A History of Traffic Management Technology

Earlier I wrote about the history of our Interstate Highway System (Part One and Part Two) and how they were partly a 1930s response to growing urban congestion, as big of a threat to the freedom of mobility as mud and ruts were only a few decades before. However the dream of ending congestion didn’t last too long. By the late 1960s the Minnesota Highway Department (MHD) realized there wasn’t political will to build our way out of congestion, and so they began looking at technology to make the most of what physical pavement  existed. One of the first ideas was the concept of the ramp meter.

The first ramp meter test in Minnesota

Ramp Meter on I-35E  MHD

These were first tested on I-35E as shown. The idea was to literally “meter” traffic so that individual motorists could find spaces to merge. Previously a long line of cars all merging at once could bring traffic to a stop. However later MnDOT began to use them to actually try to limit the number of cars on the freeway. MnDOT would calculate the capacity of freeway bottlenecks, and then use ramp meters to hold traffic above that level on the ramps. This would also repress demand by encouraging people to use surface streets for short trips, streets that generally weren’t built for that volume traffic. In the 1990s I still have memories of waiting 15 minutes at the ramp from Flying Cloud Drive to I-494.

This stopped when state Senator Dick Day (R-Owatonna) got a bill passed forcing MnDOT to declare a ramp meter holiday, basically turning them all off to study what happened.  Day and ramp meter opponents predicted nothing would happen, while MnDOT predicted gridlock and crashes. The final results were somewhere in the middle, and when the ramp meter were turned back on, MnDOT also set the philosophy somewhere in the middle; using them more than mere metering but not to hold as many people back off the freeways as before.

Thec 1970s I-35W Project

In the early 1970s came an  ambitious project for the I-35W corridor. This added permanent ramp meters , but more than that added cameras, traffic speed sensors, electronic signs, HOV bypass lanes, and a dedicated traffic management center  building. The project got started with a grant from the Urban Mass Transit Association to the Met Council. Then the MHD got a $385,000 grant for the coordination center at the downtown exits.


One of the first HOV bypass ramps  MHD

1975 Metro Traffic Control  MHD

Over time this system has expanded beyond to the entire metro freeway system, Today there’s 700 cameras on the metro freeways, managing 400 miles of freeway. With the expansion and fiber optics replacing clunky copper cables, the center relocated away from the building by I-35W to MnDOT district headquarters in Roseville. For comparison here’s two photos from the traffic management cener

Regional Traffic Management

Metro Traffic Control today


Signs and Radio

Along with cameras and sensors to communicate to traffic management came tools to communicate from traffic management back to drivers. Here’s a sign that came with the early 1970s project, which displayed a “traffic grade” on the entrance from downtown.

Early "Traffic Condition" signs

There are of course Variable Message Signs, also known as Dynamic Message Signs (DMS)- Electronic or Electromechanical signs that can display customized messages. The New Jersey Turnpike used to have ones utilizing neon tubing to spell out messages that could selectively be lit up. And as far as my memory goes, into the early 1980s, there was one on I-35W in Burnsville. I never saw it lit up so I don’t know what technology it used, but I’m assuming it was incandescent eggcrate letters like the traffic grade sign. If you’ve seen a 1980s game show you know what they look like.

Around 1990 more substantial deployment happened. These DMS signs were electro-mechanical. The portable ones used flip pixels to form crude letters, while the overhead ones had three lines formed by rotating drums of fixed messages. The portable flip pixels signs could display any message but the overhead ones could only display the most common crash and construction scenarios. These had yellow letters painted on black; the yellow paint was luminescent and was front-lit by black light fluorescent tubes at night.

These were superseded by the familiar all-electronic LED signs, first with amber LEDs and now with signs capable of full color. In Minnesota the color capabilities of the signs aren’t used a lot, in practice only the MnPass lane control signs display something more than yellow on black text.  (And it’s a myth that AMBER alerts were named for the color of the older signs, they’re actually  in memory of Amber Hagerman, a 9 year old girl from Arlington TX.)  Amber only portable signs are still standard and there’s a few amber only overhead signs and electromechanical portable signs left.

Another tool for communicating with drivers was radio. There was a pilot program using an AM station for I-35W in Richfield back in the 1980s, but this really got it’s start in 1989 with a 25 year between MnDOT and KBEM-FM to broadcast traffic information. Eventually 25 “tune radio to 88.5 when flashing” signs went up, and DMS signs could also display this message. In 2004 the contract was downscaled and the signs removed due to budget cuts, as well as likely MnDOT realizing that in-car navigation systems that can graphically display travel times and incidents were the future.

