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Socket Ryanist
Aug 30, 2004

Behold, the 360-degree freeway onramp!

http://maps.google.com/maps?q=san+f....00284&t=h&z=19

(with a parking lot in the middle of it of course)

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Socket Ryanist
Aug 30, 2004

Cichlidae posted:

Yep, the loop is necessary to gain the elevation to get to the second deck of the freeway!
The freeway only has one deck though?

Socket Ryanist
Aug 30, 2004

Green arrows mean the same thing and are less confusing, so why?

Socket Ryanist
Aug 30, 2004

I pity anyone who lives on treasure island because fuuuuuck

http://maps.google.com/maps?f=q&sou...002401&t=h&z=19

There's about 10 car-lengths between the stop sign and a merge with 50+ mph traffic (as high as 70 sometimes). Fuuuuuck!

Socket Ryanist
Aug 30, 2004

Dominus Vobiscum posted:

That's an odd one, given that they're trying to reduce the amount of text on signs. I can't imagine it'd be used anywhere other than intersections with a history of right-turning vehicles running into people making u-turns. Why not just prohibit u-turns instead?
Because people making U-turns have the right of way (as they have a green light, and not a red one). The sign is just informative.

Sometimes people need to make u-turns! (roads with medians and they need to enter a driveway on the opposite side).

Socket Ryanist
Aug 30, 2004

Berkeley, california has something which is kind of like a fused grid or new urbanist design but a little simpler: It was originally built with a plain old grid, but afterwards, they blocked off certain movements to cars (only cars, bicycles can still use them). To a pedestrian, it's pretty much indistinguishable from a regular grid, but from a driver's perspective, it's much more like a hierarchy or fused grid.

Socket Ryanist
Aug 30, 2004

Cichlidae posted:

What method do they use to block motorists? Are there barriers, curbs, and grass, or do they just put up turn restriction signs and pavement? Obviously, the former is much nicer, and in areas that have already been built up, it seems like a great way to encourage other modes of transportation and lower speeds on minor roads.
They use a couple different methods. The most common one is a pair of concrete "barrels" that are just wide enough apart for a car to go through, and then a little metal thing sticking up that most cars are too low to clear but firetrucks/ambulances can clear easily.

here's an example

Socket Ryanist
Aug 30, 2004

Minister Robathan posted:

One thing I've always wondered about stack interchanges, specifically 4-level stacks, is why they make everything cross at the centre, instead of spreading the ramps out (provided there's enough room). Like in this case, it *seems* that it would be cheaper to not have all the ramps cross directly at the centre, in order to cut down on the height required. The difference in cost might actually be marginal compared to the cost of the enlarged footprint, but I was wondering if there's any specific reason that it's done in this way.
The answer is turning angle. Having it this way provides the gentlest possible curve and therefore lets people maintain speed through the intersection, which is important for freeway-freeway interchanges.

Someone posted a "three level stack" (I forget what they called it) early, which looks kind of like a spiral.

Socket Ryanist
Aug 30, 2004

Ah here it is:

Cichlidae posted:


This is a turbine interchange. It feels like you're driving down a toilet.

What I don't get is why one pair of turning ramps is underneath the straight-through roads. It would make sense to me for both sets of turning ramps to go above, and the straight-through to stay level, since gravity would help you with your deceleration and acceleration.

Socket Ryanist fucked around with this message at 09:52 on Aug 11, 2009

Socket Ryanist
Aug 30, 2004

Cichlidae posted:

One funny thing about this interchange that you may have noticed: the West to East through lanes exit from the right. Any guesses as to why this happened?
They're not really through lanes. The freeway which comes in from the left ceases to be a freeway after the interchange: the road on the right is a rather inconsequential (as far as I can tell) surface street. US 6 (which was on the freeway) takes a right turn and follows 95 south, and then 195 over the river (whereas I am guessing that it previously followed the above-noted surface street)

Either that, or it has something to do with that lone, out-of-place looking building which looks like it would be in the way of making the through lanes stay on the left.

