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Proposed Howard Terminal Stadium (EastBayTimes)
Santa Clara Cyclists Try to Save Freedom Bridge (MercNews)
Free Hugs at Fairfax Street Event (MarinIJ)
Motorists Plowing into Houses, Buildings and Toll Booths (SFExaminer1, SFExaminer2, EastBayTimes)
San Francisco Transit and other Construction over the Decades (SFGate)
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GGB Authority may spend money to remove toll plaza because drivers can't be bothered to drive slowly enough to navigate safely through it. These are the unintended consequences of adding a zippered lane and removing cash tolling from the bridge. It's simply enabling people to drive faster and more dangerously.
SF Guest
You sound off as if the toll plaza was placed there to deliberately induce slower traffic when the main objective was to collect toll fees whereas induced slower traffic was the side effect and not the main objective. Removing the plaza is not carte blanche for speeding; it merely allows an unnecessary slowdown for antiquated cash payments. If speed is deemed unsafe that's the purpose of having metering lights.
You had me until metering lights. Metering lights are used to increase speeds, not lower them.
farazs
Part of the problem is simply that lanes increase from 3 on the bridge to 8 for the toll both and then back to 3. This leads to people jockeying for the empty lane as they approach the toll booth. If toll is automated and no one has to stop anyway, then why not just have 3 or 4 lanes at the toll booth. That should slow things down and keep traffic in order.
The average speed on the bridge has increased from 35 mph to 50 mph with the addition of the zippered lane (which is 5 mph over the speed limit on the bridge). The lane configuration at the toll plaza has nothing to do with this.
Perhaps you didn't read the article before commenting – it was specifically about drivers crashing in to the toll plaza. The problem here is not the average speed of vehicles across the span of the bridge going in either direction, but the speed when passing through toll booths in the southern end.
Perhaps you didn't read the article. Before the movable zipper lane was put in, the average speed on the bridge was 35 mph and there were only 10 crashes at the toll plaza. After the zippered lane was installed, average speed on the bridge increased to 50 mph and there were 84 crashes, some of which required lane closures for repair of the structure.
If the increase in speed of cars on the bridge is in no way correlated with the number of crashes going up so dramatically, then what, pray tell is? Bear in mind, nothing else changed…
The implication is not that the toll plaza is there to deliberately induce slower traffic. Rather that it is a hazard that drivers should recognize and adjust their speed for it, just like a curve on a winding road. The fact of the matter is that people are exceeding the design speed on the bridge now that a zippered lane exists, traveling at 50 mph rather than 35 mph, which is classic risk compensation behavior. This is making the roadway more dangerous, not the toll plaza, which was there before the rise of adverage speeds.
The response from the bridge authority should be to come up with treatments to slow vehicles down as they cross over the bridge. The removal of the toll plaza will simply enable people to speed even more. This is particularly troubling when you consider that Doyle Drive has a 35 mph posted speed limit, so people should be slowing down as the cross the bridge, not speeding up.
Correlation != causation.
Often introducing efficiency in one aspect exposes an existing hazard in another. Not mentioned in that one stat you keep quoting is what was the historical rate of crashes as compared to the historical number of vehicles crossing the bridge. Other interesting things would be break down by lighting conditions and morning vs. evening (i.e. when the zipper lane configuration changes).
It may very well be strictly enforcing a 35mph limit on the bridge as a whole may reduce the amount of cars crashing in to the toll plaza, but that may not be the best way of addressing the problem. A reductionist approach is misleading – there are multiple factors to consider.
How are metering lights used to increase speeds?
Metering lights are used to "meter" the amount of traffic on a freeway to eliminate congestion, thus keeping speeds higher.
Most people will agree the new gantry is a good thing since it will do away with the need for lane closures for maintenance.
"It allows all the equipment to be above the roadway and access to maintenance above the roadway so you don't need lane closures to do maintenance," Mennucci said. "We think it's good customer service not to close the lanes and it's much safer."
p_chazz
Why would the Bridge District deliberately leave a hazardous barrier in place in order to reduce speed? Surely there are other, safer ways to accomplish this. Especially since the booths are an aging piece of infrastructure that no longer serves the purpose for which it was intended.
Jeffrey Baker
The speed limit on Doyle is a classic example of road engineering and policy done inconsistently. The design speed of Doyle is, conservatively, 250 MPH. The 35 MPH limit is a sad joke.
Maybe we can figure out how to use them for euthanasia instead!
RichLL
The explicit intent of metering lights is not to increase speed. However, a higher average speed would be an indicator that they are working.
The purpose of them is twofold – to increase capacity/throughput and to allow safer merging (I've only ever seen metering lights in merge situations).
