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On my commute to work, there's an intersection where one direction always has a red signal when the opposite direction has a green signal. The only sign is "delayed green." This means you can safely turn left when the light is green. There is no left turn arrow. I would say this is pretty confusing to anyone who is not familiar with this intersection. Would you ever design something like this? I can see its usefulness if there's a good balance of cars turning left and going straight, but surely there are less confusing options?
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Aug 6, 2009 12:26
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Cichlidae posted:A month ago, when we had the tornado in Wethersfield and really nasty hail, I was driving past at the right time to see it lose power and it went into flashing yellow. May as well just have it turn off, there's no need to slow down. To answer your question, though, there are a few reasons. Thanks. Yet another lesson here: Just because it's being done on state highways doesn't necessarily mean it's in the MUTCD. You should do a post on signal warrants once you're done with interchanges.
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Aug 6, 2009 13:33
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Cichlidae posted:The issue there, if you're talking about the curvature, is the slope. On a freeway, you should keep the slope below 3 percent, but can knock it up to a few percent more if you put up some warning signs. Trucks still hate it, though. So, what can we do? Two obvious answers pop up: level the mountain, or go through it. I think the former is squarely out of the picture, so let's talk tunnels.
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Aug 6, 2009 14:18
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 Pic 1 Pic 2There's a parking lot in my town where the exit has a right-turn only lane to turn onto the four-lane highway, and the other lane turns left onto the highway and goes straight onto a two-lane side street. The problem is, the parking lot has no arrows on the pavement indicating this (which, obviously, is the owner's responsibility, not the city's), and the traffic light controlling the intersection doesn't use a directional arrow in the right-turn only lane. Common sense dictates that the right lane is for right turns only, but to be honest, it can be difficult from that position to see that the left lane is the one the continues straight into that side street, because of the way the road curves. Last night I had a woman almost hit the right side of my car trying to go straight in the right-turn only lane. (Luckily there was no oncoming traffic and I was able to just move to the left and let her pass--I don't think she ever realized her mistake.) So basically I was where that silver car is, headed in the direction of the Goodyear, and she was to the right of me. Problem is, in addition to there being no idiot signs, both our traffic lights display solid green. My question is, would there be a problem with giving the right lane a directional arrow? There are no sidewalks, and thus no pedestrian traffic to yield to, but maybe I'm overlooking something. Would it be worth my time to talk to the city? Please pardon my rambling and lack of proper engineering terminology. At least I didn't write 10 pages about span wire.
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Aug 6, 2009 15:11
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Cichlidae posted:I've collected a few varieties of diamond interchanges for your benefit. These are just variants on diamonds, and it's still not a complete collection. Let me know if you'd like to see more, otherwise I'll move on to weird ones like SPUI and spupclos. These posts remind me when I was a little kid and I'd find those Audobon Society Fieldguides. I'd flip to the pictures section and just look at all the different examples of rocks or bugs or whatever. These posts rock, though I'm waiting with baited breath for Congestion 102. As far as that picture you posted earlier about engineers screwing up, was that the case where the loop was build much earlier (say the 60's) with weaker long haul trucks in mind, with the straight shot built later?
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Aug 6, 2009 15:46
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Cichlidae posted:Double rights aren't all that common, for a few reasons. We try to avoid them anywhere they're not strictly necessary. How about a triple right? That turn can actually get fairly exciting, as a lot of the traffic using that ramp is heading for the left turn lane to Spring Road that begins right there. Technically the leftmost right turn lane connects to the #2 lane on Cobb Parkway, but usually at least half the traffic in the middle right turn lane (and even some people in the rightmost turn lane) will also be trying to make the left onto Spring Road and will just barrel over that way no matter where the traffic in the left-hand right turn lane is going, so using the leftmost right turn lane to go straight down Cobb is dangerous during rush hour. Making matters worse is the fact that the #3 and #4 lanes on Cobb both become right-turn-only lanes within three blocks, so if you use either of the inner right-turn lanes, you'll have to shove your way over yourself very quickly if you're going any further down Cobb Parkway. (That's actually a rather common thing around here, it seems; there are some stretches of road where the right-hand lane will be a left-turn-only lane within a few blocks...) Spring Road itself also has a double right turn lane onto Cobb Parkway, but it's usually much calmer.
