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Is there a reason theres no green right turn arrow while the cross streets have left turn arrows (with no U turn signs posted)? Obviously wouldn't activate if the pedestrian button is hit.
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Aug 4, 2009 21:21
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I moved to Houston, Texas, recently, and there's two things unusual about the street lights. The first is that almost all are horizontal instead of vertical. (Red/yellow/green are side-by-side rather than above each other). The second is that there are often two red lights. On these intersections, I never see one used independently of the other, so you'll see a light like this: R R Y G And it'll work just like every other light, except it has two reds turned on instead of one. Maybe it's just for extra emphasis, I guess. "Really don't go through here." Are there any particular reasons for these?
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Aug 4, 2009 21:40
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Simkin posted:Gov't street/Highway 1 sees the heaviest volume, with Hillside secondary to that. The only building that your plan would demolish is a lovely liquor store that sells to meth addicts, so no big loss. We can only hope  I'd never have dreamed looking at the satellite maps that Victoria would have so much traffic. Do they mostly drive in from the mainland or take ferries?
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Aug 4, 2009 21:55
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ilkhan posted:Is there a reason theres no green right turn arrow while the cross streets have left turn arrows (with no U turn signs posted)? Obviously wouldn't activate if the pedestrian button is hit. We do put those in some places; they're called a "right turn overlap." It provides a moderate increase in capacity over the standard right turn on red, but I would avoid using it at any intersection that has even a hint of pedestrian activity. Around here, the vast majority of peds don't hit the ped buttons. I sat at one intersection I was studying and counted them: 92 pedestrians crossed the road in 1 hour, only 8 of them hit the button. Another problem is that it requires an additional signal for the right turning traffic, which, of course, costs money. Like I said, we use them occasionally to buff up right turn capacity, but in the vast majority of cases it's not worth the extra time or money.
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Aug 4, 2009 21:59
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Malderi posted:I moved to Houston, Texas, recently, and there's two things unusual about the street lights. The MUTCD specifically says that signal heads should be mounted vertically, except when there are sight line restrictions (like bridges) that could obscure the top of them. I don't know why Texas would specifically buck the standard like that. There are provisions, however, for having dual red indications. It does seem to provide a much stronger indication than just one would do. The MUTCD's section on signal faces has this:  Seeing as the R R Y G is available in both horizontal and vertical configurations, why doesn't Texas go tall like the rest of us? Maybe because horizontal indications are cheaper, since they require shorter mast arms or span poles.
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Aug 4, 2009 22:19
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Wind?
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Aug 4, 2009 22:26
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Thomamelas posted:Wind? They've got the same cross-section no matter how they're oriented. Wind really isn't a serious issue with signal heads, anyway, since they're so heavy. The only time we really design for wind is if they're within a few feet of other wires or objects.
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Aug 4, 2009 22:38
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Cichlidae posted:We do put those in some places; they're called a "right turn overlap." It provides a moderate increase in capacity over the standard right turn on red, but I would avoid using it at any intersection that has even a hint of pedestrian activity. Around here, the vast majority of peds don't hit the ped buttons. I sat at one intersection I was studying and counted them: 92 pedestrians crossed the road in 1 hour, only 8 of them hit the button. Thanks for the answer. And I know a couple intersections that could use the yield to U-turn on red signs. Couple regional questions: How common are 2 right turn lanes in other areas? Why are protected left turns so regional? This areas has them everywhere, but driving in Reno pisses me off because they seem to have said "protected left turn? Why would we want to protect people turning left in the middle of rush hour traffic?" ilkhan fucked around with this message at 23:35 on Aug 4, 2009 |
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Aug 4, 2009 23:31
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ilkhan posted:Heh. Im outside of Sacramento, so the answer is "what pedestrian activity?" Double rights aren't all that common, for a few reasons. We try to avoid them anywhere they're not strictly necessary. 1) Only one lane (the inner one) can safely turn right on red. 2) They require their own signal heads and phases, which costs money. 3) Since the driver is on the left side of the car, he doesn't have a good view of his right side, and therefore double rights are much slower than double lefts. 4) It's very dangerous for pedestrians, who now have to dodge 2 streams of cars. 5) Big trucks overhang into the inner lane. 6) You have to trust people not to turn from the rightmost lane into the left lane. 7) It introduces some confusion as people figure out which lane they need. 8) Unlike double lefts, cars going around a double right won't stagger themselves, which makes merging downstream difficult. That's just off the top of my head. Obviously, the big reason to put one in is to increase capacity. If the need were that dire, I'd prefer to have a freeflow right turn with a lane add. Obviously, not all jurisdictions agree. As to Reno, it seems pretty silly not to have protected lefts, unless the through traffic is just so heavy that they can't afford taking a little extra time from them to provide the protected movement. In that case, though, it's just that much harder for left turners to find a gap. I'd imagine that the left turn bays are tremendously long, but land is pretty cheap out in Nevada.
