Analyzing a Corridor
Previously we went into what the warrants for signals were and went through some examples. So now let’s look at all the signals on a corridor. I picked South Lyndale Ave (with the exception of the signal at the ramp to MN 62, which is Mn/DOT operated. I’m going to cheat and just say that one is warranted rather than try to get data). This corridor has many busy intersections, some not so busy. Some signals have been there forever, and some have been recently reconstructed. Once again here is the chart for vehicle warrants:
4 Hour Vehicle Traffic Signal Warrants
Lyndale Warrant Analysis Raw Data
So the Four Hour Vehicle Warrant, the signals at the I-94 Ramp, Franklin Ave, 22nd St, 24th St, 26th St, 28th St, Lake St, 31st St, 35th St, 36th St, 38th St, 40th St, 46th St, 50th St, 54th St, and the west ramp of MN 62 meet vehicle warrants. 33rd St, 34th St, 43rd St, 48th St, Minnehaha Pkwy, 53rd St, 56th St, 58th St, and 61st St do not.
A few random notes:
1) I didn’t note what times I took data for because it’s not important beyond being the highest time available, it was generally 7:00-9:00 AM and 4:30-6:30 PM, provided data existed for those hours. If the PM rush hour wasn’t available, the noon “mini-rush hour” was. Asterisks are where Lyndale Ave is the side street.
2) The volume required to meet warrants I got from eyeballing the graph. Real engineers use complicated spreadsheets with macros. Undoubtedly if you’re a programmer (which I most certainly am not) you’d be able to scrape data from the TMC web site and plug it in to the warrant spreadsheets.
3) 22nd was the only intersection that also met pedestrian warrants; I didn’t include the data for that here but I looked at pedestrian warrants if it looked like there was a chance of meeting it.
4) I was a bit surprised by how few pedestrians were crossing Lyndale Ave at Minnehaha Parkway, nowhere close to meeting pedestrian warrants, only 34 in the four hour-long periods. But when I’m there it’s always on my bicycle on a nice summer weekend, not a typical rush hour when traffic is counted.
5) The 4-3 conversion south of Lake St. magically made some signals warranted that were not before.
Here’s a map where I’ve indicate warranted signals in green, and those that do not meet the warrant in red.
Why no Warrants?
So why are there warrant-less signals? Warrants have existed since the beginning of the MUTCD in 1935. So “warrants didn’t exist then” isn’t an excuse. Sometimes a signal was warranted at one time, but traffic patterns have changed. This is particularly startling in Detroit, the archetype for urban evisceration, where a lot of traffic signals aren’t needed simply because no one is around anymore. But patterns change in other cities too. Usually, whenever local residents hear a traffic signal may be removed, local residents are strongly opposed, predicting all kinds of death and mayhem. So cities are reluctant to be too motivated to remove them; normally it comes up when continuing to operate the signal would involve spending money because the signal needs replacing due to deterioration or road reconstruction.
1950s era Eaglelux traffic signal
Sometimes too, cities just do whatever they feel like. Just about every signal on Michigan Ave. in Chicago has a configuration that is a direct violation of the national MUTCD, prohibiting left turns with a sign instead of a red arrow. And Washington state for years used a flashing yellow ball to indicate permitted left turns.
A Notorious Intersection
Going back to 25th St and Lyndale Ave, where a widely publicized car vs pedestrian crash was caught on security cam, it’s hard to make a judgement about who was immediately at fault for the crash. State statute 169.21 says basically that motorists must stop for pedestrians in unmarked crosswalks, but pedestrians must not cross if a motorist cannot reasonably stop. That the pedestrian said it was her fault is not relevant, and all the public has is grainy, zoomed in CCTV footage. So rather than point fingers, lets look at potential ways to fix the underlying problem. Engineers are very pragmatic; if there’s a reasonable engineering way to fix a problem that won’t create other equal or worse problems, they’ll try to fix it.
