear is from a wall or another car when looking through the mirror is very difficult.
- war1025 7y ago
  Yes I meant gap. Just typing too quick and not reading closely enough.
- war1025 7y ago
  When you are not aligned and you don't see a gap between your car and the thing next to you, that is the signal that you need to turn more in order to get where you want to be. Regarding how far back to go, I find that it's the same problem as parking forward. You just need to figure out how to judge some reference point on your car with whatever is around you. I agree that's one of the trickier things to figure out.
  - clarry 7y ago
    Yeah, the problem with turning is that you don't exactly turn in place, and if you're too far backward, you'll back into the thing you're trying to turn next to.. Forward parking sure has the same issue but for me at least it's much easier to assess depth right in front of me than 2-3 meters behind, through a little mirror. And I mean I can park in front of a wall and leave a 15-20 cm gap between the bumper and wall without much trouble, but it is seriously difficult for me to say whether there's half a meter or one and a half between my rear and the next object. I guess they invented reverse cameras for a reason, I just haven't bought one.