Category Archives: traffic signals


Always Green Traffic Control

Nick Musachio, local inventor in Minnesota, has just been issued a patent (No. 8,711,005) for his Always Green Traffic Control System. (Since this is transportation, we will abbreviate this AGTCS)

Imagine you have an isolated signalized intersection, operating near but below capacity. If vehicles were able to travel at the correct speed when approaching the intersection for a significant distance, they should be able to  travel through the intersection without hitting a red light or being delayed by standing queues. If at 45 MPH they would hit a red light, but at 35 MPH would get a green, they should be informed to reduce speed to 35 MPH. This not only reduces driver delay, but should decrease crashes and decrease emissions, both of which are exacerbated by intersection control and braking and acceleration.

How would drivers know which speed to travel? An upstream Variable Message Sign with Dynamic Speed Limits (tied into the traffic signal controller cabinet, or with the pre-programmed traffic signal timings) would tell them the best speed to avoid stopping. If only the first car in a platoon does this (on a 1 lane road), all following cars are controlled by default.

Audi has a similar in-vehicle system. That is only useful if the traffic agencies produce live feeds of traffic signal timings. Comment: it is appalling that such a traffic signal timing live feed doesn’t generally exist (even transit agencies, not historically known for their cutting edge research) have GTFS.

AGTCS is infrastructure based, and works for all vehicles anywhere an agency wants to set it up.

Some videos and simulations below.

You have got to love renderings


I found this rendering of 222 Hennepin earlier today, after reading Bill’s post on architecture. The part that I liked best is the traffic light. First it is sideways, a design that is used in some places in the world, but not Minneapolis, for a lot of good reasons.

I grew up in Columbia, Maryland, which for many years had sideways traffic lights, mainly as an architectural distinction, but which were abandoned because of the confusion created.

A major problem of such uncommon lights is that color-blind person might not know if the green is on the left or on the right. In Wisconsin (as everywhere else in the US where it is done, and standardized in the MUTCD, it is red on the left, green on the right.

In the rendering, it is the opposite.

It makes you wonder what other tricks and graphical shortcuts are going on to make the rendering desirable to approve and move into, but won’t really turn out as implied.



Auctioning Green Time

Eddie, a traveler in a hurry arrives at a traffic light from the East. He would pay up to $18 to save an hour. Sue, a less-hurried casual traveler arrives from the South, she would only pay $6 to save an hour of travel right now. Who gets the green light, who gets the red? Presently this is decided without consideration of how much Eddie or Sue would be willing to pay to save a few seconds or a few minutes. No one has the ability or the authority to make a transaction occur where Eddie can pay a few cents to Sue and get the green light while Sue waits for the light to change. Until recently, this was because it was technologically infeasible, but in recent years, advances in transportation signal technology and real-time wireless vehicle-infrastructure communications have made this once impossible transaction possible. Now it is institutional constraints that prevent this from happening. Traffic signals are in almost all towns, cities, counties, and states publicly owned and managed. Imagine instead that this was a service that private firms would bid to supply.

A new organization, LightSpeed Traffic, has paid your city $100,000 a year for the privilege of managing traffic signals. Instead of this being a cost center for the city, it is now a revenue generator. Why do they do this? A private operator is able to use traffic signals more efficiently from an economic perspective than a public agency, they can obtain revenues from sources such as:

  • Acting as the facilitator of transactions between travelers as described above to minimize weighted travel delay, Eddie pays $18/hour (30 cents a minute) and saves a minute, Sue is compensated at $6/hour (10 cents a minute), and LightSpeed Traffic keeps the difference, 20 cents a minute, to cover the costs of operating traffic signals, paying the city for the franchise, and earning some profit for shareholders. This could scale up, by summing all of the traffic from each approach, and multiplying by their respective values of time. (See for instance Varirani and Ossowski (2012), or Dresner and Stone (2008) for illustrations.)
  • Providing real-time traffic data to a new generation of GPS companies that aim to provide routing information to travelers. By investing in the signals and sensing technologies around the intersection (and at nearby intersections they also manage), LightSpeed has accurate estimates of arterial travel time, and can make predictions about future travel times, data that is extremely valuable to those providing real-time advanced traveler information.
  • Administering red-light running cameras.
  • Advertising at the traffic signal when it is red (as suggested by the linked patent). Like transit companies who sell advertising on the interior and exterior of buses and bus stops, traffic signals have laid out before them a captive audience that might be interested in real-time information, especially information that was customized by place and traveler. LightSpeed has the authority to coordinate advertising with traffic signal timings. Not making the light extra long to force drivers to wait, but simply to use variable message signs to display ads when the light is red anyway, and to benefit travelers by displaying real-time travel information when the light is green.

