Tag Archives: traffic

Impact of Arterial Bus Rapid Transit on Traffic and Users

Video and statistical analyses showed that arterial bus rapid transit (ABRT) along Snelling Avenue in Minneapolis-St. Paul had no significant impact on traffic volume and wait times at intersections. Survey results demonstrated that users prefer the A Line over local bus service and consider it roughly equivalent to express bus, light rail and commuter rail service. Though ABRT has not converted automobile drivers to transit riders, users enjoy its easy payment format, cleanliness, route service and convenience. This study also provided recommendations for future ABRT line design considerations.

“Arterial bus rapid transit is perceived positively by users. It’s much like light rail and commuter rail—people think of it as equally useful as light rail.” —Alireza Khani, Assistant Professor, University of Minnesota Department of Civil, Environmental and Geo-Engineering

What Was the Need?

Bus rapid transit (BRT) entails dedicated lanes for buses and off-board payment for users who purchase fares before boarding the bus. In recent years, arterial BRT (ABRT) has developed as an alternative for metropolitan areas that lack roadway width for dedicated lanes. ABRT uses off-board payment but not dedicated lanes; instead, it uses existing roadway arterials and limited stops, offering a fast and efficient commute for users.

In 2016, the A Line opened on the Snelling Avenue corridor in Minneapolis-St. Paul, the area’s first ABRT line. It quickly gained popularity among transit customers as an alternative to local bus service, complementing the Twin Cities’ light rail system and commuter rail service from the suburbs.

Because the A Line operates within existing lanes of traffic and does not feature pullouts at its stops, it could slow corridor traffic when buses stop to load and unload. A preimplementation study of the corridor and A Line service suggested that traffic impacts would be minimal. The A Line’s actual impact on traffic, however, had not been determined, and user perceptions had not been assessed.

The A Line, Minnesota’s first ABRT line, has a positive reputation among riders and area residents,
and has had no negative impact on automotive traffic along Snelling Avenue, according to a recent
MnDOT study.
Passengers disembark from an A Line bus on Snelling Avenue.

What Was Our Goal?

MnDOT sought to examine the traffic impacts of the A Line in its first year of deployment, and to identify and quantify the A Line’s appeal to riders, including the service’s strengths and weaknesses, and how the transit experience of the A Line compares to local service. In addition, MnDOT needed to assess the characteristics of the service that could be used in new ABRT lines in the Twin Cities.

What Did We Do?

Researchers employed two strategies to evaluate A Line performance. First, the team conducted a traffic and transit capacity study. Investigators analyzed bus system data for ABRT and regular bus service capacity. In August 2017, researchers deployed four cameras each at two intersections: Snelling and University north of Interstate 94 (I-94), and Snelling and Dayton, south of the Interstate. Cameras collected video data for weeks before the 12-day Minnesota State Fair, which is held at the fairgrounds on Snelling Avenue, and additional video during the fair through its conclusion in September. Researchers analyzed recordings of four signal cycles before and after bus arrival at the intersections for traffic queues and volume.

Next, investigators studied the results of a 2016 Metro Transit survey of passengers on the A Line and four parallel standard bus lines. The study compared transit usage data from 2016 and 2017, before and after the A Line opened. The research team surveyed A Line passengers, station area residents, business workers and owners, automobile users, bicyclists and pedestrians. Team members also reviewed a recent study of Minneapolis-area real estate developers on transit facilities and options.

Traffic moves on northbound Snelling Avenue at Dayton in this image taken from the video analysis.
Researchers used video cameras at two key intersections along Snelling Avenue to evaluate the A Line’s impact on traffic.

What Did We Learn?

Video and data analyses revealed that the A Line increased overall transit capacity, and the time its buses spent not moving while passengers were loading and unloading during a green traffic signal had no significant impact on intersection queue length or traffic flow at the two intersections—during and outside State Fair dates. The A Line carries more riders than the local bus along the same route, and the greatest rider turnover occurs at the Snelling and University station, which connects with light rail service.