The Urban Partnership Agreement “Smart Lanes”

Although the 1970s traffic management tools were a success, a second rush to deploy revolutionary new technology on I-35W 30 years later was much less successful. There was of course initial enthusiasm.  As a MnDOT report to the legislature put it:

In 2006, the U.S. DOT, in partnership with metropolitan areas, initiated a program to explore reducing congestion through the implementation of pricing activities combined with necessary supporting elements. This program was instituted through the UPAs and the Congestion Reduction Demonstrations (CRDs). Within each program, multiple sites around the U.S., including Minnesota, were selected through a competitive process. The selected sites were awarded funding for implementation of congestion reduction strategies. The applicants’ proposals for congestion reduction were based on four complementary strategies known as the 4Ts: Tolling, Transit, Telecommuting, which includes additional travel demand management (TDM) strategies, and Technology

It included such things as the Marq2 downtown bus lanes, new park and rides, and even new auxiliary lanes and highway lighting on I-35W in Bloomington. But the elements to be discussed here were the traffic control elements: “hard shoulder” use (using a safety shoulder for normal traffic operations, in this case the inside shoulder of northbound I-35W for the HOT lane), combined with Intelligent Lane Control Signs (ILCS) on the entire corridor. These are those full color LED signs  that typically would light up with diamond symbols, standard lane control signals, merge instructions, variable speed limits to slow down traffic gradually before congestion or even animated merge chevrons . The MnDOT term for the overall installations was “smart lanes”. This was the first setup of the kind in the nation, activated July 29, 2010

Smart Lanes

Ilcs Options

Intelligent Lane Control Options MnDOT

There were originally LED lights embedded in the pavement to direct motorists away from the hard shoulder when it was closed. These turned out, unsurprisingly, to be a maintenance issue with highway salt being dumped directly on them. Although they survived one winter, corrosion led to them being discontinued in 2011. Then the entire hard shoulder setup was removed with the I-35W reconstruction project. A hard shoulder operation was considered on the I-494 unbounded concrete overlay project in Plymouth and Maple Grove, but met with a cool reception by the local cities, and money was found by value engineering other projects to build a regular lane instead. There have been no further hard shoulder setups in Minnesota.

As for the ILCS system, it eventually expanded to I-94; there were 187 signs on I-35W and 110 on I-94. But the overhead signs likewise have issues. They’re expensive- about $400,000 $500,000 per site, at half mile intervals, double that of traditional DMSs that can also be spaced farther apart. The variable speed limit function never worked as intended and was discontinued in 2015. Motorist compliance with advisory speed limits is very low and they were confusing to motorists- they didn’t know if that was the speed of traffic ahead or the speed they should travel, and if so if it was the maximum speed or a suggested speed.  Also buried loops on the freeways didn’t generate enough data to update them properly and the signs would often display a speed limit over stopped traffic. A study showed no benefit in crash reduction with them in use on I-94.

Aside from the variable speed limits the signs were effective. But they also turned out to be extremely unreliable. Besides having to go out regularly to repair them, a bigger issue is that the company that made them went bankrupt and was liquidated, nullifying technical support and the service contract and meaning MnDOT can’t get replacement signs or spare parts for love or money. A decision was made to remove a number of the signs in areas they were used infrequently to use them a source for spare parts for installations closer into the downtown areas that are used more frequently. As a partial mitigation more frequent standard DMS signs were installed.

Around this time there was a change in the Manual of Uniform Control Devices to the effect that lanes that vary function by time of day are to be labeled as “Express Lane” rather than with the diamond symbol, and that signs must change to state who is allowed to use the lane at that particular time. So the  opportunity was used to update all the signs, including the fixed ones, for compliance.  With the growth of technology there will be exciting new technologies for traffic management. But not all of them will be as enduring and successful as we had hoped.


About Monte Castleman

Monte is a long time "roadgeek" who lives in Bloomington. He's interested in all aspects of roads and design, but particularly traffic signals, major bridges, and lighting. He works as an insurance adjuster, and likes to collect maps and traffic signals, travel, recreational bicycling, and visiting amusement parks.

10 thoughts on “A History of Traffic Management Technology

  1. Lou Miranda

    “By the late 1960s the Minnesota Highway Department (MHD) realized there wasn’t political will to build our way out of congestion”

    and now we know that’s not possible.

    1. Monte Castleman Post author

      Sure it is. We’ve built our way out of congestion on the street in front of my house. People from Blaine aren’t coming down to drive back and forth on my street just because there’s extra capacity. So we’ve built our way out of congestion on the street in front of my house, therefore there’s a limit to induced demand on the street in front of my house.

      The same principle applies to freeways. I don’t get up and drive on the freeways just because there’s empty space. So the number of people wanting to take trips on the freeway has some hard limit. Do you really think that if I-35W was 1000 lanes wide there’d be congestion? I think not, so the number of lanes to build our way out of congestion is some number between 5 and 1000.

      1. Lou Miranda

        “and now we know that’s not reasonably financially, environmentally, or geometrically possible.”

        See Katy Freeway in Houston, etc.

    1. Monte Castleman Post author

      I know exactly what you’re talking about but I figured the article had enough points without mentioning them. Since I wondered about it too I sent an inquiry to MnDOT, (although getting useful information from them is hit and miss).

