Did your state's early interstate system evolve intelligently?

[flowmotion]

I've taken courses in traffic engineering that have dealt with signal timing and progression. The concept of "mandatory red" was never discussed. The whole objective of signal coordination is to keep traffic moving, so purposefully stopping platoons of traffic multiple times doesn't really make sense with that goal.

I think it's interesting that traffic engineering instruction still focuses on "keep the traffic moving" rather than pedestrian safety, speed limit enforcement, and so forth. "Mandatory Reds" are pretty obviously widely employed, so it must be something that's taught in the trades rather than in school.

Either way, Traffic Engineering in San Francisco must be so unique that the Engineers probably must frequently 'throw out the book' and figure out the best contextual solution. I've been looking at the City's bicycle lane plans, and there seems to be a lot of very good thought put into integrating bikes into the street network while still maintaining auto traffic.  I'm sure a lot of local engineers have an instinct for what works based on their knowledge of local drivers and traffic behavior that can't be summed up in signal timing tables.

Now I'm feeling regret for dragging the thread totally off-topic. So, US101 in CA between SF and LA should have been included in the Interstate system ... I can't imagine the logic which would have excluded it.

[agentsteel53]

I think it's interesting that traffic engineering instruction still focuses on "keep the traffic moving"

that is the basic function of roads.

rather than pedestrian safety

a secondary function, to be subjugated to the right of basic travel.  if pedestrians want to travel on the right of way, they should learn to run at 35 mph.

speed limit enforcement

an arbitrary set of standards, without any sort of redeeming value.  speed limits are the lowest common denominator of the bureaucrat - preventing the driving populace from going at reasonable speeds, for the sake of raising revenue.

[NE2]

a secondary function, to be subjugated to the right of basic travel.  if pedestrians want to travel on the right of way, they should learn to run at 35 mph.

Bullshit. There's no right to travel at 35 mph.

[agentsteel53]

Bullshit. There's no right to travel at 35 mph.

it is an arbitrary number, but the fact is, that road design should allow for travel at velocities which are within the normal range of motor vehicles.

that is what roads are designed for.

[TheStranger]

So, US101 in CA between SF and LA should have been included in the Interstate system ... I can't imagine the logic which would have excluded it.

It was submitted (in two segments - 101 from LA to SF, and then from the Golden Gate Bridge to Route 37) in the late 1940s proposals but rejected - I do wonder if the reasons for this not being added were ever written down somewhere.

Personally I do like the fact that you still have two major American cities connected directly by a US highway rather than an Interstate, though that's more a function of geographic circumstance than anything else.  (And one could argue that when I-5W existed, that this was more of the case on the Interstate end, even if 5W only came within 5 miles of SF city limits.)

[NE2]

Bullshit. There's no right to travel at 35 mph.

it is an arbitrary number, but the fact is, that road design should allow for travel at velocities which are within the normal range of motor vehicles.

that is what roads are designed for.

Maybe, but you speak of a right to travel at such velocities. There is none in the constitution or common law (the 'right to travel' comes from the latter).

[Scott5114]

The UN recently declared Internet access to be a human right, yet you don't see that in anyone's Constitution. There are a lot of things that we consider human rights that aren't actually protected de jure.

Also consider the fact that Jake usually speaks sarcastically and exaggerates things for rhetorical purposes and you'll soon realize that this is a debate you would be foolish to spend much more time on.

[NE2]

Those commies at the UN would be more likely to declare jaywalking to be a human right. Fuck 'em.

[agentsteel53]

Those commies at the UN would be more likely to declare jaywalking to be a human right. Fuck 'em.

I have a strict policy against sexual intercourse with communists.  In fact, the only people who meet my standards of desirability are Ayn Rand and her evil twin Bearded Spock.

[Scott5114]

Those commies at the UN would be more likely to declare jaywalking to be a human right. Fuck 'em.

Jaywalking isn't a human right because it interferes with the human right to drive at 35 MPH.

[roadfro]

I think it's interesting that traffic engineering instruction still focuses on "keep the traffic moving" rather than pedestrian safety, speed limit enforcement, and so forth. "Mandatory Reds" are pretty obviously widely employed, so it must be something that's taught in the trades rather than in school.