Surveys identified the five attributes most important to satisfactory transit service: easy fare payment format, hours of operation, complaint resolution, personal safety while riding and courteous transit drivers. A Line users were more satisfied with ABRT than with local bus service, and showed no significant difference in satisfaction with the A Line compared to express buses, light rail and commuter rail. For most individual service attributes such as payment procedures, travel time, shelter cleanliness, and route and bus signage, the A Line performed better than local buses, the same as light rail but not as well as commuter rail. Nonuser surveys indicated a positive perception of the ABRT, but mixed impact on pedestrian and bicycling activities and little impact on reducing preferences for using automobiles instead of transit.

What’s Next?

To improve A Line service, transit managers should focus on operating hours, the on-board safety of riders, reliability and total travel time. Researchers noted that rider satisfaction does not consider costs associated with improved service and recommended that future ABRT plans weigh improvements in the five key attributes of transit service against costs in planning new lines. The study findings and recommendations will be used in planning future ABRT lines.

“We will use this study to show MnDOT staff that arterial bus rapid transit should have minimal to no impact on existing traffic and signal operations.” —Carl Jensen, Transit Advantages Engineer, MnDOT Metro District

This Technical Summary pertains to Report 2018-35, “After Study of The Bus Rapid Transit A Line Impacts,” published December 2018. For more information, visit MnDOT’s Office of Research & Innovation project page.

Evaluating the Use of Central Traffic Signal Control Systems

MnDOT sought to determine the full range of intersection control information (ICI) currently used in the state and how it could best be made accessible for state transportation system needs. Researchers created the Regional Database of Unified Intersection Control Information, a machine-readable, cloud-based unified ICI system. They determined steps MnDOT could take toward more effective use of its central traffic signal control system, such as mitigating traffic disruption around construction zones and participating more fully in emerging technologies such as vehicle information systems and vehicle automation.

What Was the Need?

Traffic signal control has evolved since the 1950s from simple time-based signal protocols to current dynamic systems that allow adjustment of signals to traffic conditions. Intersection control information (ICI) is increasingly important to transportation agencies, researchers and private companies involved in developing traffic models and technologies. 

Historically, the availability of traffic signal control information in Minnesota and traffic data formats have varied across jurisdictions. Nationally, increased use of central traffic signal control systems (CTSCS) has supported recent trends toward more dynamic traffic models and control, as well as toward advances in automated intelligent vehicles. This quickly evolving environment makes the creation of a unified, standardized system of ICI in Minnesota both feasible and necessary. 

MnDOT sought to examine the use of CTSCS to manage all aspects of traffic near construction zones more strategically and effectively in order to mitigate the frequent and often severe disruption of traffic these zones can cause. This project was initiated to determine the state of Minnesota’s ICI systems and to develop guidance for reaching MnDOT’s goal of a unified ICI and better statewide traffic management through CTSCS. 

A bird’s-eye view of a diverging diamond interchange in Bloomington, Minnesota. Two diamond-shaped formations of many converging and diverging lanes of traffic are seen on either side of a multilane highway.
Unified ICI can identify all the parameters traffic signal controllers need to effectively manage challenging highway configurations like this diverging diamond interchange in Bloomington.

What Was Our Goal?

This project had three objectives:

  • Deliver guidance and tools to collect ICI from all Twin Cities metro area jurisdictions and automate the importation of this information into each jurisdiction’s CTSCS and signal performance measure (SPM) applications. A stated priority was the ability to import this data into MnDOT’s digital products used in construction design.
  • With the help of all stakeholders, define the most inclusive format to represent all required information.
  • Design a Regional Database of Unified Intersection Control Information (RDUICI), and propose methods and tools for importing and exporting data between the RDUICI and all CTSCS and SPM applications by local jurisdictions. 

“A unified set of intersection control information is valuable for developing a regional signal timing database to model construction project impacts and provide standardized information for use with connected vehicle technologies.”

—Kevin Schwartz, Signal Optimization Engineer, MnDOT Metro Traffic Engineering

What Did We Do?

Researchers distributed surveys to signal operators and transportation model builders to identify the contents and develop the format of the unified ICI. 

A survey sent to 153 signal professionals sought to learn how operators in diverse jurisdictions store and distribute ICI. Responses from 42 participants helped researchers assess the availability of ICI and the degree of effort a regional unified ICI would require.