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Aug 4, 2009 23:47
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Cichlidae posted:As to Reno, it seems pretty silly not to have protected lefts, unless the through traffic is just so heavy that they can't afford taking a little extra time from them to provide the protected movement. In that case, though, it's just that much harder for left turners to find a gap. I'd imagine that the left turn bays are tremendously long, but land is pretty cheap out in Nevada. Yeah, it just pisses me off without a protect left turn and felt like venting.
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Aug 4, 2009 23:53
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Cichlidae posted:They've got the same cross-section no matter how they're oriented. Wind really isn't a serious issue with signal heads, anyway, since they're so heavy. The only time we really design for wind is if they're within a few feet of other wires or objects. The cross-section would be the same, but for the ones on wires I could see that their ability to swing in the wind would be less since you're going to have them attached to two wires rather then just the one. For the ones inside Houston's loop that are mounted on the overhanging poles, I have no idea.
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Aug 4, 2009 23:56
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ilkhan posted:Thats a big list. Theres a couple double rights and I know of 2 triple lefts in the area. Areas that will last a long time and are built for it mainly. Feel free to vent, that's one of the reasons I made this thread! I want to learn about your cities. One more note about double rights is that they're quite rare here outside of freeway off-ramps. A single right turn lane, with right turn on red, can handle about 500 turns per hour, ballpark figure. Give them an overlap right, with near-continuous green time, and you can bump that up to 1000 per hour, maybe even more. Freeflow rights with a lane add can theoretically handle up to 2000 per hour, but I wouldn't trust them with more than about 1200. Compare those numbers to a double right, which is basically one RTOR lane and one NTOR (No Turn On Red), minus a few percent, and you've got about 900 or 1000 turns per hour. Bump up the signal time with an overlap, you might push through 1500. That's not all too much more than you get with a single right! And with that kind of volume, unless you're on a huge arterial with 2-3 lanes, traffic will be bottlenecked long before they reach the intersection, hence why we normally limit double rights to freeway lanes (can serve 2000 veh/hour).
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Aug 5, 2009 00:05
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Thomamelas posted:The cross-section would be the same, but for the ones on wires I could see that their ability to swing in the wind would be less since you're going to have them attached to two wires rather then just the one. For the ones inside Houston's loop that are mounted on the overhanging poles, I have no idea. If wind is really a problem, we can put a second span wire across, like so:  If Texas is worried about saving money, I can see them leaving it out, but it's really a minimal cost. You're probably paying $50,000 to put that signal in, so why not drop another $100 or so if it's just wind that's bugging you? It's more likely it's because they can shave a couple feet off of the poles. Signal heads must be at least 16 feet from the pavement, and if they're hanging vertically, Texas' poles would need to be 3 feet taller. Those signal heads may look small, but most of the lights are 12" (30 cm) around, and the head itself weighs a few hundred pounds! Fun fact: The object that connects a signal head to its span wire is known as a "nipple." One of my coworkers got in a lot of trouble because his emails kept tripping the email spam filters. You guessed it: he was talking about signal nipples. Really, there are plenty of good sexual puns in signal design!  Hey baby, gimme an easement and I'll erect a shaft on your property... then I'll twist your nipples and get head a couple of times. Next, I'll pop open your cabinet and tweak your knob for a while. We'll tear out the stop signs and turn on that red light, baby!