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Aug 6, 2009 16:20
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There's a thing at one intersection in my hometown that I've never understood. There's a signal at the intersection of Main and Forest, and if you're traveling northwest on Main Street, there's a No Turn On Red at that intersection. But there's no traffic which could possibly be hit by a right turn on red, since the only green is on Forest Street.
Der Metzgermeister fucked around with this message at 16:40 on Aug 6, 2009 |
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Aug 6, 2009 16:33
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Another thing that kills me about Atlanta is that they are constantly turning off the traffic signals downtown, usually for several blocks around the building I work at. On rare occasions they'll have police directing traffic, but usually not, and a lot of times when they turn 'em off, they blink yellow one direction and red another, not red in all directions. Trying to cross a five-lane one-way street during rush hour with no signal is really fun. My favorite moment was one busy evening when they turned off all of the signals along Centennial Olympic Park and had no police directing traffic, but instead put a police officer at this intersection where the traffic signal was still on. The best part was that he was directing traffic completely opposite the still-working signal. If you can't tell from Google Maps, the intersection is completely blind from both streets due to the bushes in the median. I fully expected to get creamed by some dude racing down Spring Street who saw the green light instead of the nearly invisible cop standing on the side of the road with his hand out.
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Aug 6, 2009 17:05
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Wombot posted:Ah, 2 RTOR lanes, my favorite part of exiting SR 520 in Bellevue, WA. Yep, that's a pretty good explanation of why we don't like double rights! Whoever put dual RTOR in there, though, was crazy. Cars shouldn't pull onto the crosswalk in any case, because it makes peds cross behind them, which hinders visibility. quote:Bonus: Yep, I've driven over the pontoon bridges there. I've always wondered how they keep up with the tides. Is the road flexible enough that it just bends along with them, or is there a ramp? And the video of how they open is pretty neat.
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Aug 6, 2009 17:13
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PessiMister posted:On my commute to work, there's an intersection where one direction always has a red signal when the opposite direction has a green signal. The only sign is "delayed green." This means you can safely turn left when the light is green. There is no left turn arrow. I would say this is pretty confusing to anyone who is not familiar with this intersection. Would you ever design something like this? I can see its usefulness if there's a good balance of cars turning left and going straight, but surely there are less confusing options? That, as I mentioned once before, is called split phasing. You can see what I have to say about it here. It's not an ideal configuration, because it restricts capacity, but it's often warranted on safety grounds. There is a similar configuration that can handle a large left-turning volume with relative ease, and that's the lead left, also called an advance left. It works like this (if you don't remember the phase numbers I taught earlier, just look at the arrows): 
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Aug 6, 2009 17:20
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Can you give an opinion on this recently modified intersection? I don't have any complaints about it, and never used it before, but it was just changed and Id like your opinion.   Click here for the full 990x1000 image. edit: the NB I80 exit Ts into douglas with a double right turn. D'oh! ilkhan fucked around with this message at 17:27 on Aug 6, 2009 |
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Aug 6, 2009 17:24
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Dominus Vobiscum posted:Thanks. Yet another lesson here: Just because it's being done on state highways doesn't necessarily mean it's in the MUTCD. Oh boy, that's going to be a fun lesson! Wouldn't my life be easier if everyone knew that you actually need a REASON to put in a signal?  I can't back out of my driveway in my 20-foot car! I need a traffic signal! I almost got rear-ended at this stop sign! Put a signal in now! Think of the children! If you don't put in a signal out here in the middle of nowhere, who knows how many little angels you're killing? It's hard to turn out of Dunkin Donuts when I'm being chased by the illuminati. Please signalize... but don't use a mast arm, or I'll murder you. But you put a light up at the bottom of that freeway offramp, why not my pissant residential street? Do you hate low-income families?
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Aug 6, 2009 17:26
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nm posted:The problem is that much of the traffic is often tryoing to reach areas that would be bypassed by such a tunnel. It's not unheard of to put ramps going to and from the tunnel itself. In fact, it would make evacuation that much easier in the case of an emergency. It's not like the whole thing has to be a tunnel, anyway, just the really rough bits that limit capacity.