A second survey was sent to 58 designers, modelers and planners who have experience working with MnDOT signal information to learn about ICI’s various uses; 25 people responded. Researchers also interviewed a selected group of signal operators and modelers to gain more detailed information. 

A four-sided traffic signal hangs from a pole over an intersection. The traffic light illuminated on the visible side is red.
Most of Minnesota’s traffic signals use complex controllers to manage traffic, responding to information gathered from multiple sources, such as loop detectors and other sensors.

These surveys and in-depth interviews allowed researchers to create intersection models of varying complexity to drive the identification and categorization parameters of the proposed unified ICI. Researchers developed a complete unified ICI for a diverging diamond interchange, a complex interchange that is difficult to represent with traditional intersection models. Researchers also developed a relational database schema for containing the data set in a machine-readable format. This schema is a starting point for developing a system for standardizing the management and availability of ICI across jurisdictions. 

What Did We Learn?

Researchers documented all intersection signal control codes in use. They showed the feasibility of a unified ICI and demonstrated it through the example of a fully coded diverging diamond interchange. They learned that some data in older formats would need to be digitized to be included.

“Identifying the needs of different stakeholder groups allowed us to produce an organized, comprehensive format for intersection control information.”  

—John Hourdos, Research Associate Professor, Minnesota Traffic Observatory, University of Minnesota

Further investigation and communications with the software developers of MaxView, MnDOT’s CTSCS, showed researchers that current systems could not be used to store the entire unified ICI. While the systems contain much of the unified ICI data set, some detailed geometric information is missing that is critical to understanding the intersection control. MaxView also contains information that is not readable by other systems. 

Because of these challenges, researchers suggested managing unified ICI through a custom-built, centralized cloud repository. This solution would only require that vendors develop tools for exporting the information they have in a unified ICI format. The cloud repository would then be accessible to signal control vendors and to MnDOT, and security would remain intact. 

What’s Next?

MnDOT now has the full range of intersection signal control data used across the state. Researchers have determined it can be imported, stored and delivered through a cloud-based method. With these findings, the agency can begin to consider projects that use CTSCS for construction zone disruption mitigation and intelligent vehicle technologies.

This Technical Summary pertains to Report 2019-14, “Evaluation of a Central Traffic Signal System and Best Practices for Implementation,” published March 2019.  Visit the MnDOT research project page for more information.

Building More Accurate Traffic Modeling for Twin Cities Construction Projects

MnDOT is exploring different software options for developing a “mesoscopic dynamic traffic model” that can more accurately predict road construction impacts than current macroscopic models like the Twin Cities Regional Travel Demand Forecasting Model.

“Dynamic traffic assignment is an emerging model type, and there are a lot of software platforms with different methodologies. MnDOT was interested in reviewing their pros
and cons,” said Jim Henricksen, Traffic Forecaster, MnDOT Metro District, who helped lead a recent research project that analyzed different software packages.

“A team maintains the Twin Cities Regional Travel Demand Forecasting Model. Any mesoscopic model would require a similar maintenance effort to keep the model from becoming obsolete as construction adds new lanes,” said John Hourdos, Director, Minnesota Traffic Observatory, University of Minnesota, and principal investigator for the study.

What Was the Need?

Traffic modeling is a valuable tool used in transportation planning to predict the impacts of new construction or maintenance projects. MnDOT currently has modeling tools available in two scales: macroscopic and microscopic. Macroscopic-scale planning level tools such as the Twin Cities Regional Travel Demand Forecasting Model predict driver route choice and the number of drivers that will travel on a given road at a given time. Microscopic-scale traffic simulation, on the other hand, models driver behaviors such as gap acceptance or acceleration rates. MnDOT uses microscopic-scale simulation to plan capacity-increasing projects, but the tool is only feasible on the corridor level because generating the simulation requires a large amount of data and computing power.

To bridge these two scales, MnDOT is developing a mesoscopic-scale dynamic traffic assignment (DTA) model for the Twin Cities. This model falls between microscopic- and macroscopic-scale modeling in scope and complexity. It simulates the movement of individual vehicles based on traffic flow equations rather than driving rules, which requires less detail and computing time than a microscopic simulation and can be used over a wider area. MnDOT will use this model for applications such as staging construction seasons to minimize the disruption caused by multiple large projects, or coordinating traffic modeling across the road networks operated by MnDOT, counties and cities.