Of course, for a constant number of lanes, capacity is proportional to average vehicle speed. But I don't think it's accurate to describe metering as existing for speed. There again, I'm not convinced they work at all, and am perfectly happy to make an un-managed, un-metered merge.
I'm sure gneiss does not literally think we should leave this rusting structure in situ as some bizarre kind of traffic-calming device. But it is classic streetsblog thinking to want to place obstructions and obstacles in the way of traffic making reasonable progress.
farazs makes a good point that there are more lanes at the plaza. And removing the toll booths will presumably create even more. But gneiss's argument seems to be predicated on the idea that people need to start slowing down 2 miles from Doyle Drive, and that makes no sense to me.
50 is fine on the bridge and if we need a 35 limit on the southern approach then so be it. That can be achieved with lights, signs and enforcement – same as everywhere else – as you suggest.
The roadway widened to 8 lanes because of the toll collection time. No toll collection, no need to widen the roadway. They should narrow it when they put the gantry in – QED
So why would you explicitly want to constrict capacity unless you were on some kind of war on moving around?
davistrain
Regarding "Integrate Housing and Transit" (from the Examiner): One of the commenters on that op-ed item, who goes by the name "ww" recommended filling a vacant warehouse with bunk beds, which certainly would provide minimal shelter, but in an environment that made me think of World War II Army barracks. It seems to me that the typical American would have to be in dire straits before bunking down in one of these abodes. Apparently "ww" looks upon "privacy" as an optional extra,
baklazhan
"for a constant number of lanes, capacity is proportional to average vehicle speed" – well that's just wrong. A 10 mph lane with 1 second following distances carries more cars per hour than a 60 mph lane with 2.5 second following. And of course this assumes that each vehicle is carrying the same number of people.
Except that the distance between cars cannot be controlled. That depends on the individual drivers – some like to leave more space than others.
In most situations, increasing the average speed is the simplest way to increase capacity, which is why there is sometimes a conflict between the two goals of throughput and safety.
Well I guess some people might follow at one second at 60 mph, but it's really not a good idea. In any case, increased speed does not do much to increase capacity. At 2 seconds following distance, going from 30 to 60 mph increases capacity by all of 8%. Capacity is determined almost entirely by following distance, so it's typically higher at lower speeds, because people can safely follow more closely. If you try to have high speeds and low following distance, you can boost it a little– right up until someone blinks and then your capacity is suddenly zero for the next few hours.
But really, if it's capacity you're after, the obvious low-hanging fruit is to increase the average vehicle occupancy.
There are many "hazardous barriers" that drivers must avoid, particularly in San Francisco. These particular ones are relatively benign and can easily be fixed. A couple miles further are many "barriers" which are soft and squishy and cannot easily be fixed. I'd rather the bad drivers hit the benign ones, and learn their own limitations, before coming to the squishy ones.
OK, so I think we all want to be clear about your suggestion. Is your idea seriously to place artificial barriers to normal progress for purely ideological purposes?
Well, far and away the biggest determinants of capacity are road width and average speed. Sounds like what you are really saying is that you don't want to increase either, but then what does that leave given the increase in population?
Like I said, following distance could be a factor but it cannot be controlled, absent driverless cars
citrate reiterator
Whether or not you agree with baklazhan, I think they would describe their purpose as "wanting to prevent cars from crashing into people at high speeds and causing injuries/fatalities," rather than "purely ideological."
Nope. Purely ideological. You and your ilk will stop at nothing in your anti-car echo chamber.
The "ideological" part comes when every suggestion that a particular commentator makes is orientated the same way i.e. to either slow cars down, or take away parking from cars or otherwise generally make life more difficult for drivers.
If you sometimes suggested things that are worse for drivers and at other times suggested things that are better for drivers, you'd be seen as more objective and balanced. Otherwise the risk is exactly what murph at least has the honesty to admit to – an anti-car bias.
It would be ridiculous to leave the toll booths in place simply to frustrate and slow drivers. And in fact their removal would allow for extra lanes to relieve congestion there.
Balanced and objective are not the same thing. A "balanced" opinion of the kind you describe merely means that the person holding it is mostly happy with the current balance of space allocated to cars, transit, bikes, etc. But there's no "objective" evidence that this particular balance is the best: so that position is just as biased as someone who wants substantially more or less space to be allocated to a particular mode. It is also fallacious to describe every position that could negatively affect some drivers as necessarily having a secret "anti-car" motivation, which was my point above.
Assuming that extra lanes will relieve congestion is also dubious, which we know from research on highway widening, and the toll booths don't literally have to be kept in order to calm traffic, as others have said in this thread.
There can be no "objective evidence that this particular balance is best" because the word "best" there is entirely subjective.