Presently a few companies operate traffic signals under contract to municipalities, notably in Sandy Springs, Georgia. None yet use signals innovatively as described above.

Obviously this can get quite complex: there may be more than one approaching driver, how do you decide the baseline to estimate vehicle time-saved or time-list by adjusting signal timings, how does this work in networks instead of just isolated intersections.

But scarce resources (like two vehicles seeking to use the same space at the same time) can be allocated in many ways other than arbitrarily or first-come first-serve, to the benefit of all. Sometimes the best solution is a yield sign, sometimes a stop sign, sometimes a roundabout, sometimes a traffic signal, sometimes a grade separation. To be clear, it is not always a traffic signal. When it is a traffic signal, there might be some merits to thinking creatively about the organization and operation of the market that is created by the rationing of time for the benefit of all.

SMART Signal

UM News reports on my colleague Henry Liu’s new SMART Signal Technologies startup: University of Minnesota startup to improve traffic flow on congested roads:

“Based on research from the University of Minnesota, SMART Signal Technologies, Inc., will commercialize a system to better predict and manage the flow of traffic on roads controlled by traffic lights. The system could potentially cut down on traffic congestion and help drivers save both time and fuel.
Using data from existing traffic signal equipment, the system accurately calculates queue length at signalized intersections. These data, collected in real time and archived in a database, will allow cities across the state to better mediate the flow of traffic at peak times using real time performance measures provided by the system.”

I have talked about this before. I hope it gets widely deployed, what we don’t know about travel times arterials in real-time is embarrassing.

SMART-Signal Live


My colleague Henry Liu has been working with MnDOT the past several years on deploying the SMART-Signal system. It is live on Mn trunk highway 13, and the real-time intersection level of service, queueing, and speed data coming from the system are available online here. As the website says:

“Although measuring and archiving freeway traffic performance using commonly available loop detector data has become a norm for many transportation agencies, similar approaches for urban arterials do not exist. In practice, operational data from traffic signal systems are neither stored nor analyzed, which prevents proactive management of arterial streets. The development of the SMART-Signal (Systematic Monitoring of Arterial Road Traffic Signals) system fills in this gap. The SMART-Signal system simultaneously collects event-based high-resolution traffic data from multiple intersections and generates real-time arterial performance measures including intersection queue length and arterial travel time. The development of the system has laid the groundwork for better traffic models and control strategies and opens up entirely new opportunities for managing traffic on congested roads.
In the SMART-Signal system, a complete history of traffic signal control, including all vehicle actuation events and signal phase change events, are archived and stored. At each intersection, an industrial PC with a data acquisition card is installed inside the controller cabinet, and event data collected at each intersection are transmitted to the data server in real-time using an Ethernet connection. Using the event-based data, a set of arterial performance measures, especially intersection queue length and arterial travel time, can be estimated. SMART-Signal uses a newly developed algorithmic approach to queue length estimation based on traffic shockwave theory. Cyclic traffic shockwaves at an intersection can be reconstructed using event-based data, allowing for queue length estimation even when the queue of cars extends beyond the upstream vehicle detector. To measure travel time, SMART-Signal simulates the movements of a virtual “probe vehicle” along the arterial road. As the virtual probe moves, it can modify its own state in response to the state of traffic around it by accelerating, decelerating, or maintaining a constant speed at each time step as it encounters queues, traffic signals, and changes in traffic density. SMART-Signal can also optimize traffic signal parameters using the collected high-resolution data. Instead of relying on traditional offset optimization approaches, which are based on manually collected volume data on a typical day, SMART-Signal can account for traffic flow variations by using archived traffic signal data and the derived performance measures.
The SMART-Signal system has been field-tested on three major arterial corridors in Minnesota including six intersections on Trunk Highway 55 in Golden Valley, eleven intersections on France Avenue in Bloomington, and three intersections on Prairie Center Drive in Eden Prairie. A demonstration project is also being carried out on Orange Grove Boulevard in Pasadena, California. A large-scale implementation project currently under discussion with the Minnesota Department of Transportation will monitor 100 intersections in the Twin Cities area using the SMART-Signal system. “