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Aug 6, 2009 17:28
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Elijah posted:
The best option there is to have a lane use sign put up. You might have trouble finding who needs to pay for it, but a sign is pretty cheap and doesn't need much maintenance. For a small entrance like that, I'd put one on the side of the road and one on the span. Heck, print this out and bring it to the town engineer; that should solve things:  Really, though, it depends on who owns the signal. If it's a state signal, the state will put up the signs, but whoever owns the driveway will have to pay for it. Either way, in a few years, the new MUTCD will come out and require private property owners to meet the regulations. Then you go up to whoever owns that driveway and wave it in his face.
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Aug 6, 2009 17:40
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Solkanar512 posted:These posts remind me when I was a little kid and I'd find those Audobon Society Fieldguides. I'd flip to the pictures section and just look at all the different examples of rocks or bugs or whatever. These posts rock, though I'm waiting with baited breath for Congestion 102. I really have no idea. That road is in Italy, and that's waaaaaay out of my jurisdiction. The grade doesn't look terribly steep, and there's plenty of embankments already. If you're ever near Naples, though, go and have a look. Be sure to report back with any findings!
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Aug 6, 2009 17:41
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How about this exit in Denver? (no googlemaps link; for some reason trying to get it to agree to Kipling & I70 puts it at Kipling & 6th Ave  ) The red lines are the left turn routes you'd expect to have to take, and green is the route you have to take to not get back on I-70. Admittedly, I've only been driving for 6 months or so, but that one always gets me. I seem to always end up trapped in the left lane, right beside someone that doesn't realize following the normal turn pattern puts you.. back on I70. It's the only one I've seen with a layout that annoying. Though Kipling & 6th Ave has the awesome 100 foot enter/exit merge lane, which is really, really safe during rush hour. Unrelated, what's the point of having obscenely long turn-only lanes? Southbound Wadsworth turning left onto 29th is a great example here, it's at least 1000 feet long, and solid white line for >90% of that, which is way out of range to see what street it is. It's hardly a busy intersection, and since you can technically get a ticket for crossing the solid line, what were they aiming for? "Let's make everyone do a U-turn!"?
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Aug 6, 2009 17:45
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dennyk posted:How about a triple right? That turn can actually get fairly exciting, as a lot of the traffic using that ramp is heading for the left turn lane to Spring Road that begins right there. Technically the leftmost right turn lane connects to the #2 lane on Cobb Parkway, but usually at least half the traffic in the middle right turn lane (and even some people in the rightmost turn lane) will also be trying to make the left onto Spring Road and will just barrel over that way no matter where the traffic in the left-hand right turn lane is going, so using the leftmost right turn lane to go straight down Cobb is dangerous during rush hour. Making matters worse is the fact that the #3 and #4 lanes on Cobb both become right-turn-only lanes within three blocks, so if you use either of the inner right-turn lanes, you'll have to shove your way over yourself very quickly if you're going any further down Cobb Parkway. (That's actually a rather common thing around here, it seems; there are some stretches of road where the right-hand lane will be a left-turn-only lane within a few blocks...) Yep, that's pretty bad. When confronted with the kind of volumes that warrant three right turn lanes, an engineer has to sit back and seriously think about building another ramp or flyover somewhere. In this situation, it could be worthwhile to add another ramp from 285 that connects to Circle 75 Parkway SE. Of course, having a road with three through lanes to receive the triple right is a problem, too. In that case, as you mentioned, it's weaving that gets to be a pain.
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Aug 6, 2009 17:47
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Der Metzgermeister posted:There's a thing at one intersection in my hometown that I've never understood. There's a signal at the intersection of Main and Forest, and if you're traveling northwest on Main Street, there's a No Turn On Red at that intersection. But there's no traffic which could possibly be hit by a right turn on red, since the only green is on Forest Street.
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Aug 6, 2009 17:51
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Cichlidae posted:The issue there, if you're talking about the curvature, is the slope. On a freeway, you should keep the slope below 3 percent, but can knock it up to a few percent more if you put up some warning signs. Trucks still hate it, though. So, what can we do? Two obvious answers pop up: level the mountain, or go through it. I think the former is squarely out of the picture, so let's talk tunnels. Naw, I mean the quality of the road, I have no problem going down it, or coming up it, even heavy. I worry that in tunnels they stay colder, longer so they are slick as poo poo. Donner is always in a state of major road damage. Is there any surface to lay down to stop this?