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Aug 5, 2009 00:20
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One of the most irritating cloverleaf interchanges I've ever encountered is here in my hometown (Saugus, MA): This is the interchange, with arrows added to show the one-way sections. As you can see, it's centered around Route 1. The green arrow shows the only way to get into Burger King if you aren't on Route 1 South when you're going past it. The main difficulty here is in getting from the mall to the Burger King, which I'll sometimes do for dinner since I work behind the mall. Because of the way the interchange is laid out, the only way to do this is to go over the overpass, onto the highway, back onto the overpass going in the other direction, and around into the parking lot on the branch heading to Route 1 South, demonstrated in the following picture (start on the green line near the mall, then switch to blue after Route 1 North):  Would this be worth fixing at all? If so, how would you do it? Removing the "no left turn" would probably not be the best way to go about it, I think, since it's nearly a u-turn to get onto it across a high-traffic area. Edit: Fun fact! According to Roadside America, Saugus's stretch of Route 1 has more restaurants per square mile than anywhere else in the world. I'd be curious to see if obesity rates are higher in Saugus than the surrounding area for that reason. Der Metzgermeister fucked around with this message at 01:56 on Aug 5, 2009 |
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Aug 5, 2009 01:36
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Thanks for answering my (many) questions. Drivers not being able to judge space is the best explanation I've heard yet for people leaving huge gaps in traffic while parked, but I'm not fully convinced. Are that many people so bad at judging distance that they leave 2-4 car lengths of space (or more) between them and the next car? Even if you just want an emergency out or are worried about being rear-ended you can get by with much less. I'm talking about spaces so wide that other cars could easily pull into them (and do, rarely). Also, does construction projects take so long on purpose? I knew a guy that ran a local construction company and he would often put up barriers months before he did work, so that it was obvious that he took the job. He'd take much more work than he could handle to have a steady stream of income. It'd be fine by me if he'd just wait to block off the road until he was ready to work on it. Anyway, I see projects that take forever even when they are working on it. My dad used to joke that engineers put up runways overnight but it takes construction companies years to complete road construction. Any thoughts?
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Aug 5, 2009 01:52
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Der Metzgermeister posted:One of the most irritating cloverleaf interchanges I've ever encountered is here in my hometown (Saugus, MA): Alright, this is a pretty good one! If access to Burger King weren't an issue, I'd turn this cloverleaf into a parclo (partial cloverleaf), deleting 2 ramps to eliminate the weaving problem on US 1, like so:  Unfortunately, that particular arrangement wouldn't help your commute too much. Instead, it would be easy enough to do this:  This adds two signals to Essex Street, which shouldn't be a big deal, and it also provides Burger King access and makes your life easier. The downside is it removes a couple more free movements, decreasing capacity a little. Honestly, though Essex Street is only one lane in each direction. It can probably handle it. Also, this option is very cheap, and would free up some more land south of the interchange for development.
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Aug 5, 2009 01:57
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Arafa posted:Thanks for answering my (many) questions. We've had a few people chime in with different reasons. If you want one more, I saw a similar situation yesterday. One guy stopped a good 30 feet behind the stop bar (which is a bad idea, our detectors only go 25 feet back, so there's a chance your phase might get skipped). He watched the sidestreet light like a hawk, and when it turned yellow, he started coasting forward, picking up enough speed to hit the stop bar right as the light turned green. He was probably looking to up his gas mileage, since starting abruptly isn't very efficient. It's still dangerous (if he misjudged the light, he could have hit someone) and looks pretty stupid. quote:Also, does construction projects take so long on purpose? I knew a guy that ran a local construction company and he would often put up barriers months before he did work, so that it was obvious that he took the job. He'd take much more work than he could handle to have a steady stream of income. It'd be fine by me if he'd just wait to block off the road until he was ready to work on it. Some contractors are dicks. They'll take more than they can handle just to starve the competition, front-load the contracts to make more profit, and spend lots of money looking for bad estimates or loopholes so they can perform unbalanced bidding. Some other states have provided incentives (money) to contractors that finish work early, and, wouldn't you know it, they finish way before their estimated date of completion! Unfortunately, incentives aren't allowed in Connecticut. quote:Anyway, I see projects that take forever even when they are working on it. My dad used to joke that engineers put up runways overnight but it takes construction companies years to complete road construction. Any thoughts? What makes it even worse is how inconsistent contractors are when you're stuck with the low bidder. You could have 5 great contractors that finish up ahead of time and get to the next job, but the 1 guy who's trying to screw you over can outbid them and really ruin the project. Of course, he's much more visible to the public than the good ones, so there's a (somewhat deserved) perception that contractors are horrible overall. Edit: I'm not saying engineers are infallible, though. An engineer designed this: 