To assist in developing this system, MnDOT needed information about the capabilities of available modeling software packages in addition to the needs, desires and restrictions of the agencies and consultants who will be using the model.

What Was Our Goal?

The goal of this project was to better understand the capabilities of commercially avail-able modeling software packages to address MnDOT’s modeling and simulation needs.

What Did We Do?

Investigators interviewed stakeholders about their understanding of and need for mesoscopic traffic simulation and DTA. Stakeholders included individuals who have used or requested data from the Twin Cities Regional Travel Demand Forecasting Model maintained by the Metropolitan Council. Investigators also reviewed four case studies of mesoscopic DTA models used in Manhattan; San Francisco; Detroit; and Jacksonville, Florida.

To supplement the findings from the interviews and case studies, investigators conducted a comprehensive review of the claimed capabilities of six commercially avail-able traffic simulation software packages: TransModeler, Aimsun, DynusT/DynuStudio, Dynameq, Cube Avenue and Vissim. Investigators didn’t test the software, but instead reviewed manufacturers’ documentation and literature to identify limitations of their methods and whether those methods are applicable to MnDOT’s needs.

Traffic in a highway work zone.
DTA can aid in staging multiple major construction projects in the Twin Cities to minimize the disruption they cause to travelers.

What Did We Learn?

To compare the capabilities of the various simulation software packages, investigators created a matrix that included comprehensive notations about a software package’s claimed features that may not fully meet MnDOT’s simulation needs. For example, some software packages claim to model actuated signals, but they create models based on Highway Capacity Manual assumptions rather than real-world conditions.

DynusT is the most commonly used simulation program, possibly because it is open-source and the easiest software to use, although it requires DynuStudio, a commercial graphical user interface and data management system. DynusT also has some limitations, such as not considering the individual lanes in each roadway segment, which would limit its effectiveness in modeling roads where individual lanes have imbalanced densities.

Most interviewees had only limited experience with mesoscopic modeling. Incorporating traffic signals in a simulation network is a significant challenge, according to interviewees, because currently a database of signal timings isn’t available.

While all four of the DTA case studies reviewed required more data, calibration and validation than older models, each of the developers reported that these challenges had been mitigated, and the models created could answer complex questions that previous models couldn’t.

What’s Next?

Traffic simulation and modeling is a fast-developing field, particularly mesoscopic-scale modeling. Each of the software packages reviewed in this project has had at least two new versions in the past 18 months, and while their modeling approaches are fundamental to the software in some cases, in other cases capabilities will be added or improved as software develops.

The foundation of a mesoscopic model for the Twin Cities has been built and tested in Transmodeler (with significant pro bono work from the software developer). However, MnDOT has also used its existing DynusT model for several projects beyond its initial purpose, and the agency will use the information gathered in this project to determine which approach is more practical for MnDOT and its consultants based on cost, capabilities and data availability. Transmodeler is generally more powerful, but it will also incur greater costs, particularly since every consultant would need to acquire its own copy of the software.


This Technical Summary pertains to Report 2017-10, “Framework and Guidelines for the Development of a Twin Cities Mesoscopic DTA Model,” published April 2017.

Choosing Effective Speed Reduction Strategies for Roundabouts

Using survey results and prior research, this project developed a new resource to enable Minnesota local road engineers to select appropriate speed reduction measures for roundabouts. Further research is needed to determine the relative effectiveness of different measures alone and in combination.

“Although roundabouts are becoming common, single-vehicle crashes from drowsy, inattentive or unfamiliar drivers are still a concern, particularly in rural areas,” said Joe Gustafson, Traffic Engineer for Washington County. “This project provides an overview of existing speed reduction treatments that have been used in both roundabout and nonroundabout contexts, and a framework to properly evaluate the effectiveness of new treatments.”

“Rather than try to identify the right combination of treatments, the research was designed to give engineers a variety of options to consider for a given location,” said Susan Chrysler, Senior Research Scientist, Texas A&M Transportation Institute.

Gustafson served as the technical liaison for the study, and Chrysler was the principal investigator.

What Was the Need?