And I'm not using "balanced" and "objective" to mean the same thing, otherwise I'd have only used one of them. "Balanced" means an attempt to see things from all points of view and not favor one interest group at the expense of another. While "objective" means actively seeking to dismiss one's own bias. So in my case I'll sometimes oppose the driver case and sometimes support it. Anyone who always goes one way or the other is inherently suspect.
As for the extra lanes, it would surely help locally, but the problem is that we can't put more lanes on the bridge so there will always be congestion and merging issues at either end, especially since the Doyle Drive re-do didn't add lanes either. That said, the toll booths should go and if we need to take other steps to enforce 35 mph or whatever, then so be it.
Ramp metering is defined as a method by which traffic seeking to gain access to a busy highway is 'controlled' at the access point via traffic signals. This control aims to maximize the capacity of the highway and prevent traffic flow breakdown and the onset of congestion.
In general bridge metering lights are enabled to enhance safety by restricting and controlling the flow of traffic when non-manufactured congestion occurs after leaving the toll plaza. A motorist would not be able to speed for any length of time in non-manufactured congestion with metering lights enabled.
In general bridge metering lights are turned on only when traffic after the toll plaza is heavy. There is no reason to have metering lights on with no congestion.
To leave the toll plaza intact for the sole purpose of manufacturing congestion is a safety hazard similar to having traffic backed up at a freeway exit with the freeway itself freely flowing. I recently witnessed a car rear ended while stopped behind a row of cars trying to exit. The person who rear ended the other car didn't see the exit lane backed up in time and wasn't speeding.
Many motorists like to make last minute lane changes at toll plazas while jockeying for the least congested lane to use. What's dangerous is not necessarily the speed motorists enter the toll plaza but the fact that you have differing speeds and closed lanes forcing mandatory lane changes while others at the toll plaza are totally stopped is what makes it harder to negotiate.
The new gantry is a welcome improvement (and not for the reason I would regularly drive on this bridge) and removes the need for second guessing and superior driving skills negotiating a toll plaza with closed off lanes.
Right, that's what I was saying re: "best."
The problem with saying that you sometimes oppose and sometimes support the driver's case and using this as evidence for objectivity is that we're really only discussing a pretty narrow window of cases, that don't constitute a very broad ideological range. Most of the civic projects we're talking about on Streetsblog are not radical departures from what we already have. Even if you accepted every single improvement suggested by Muni's TEP data that would take some space away from cars, for instance, that would still leave the vast majority of road infrastructure dedicated to private vehicles. It's not like we're talking about a ballot measure to reduce private car ownership to 1920s levels by fiat.
That's why I don't think that being sometimes for cars over transit and sometimes for transit over cars is evidence of objectivity, as much as evidence for preferring a balance of transit vs. car prioritization that is pretty close to what we have now. (One can even imagine how switching views like this could actually arise from a lack of objectivity: imagine, for example, someone who is for transit projects when they wouldn't affect their own personal ability to drive to work, and against them when they would.)
The average car is 15 feet long. At 30 mph, it takes 0.34 seconds to pass you. At 60 mph, 0.17 seconds. So if the following distance is 2 seconds, a lane with 60 mph cars will have a car pass by every 2.17 seconds, while at 30 mph cars will pass by at 2.34 seconds. That's an 8% increase in the number of cars traveling in the lane.
Maybe you can't control following distance, but there's no reason to believe that it's lower at higher speeds, unless the drivers are insane.
If cars were traveling at 10,000 mph, capacity would increase by another 8%. In other words, increased speed does not help capacity much. High speed trains do have high capacity, but it's not because they're fast, it's because they can each carry hundreds of people. "Normal speed" subways also have high capacities– the highest capacity existing subways carry 80,000 people per hour on a single track, the equivalent of 44 lanes of single occupancy vehicles.
When it comes to trains, there is one way that speed helps capacity– faster speed means that the trains can turn around faster, and make another trip, so you can carry more people with the same number of trains and crew. This obviously doesn't apply to private cars, though.
They're not artificial barriers to normal progress. Normal progress does not involve crashing into tollbooths.
I see what you are saying but taking your argument to its logical limits, you are implying that traffic capacity with 10,000 mph cars is little more than traffic capacity with 1 mph cars, and I can't get my head around that.
Look at it another way. If my trip is 30 miles then the difference between 30 mph and 60 mph is that at 60 my travel time is 30 minutes less, meaning that my car is off that road for 30 minutes longer, meaning the space it took is available for another vehicle. I've seen signs on freeways in Europe that have markings on the road indicating the optimal gap to leave – about two car widths if I recall correctly. Clearly those markings are designed to encourage drivers to leave no more space between vehicles than needed, for capacity reasons.
I do see, however, how having to leave larger gaps between vehicles at higher speeds will reduce the capacity advantage of faster traffic.