Cichlidae fucked around with this message at 03:40 on Aug 5, 2009 |
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Aug 5, 2009 02:06
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Wanted to say thanks for the wonderful and informative thread! I used to live in CT, so I'm familiar with the some of the road oddities that it had. You probably would know which exit ramp I'm referring to, but I heard that there was an exit ramp near Windsor Locks that was so poorly designed people got into fatal accidents a lot until they redid it. Another question: do you think that CT will ever switch to mile marker exit numbers instead of consecutive numbers? You also mentioned the Budapest metro, the city itself still uses mass transit, I know in the early 90's it used electric buses, diesel buses, trams, longer distance trains (Amtrak equivalent), as well as their subway. Compared to NYC and London subway systems, it isn't a vast line, but since the city has other mass transit resources, the crowds can be dispersed easier. Compare: Budapest Metro with: NYC Subway London Underground
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Aug 5, 2009 05:42
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I see quite a few yellow advisory speed limit signs that do not seem to be consistent with a curve's sharpness or its banking. What determines the use of yellow advisory speed limit signs? Or are they just easier for "concerned citizens" to get placed along the road (when compared to real white speed limit signs)? Swap_File fucked around with this message at 06:39 on Aug 5, 2009 |
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Aug 5, 2009 06:23
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I love this thread. It's answered so many questions I've had over the years about why our roads are the way they are. Awesome! A bridge just got rebuilt in my area, and I absolutely love what they did. They improved this tragedy, which had awful weaving (weaving, right?) problems where the cloverleaf merged with M53. I drat near got into an accident every time I got on and off that exit. I mean, it doesn't hold a candle to some of the terrible intersections posted in this thread, but I hated it.  Click here for Google Maps. They replaced the intersection with roundabouts at both sides of the bridge, eliminated that terrible parclo, and the flow of traffic is so much smoother and constant now. I couldn't find any pictures because they JUST opened it, but MDOT made a video of it. Cool. https://www.youtube.com/watch?v=sgzgBqX8jAM Roundabouts are awesome, end of story.
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Aug 5, 2009 06:41
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Best thread ever, and thanks for answering my bike trails question wayyy earlier. So you want to learn about our cities eh? Welcome to Lincoln, Nebraska. 250,000 people and no traffic engineer (fired ours cause of budget cuts about a decade ago). As you might be able to predict, traffic is kind of a mess in our humble little town. It's Nebraska, so we have no hills or anything crazy like that (although to the west of the city there is a fairly major floodplain and lots of railroad tracks) so you'd think it would be easy Of course, there are a few issues. As the screen shot here of google maps should be fairly clear, there are no freeways or expressways through the city.  I-80 runs to the very far north. Highway 34 cuts directly through the middle of the city and is a congested mess that can't be widened due to historical buildings and the like. You might also notice there are only two direct north to south routes that go through the entire city - 27th street and 84th. 27th street is 2 lanes in most of the south end of town due to a historical district/rich person neighborhood. Highway 2 is covered in stop lights and is routed directly through downtown Lincoln/residential streets. The homestead "expressway" has 5 at grade stop lights on a 65mph "expressway" All you people living in big towns, at least you folks HAVE traffic engineers. Please come work pro bono and fix my city or at least fix this intersection:  http://maps.google.com/maps?f=q&sou...006968&t=h&z=18 that's 3 4 lane roads meeting. There are stop lights at warlick/old cheney, old cheney/14th and old cheney/Brook ridge circle. Yield signs/stop signs where 55w and 14th street merge onto warlick. It's a god awful mess the city can't fix because they literally have no one capable of fixing it. /sob adaz fucked around with this message at 07:47 on Aug 5, 2009 |
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Aug 5, 2009 07:37