It's more like traffic engineering focuses on "keeping all traffic moving safely and efficiently". The "all" encompasses vehicles, bicyclists and pedestrians, not just vehicles alone--although admittedly it has been only recently in the traffic community that more equal consideration has been given to multi-modal transport as opposed to singular focus on vehicles, and vehicle transport is still the predominant consideration. It's the actual design of the road and related traffic controls that traffic engineers concern themselves with--things like enforcement are left up to the police and public safety officials (but sometimes with input from the engineering side).

I would argue that "mandatory red" is not something widely employed, at least not consciously. Again, in the interest of keeping traffic moving, there is little reason why there would be a need to deliberately stop traffic if it is possible to keep it moving. If talking about coordinated signal systems, traffic moving much faster/slower than the assumed progression speed (typically at or near a posted speed limit) may find itself drifting outside the progression window, thus encountering more red lights and making it seem like being forced to stop.

[J N Winkler]

I would argue that "mandatory red" is not something widely employed, at least not consciously. Again, in the interest of keeping traffic moving, there is little reason why there would be a need to deliberately stop traffic if it is possible to keep it moving. If talking about coordinated signal systems, traffic moving much faster/slower than the assumed progression speed (typically at or near a posted speed limit) may find itself drifting outside the progression window, thus encountering more red lights and making it seem like being forced to stop.

Aren't there combinations of speed limit and signal spacing which render signal progression non-attainable at certain points within a district subject to traffic signal control?  This could result in apparent "mandatory reds" along certain itineraries within that district.

[mtantillo]

I would argue that "mandatory red" is not something widely employed, at least not consciously. Again, in the interest of keeping traffic moving, there is little reason why there would be a need to deliberately stop traffic if it is possible to keep it moving. If talking about coordinated signal systems, traffic moving much faster/slower than the assumed progression speed (typically at or near a posted speed limit) may find itself drifting outside the progression window, thus encountering more red lights and making it seem like being forced to stop.

Aren't there combinations of speed limit and signal spacing which render signal progression non-attainable at certain points within a district subject to traffic signal control?  This could result in apparent "mandatory reds" along certain itineraries within that district.

Yes.  Like any crosstown street in Manhattan (the avenues are coordinated, the cross streets, therefore, are not).  

Mandatory reds are sometimes employed by traffic engineers to "regroup a platoon".  Basically, if you coordinate well along a corridor, most traffic will never see a red for a while...this lets the platoon of vehicles spread out.  Then you come to an intersection with a short green (lot of cross traffic), and the entire platoon can't fit through because it is too spread out.  So rather than risk artificial congestion due to the platoon not making it through the signal, they time it a little out of sync to catch the front of the platoon just as it turns red which forces the platoon to re-group.  Then when the signal turns green, those cars in the regrouped platoon can all get through.   

Obviously, significant work needs to be done to ensure that the volumes and progression can support this, because its very easy to screw this up and make things worse. 

[roadfro]

I would argue that "mandatory red" is not something widely employed, at least not consciously. Again, in the interest of keeping traffic moving, there is little reason why there would be a need to deliberately stop traffic if it is possible to keep it moving. If talking about coordinated signal systems, traffic moving much faster/slower than the assumed progression speed (typically at or near a posted speed limit) may find itself drifting outside the progression window, thus encountering more red lights and making it seem like being forced to stop.

Aren't there combinations of speed limit and signal spacing which render signal progression non-attainable at certain points within a district subject to traffic signal control?  This could result in apparent "mandatory reds" along certain itineraries within that district.

If you're talking overall progression for a network of signalized intersections, then yes it is conceivable that there will be points in the network that progression will be much less than desired. This can depend on a number of factors which can include speed, spacing, movements (one-way vs. two-way, left turn control) and signal phases (protected left turns, etc.).

However, if you're just looking at the signal coordination of a single roadway, a decent progression window can be achieved for the entirety of the arterial. This is relatively easy to obtain, just by putting the start of coordinated signal phase the same for each intersection, then adjusting the offset that phase to account for the speed and distance between signals. Traffic analysis software such as PASSER II and Synchro can determine appropriate settings for a coordinated arterial relatively easily, with speed and turning counts used as minimal inputs.