Lyndale Ave is above the threshold where a 4-3 road diet is workable so we’re stuck with the 4-Lane Death Road. Generally speaking, anything over 15,000 to 20,000 vehicles a day isn’t workable because congestion overwhelms the road, and if there’s a lack of a hierarchical road network, motorists start using local streets instead (this part of Lyndale is at 22,000). Motorists become angry and impatient, thus making poor and even reckless decisions zipping down local streets that weren’t designed for them and where residents may not expect. This seems to be a recipe for disaster.
If you look only at the arterial, the costs of congestion might be worth the benefits of safety on the arterial. But dealing with motorists diverting onto local streets adds a lot of costs and complexity. As we’ll find out later, stop signs (to say nothing about “Slow, Children” signs and similar) are completely inappropriate, ineffective, and even dangerous. Thus they’re very strongly discouraged in the MUTCD for traffic calming or speed control. And when you start stationing police there on a semi-permanent basis or making physical changes like traffic circles, diverters, and chicanes to each and every local street, soon you’re talking about a lot more money than some new paint on the arterial.
I’d also suggest that despite the tendency toward the reaction to blame suburban commuters for all the cars on the streets, Lyndale Ave is probably almost entirely Minneapolis residents. Despite the horrific congestion on our freeways, it’s simply not attractive for suburbanites heading home from downtown to try to get off and navigate city streets, especially with the MnPass lanes available for people that are unlucky enough to have to drive in rush hour regularly. Traffic counts would seem to back me up. There’s over 30,000 vehicles a day north of Franklin. Half the traffic is gone by the time you get past Lake St, and on the MN 121 entrance to I-35W and MN 62, there’s only 7000, and only a subset of that would have traveled the entire length.
Lyndale Ave and 25th St.
So what else can be done? Legally it’s a crosswalk (despite the media calling it jaywalking) and there’s not a ‘No Pedestrians’ sign. But the lack of a painted crosswalk, and the lack of even curb cuts, sends a message to both motorists and pedestrians that this isn’t a place for pedestrians to cross. Adding marked crosswalks and curb cuts would be a good place to start. Maybe there’d even be space to build a pedestrian refuge island. But what if we could do even better and make motorized traffic just disappear for a short time to allow pedestrians to cross? We’ve talked about a lot of the warrants, but here is the final one: Warrant 6: Coordinated Signal System:
Progressive movement in a coordinated signal system sometimes necessitates installing traffic control signals at intersections where they would not otherwise be needed in order to maintain proper platooning of vehicles.
Standard:
The need for a traffic control signal shall be considered if an engineering study finds that one of the following criteria is met:
- [not relevant]
- On a two-way street, adjacent traffic control signals do not provide the necessary degree of platooning and the proposed and adjacent traffic control signals will collectively provide a progressive operation.
The Platoon
When you have a number of signals, you can time them to create a “Green Wave” with platooning. The idea is that you want to keep the cars together and try to give them green lights as they arrive at each intersection. Spaces between platoons give pedestrians a chance to cross and motorists a chance to enter from side streets and driveways. Doing this in a stream of traffic would at best slow the traffic down, and at worst, it results in crashes when pedestrians and motorists get impatient and start to take chances.
In the name of research, I did something I normally try to avoid at all costs: drive surface streets at rush hour. Driving southbound at 6:00 PM, I tried to drive a steady 30 mph. North of Lake St I was unable to do that with the streets being swamped with traffic and turning cars and stopping buses. South of Lake St I was able to do it for the most part. I was stopped for seven out of the 21 signals between Franklin and 58th, in some cases arriving a few seconds too late or soon.
There’s obviously been some attempt at progression but it needs tweaking. Minneapolis is way, way behind in terms of traffic signal technology and ideology; in the suburbs every one of the signals would have sensors for the main street (as well as flashing yellow arrows) and with advances in traffic control, the signals could figure out the queue length of the next signal and traffic speeds and adjust themselves accordingly. There was obviously no attempt to ensure platooning in both directions, leading to excessive delays when people want to cross at unsignalized intersections. There’s plenty of time when traffic has ceased in one direction, but it’s almost always flowing in the other. (It should be noted that this is where refuge islands would help immensely.)
