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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.