2017-14-p1-image

Roundabouts can provide a safer alternative to traditional intersection control devices like traffic signals and stop signs. Roundabouts have been proven to reduce crash severity by requiring drivers to decrease speed during the approach to the intersection. But failure to slow down sufficiently could result in a crash.

Signs and markings are key treatments used to communicate to drivers that they must slow down as they approach the roundabout. When navigated appropriately, roundabouts can eliminate or reduce the severity of crashes, reduce delays and reduce fuel consumption.

What Was Our Goal?

This project had two goals: to analyze existing research and conduct a survey of roundabout design and installation practitioners to determine best practices; and to develop a resource that engineers can use to identify appropriate speed reduction treatments for high-speed approaches to roundabouts.

What Did We Do?

Investigators surveyed transportation engineers from Minnesota and other states, along with technical consultants, to learn their experiences managing roundabouts with high-speed approaches. The survey addressed geometric design parameters and traffic control methods, changes in maintenance practices, crash history and speed reduction measures that were considered or eventually enacted.

Previous research on the subject was studied, including the Federal Highway Administration report Roundabouts: An Informational Guide and National Cooperative Highway Research Program Report 672: Roundabouts: An Informational Guide, Second Edition. Design manuals from four states were reviewed to provide a sample of the material avail-able to practitioners seeking guidance on design of high-speed roundabout approaches.

Based on their research, investigators provided information on the effectiveness of various treatments and on their installation and maintenance costs. They also developed a methodology for conducting a speed study to assist engineers in determining the most effective treatment for a given intersection. Treatments for alerting drivers that a round-about is ahead include traditional signs, pavement markings, illumination and other indicators, plus advanced devices like speed-activated, LED-enhanced warning signs.

What Did We Learn?

Each roundabout presents unique challenges. Local road engineers need to evaluate the characteristics of the intersection being considered (such as geometric design and adjoining land use) and the costs of installation and maintenance before recommending a specific treatment or combination of treatments.

Other findings include the following:

  • Speed reduction techniques found effective for horizontal curves, urban-rural transition zones and isolated rural intersections should be effective for rural roundabouts with high-speed approaches.
  • In rural locations, speed reduction treatments that have been used at railroad crossings, T-intersections and work zones may also be applicable to roundabouts.
  • Some unique treatments used internationally hold promise, but further study is needed before these treatments can be recommended for use in the United States.

What’s Next?

This study was the first phase of research. The findings provide the methodology to select, install and evaluate treatments at different locations. Further research is needed to accomplish the following:

  • Analyze the effectiveness of speed reduction treatments at different locations
  • Determine the impact of different combinations of treatments
  • Establish the comparative benefits of two or more treatments that fall within the same general cost and maintenance grouping
  • Analyze the impact of roundabout infrastructure (such as gateway treatments and illumination), various pavement markings and the long-term effects of specific signing treatments.

This Technical Summary pertains to the LRRB-produced Report 2017-14, “Strategies for Effective Roundabout Approach Speed Reduction,” published May 2017. 

ATM Queue Warning Systems Can Reduce Freeway Crashes

ATM queue warning systems were developed and deployed on two freeways to alert motorists to queuing conditions ahead that could lead to rear-end crashes. At one test site, the prototype system substantially reduced crashes and near-crashes. At the other site, it reduced speed variances.

“The big lesson learned was that the detection method had to function quickly and display a message that was timely and accurate. This gains the trust and confidence of the motoring public,” said Brian Kary, Freeway Operations Engineer, MnDOT Metro District.

“Deploying the product of this research was not difficult. The challenge came in closing the gap to alert the drivers to slow down,” said John Hourdos, Director, Minnesota Traffic Observatory, University of Minnesota.

Kary served as the technical liaison for the study, and Hourdos was the principal investigator.

What Was the Need?

To reduce congestion and improve safety, MnDOT has deployed active traffic management (ATM) technology on two highways in the Twin Cities freeway network. The ATM system incorporates intelligent lane control signals (ILCS) placed over selected lanes at half-mile increments to warn motorists of incidents or hazards ahead. With advance warning, drivers can slow down and possibly avoid crashes.