The gap markings on the freeway show *at least* how much distance to leave and not *at most* and they are there solely for safety reasons. Between weather conditions, stopping capability of the vehicle (brakes/tyres/load) and the drivers own reaction time, a traffic authority has no standing to prescribe an 'optimal' distance.
I thought it was about saving the $10k spent in replacing toll-both barriers every time an idiot crashes in to them. No fatalities reported due to those crashes. The minimum liability insurance for property damage in CA is $5k, so the GG authority would have to spend $5k out-of-pocket per crash, even if it managed to redeem the other half from insurance. Going to court over each crash would be way more expensive.
We can only hope that they at least wrote a ticket for each of those crashes. Basic speed law and failure to control the vehicle are obvious candidates.
You teased this before on an unrelated topic that I had you, but I have no reason to believe that will ever be the case regardless of what compelling points and arguments I present. Bearing in mind that you will never like a comment made by me doesn't dissuade me from presenting my minority viewpoints especially where reducing motor vehicle speeds is not tantamount in a discussion where pedestrian safety is not a factor.
OK, but I'm pretty certain I've seen road signage indicating not to leave large gaps either. At least in slow or stopped traffic conditions, congestion is worse if vehicles leave large gaps.
And if baklazhan's claim that closer following is a bigger driver of throughput than average speed, it would appear to be in the interests of traffic authorities to take steps to ensure that the gaps are not too large
That is not how I read baklazhan's posts. He's talking about how increasing average speeds adversely affects the ability to follow closely so that any increase in actual throughput is not directly proportional to higher speed. His math demonstrates this pretty much spot on. More pertinently, he's talking in the context of a bottle-neck – a specific stretch of road and not end-to-end trips. That you reach your destination sooner by going faster by end-to-end average is not relevant to the bottle-neck.
Gaps are not an individual parameter but directly depend on speeds. As such, it is not one that traffic authorities can control – one needs what one needs to be safe and erring on the wrong side(closer) has way more cons than erring on the far side. Beyond that, a person deliberately leaving a larger gap is not a real problem because surrounding traffic will somehow adapt to use it. It is only a problem if the flow is discontinuous – say like leading in to a light-controlled intersection.
Well, 1 mph does have lower capacity, it's just that as you get above ~20 mph you get diminishing returns. Regardless of how fast you go, if you leave two seconds between cars you'll always be limited to 1800 cars per hour – one car every two seconds.
I'm not familiar with these signs on European freeways, but leaving two car lengths at 60 mph would mean that you're following at one third of a second. That is crazy driving. The CA DMV recommends three seconds. I doubt any road agency recommends much less.
There is certainly a dilemma – in cases where we cannot add lanes, then increasing capacity must rely on ideas like increased speed and decreased distances between vehicles.
The fact that those may compromise safety is simply a restatement of the conflicts that SFMTA faces anyway. It has a twin mandate of increasing safety and keeping the traffic moving. And that's a balancing act – success in one may imply failure in the other.
So ultimately it comes down to what the voters really value. They may pay lip service to slogans like Vision Zero. but how much inconvenience and congestion are they willing to tolerate so that someone they don't know has a slightly higher chance of not dying?
The number I saw was a two second gap, and those signs may have been such that a two second gap was suggested. It's not like i got out and measured them.
My point was more that if we don't increase speeds and we don't reduce gaps then we have to add more lanes.
Nobody likes that idea but if all the other ideas fail them what remains, no matter how ugly, becomes inevitable.
> increasing capacity must rely on ideas like increased speed
True, but only to an extent. If people do not feel safe at the posted speed limit given the lane widths and the reduced visibility(->fog), they will drive slower. If the speed was lowered below 85%ile on a traffic engineer's recommendation, then there may be some wiggle room for increasing it. Nevertheless, increasing speed will always increase distances – gains in efficiency will not be directly proportional – nothing any agency can do about it. Moreover this can't be done in isolation – S.B. GG leads to a 35mph zone, increasing speeds from current 45 mph will only cause congestion to back up on to it faster, unless speed limit is increased further up the pipe as well.
> decreased distances between vehicles.
This is not an independent parameter! It is not an idea! It is not something any agency can manipulate! It is just an observable phenomenon useful for measurement and analysis … at least until the advent of complete and connected automated driving.
Also consider how reducing safety affects congestion. Would you rather have a GG that requires 5 minutes longer on an average – or one that takes 5 minutes less but takes up to an hour once every week due to a collision? This kind of uncertainty has -ve repercussions on scheduling of both personal life and economic activity.
Or the option you didn't mention– make more effective use of the infrastructure we have, by getting more than one person in each vehicle. This has the added bonus of reducing congestion of local streets, and parking, and pollution. And not costing billions of dollars.