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naguchanzilla posted:Wanted to say thanks for the wonderful and informative thread! I used to live in CT, so I'm familiar with the some of the road oddities that it had. Windsor Locks has gotten a few modifications, just in the last 15 years. Exit 38, Day Hill Road, is going to get fixed in a few years' time. Exit 39 is a simple half-diamond, and works just fine. 40 was completely redone in the early 1990s, from a trumpet to a directional T.   41 had most of its ramps deleted along with the Exit 40 work. 42 was also modified slightly to smooth out some of the curves on the ramps, nothing major. 43 was deleted, and 44's terminus with US 5 was realigned and teed up into a signal.   As to exit numbers, there's very little chance of them being renumbered here. There are so many exits spaced so closely that we'd need a smattering of A's and B's along with the numbers. Additionally, if we finally switch over to kilometers in 10 years, we'd have to change all the numbers again. quote:You also mentioned the Budapest metro, the city itself still uses mass transit, I know in the early 90's it used electric buses, diesel buses, trams, longer distance trains (Amtrak equivalent), as well as their subway. Compared to NYC and London subway systems, it isn't a vast line, but since the city has other mass transit resources, the crowds can be dispersed easier. Thanks for the info
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Aug 5, 2009 12:21
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Cichlidae posted:Seeing as the R R Y G is available in both horizontal and vertical configurations, why doesn't Texas go tall like the rest of us? Maybe because horizontal indications are cheaper, since they require shorter mast arms or span poles. It looks like they save money on near and far lights and just use triple fars on a mast arm. Here is a typical Street View. It makes sense based on that configuration. The double reds apparently are used for left turns so drivers don't get confused when the through red lights change. I would be confused without near signals but that's because I live where we typically have snow covering stop lines in the street for several months. It also would be a bitch because if the pole gets taken out in an accident there is no redundancy leading to more accidents until you get a signal maintenance crew out there to fix things. Neutrino fucked around with this message at 17:03 on Aug 5, 2009 |
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Aug 5, 2009 17:00
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Swap_File posted:I see quite a few yellow advisory speed limit signs that do not seem to be consistent with a curve's sharpness or its banking. Those are determined based on the design speed of a curve. Remember, design speeds are calculated for large trucks, not for normal cars, which can safely drive much faster. The signs are posted only when the design speed is 10 mph or more below the posted speed limit. One of my projects was to smooth out a curve that had a 10 mph design speed and a 20- to 30-degree uphill grade. Ouch!
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Aug 5, 2009 17:11
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60 Hertz Jig posted:I love this thread. It's answered so many questions I've had over the years about why our roads are the way they are. Awesome! Yep, that's weaving, caused in this case by the adjacent loop ramps. Sweet, a pair of high-capacity roundabouts. Those aren't the recommended pavement markings, but I can forgive that. I don't know how much videos help, but they're always fun to make, and anything that helps people learn to drive is worthwhile. I hope they're including this in driver's ed as well, so we can get the next generation of drivers started on the right foot!
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Aug 5, 2009 17:25
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adaz posted:Best thread ever, and thanks for answering my bike trails question wayyy earlier. This one is pretty tricky, but there are a lot of ways to improve it. If the intersections can't handle the capacity they have, I'd consider carrying 55W over Old Cheney Rd with a couple of overpasses, and realign South 14th Street to handle turning traffic. The ramp shown in the lower left is optional.  Of course, this assumes that there's not much turning traffic, or the stretch of 14th between the two roads could get congested. You'd need a full traffic study of the area to really understand what's the best option, and that's all but impossible without a traffic engineer. Write to your mayor, I guess!
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Aug 5, 2009 17:36
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Neutrino posted:It looks like they save money on near and far lights and just use triple fars on a mast arm. We use far side only in CT whenever possible. Signal heads should be between 40 and 120 feet in front of the stop bar (150 in a pinch), and it's hard to get that kind of spacing on near-side spans. Of course, we have a lot of plows, so it's generally obvious where the stop bars are. Just for you, though, here's a rarity: a partial stop bar.  The story here is that when the DOT put in a driveway, it's left turn in only, so there's no reason for through traffic opposite the driveway to stop at all. They didn't bother to put up signal heads for the through movement, or a stop bar, instead just using a pole-mounted head in the median for the left turn. Well, remember what I said about designing for the stupidest drivers? Those 1 in 5000 idiots (I like to pretend they're all out-of-staters) saw the left turn red light and thought, "Oh poo poo, better stop!" They'd screech to a halt in the middle of 50 mph traffic. Yeah... the DOT had to drop 10 grand just to put up a signal that stays green all the time. I can proudly say, only in Connecticut do we have drivers so stupid that you have to tell them to go constantly or they'll just stop.