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Aug 6, 2009 18:02
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Not really a nuisance, but something I've never seen before- http://tinyurl.com/ox6z3q It got cut off, but First Colonial Rd is the main road heading North-South Driving in Virginia Beach from North Carolina, these were a bit confusing at first. The main Laskin Rd in yellow has no side driveways. But, being a highly retail-oriented area, to get to the shops on the side, one must turn onto the secondary Laskin Rd and go from there. Which is all fine and dandy, until you're trying to leave the shops and get back onto Laskin Rd. For example, say you're coming from the east on the secondary road, trying to proceed west on the main road. There are cars waiting to turn left from First Colonial Rd and go in the same direction as you're heading. How are you supposed to make your "right then left" turn from the secondary road, without first turning left onto First Colonial, making a U-Turn, then following the rest of traffic?
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Aug 6, 2009 18:44
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Thanks for the thread! It's been an enlightening read. Wanna take a crack at this one? Google maps Hmm, Google got its labels mixed up that's actually Cedar St. -- MLK is a couple miles west. Traffic volumes on Cedar and Edgewood are both pretty high, also high on Pennsylvania but not as high as the other two. Notice the grade level crossing of the two ramps just east of Edgewood/Cedar with only yield signs. By far the worst is traveling on southbound Cedar trying to get to I96. You need to make an unprotected left onto ramp, survive the at-grade crossing, then the merge in from the left, then the rush of lane switching around the curve as cars queue up for eastbound or westbound 96. The department of transportation has this intersection scheduled for complete replacement in 2010, but they haven't release the final plan yet. Apparently the finalists are "one giant signaled intersection" and "a series of roundabouts". What are your thoughts?
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Aug 6, 2009 19:43
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Cichlidae posted:Let me know if you guys are ready for the weird stuff! A lot of it is purely theoretical, so I won't be able to find real-world examples. Exciting, non? Hell yeah, bring on the crazy stuff, even if it is just the product of a fever dream, or an idle mind trying to escape the pain of having to deal with people wanting signals for their driveway.
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Aug 6, 2009 20:00
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Cichlidae posted:Yep, I've driven over the pontoon bridges there. I've always wondered how they keep up with the tides. Is the road flexible enough that it just bends along with them, or is there a ramp? And the video of how they open is pretty neat. Well, tides aren't an issue, as both the I-90 and SR-520 bridges are over Lake Washington. The real problem is severe weather. One of my first memories is actually watching the old I-90 floating bridge sink on Thanksgiving '90. They do have flex points built between the pontoons, but get a bad enough storm, and it'll rip them to pieces. Actually, Interceptor, do you ever drive your rig over SR-520 when you're up this way, or do you stick to I-90 because you're not that loving insane?
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Aug 6, 2009 20:56
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dennyk posted:Another thing that kills me about Atlanta is that they are constantly turning off the traffic signals downtown, usually for several blocks around the building I work at. On rare occasions they'll have police directing traffic, but usually not, and a lot of times when they turn 'em off, they blink yellow one direction and red another, not red in all directions. Trying to cross a five-lane one-way street during rush hour with no signal is really fun. We usually allow our signals to blink yellow for the artery, and red for the side street. Signals in low-volume locations switch over to blinking at night in order to save power. It tends to move people through a little faster, too. In high-volume locations, the opposite is true, as you found out. Having just one signal down on a major road is a big deal, and merits 24-hour service to get it running again. I don't know why Atlanta would shut them off constantly. quote:My favorite moment was one busy evening when they turned off all of the signals along Centennial Olympic Park and had no police directing traffic, but instead put a police officer at this intersection where the traffic signal was still on. The best part was that he was directing traffic completely opposite the still-working signal. If you can't tell from Google Maps, the intersection is completely blind from both streets due to the bushes in the median. I fully expected to get creamed by some dude racing down Spring Street who saw the green light instead of the nearly invisible cop standing on the side of the road with his hand out. Wow, that is pretty awful. It's possible that some of the vehicle detectors were broken, so the officer was still needed, but the signal should have been shut off. Is there any possibility that your cops just want lots of overtime, and ask the state to shut off signals so they can put some time in?