So how do we set up a situation where motorists on Lyndale Ave can travel without hitting too many lights and motorists and pedestrians at non-signalized intersections get a chance to enter the roadway and cross it? An engineer I talked to, in typical engineer fashion, didn’t want to give an answer without having done a traffic study, but when pressed, the engineer commented that generally on a 30 mph urban street, a 1/2 mile spacing is enough; a source online suggested 1/4 to 3/8th mile. In order to enable a bi-directional green wave, they they should be as evenly spaced as possible, or failing that, in even multiples. (In no case can signals be less than 1000 feet; that’s not a problem on Lyndale Ave, but in downtown it’s best to just forget about it and turn all the signals green at once.)
Obviously some unwarranted signals would have to be removed, some warranted only by Warrant 6 kept, moved, or built. Maybe even some warranted signals might have to be removed–remember, just because you have a warrant does not obligate you to build or maintain a signal. But in the end, you make things better for all people, whether in a car driving down Lyndale Ave, in a car trying to enter or cross, or on foot trying to cross. Even in an urban environment, transportation doesn’t have to be a zero sum game.
The next article will look at warrants and justifications for traffic control devices other than signals.
This stuff is important to me, so I’m going to cover a few points that stuck out:
– The footage on the personal security camera for the crash at 25th/Lyndale isn’t grainy. It’s very clear that she’s standing in the roadway (not on the curb, not at the bus stop confusing drivers what she’s trying to do), which gives her clear legal right of way. She waited and waited and then left her spot when there was a break in traffic, more than enough for drivers to have ample time to react and stop. This was obvious since the vehicle in the left southbound lane did in fact stop for her, but the red car veered around it and hit her. There was no question under the law or even the practical situation that every car should have been able to stop.
– 15-20,000 is not the limit of what’s workable for a 4-3 conversion. It’s just a rule of thumb. Hourly counts per lane matter more, but even then, whatever the threshold we set frames the discussion around avoiding vehicle delay as the primary goal above other ones. But, as we know, traffic counts well in excess of 25,000 have worked across the country with very minimal impacts to motorists.
– We actually have ways of making using side streets less desirable even in the face of increased arterial congestion (for motorists). We can divert them. Physically calm them with chicanes. Etc.
– As you note, most people driving on Lyndale at peak hours do live and/or work in the area and aren’t Bloomington residents taking a scenic drive home. With that in mind, we can also accept more congestion on Lyndale (for motorists) as an outcome if we make other modes more attractive. Biking and transit are good ways to get around for commutes of 1-7 miles, and as I have written on this site, there are many people who live and work in Minneapolis that drive for very short trips.
– Your discussion around platooning and light timing proves that engineers are neither pragmatic nor do they care about what the law states. Pedestrians don’t have to wait for a gap in traffic (which, as Lyndale proves, is very difficult given 2 lanes in each direction).
– I respect your or anyone elses interpretation on this one. As I noted I had a difficult time interpreting it, and at any rate fault was not the point if we could do something to prevent the underlying situation.
– SInce AFAIK there hasn’t been a traffic study on Lyndale Ave, the rule of thumb is all I had to work with. If people in the neighborhood are passionate about a potential road diet maybe they should lobby for getting a traffic study done.
– As I noted, traffic calming on side streets is an option, but if you calm one street drivers will divert to another and pretty soon you’re playing “whack-a-mole”, and it becomes a much more expensive and elaborate project than re-striping the arterial. I didn’t say it wasn’t an option, just that it becomes more expensive complex than what some people imagine.
-Fair point, if we mess things up for motorists maybe bicycling or walking to and from a bus stop in the rain, cold, snow and heat or becomes more attractive relatively.