Socket Ryanist
Aug 30, 2004

Calast posted:

OP, thank you so much. This thread has been amazingly fascinating, and I'm learning compassion for the people who have to deal with fixing such amazing SF Bay Area traffic nightmares as:

http://maps.google.com/maps?f=q&sou...004892&t=h&z=18

That one there, they're planning on making it a dogbone roundabout. (If it's unclear, there's no stop on Gilman, it's four lanes wide there, and all the intersections on the sides have stops. It's a nightmare.)
Oh god gently caress that exit! So many times coming southbound (westbound?) on 80 and having to make a left.... I shudder :(

They should just make it a four-way stop like the similar Central exit further up north. A roundabout would make more sense but that costs $$$, a couple extra stop signs would do a BIG help and not cost $$$

Re: wrong-way multiplexes, in the san fernando valley they just sign "Ventura fwy east, ventura fwy west" rather than 101 north/south (ventura fwy is also 138 I think?)

Socket Ryanist
Aug 30, 2004

There's a big party venue I go to that has three dancefloors, a coat check, bathrooms and the main entrance all connected by a rotunda, which turns into a giant traffic jam as people are moving around.

I've suggested to several people putting a pole in the middle and telling people to walk counterclockwise.

Socket Ryanist
Aug 30, 2004

Samurai Sanders posted:

Another question you may not be able to answer: why would a road construction crew ever do their work right in the middle of a very busy street, right in the middle of the Goddamned day? Because it's been going on for months now on my way to work. Why not do the work at night, like they usually do on the highways?
Night work = overtime pay

Socket Ryanist
Aug 30, 2004

Wikipedia says that campus used to be an air force base, so I would guess that red line is a former runway

Socket Ryanist
Aug 30, 2004

Lobstaman posted:

Why not put a barrier toll on the wee bit of I-684 that passes through Greenwich, where there are no on or off ramps for CT drivers.
NYDOT maintains that stretch

Socket Ryanist
Aug 30, 2004

nm posted:

No, most states don't have this. Most states make it a standard strict liablity crime to do over XX mph.
A lot of states have a prima facie law. I can think of 5 off the top of my head and I'm pretty sure the number is between 15-20, but yeah most states it's absolute.

Socket Ryanist
Aug 30, 2004

Does anyone besides california have the magic "Sometimes I'm a lane and sometimes I'm parking!" lanes that we do? Do these actually help?

Socket Ryanist
Aug 30, 2004

Choadmaster posted:

I should note that there is an upper limit to the 85th percentile rule; I think it's 55 MPH. Anything more than that they get to set wherever they please.

Edit: 55 is also the default speed limit on a highway if not otherwise posted. There's a strange stretch of the aforementioned highway near my house where there's an "End 35 Speed Limit" sign and then a quarter mile later a "Speed Limit 35" sign. I think that short stretch exits the city border and the county never felt it worth the money to do a survey for that quarter mile. There are no intersections or driveways, so I try to take advantage of that short 55 MPH stretch as best as possible :D.
Actually the default speed limit is 65 for a road that has a median or more than one lane in either direction, and 55 for an undivided two-lane road (or one-lane one way street).

Socket Ryanist
Aug 30, 2004

Well regardless of the default speed limit you also have to follow the Basic Speed Law -- don't drive at an unsafe speed.

Posting a speed limit sign won't help you much because, in california, speed limits below 55 mph are not absolute--they are only prima facie evidence of unsafe speed. That is, if you are going 54 in a 25, but can prove in a court of law that there was nothing unsafe about going 54 in a 25, then you get acquitted (This is actually not as hard as you might assume it is).

Socket Ryanist
Aug 30, 2004

Okay correcting myself: the default absolute maximum speed is what I posted before. The default prima facie speed limit is:

CVC 22352 posted:

(1) Fifteen miles per hour:

(A) When traversing a railway grade crossing, if during the last 100 feet of the approach to the crossing the driver does not have a clear and unobstructed view of the crossing and of any traffic on the railway for a distance of 400 feet in both directions along the railway. This subdivision does not apply in the case of any railway grade crossing where a human flagman is on duty or a clearly visible electrical or mechanical railway crossing signal device is installed but does not then indicate the immediate approach of a railway train or car.