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Aug 6, 2009 21:46
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ilkhan posted:Can you give an opinion on this recently modified intersection? I don't have any complaints about it, and never used it before, but it was just changed and Id like your opinion. It looks just fine, except for one thing:  Those two ramps that merge into the loop... they are redundant! You only need one. There could be some nuance that I can't see under the yellow line, but it certainly looks like one should be removed. I like how there are two extra ramps (I can't see the cross street's name, but it goes from that to Pager Pass Rd, and from Pager Pass to 80). Those ramps take a lot of traffic off the already-busy intersection on the right side of the picture.
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Aug 6, 2009 21:52
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Vanomaly posted:How about this exit in Denver? (no googlemaps link; for some reason trying to get it to agree to Kipling & I70 puts it at Kipling & 6th Ave This is why we try to spread out the two intersections of a diamond interchange. One thing strikes me as especially odd, though... do drivers there actually turn into the correct lane? In New England, if you're turning right, you turn into the leftmost lane, and vice versa. Not just a few people, but EVERYONE. I didn't realize that that rule was ever obeyed. quote:Unrelated, what's the point of having obscenely long turn-only lanes? Southbound Wadsworth turning left onto 29th is a great example here, it's at least 1000 feet long, and solid white line for >90% of that, which is way out of range to see what street it is. It's hardly a busy intersection, and since you can technically get a ticket for crossing the solid line, what were they aiming for? "Let's make everyone do a U-turn!"? The solid white line is generally only 50 feet long; that they made it longer than that shows that there's an underlying problem. As I mentioned before, the length of a turning lane in feet is about equal to the number of cars making that turn in the peak hour. If that lane really is 1000 feet long, that means that 1000 cars turn left there. That's way too much for a single left to handle. Now here's the tricky part. If you put in a double left, then you cut your storage length in half, meaning it should only be 500 feet. There's a problem that I can't tell just from your description. Maybe a side street comes on before that, and there was a safety problem with people weaving over from the right to get in the left turn lane. Even then, a solid white line won't stop people from driving (unless you enforce it very zealously). Experience here has shown that nothing short of a smash-your-car curb will keep people from cutting into a lane like that.
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Aug 6, 2009 22:01
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InterceptorV8 posted:Naw, I mean the quality of the road, I have no problem going down it, or coming up it, even heavy. I worry that in tunnels they stay colder, longer so they are slick as poo poo. Donner is always in a state of major road damage. Is there any surface to lay down to stop this? Pavement management isn't my specialty, but asphalt is performance graded based on high and low temperatures. They could be using substandard asphalt, or, more likely, too thin a layer. If you tell me what kind of damage is present (alligator cracking, rutting, raveling), then I can tell you what exactly is causing it. For really heavy-duty pavement, though, nothing beats concrete. The ride quality's not so good, but it can handle a lot of traffic. Rhode Island doesn't even use concrete pavement, but they have a layer of it under the asphalt on I-95 since the volumes are so high.
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Aug 6, 2009 22:03
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FakeUsername posted:Not really a nuisance, but something I've never seen before- These are frontage roads, and they're very popular in Paris, among other places. It's an excellent way to separate through and local traffic, so that they don't get in each others' way. Unfortunately, as you say, that is the simplest way to perform a U-turn; it's just the nature of that kind of facility. If it's really a huge concern, it would be possible to put a U-turn lane on the outer Laskin Rd, but the extra phase it would need would screw up the capacity of all the other approaches. Overall, I'd say the increased safety and capacity of the frontage roads outweighs the difficulties they make for U-turning traffic. Your city must have thought the same thing. Don't sweat the small stuff, right?