– Creating safe gaps for pedestrians where there’s an obvious problem for them crossing seems to be extremely pragmatic to me, and there’s nothing illegal about it.
I think if we want to change Lyndale to be better for pedestrians, people on bikes, and even transit (per the city’s recent;y adopted modal hierarchy), a traffic study is not the place we should start. I’m 98% certain what the outcome of one would be.
I don’t think calming side-streets needs to be so elaborate or expensive that we can’t eliminate the vast majority of cut-through traffic on the cheap. I’d start with more stop signs at every corner. Bolt-down posts can be used to narrow intersections, or even mid-block. Or, they could be used to close off streets as through-routes to cars while letting bikes through. We don’t need concrete today to do those type of things.
I don’t think walking or biking in the rain or cold or heat should be seen as such a negative. If businesses want to build skyways in downtown for people to have climate-controlled walking environments, sure. But it’s a part of our existence to deal with the elements every now and again. For every bitterly cold or rainy day, there are 5 perfectly comfortable ones. I’m obviously expressing an opinion here, but public policy should not default to prioritizing driving simply because it means you don’t get wet while doing it.
My point on engineers had nothing to do with illegality, rather that they’re not pragmatic as you state. The law does say pedestrians have the right of way while crossing. But “pragmatism” means engineers admit drivers won’t follow this law and it’s simply best to devise a system of signals that create gaps for pedestrians, eventually, no matter how long they have to wait and no matter how dangerous it is when they do cross. Engineers are quick to justify a road’s design because calming it will cause irrational drivers to go onto side streets, but they give none of that foresight or design forgiveness to what pedestrians/cyclists will do when faced with long waits or a crappy bridge over a road to cross or long lights on a bicycle boulevard etc etc. This is why it’s not pragmatism, rather clear priority backed up mostly by policy baked into engineering guidelines.
I don’t understand why we assume that “creating congestion” on a primary street means we’ll push drivers to side streets, any more than we could assume that “creating congestion” (alternately described as “making a place safer and faster for walking, biking, busing, etc”) actually induces driving demand downwards.
I also don’t understand how it’s legitimate for the platoon effect to be used to justify traffic patterns, when the law states that drivers must yield to pedestrians regardless of how platooned they are.
If you create congestion, the path of least resistance for motorists is to try to drive around it rather than start riding a bicycle in zero degree weather. This phenomenon is found on the FHWA informational site on road diets too:
http://safety.fhwa.dot.gov/road_diets/info_guide/ch3.cfm
See section 3.5.2
That section (actually, the entire resource) says nothing about odds of motorists in taking side streets vs changing modes (or, less impactful to their lives, shifting the time they travel) given an increase in congestion. I don’t know how much it would vary, but I’d guess the odds of mitigation would be higher in an area like Uptown than, say, more suburban parts of Bloomington (or beyond, where many of the studies are done by the FHWA) where transit runs considerably less often and there are far fewer destinations to get to.
I’m interested in your take of how many days out of the year are either 1) raining 2) snowing 3) below freezing (~150 days a year where the low is below 32) or below 0, whatever the threshold we want to say people simply won’t bike (or it’s too unsafe for kids to be exposed too long, or whatever). Compare that number of days to places with 30% average annual bike mode share. And then take into account that buses and trains usually have roofs and heat and A/C and they’re pretty good alternatives to biking if the cold/rain is something you don’t like. I dunno, food for thought.
I wonder if transit had been afforded the bells and whistles roads got back in the 50s and beyond if it wouldn’t be much more competitive. No need to pay to get on slowing the bus down (equivalent to almost no tollbooth freeways in urban areas), a rapidly-built network of grade-separated facilities without regard for the people they displace (200’+ open cut trenches in places of housing) or the ones that remain (20′ tall sound walls and viaducts 3x the size of elevated rail viaducts), and on. Who knows for sure I guess.