(B) When traversing any intersection of highways if during the last 100 feet of the driver's approach to the intersection the driver does not have a clear and unobstructed view of the intersection and of any traffic upon all of the highways entering the intersection for a distance of 100 feet along all those highways, except at an intersection protected by stop signs or yield right-of-way signs or controlled by official traffic control signals.

(C) On any alley.

(2) Twenty-five miles per hour:

(A) On any highway other than a state highway, in any business or residence district unless a different speed is determined by local authority under procedures set forth in this code.

(B) When approaching or passing a school building or the grounds thereof, contiguous to a highway and posted with a standard "SCHOOL" warning sign, while children are going to or leaving the school either during school hours or during the noon recess period. The prima facie limit shall also apply when approaching or passing any school grounds which are not separated from the highway by a fence, gate, or other physical barrier while the grounds are in use by children and the highway is posted with a standard "SCHOOL" warning sign. For purposes of this subparagraph, standard "SCHOOL" warning signs may be placed at any distance up to 500 feet away from school grounds.

(C) When passing a senior center or other facility primarily used by senior citizens, contiguous to a street other than a state highway and posted with a standard "SENIOR" warning sign. A local authority is not required to erect any sign pursuant to this paragraph until donations from private sources covering those costs are received and the local agency makes a determination that the proposed signing should be implemented. A local authority may, however, utilize any other funds available to it to pay for the erection of those signs.

Socket Ryanist
Aug 30, 2004

How about putting an island in the middle of the road with a sign on it, or putting in rumble strips a little bit before the crosswalk on either side? That's what europeans would do.

Socket Ryanist
Aug 30, 2004

Commuters do support public transit funding though: They want OTHER people to stop driving so that the roads will be nice and empty for them to drive on!

Socket Ryanist
Aug 30, 2004

Sgs-Cruz posted:

Or maybe it wouldn't work because you'd have too high of a burden of proof in showing that it's truly not a new company. Frustrating, anyway.
This is one of the problems with corporate ownership, in general. For companies which are sole props or partnerships of a small number of people, accountability is pretty easy.

Socket Ryanist
Aug 30, 2004

Some freeways in Chicago actually have three roadways, with the middle, reversible roadway having periodic ramps to and from the outer ones.

Socket Ryanist
Aug 30, 2004

Cichlidae posted:

What method do they use in Chicago to keep traffic from entering in the wrong direction? Bollards?
Overhead LED signs I think, possibly with cones? Nothing solid.

Socket Ryanist
Aug 30, 2004

Pagan posted:

First, in areas like that, do you guys make sure it's easy to "escape"? I noticed that the curbs on the median were sloped, instead of square, so it was easier to drive over. When designing stuff like that, do you anticipate that ppl will gently caress it up, and give them ways out?
I think freeways (interstate highways in particular) are required to have sloped curbs. I'm pretty sure this is because accidentally hitting a sloped curb at 70 mph has a way lower chance of resulting in your car flipping over.

Socket Ryanist
Aug 30, 2004

It's illegal to enter ANY intersection if you do not have a clear exit. The ones marked with boxes are just particularly troublesome intersections.

Socket Ryanist
Aug 30, 2004

California still hasn't gotten around to enforcing "Signal before you turn" and "Stop at stop signs", so I dunno how long we are to enforcing those.

Socket Ryanist
Aug 30, 2004

One particularly egregious mistake in my hometown is that, on some intersections, the stop bar is painted beyond an unmarked crosswalk (legally, you have to stop before the crosswalk, even though the stop bar is painted past it). Combine this with hedges that reduce your visibility of the sidewalk and bicyclists who go down the sidewalks at decent speeds and you have accidents waiting to happen.

Socket Ryanist
Aug 30, 2004

smackfu posted:

Yeah. It's really the town that should be forcing Walmart to improve the roads, like they do when people want to put in new developments. There's a power imbalance though, because the town really wants that tax revenue, but Walmart doesn't care too much which town it builds in. So the town can't really hardball it.
They're not going to get much tax revenue when their residents lose their jobs because the stores they previously worked for are now out of business.