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Aug 6, 2009 22:08
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ibpooks posted:Thanks for the thread! It's been an enlightening read. Wanna take a crack at this one? I learned very quickly not to trust Google's roads. There are misspellings, omissions, route numbers on the wrong roads... the only maps I can really trust are the ones put out by the DOT, and even those have rare errors. quote:Traffic volumes on Cedar and Edgewood are both pretty high, also high on Pennsylvania but not as high as the other two. Notice the grade level crossing of the two ramps just east of Edgewood/Cedar with only yield signs. By far the worst is traveling on southbound Cedar trying to get to I96. You need to make an unprotected left onto ramp, survive the at-grade crossing, then the merge in from the left, then the rush of lane switching around the curve as cars queue up for eastbound or westbound 96. This one's not too tough, really. That at-grade crossing has to go, and while they're at it, may as well touch up the rest, right?  I don't know what the volumes are like on S Pennsylvania, so I assumed they were low to the north of the offramp and high to the south. The ramp treatment here really depends on volumes. I stuck in a jughandle to the north of the ramp and a freeflow ramp to the south, helping out that heavy movement. You could equally well do a Michigan Left (if there were enough room), or put up a bridge and grade-separate it, sticking a few ramps down to form a diamond. Given that they said they're using roundabouts, I'd say the volumes aren't as high as I estimated (roundabouts are for relatively low, balanced volumes, remember!). In that case, they'd go in well at the intersection of S Pennsylvania and Pierpoint, as well as the offramp and S Pennsylvania. The French government recommends putting roundabouts at the end of ramps, because they serve as an excellent transition between high-speed and low-speed travel. Another less-likely option is that they'd try to tie S Pennsylvania into the big intersection they're creating with Cedar and Edgewood, but that would take a lot of land and not be very efficient. What I drew up there, along with a couple roundabouts, is probably what'll happen.
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Aug 6, 2009 22:23
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Wombot posted:Well, tides aren't an issue, as both the I-90 and SR-520 bridges are over Lake Washington. The real problem is severe weather. One of my first memories is actually watching the old I-90 floating bridge sink on Thanksgiving '90. Ah, cool. It was close enough to the ocean that I just assumed it was salt water. That also explains why they're not particularly worried about shipping traffic, either. The USCG is responsible for navigable waterways, and they have some crazy restrictions about bridges.
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Aug 6, 2009 22:25
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Thanks for keeping this going and answering all the random questions, by the way. I don't know why, but this is completely fascinating!Cichlidae posted:One thing strikes me as especially odd, though... do drivers there actually turn into the correct lane? In New England, if you're turning right, you turn into the leftmost lane, and vice versa. It's possible I'm retarded (it's rather late for me), but this reads like you turn into the furthest lane for both right and left turns? Including multi-lane-lefts? I have to be reading that wrong! As for going into the correct lane, people generally go absolutely anywhere on single-lane turns, and on multi-lane turns, the "outer" lane goes anywhere except the inner lanes. I'd assume that is the same as anywhere else? I can't see merging from the left to right left-turn lane at mid turn working well at all. Cichlidae posted:The solid white line is generally only 50 feet long; that they made it longer than that shows that there's an underlying problem. As I mentioned before, the length of a turning lane in feet is about equal to the number of cars making that turn in the peak hour. If that lane really is 1000 feet long, that means that 1000 cars turn left there. That's way too much for a single left to handle. Now here's the tricky part. If you put in a double left, then you cut your storage length in half, meaning it should only be 500 feet.  Click here for the full 327x671 image. According to my primitive use of Google Map's distance bar, it appears to be roughly 880 feet from start to end. It turns into a residential area, which doesn't look that busy. I know I've never seen more than one car turning down there, and I pass it every few days at most. As you can see in the picture, the solid line (circled at the beginning) is way worn down from people just crossing at will, like you said 
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Aug 6, 2009 22:50
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Cichlidae posted:Pavement management isn't my specialty, but asphalt is performance graded based on high and low temperatures. They could be using substandard asphalt, or, more likely, too thin a layer. If you tell me what kind of damage is present (alligator cracking, rutting, raveling), then I can tell you what exactly is causing it. For really heavy-duty pavement, though, nothing beats concrete. The ride quality's not so good, but it can handle a lot of traffic. Rhode Island doesn't even use concrete pavement, but they have a layer of it under the asphalt on I-95 since the volumes are so high.
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Aug 6, 2009 23:22
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Vanomaly posted:Thanks for keeping this going and answering all the random questions, by the way. I don't know why, but this is completely fascinating! Yeah, I was talking about single turns. For multiple turns, the inside lane sticks to the curb, and the outer lane picks whatever's convenient, with exceptions. I've seen a double left onto a four-lane road (287 onto 15, if you're familiar with Connecticut), and the leftmost lane grabs the left two receiving lanes, while the second turning lane grabs the right two. quote:
Looking at that picture, there's something else substandard! When a lane becomes a turn lane, it's essential to put a turn arrow, so people realize that it's not a shoulder or just a random white line. There is clearly no arrow at the beginning of that turn lane! If someone gets into an accident there, whoever owns the road could be held responsible for maintaining a substandard facility.