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Aug 5, 2009 17:46
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Cichlidae posted:Yep, that's weaving, caused in this case by the adjacent loop ramps. I'm not sure how much they would help either, but I think it's pretty cool that the DOT here is starting to post videos on YouTube. If they can reach enough people, maybe we can teach America how to drive. (tall order, I know)
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Aug 5, 2009 17:46
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Cichlidae posted:Just for you, though, here's a rarity: a partial stop bar. Dumb question: Why do they use a full signal, when only the green light will ever be used?
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Aug 5, 2009 18:47
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Cichlidae posted:We use far side only in CT whenever possible. Signal heads should be between 40 and 120 feet in front of the stop bar (150 in a pinch), and it's hard to get that kind of spacing on near-side spans. Of course, we have a lot of plows, so it's generally obvious where the stop bars are. Just for you, though, here's a rarity: a partial stop bar. Why didn't they just use single-head green up arrows? They use those here at Florida T intersections (I wonder why they got that name), and it's even less ambiguous than a regular signal that's green all the time because you'll know it'll never change. Are three-head signals cheaper?
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Aug 5, 2009 19:01
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60 Hertz Jig posted:I'm not sure how much they would help either, but I think it's pretty cool that the DOT here is starting to post videos on YouTube. If they can reach enough people, maybe we can teach America how to drive. The RIDOT has Facebook, MySpace, Blogger, and Twitter accounts. What the heck would a DOT post on Twitter? Status Situation modified: incident, cleared on I-295S at Exit 9A - Route 146 South - Lincoln Ah. SO glad I don't work there anymore; I can't imagine how frustrating it would be to waste valuable incident management time updating Twitter.
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Aug 5, 2009 21:57
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smackfu and Dominus Vobiscum posted:They have one of those near the mall in Waterbury, off of 84. In that case, the intersecting road is an onramp and is one-way going away. 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. 1) If you look at that MUTCD page I posted earlier, there's no support for single face signals. 2) I don't know if we'd be able to get them any more cheaply than the standard kind. 3) We'd have to do all the calculations over again for the mast arm, which costs more than "just do what we always do." 4) Just in case we ever DO need to stop traffic there, say for an emergency evacuation, the capability exists. 5) Target value is much higher for 3 faces than one.
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Aug 5, 2009 22:00
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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.  This is a standard, boring diamond interchange. Four ramps, two signals. These two signals should be coordinated, otherwise cars will queue up over the bridge, which is obviously not good.  This is a folded diamond, which is another kind of parclo (partial cloverleaf). Imagine that it's a diamond that got punched so hard that it prolapsed. A pink sock interchange, if you will. Still two ramps and two signals.  Here's a split diamond, which has two overpasses instead of one. This arrangement requires two more signals, but creates frontage roads on both sides of the freeway. It's also a little tough to sign properly.  When space is tight, the tight diamond is the way to go. It has four signals and adds two more bridges (ramp-over-ramp), but it only takes half as much space as a normal diamond. If you brought the ramp ends together to make one intersection on each side of the freeway, we'd have hook ramps, but that's a discussion for another time.  If you're not fond of signals, the dogbone diamond is the way to go. The on- and offramps are channelized by the roundabouts, which ensure traffic won't go the wrong way. Additionally, with this configuration, there are shorter queues at the bottom of the ramp. 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?