The deployed system, however, does not specifically target the prevention of rear-end collisions, which are the most frequent type of crashes on freeways. Research has shown that rear-end collisions tend to occur during extended lines of stop-and-go traffic and at end-of-queue locations. Overhead, real-time electronic messages that warn of queuing conditions ahead can prepare motorists to reduce speed and avoid potential rear-end collisions. Such messages have the added benefit of improving mobil-ity since fewer crashes will improve traffic flow.

What Was Our Goal?

This project sought to develop and field-test two different prototypes for ATM queue warning systems. One prototype would address stop-and-go traffic and end-of-queue situations. The other would address shock waves, a crash-facilitating condition where there is a sudden change in traffic movement that causes a cascade of braking. The long-range goal of the project is to develop a unified ATM queue warning system that can be deployed at other locations within the freeway network.

What Did We Do?

Development of two prototype high-resolution ILCS warning systems began in 2014. The systems were then deployed on two high-traffic freeways in the Twin Cities: one on Interstate 35 West (I-35W) and the other on I-94. Both were still in operation in mid-2017.

The two locations have significantly different traffic conditions. On I-35W, congestion creates expanding queues that extend from the Trunk Highway 62 (TH 62) interchange to the 50th Street overpass. At the I-94 location, crashes are most likely to occur due to shock waves that can often quickly develop near the Portland Avenue overpass.

2017-20-p2-imageTo capture traffic data, researchers used either live video from closed-circuit-camera detector stations or data from existing in-pavement loop detectors. The ILCS units dis-played the message Slow Traffic Ahead, which would direct drivers to reduce speed due to the congested lanes ahead. Other messages, such as Prepare to Stop or Traffic Ahead 10 MPH, were considered but not tested during this initial study.

A server installed at the Minnesota Traffic Observatory at the University of Minnesota archived the time and location of each queue on I-94 and measured its duration and length. This provided the data needed to develop two algorithms that can be used to develop a rear-end-collision warning system that can be installed at freeway locations where similar queuing conditions exist.

What Did We Learn?

The data collected show that warning messages delivered by the ATM system can be effective in alerting drivers to queuing conditions. The ultimate benefit is a reduction in rear-end collisions in downstream locations on the freeway.

Data recorded at the I-35W location revealed that:

  • Messages delivered by the ILCS system helped drivers maintain a steady speed and eliminate stop-and-go travel.
  • The contents of warning messages should be crafted to have an impact on all motorists. Drivers responded differently to specific messages.
  • Queue warning systems can be made more effective through deployment of a real-time, lane-specific ILCS system and collection of high-resolution data.
  • Some drivers did not always heed the first queue warning message to decrease speed, but they did slow down further along the roadway.
  • There was no significant difference in impact between warning messages issued during the morning peak travel period and those issued during the evening peak.

In the first three months of queue warning system operation, the crash frequency re-corded at the I-94 test site was 9.34 crashes per vehicle miles traveled (VMT) and 51.8 near-crashes. This was a 22 percent decrease from the 11.9 crashes per VMT recorded at the site in 2013 monitoring data, and a 54 percent decrease from the 111.8 near-crashes recorded there in 2013.

The research showed that to prevent potential collisions, the ATM system had to deliver messages quickly and accurately to give drivers enough time to adjust their speeds. Also, the control algorithms developed in this project can provide the queue-estimation projections needed by MnDOT and other transportation departments to enhance the effectiveness of their ATM systems.

What’s Next?

While the deployment of the two queue warning system prototypes was a relatively cost-effective option, a longer trial period of two to three years is needed to ensure that the ATM system delivers sustainable benefits.


This Technical Summary pertains to Report 2017-20, “Development of a Queue Warning System Utilizing ATM Infrastructure System Development and Field Testing,” published June 2017. 

Infrared Sensing Not Yet Suitable for HOV/HOT Lane Enforcement

Could the same infrared technology that’s used by security firms to detect trespassers be used to spot carpool lane violators? Not yet, says new research sponsored by MnDOT, which shows that to consistently detect passengers through windshield glass, the system would require a laser that might harm people’s eyes.

“Some vendors have proposed significant investments in sensing technology for HOV/HOT lane enforcement,” said Nikos Papanikolopoulos, Professor, University of Minnesota Department of Computer Science and Engineering. “This research demonstrated that it’s not safe, so the tests saved a lot of money and protected the well-being of drivers.”