    2. Monte Castleman Post author

      Finally got a response from MnDOT:

      “Thanks for your question. I did some checking with traffic management staff and no one has the full story, but they were part of a test for the first generation of optical traffic detection. It looks like this research was happening about 25 years. They were abandoned in the early 2000s and we just haven’t gotten around to removing them since then.

      As you noted we use many imbedded loop detectors for volume and speed data. In recent years we have begun to deploy more optical sensors on the freeway system to replace the imbedded loop detectors. These are pole mounted on the side of the freeway”

  2. Andrew Evans

    Has there been any luck with creating technology, sings, or something that could (or did) help with phantom traffic jams?

  3. Matt SteeleMatt

    Great article. Thanks for the history. I miss the ILCS signage and the advisory speed limits on each lane. I thought those were a great idea.

    Do you have any info on the following tech?
    – The “Alternate Route” arrows along the 494 corridor (I’ve never seen them used)
    – The in-pavement LEDs to dynamically indicate when the Priced Dynamic Shoulder Lane was closed at about 38th St (I forget if this was installed as part of the UPA project or the Crosstown project)
    – The “Next Bus” signage installed by the UPA on side streets in the south metro, which seems to be poorly maintained.
    – The bus gate tech for 46th St Station and Cedar Grove Station that apparently prevents local buses from using those stations.
    – What other tech might have made it to the planning stages but was never built?

    1. Monte Castleman Post author

      The “Alt Route” signs: These are part of deliberately overbuilding American Blvd (and to a lesser extend 76th / 77th both to induce local traffic off the freeway and to service as an alternate route during incidents and during the planned complete reconstruction of the mainline and believe had I linked signals that could alter timing in incidents. Like a tot of bleeding edge tech it became troublesome to maintain and wasn’t compatible with the standard linked controllers that became common later, so all the proprietary hardware controlling it was replaced with standard controllers that are now hooked into the Bloomington / Hennepin fiber optic network. No one has ever bothered to go out and remove all the arrows but they’re not hooked up to anything anymore. I did see them lit once or twice.

      The LED lights were part of the UPA, I mentioned them briefly in the article. They were destroyed after one winter by the road salt being dumped directly on them.

      Besides their relatively common optically programmable visibility signals, 3M made a bunch of quirky traffic signal tech that was never in wide use. Of note was a bimodal (red yellow in a single section) arrow that changed color by a motorized lens, a pedestrian signal that could show “Dont Walk” to people on the curb and “Walk” to people in the street, and a signal that showed a ball when you were far away and an arrow when you were close (one of these existed at Elm Creek Blvd and County 81 for a number of years).

      Electronically programmable visibility signals where you could use a computer or phone to remotely disable rows of LEDs are no longer made because they had a really bad water intrusion problem due to shoddy manufacturing. (There’s a lot o these in downtown Minneapolis). Now we’re back to “optically programmable” signals”where you “program” them by putting black tape over an internal lens. 3M got out of the business a while after their patent expired and McCain made a cheaper knockoff.

      Low pressure sodium streetlamps were never common in Minnesota like they were in Europe was electricity was more precious and areas near major observatories. But the major north south streets in Richfield had them from the early 1980s to early 1990s and there were few by Met Stadium. The last installation in Minnesota that I’m aware of bit the dust when the Thunderbird Hotel came down. But I was lucky enough to get a low pressure sodium streetlight for my collection.

      Not really street related, but there was the “halarc” self-ballasted metal halide lamp designed as an incandescent retrofit by the U.S. while the Europeans were developing self-ballasted fluorescents as retrofit. Obviously the latter won out. Also “white sodium” was common Europe, with a sodium arc tube under “super-high-pressure” to produce a very pleasing, incandescent like light. These saw some use in Europe but not really here.

      There are the traffic signal controllers that used vacuum tube electronics to generate timing while using the traditional camshaft and fingers to switch the lights. You’d turn a rheostat to vary an RC timer, along with a massive, probably PCB filled capacitor, to generate the timing, eventually the capacity would charge enough to discharge through a vacuum tube and trip a solenoid to rotate the camshaft. . The advantage of this over the typical rotating dial with keys and gears is that you could use a vehicle sensor, generally a metal pressure plate in the road, to also advance the camshaft. These were only a couple of years before everything got transistorized.

      A standard NEMA controller has a bunch of features, like flashing walk, that would be MUTCD violations if enabled, and a bunch of useless inputs and outputs, like an output to drive the middle section of a three light pedestrian signal rather than flashing the don’t walk. They can’t drop these because then it wouldn’t meet NEMA speck, but Some newer controllers some of these wires can be reassigned to stuff that’s actually useful, like preempt or additional phases.

  4. Conrad ZbikowskiConrad

    Very informative article. I am impressed by how display technology is advancing faster than projects can be implemented. By the time a sign goes up, there may be a cheaper, brighter option.

    I will be interested to see how real-time congestion pricing affects traffic. There is some kind of algorithmic pricing on the HOV lane on I-35W south of Downtown Minneapolis. Or maybe it’s a human putting in the price. I will follow New York City’s example when congestion pricing is implemented in southern Manhattan.

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