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Aug 6, 2009 02:38
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In Europe many traffic lights turn red -> yellow -> green, why -- is this something useful, would the USA ever do something like that? My only guess is since most the cars are manual it lets people get in gear before going, but from what I've seen the second it turns yellow (usually for one second) everyone just accelerates really fast. found some info, http://federalist.wordpress.com/2008/05/08/traffic-signals-yellow-before-green/ looks like it can smooth traffic a bit? one more thing, why are some lights on yellow, black, white background, do the colors make any difference whats your preference? problematique fucked around with this message at 03:56 on Aug 6, 2009 |
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Aug 6, 2009 03:51
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problematique posted:In Europe many traffic lights turn red -> yellow -> green, why -- is this something useful, would the USA ever do something like that? Yes, that article explains it very well. It lets Europeans prepare to start up faster. While they're generally smart enough to scan the intersection and make sure nobody's coming, the same doesn't apply to American drivers. Remember how I said knowing too much about the signal can be a safety hazard? We time how long the all-red period is based on the assumption that people don't go until the light is green. If they started beforehand, we'd have to extend the all-red period, basically making the whole thing moot. That's why they're specifically prohibited here. Because people drive like idiots. I hope you're seeing an ongoing theme by now
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Aug 6, 2009 03:57
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After bouncing down and bouncing back up, how would you completely unfuck Donner pass?
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Aug 6, 2009 05:21
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Here's an old Texas tradition. I've never really seen these outside of smaller country towns but I can't imagine they're anything but a hazard, especially if you add driver stupidity and impaired drivers into the mix. Basically, since the picture is somewhat of poor quality, they built the highway between two bi-directional roads. Both directions of traffic on the road must yield to the freeway traffic coming off the highway, and the oncoming traffic has to yield to the traffic entering the ramp. If the guy in the oncoming lane misses the yield sign then you're looking at a severe head-on collision. That's made worse by the fact that you have almost no real maneuvering room because you're shooting directly on to a narrow two lane road from an angle. They're quite scary but fortunately I haven't run into any newer roads designed like that.
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Aug 6, 2009 07:14
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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. Ah, 2 RTOR lanes, my favorite part of exiting SR 520 in Bellevue, WA. http://tinyurl.com/2xRTOR  I tried finding the signs on Street View, but they're too blurry. Basically, traffic is allowed (through signage), to turn right on red from either lane, after stopping. However, the stop line is located waaaaay the gently caress back from the intersection, and has obstructed sight lines towards oncoming perpendicular traffic. This means that everyone ignores the lines, and stops at the crosswalk, where they have a slightly better sightline. Not by much though. If you notice on that picture up there, those two lanes feed a 4 lane road. 2 left turn lanes, and 2 straights. The right turn lanes technically feed directly only the 2 straights, but no one ever pays attention to that. You end up with traffic in the outside lane filling both the left turn lanes in addition to the correct straight lane, and then the inner right turn lane filling the outer 3 lanes, depending on what the outside does. And that's all before the right-turn light turns green! Bonus:  Remember those 2 straight-thru lanes from above? When they pass through that intersection, they shift to the right half a lane. That's just enough to cause people to swap lanes in the middle of the intersection, unawares, and shove outside traffic into the curb. It doesn't help that there are curbs on both sides, and the lanes are pretty narrow. Not the most hosed up thing in this thread by far, but it's up there on the annoying scale. PS: Ever dealt with floating bridges? Come to Washington, we've got two. I just learned how the SR-520's draw-span works, blew my mind: https://www.youtube.com/watch?v=7cEe2U6KEk4
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Aug 6, 2009 09:12
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InterceptorV8 posted:After bouncing down and bouncing back up, how would you completely unfuck Donner pass? 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. Look at Switzerland: tons of 4000-meter mountain peaks, and plenty of tunnels. In fact, all over Europe, you'll see tunnels. On my freeway job in France, we even put in tunnels in flat terrain under a forest to save a few trees. I'd need to check out the geotechnical situation, but barring a major fault, there's nothing impossible about ramming I-80 through a mountain.
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Aug 6, 2009 12:17
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| # ? May 17, 2024 17:28 |
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grillster posted:Here's an old Texas tradition. I've never really seen these outside of smaller country towns but I can't imagine they're anything but a hazard, especially if you add driver stupidity and impaired drivers into the mix. Basically, since the picture is somewhat of poor quality, they built the highway between two bi-directional roads. Both directions of traffic on the road must yield to the freeway traffic coming off the highway, and the oncoming traffic has to yield to the traffic entering the ramp. Those are called slip ramps, and are used widely wherever frontage roads abut a freeway. Generally, though, they come with acceleration and deceleration lanes; it appears that those are lacking in your situation. Without accel and decel lanes, it's just like any other poorly designed interchange, forcing people to drive unsafely in order to merge in time.
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Aug 6, 2009 12:19
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