Also I think we have technology to be much more adaptive to weather today. I know this first hand… When I bike to work, I keep an eye on the radar so I can choose to head home a little early or stay a little later if there will be a storm rolling through. We have radar screens and bus schedules and all the rest on these magical little devices we carry with us everywhere. That’s mitigated much of the “downside” of weather events impacting travel.
This is just like some streets in Saint Paul, only more so! (lol) The starting point for the conversation shouldn’t be a “study”, or if it is, the starting point of the study should be creating safe ways for people to cross the street on foot, especially during busier times of day. That should be the given baseline, and the other variables like congestion or access should be negotiated only after you have addressed the basic human right to walk across the street.
I’m getting ahead of myself and will cover this in Part 3, but stop signs are ineffective, and even counterproductive and dangerous when attempts are made to use them for traffic calming and speed control, something that’s been the consensus of over 70 studies, which is why there’s clear discouragement in the MUTCD from attempting to use them for that purpose. So your limited to physical changes to the roadway. Those can be done of course, but they’re not inexpensive.
Forgive me for not trusting anything the MUTCD says. Is there other evidence of this? They seem to work very well in dense urban areas, anecdotally. (46th and Grand, 51st and Xerxes, etc).
He’s not referring to local commercial node examples where there is a more even spread of vehicles. He’s referring to the Minneapolis tendency to put stop signs every other block in residential areas for “traffic calming”. In my own experience, I’ve found that at such setups, drivers tend to zip ahead from the stop sign far faster than they would otherwise. I noticed this in my old neighborhood as the city started adding stop signs.
Yeah the “basket weave” is a bit counter productive apparently.
Is this actually true? While I find anything above 20 to be way too fast for my street, I don’t really see cars going above 30 between stop signs. When I ride on Bryant between Lake and Franklin, a common cut-through for vehicles despite the speed bumps, vehicles move quicker than I’d like, but still below the speed limit. Is there evidence to suggest that removing those stop signs would reduce speed mid-block somehow?
The ‘jam on the gas between stop signs or lights’ effect is very real on arterials with 35+ mph design but a posted 30 mph speed limit, but I just don’t see it happening on Minneapolis neighborhood interiors (or at least, at speeds traffic engineers/MUTCD insisting on 30 mph limits would find unacceptable).
The problem with defending or refuting some of these points you bring up is I’m not an engineer, so I don’t have access to a lot of the original studies not subscribing to engineering journals and such. When multiple studies become engineering consensus and appear in the MUTCD and the FHWA site, then they are more available. Because they are the consensus of engineers I repeat them in good faith without further comment or original sources.
Same way with signal warrants topping off at 80. That’s the consensus of engineers; As just a nerd with internet access I couldn’t make my own judgement on whether it’s too high, to low, or just right.
The next part of the series will have a link to a summary of some of these studies. Are they valid on your specific street? I don’t know, but I trust them in general, engineers are a lot smarter at this than I am.
I’m not aware of any studies that have been done. But my own anecdotal evidence from my old neighborhood (Diamond Lake/Nokomis area) suggest that yes it does happen. I’ve also seen plenty of rolling stops along 60th (and been guilty of it myself if there was no other traffic at the intersection).
re: the last point:
It’s especially pragmatic when you consider how unlikely it is that a driver is going to stop for a pedestrian who is standing on the curb. There has to be a gap for the pedestrian to at least take a step or two into the intersection with enough time for the oncoming drivers to react and stop.
How does that have any bearing on the situation? Pedestrian stands on the curb and holds out a “stop” hand towards oncoming traffic = much more safe and effective, yet still ignored, than actually stepping into a lane.
If you make a street congested, cars might drive on side streets. So engineers say we can never allow congestion to happen, cars must flow smoothly at all times.
If you make a street really difficult to cross by saying “patiently wait for a gap in the cars,” pedestrians are just going to start trying to dart into traffic. So engineers should say “Let’s make the road easier to cross” so this side effect doesn’t happen. But instead they just double down on making it easier for cars, because how can we plan for pedestrians if it might rain one day and we all know no one walks in the rain.