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Aug 6, 2009 23:40
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ilkhan posted:I80 between auburn and reno (the sierra nevada stretch) is basically repaved every 2-3 years because of the snow and the volume of truck traveling it. The road is consistently horrible. There are some pretty neat innovations that have come up in the last decade to fight snow. Embedded pavement sensors can detect when the pavement temperature drops below freezing, and notify the plows to come get rid of the snow/ice. Additionally, some states have been experimenting with nozzles that automatically spray anti-freeze solution onto the pavement once it hits freezing. It sounds like frost heaving can be a problem there, too. Frost heaving is caused by boulders underneath the pavement being lifted upward by fine particles and ice, cracking the pavement. This can be fixed by digging up the sub-base and swapping it with gravel or sand. The cost would be tremendous, but replacing the road every 3 years isn't cheap, either.
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Aug 6, 2009 23:43
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Wombot posted:Well, tides aren't an issue, as both the I-90 and SR-520 bridges are over Lake Washington. The real problem is severe weather. http://www.youtube.com/watch?v=qchD9ltCPG8&feature=related SR 520 Floating Bridge - Simulated failure by earthquake http://www.youtube.com/watch?v=qIiuDUgvZpY&feature=related
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Aug 6, 2009 23:45
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Simkin posted:Hell yeah, bring on the crazy stuff, even if it is just the product of a fever dream, or an idle mind trying to escape the pain of having to deal with people wanting signals for their driveway. You'll regret that  Here's the first one, a Single Point Urban Interchange, or SPUI for short. They're becoming quite popular due to their need for only one signal, and the efficiency of pushing through pairs of left turns at once. Unfortunately, they require a very wide bridge.  Ah, the fabled Spupclo. It's a parclo mixed with a SPUI! Great for diagonal interchanges where other things wouldn't fit.  But wait! Act now, and you'll get two ADDITIONAL ramps absolutely FREE! Remove a pair of left turns and make your life more efficient!  Got three intersecting roads? NO PROBLEM! Stick another few ramps on, and you've got a three-level stacked spupclo! Or, as I call it, a TLSSPUIPC!  This traffic circle interchange is pretty common in Massachusetts. All the downsides of a traffic circle, and two bridges to boot!   MEINE AUTOBAHN  The quadrant interchange is great for low-volume connections, or places where all ramps need to go through a tollbooth. It introduces weaving, though, so be careful!
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Aug 7, 2009 00:38
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http://maps.google.com/?ie=UTF8&ll=33.885033,-84.470505&spn=0.000608,0.001124&t=h&z=19 This one isn't horrible, but I don't get it it. Also, does this count as a cloverleaf, or what? During busy hours, it can still get backed up due to there being no merge lane on to NW Expressway. Also, there are fairly major lights directly north and south on May Ave, and the ones on may are stacked fairly closely. Both of these roads are theoretically 45, though may tends to be about 30 there and NW Expressway is 55 or so. Why, why does OKC love Cloverleafs so much? We have lots of them. Also, why did they do http://maps.google.com/?ie=UTF8&ll=33.885033,-84.470505&spn=0.000608,0.001124&t=h&z=19?  Note the very long ramp from I-35NB to I-240. It actually starts south of where I cropped it in, and is long enough that people hit some pretty crazy speeds on it. Also, there's some weirdness with jersey barriers and chain link fences that mess with lines of sight when you're trying to get from 240 to 35NB, making it hard to determine if people are on the ramp to 240 or still on 35. This is one of the biggest interchanges in the city to boot, and routinely is backed up. What can be done short of demoing the whole loving thing?