Mandatory reds are sometimes employed by traffic engineers to "regroup a platoon".  Basically, if you coordinate well along a corridor, most traffic will never see a red for a while...this lets the platoon of vehicles spread out.  Then you come to an intersection with a short green (lot of cross traffic), and the entire platoon can't fit through because it is too spread out.  So rather than risk artificial congestion due to the platoon not making it through the signal, they time it a little out of sync to catch the front of the platoon just as it turns red which forces the platoon to re-group.  Then when the signal turns green, those cars in the regrouped platoon can all get through.

Like I've said, I've never heard the term "mandatory red". The above example makes sense, but one has to wonder if there are other ways to achieve a similar purpose. I'm going to have to talk with my traffic engineering professor and consult some sources--I'm genuinely intrigued as to just how common this is. Although even the whole concept of coordinated signal timing and progression is still new to many jurisdictions...

[ShawnP]

Thanks for the linky. Interesting reading on the history.

[vdeane]

Mandatory reds are sometimes employed by traffic engineers to "regroup a platoon".  Basically, if you coordinate well along a corridor, most traffic will never see a red for a while...this lets the platoon of vehicles spread out.  Then you come to an intersection with a short green (lot of cross traffic), and the entire platoon can't fit through because it is too spread out.  So rather than risk artificial congestion due to the platoon not making it through the signal, they time it a little out of sync to catch the front of the platoon just as it turns red which forces the platoon to re-group.  Then when the signal turns green, those cars in the regrouped platoon can all get through.   

Why does traffic need to be in platoons at all?  When I'm driving, the last thing I want to be in is a platoon.  I prefer to choose my own speed, not give that choice to the vehicle in front of me.

[corco]

Why does traffic need to be in platoons at all?  When I'm driving, the last thing I want to be in is a platoon.  I prefer to choose my own speed, not give that choice to the vehicle in front of me.

While I agree with you from a driving standpoint, it helps traffic at unsignalized cross streets/driveways turn- a steady stream of cars is harder to turn into than clumps with gaps

[roadfro]

Why does traffic need to be in platoons at all?  When I'm driving, the last thing I want to be in is a platoon.  I prefer to choose my own speed, not give that choice to the vehicle in front of me.

Coordinated signal timing is based on platoons. The idea is that subsequent signals are timed such that the platoon of vehicles departing the first signal at the onset of green will reach the next signal during green as a group, so the entire group can pass through multiple signals in a row without stopping. Vehicles that deviate too far from the travel speed of the platoon (i.e. the speed the signals are timed for) will eventually encounter a red signal by either arriving too soon at a light (traveling ahead of the group) or arriving too late (slowing behind the pack).

Outside of coordinated signal timing, there isn't much need to keep traffic in platoons. I'd say platoons in any other instance could be more harmful--hence why ramp meters exist.

[Brandon]

However, some roads work much better than others at this.  Take, for example, Telegraph Rd (US-24) in Michigan versus IL-59 in Will and DuPage Counties, Illinois.  The absence of left turn signals along US-24, IMHO, makes these platoons more predictable and flow much better for miles on end than the over-signalization with dedicated left turn signals long IL-59.

[InterstateNG]

However, some roads work much better than others at this.  Take, for example, Telegraph Rd (US-24) in Michigan versus IL-59 in Will and DuPage Counties, Illinois.  The absence of left turn signals along US-24, IMHO, makes these platoons more predictable and flow much better for miles on end than the over-signalization with dedicated left turn signals long IL-59.

In most of Oakland County, yes, even with the mandatory red at 15 Mile.

Once you get south of 696, the lights aren't synced as well.

[brownpelican]

<---Is glad that I-10 wasn't routed to follow Chef Menteur Highway (US 90). Parts of that road may be gone.

I bet Baton Rouge area leaders today wished that I-410 (would have roughly followed Airline Highway) was built now that I-10 and I-12 has heavy traffic today.

I think the state did a good job with most interstate routing.

[Brandon]

However, some roads work much better than others at this.  Take, for example, Telegraph Rd (US-24) in Michigan versus IL-59 in Will and DuPage Counties, Illinois.  The absence of left turn signals along US-24, IMHO, makes these platoons more predictable and flow much better for miles on end than the over-signalization with dedicated left turn signals long IL-59.

In most of Oakland County, yes, even with the mandatory red at 15 Mile.

Once you get south of 696, the lights aren't synced as well.

Never had a problem with them between 696 ad 94.  I usually find the mandatory red is at Ford Rd.