Socket Ryanist
Aug 30, 2004

Nexis posted:

In a CBD (Central Business District) you generally do not have pushbuttons on the signals. In the city we had ~300 signals downtown, all 2 phase with peds. It generally is not worth installing pushbuttons since the signals aren't actuated anyway. Just bring the ped up every time the phase comes in.
What about nighttime?

Socket Ryanist
Aug 30, 2004

Nexis posted:

Nope, pretimed. Peds come up every cycle.
Huh, even at intersections between a major street and minor street?

Socket Ryanist
Aug 30, 2004

Cichlidae posted:

Yes, that's less than 1,000 feet of 2-lane section on an on-ramp. What's the point?
That looks like a badly-painted gore that someone mistook for a lane, to me.

Socket Ryanist
Aug 30, 2004

What's with this?
http://maps.google.com/?ie=UTF8&ll=37.844948,-122.297656&spn=0.001192,0.00284&t=k&z=19

The right lane was gained from the entrance ramp of the previous exit, and instead of being forced to exit, the exit splits off and then the right lane immediately ends.

What's the advantage of this over just forcing the right lane to exit?

Edit: Also, I wish more states would do what California does and change the dashed lines to indicate that a lane is about to end or split off. It's very helpful!

Example here: The "faster" dotted lines indicate where the split is going to be http://maps.google.com/?ie=UTF8&ll=37.73301,-122.412259&spn=0.001194,0.00284&t=k&z=19

Socket Ryanist fucked around with this message at 23:43 on Oct 24, 2009

Socket Ryanist
Aug 30, 2004

Cichlidae posted:

Wow, that's monumentally complicated. I'd need to spend my career working with those interchanges to have any hope of effectively improving them. Providing sufficient capacity here is the main concern, and meeting all the standards is secondary. The most cost-effective solution, once freeways get this big, is to build bypasses and otherwise reduce the volumes. Increasing capacity at this point is a losing battle; adding more lanes would make some weaving problems, and the right-of-way just isn't there.
There ARE bypasses--they have worse traffic than that interchange does!

Socket Ryanist
Aug 30, 2004

Cichlidae posted:

More bypasses, then! Dozens and dozens of concentric rings. Raze the city and pave the whole thing!
The only way to fix it is to flush it all away

Socket Ryanist
Aug 30, 2004

Here's an interesting interchange:

http://maps.google.com/?ie=UTF8&ll=40.891683,-72.483845&spn=0.02378,0.038409&t=k&z=15

As you can see, there is an exit on westbound 27 for the road which just diverged from it, which is kind of silly and redundant and I don't know why it even existed in the first place.

Additionally, the split to the right used to have an eastbound connection from the upper road, with a traffic light where it crossed westbound 27. People eventually realized this was silly (since there're several other ways to get there and there isn't that much traffic) and just killed the road and turned it into a U-turn ramp.

Socket Ryanist
Aug 30, 2004

How would you fix this clusterfuck of an intersection?

I would block off the lower left (santa fe ave) and upper right (oakview ave) legs of the intersection, turning them into cul-de-sacs (with pedestrian and bicycles allowed through) and turn it into a two-way stop with curtis/berkeley park having stop signs and colusa having none.

Socket Ryanist
Aug 30, 2004

Cichlidae posted:

Dump the on-street parking, make the island a circle, put in truck aprons if needed, and widen the approaches a bit. It's important to remember that a roundabout will operate more efficiently than an all-way stop in all situations.
Aren't the two approaches on the left a little bit too close together to do that?

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Socket Ryanist
Aug 30, 2004

Cichlidae posted:

You could dead-end one of them, as you mentioned before, or just fool around with the geometrics until it works. Better yet, why not transform the southwestern Santa Fe Avenue into one-way eastbound? It would preserve business access, add more on-street parking, and fix the geometric issue.
Street view shows only one business on that road and it's on the corner, or maybe I'm not looking closely enough...

The top road labeled "santa fe ave" is actually colusa, google maps labeled it wrong.

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