Linklist: May 4, 2012

Wired: Get Ready To Kickstart Project Hexapod:

“Meet Stompy. He’s a hexapod – a six-legged robot being built by a team of 15 students and three instructors at Artisan’s Asylum in Somerville, Massachusetts. And if the rendering above didn’t tip you off, Stompy holds two passengers, can walk over a car and takes up nearly two lanes of road. Needless to say, Stompy is awesome.”

Bloomberg: ‘Jetman’ Soars Over Rio: Video

“Yves ‘Jetman’ Rossy, a record-holding Swiss aerialist, flew his carbon-kevlar jetwing over Rio de Janiero on Thursday morning. During his 11-minute flight he reached a speed of 186 mph and an altitude of almost 4,000 feet.”

Amanda Erickson @ Atlantic CitiesGreening Traffic Lights By Turning Them Off :

“But how’s this for an idea to make traffic patterns greener (and, proponents say, safer): stop using traffic lights altogether. The so-called “naked streets” movement has gained traction across Europe, even in major cities like London.”

[Note to jargon-heads, naked streets = shared space].

Standing There Like Idiots

There are many useless traffic signals. (Some are also useful).
The most useless traffic signal I see everyday (multiple times) is at the intersection of Beacon St. and Harvard Avenue. Not only is there little traffic for the traffic light, so a stop sign (or better a yield sign, roundabout, or shared space) would do, the pedestrian signal has Beg buttons. I just saw someone who looked a lot like Eric Kaler (who is obviously not an idiot) waiting and needlessly obeying the law while pushing the pedestrian signal actuator multiple times to call for a walk signal, which eventually came. If no one pushes the actuator, you actually don’t get a walk signal, so it is working, just pointless.
Why do we have these signals, on a university campus of all places, making pedestrians (who probably are equal in number to cars at this intersection) stand there like idiots while cars can drive through, and even make a “right turn on red”?

Linklist: February 21, 2012

KurzweilAI: Traffic intersections of the future will control autonomous vehicles : “Intersections of the future won’t need stop lights or stop signs. They’ll look like a somewhat chaotic flow of driverless, autonomous cars slipping past one another as they are managed by a virtual traffic controller, says computer scientist Peter Stone, a professor of computer science at The University of Texas at Austin.” [Interesting, but I disbelieve this is the likely technology path, there are 1 million signalized intersections and lord knows how many stop signs in the US, autonomous vehicles will develop protocols with each other before most jurisdictions fix their pathetically antiquated traffic signal controllers.]

Joe Verdoorn @ Newgeography Unintended Consequences of the Neo-Traditional City Planning Model: “This tactical criteria of the Neo-traditional model, however, can create unintended negative consequences. The criteria to which I refer includes:

  • grid street patterns
  • connectivity to adjacent neighborhoods
  • mixed, non-residential land uses
  • alley access/rear loaded house

The inflexible application of these tactical criteria enhances opportunities for criminal activities to occur.”

Via Martin Engel: CALIFORNIA HIGH SPEED RAIL on Vimeo: “a short, fun jaunt through history comparing the Ca. High Speed Train budget to other big ticket national projects.”

Bradley Heard @ GGW Ride The Tide of light rail, Virginia Beach – Greater Greater Washington: “Dubbed “The Tide,” South Hampton Roads’ light rail system made its debut in Norfolk on August 19, 2011. The initial $338 million segment, operated by the regional transit agency, Hampton Roads Transit (HRT), is 7.4-miles, has 11 stops, and is currently located only within Norfolk’s city limits.

Initial weekday ridership during the first year was projected to be only 2,900. However, the 6-month data shows that those early projections have been blown away. About 4,642 people ride The Tide during an average weekday. An even higher number—4,850—use the system on Saturdays, with 2,099 usually riding on Sundays.” [Dumbing Success Down: If they forecast Zero Riders, it would have been Infinitely more successful]