“Development is still continuing in the industry, so we will cautiously evaluate sensing technologies as they come along,” said Brian Kary, MnDOT Freeway Operations Engineer. “This research gave us a solid base of knowledge about what we’ll be looking for and what we need to avoid.”

Papanikolopoulos served as the research project’s principal investigator, and Kary served as technical liaison.

What Was the Need?

High-occupancy vehicle/high-occupancy toll (HOV/HOT) lanes have gained popularity in recent years as a way to address highway congestion in urban areas. However, enforcing the provisions that either prohibit or charge a toll to single-occupant vehicles in HOV/HOT lanes can be challenging. Currently, enforcement is handled by law enforcement officers, but this is a labor-intensive process that can’t catch every violator and can create a traffic safety hazard.

Obtaining technology to assist officers with enforcement is a goal for MnDOT and many other agencies that operate HOV/HOT lanes, and several manufacturers are working to develop enforcement cameras. But this has proven to be a difficult task. Window tinting and glare from sun-light can thwart common sensing technologies like video cameras and microwave radar (commonly used in speed limit enforcement). Previous research using near-infrared sensors has shown promise, but none has produced completely successful results.

This study tested Honeywell’s Tri-Band Infrared (TBI) sensor, which was originally used to automatically detect intrusions at high-security entrance gates. In addition to a black-and-white camera and an illuminator, the TBI has two co-registered near-infrared cameras. The system takes advantage of the fact that human skin reflects infrared light much more effectively at wavelengths below 1400 nanometers. The TBI’s infrared cameras are sensitive to different wavelengths, one below and one above that threshold, and fusing the images from these two cameras makes silhouettes of faces more prominent.

What Was Our Goal?

The goal of this project was to evaluate whether the TBI sensor is suitable for HOV/HOT lane enforcement applications.

Illuminator
Infrared lasers helped the TBI sensor detect people through glass, but they also pose a danger to eye safety.

What Did We Do?

Investigators first tested the sensor outdoors on oncoming vehicles with known positions that ranged from 25 to 140 feet from the sensor. These tests demonstrated that the sensor had limited ability to penetrate modern vehicle glass, possibly because the system’s illuminator component was ineffective.

Investigators purchased two infrared lasers providing illumination at wavelengths of 1064 nanometers and 1550 nanometers to increase the TBI sensor’s ability to detect people through windshield glass. Then they conducted indoor tests to compare the impact of these illuminators with that of the original illuminator: With a test subject holding front passenger windows from several manufacturers in front of his face, the lasers were aimed at the subject while the TBI attempted to detect him.

Finally, investigators conducted outdoor tests using the TBI to detect people in three test vehicles from the front and the side under both sunny and cloudy conditions. These tests were conducted both without illumination and with the aid of high-power incandescent spotlights modified to output infrared light, and with the sensor at several different distances from the vehicles.

What Did We Learn?

The indoor tests demonstrated that when aided by supplementary illuminating lasers, the TBI sensor was capable of detecting humans through commonly manufactured vehicle window glass.

However, to achieve successful results, these lasers must operate with high power in a narrow range of wavelengths. Despite operating outside the visible spectrum, they can damage human eyes when operating at the necessary power level to enable effective detection through glass. While investigators conducted this project’s indoor tests with adequate protection, there is currently no way to ensure safe usage of the lasers in real-world applications.

In the second outdoor tests, the unilluminated sensor successfully detected a passenger only once out of 24 attempts. With illumination, the sensor successfully detected people in some cases, particularly when there was no direct sunlight or reflective glare. One surprising discovery was that high-band (above 1400 nanometers) infrared light penetrated window glass more consistently, even though the low band had more spectral energy.

What’s Next?

Due to safety concerns about using the illuminating laser at a high enough power to penetrate all windshield glass, the system is not suitable for HOV/HOT lane enforcement. There is some indication that sensor technology has improved since the release of the TBI, and MnDOT will continue to monitor industry developments, but it has no current plans to pursue using infrared cameras for this application.