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Aug 7, 2009 01:43
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I've been holding off on this, because it's rather hard to explain (even with pictures), but I think you're ready. COORDINATION 102 A few simple things to remember: 1) Please read Coordination 101. 2) Make sure you understand signal phasing 3) Our hardware may be brand new, but the technology is all 20 years old. Alright, let's get started! Here's a picture of the inside of a signal cabinet, with some very simple annotation.  That big thing in the middle is what controls the signal. Stick another box onto it, and it can control multiple intersections. We already discussed how coordination works, but how do we make it more efficient? Well, the best way to do that is through actuation. There are a few different ways to run an actuated-coordinated system. The simplest is a basic time-based system. Here's how it works. When setting the cycle length, you use the MAX timing for the artery through phase, plus the sum of the MIN timing for all other phases (including a pedestrian phase that might not be called often), plus an extra 5%, just in case. Different controllers do this differently, but most begin the cycle right as the artery through phase turns yellow. It acts like a normal actuated signal, giving each phase somewhere between the min and max, depending on how many cars show up. Some phases might be skipped altogether. By the time it gets back to the artery phase, one of three things has happened: 1) There is tons of left over time before the cycle length expires, in which case all that leftover time goes into the artery through phase. 2) There is somewhat less than the artery max timing, but more than the min. The artery through phase goes until that time expires, regardless of how many cars are present. 3) There is less than the artery min time, in which case we do something called double cycling. You don't want to double cycle, trust me. If that happens, the controller will just waste an entire cycle trying to catch up. Lots of phases get skipped, queues get huge, it's just a mess all around. Another kind of actuated coordination is a closed loop system. Closed loops are hooked up to a computer in a centralized location, which lets a human monitor the signals and screw around with timing on the fly. It also allows the signal controller to allocate unused time to phases other than the artery through phase, by inhibiting a phase's max and just giving it more and more time until it's run out of cars. If there's any time left at the end, again, it gets passed on to the artery through. This also means there's a decent chance it'll double cycle. The third kind is like a closed loop on steroids. It computerizes the whole network, using system detectors placed strategically to track individual traffic elements (cars) and dynamically change cycle times to get the highest possible throughput. This is still 10-year-old technology, but it's nowhere near 'mature' enough to use in most places. When I say that our signal controllers suck, you might not realize how restrictive they are. Here are some examples. - Most controllers can only handle 8 phases, just enough for a dual-ring quad. Some can also handle a 9-phase system, which includes a ped phase. - There are limitations on what sorts of timings they'll accept. Need an extra long all-red clearance for an alternating one way section of road? Tough. - You need to put in a yellow time. Want a yellow time of 0? Too bad, it'll have to be 0.1. - Can display up to 5 LINES OF TEXT AT ONCE! HOT poo poo! - Beige box with awful who-knows-how-many-pins connectors 
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Aug 7, 2009 01:57
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Socket Ryanist posted:I pity anyone who lives on treasure island because fuuuuuck Note the uphill grade and the fact that traffic you're merging into just came down a huge hill. The first ramp on the other side is almost as bad. http://maps.google.com/?ie=UTF8&ll=...245.52,,0,18.02 Move around a bit, the whole thing is a clusterfuck of epic proportions. Cichlidae posted:What's Cichlidae posted:As I mentioned earlier, there are really only two ways to stop speeding: changing the geometry to force people to drive slower, and ramp up enforcement. The former wouldn't work very well on an expressway, where people expect to be able to speed. The latter is feasible, but it's out of my hands; when and where the cops choose to set up speed traps is up to them.
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Aug 7, 2009 02:17
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Citizen Z posted:http://maps.google.com/?ie=UTF8&ll=33.885033,-84.470505&spn=0.000608,0.001124&t=h&z=19 It's still a cloverleaf, just a three-leaf clover (which, ironically, are quite a bit rarer in traffic engineering than their four-leaf brethren). It still has two weaving areas, plus a third on May Avenue where that other ramp comes off just north of the on-ramp. Why does OKC love them? They're cheap. Need I say more? (Your links are screwed up, by the way.) quote:Also, why did they do http://maps.google.com/?ie=UTF8&ll=33.885033,-84.470505&spn=0.000608,0.001124&t=h&z=19? What you see as a ramp is actually a collector/distributor road. It helps alleviate the weaving problems caused by the cloverleaf, but doesn't get rid of them. Luckily, cloverleafs are very easy to fix! Take out a couple loops and make a partial cloverleaf, or take them all out and make a stack. What you need depends on volume. Here's a pretty nice design that would eliminate all the weaving, put the interchange perfectly up to modern standards (except no median, that's hard to get these days), and cost not too much, since it only introduces a couple new bridges. 
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Aug 7, 2009 02:18
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