The technology may be suitable for other sensing applications that do not require high-power illumination. For example, the sensors might be useful in systems that provide information to drivers in real time, such as applications that identify available truck parking spaces in rest areas or that alert drivers to the presence of workers in work zones.

This Technical Summary pertains to Report 2017-05, “Sensing for HOV/HOT Lanes Enforcement,” published February 2017. The full report can be accessed at mndot.gov/research/reports/2017/201705.pdf. 

Project seeks to ease traffic congestion in a roundabout way

Freeways and highways aren’t the only urban roads with traffic congestion, even though traffic management strategies have been largely directed toward improving traffic flows there. So, U of M researchers have taken to city streets to reduce congestion in an innovative—albeit roundabout—way.

“There’s been a lot of research focused on controlling congestion on major highways and freeways, but there’s relatively less when it comes to looking at controlling traffic on urban arterials,” says Ted Morris, a research engineer with the Department of Computer Science. “It’s a very different picture when you get into urban arterials and the traffic behaviors going on there, because of the dynamics of route choice, pedestrian interactions, and other factors.”Image of overhead view of roundabout

Morris is part of a research team that aims to create a framework for testing and evaluating new urban traffic sensing and control strategies for arterial networks. The goal is to balance safety and efficiency for all users—especially in places where new types of urban transportation facilities are planned in the next few years.

The team is using the 66th Street corridor in Richfield as a test bed for its research. The city, along with Hennepin County, is in the process of converting a series of signalized intersections along the route to roundabouts over the next few years. The roundabout designs also incorporate new facilities for pedestrians, bikes, and bus transit as part of a multimodal approach.

Initially, the researchers sought to create a larger network of interconnected sensors and a live test bed, Morris says. But funding limitations kept the project area to approximately 10 miles of arterial roads, a portion of which will be supported by a network of interconnected traffic sensors. The research team is instrumenting major intersections along 66th Street with a reliable, low-cost, high-resolution camera mounted on a center pole and supporting electronics as the intersections are being reconstructed.

“You can zoom in pretty closely to capture all the different movements and events that we need to use for measurement and detection,” Morris adds. “The key to this, to really make it reliable, is you need to very carefully quantify gap acceptance and how that varies in time and time of day. You also need to know how pedestrian activities interact with the traffic flow.”

The use of roundabouts has grown in the region because they cost less to build and maintain than signalized intersections, they meet the latest design standards, and they improve safety by reducing traffic conflicts. But predicting the capacity of roundabouts can be especially challenging when factoring in pedestrian traffic, uneven traffic origin-destination flow, heavy vehicle volumes, and approach vehicle gap-selection timing.

In addition to creating a sensor network to obtain real-time vehicle and pedestrian data to help control traffic and keep it flowing smoothly, the researchers also are developing a traffic simulation model that includes almost all of Richfield—more than 140 signalized intersections covering 21 square miles, including the arterials. The simulation model will be used to develop and test traffic control strategies under different scenarios. Minnesota Traffic Observatory director John Hourdos is leading that effort.

This research and the field deployment system are funded through a collaborative grant from the National Science Foundation Cyber Physical Systems program. SRF Consulting is the industrial partner to help design the sensor network and evaluate the system.

MnPASS extension on I-35E shaped by U of M study

Based in part on a planning study conducted by U of M researchers at the Humphrey School of Public Affairs, MnDOT is extending MnPASS Express Lanes on Interstate 35E in the northeast Twin Cities. The extension will build on the project currently adding MnPASS lanes from Cayuga Street to Little Canada Road.

The study, funded by MnDOT and the Federal Highway Administration (FHWA), examined the feasibility of extending these MnPASS lanes from Little Canada Road north to County Road 96. During peak periods, MnPASS lanes provide a congestion-free option to transit vehicles, carpools, and motorcycles at no cost—and to single-occupant vehicles for a fee.

Led by Director Lee Munnich and Associate Director Frank Douma of the Humphrey School’s State and Local Policy Program, the U of M research team worked with Parsons Brinckerhoff to develop and evaluate several concepts for the MnPASS extension. The goal was to provide an option that reduced congestion for all users, including drivers in the general-purpose traffic lanes and transit users. The team also included Mary Vogel from the U’s Center for Changing Landscapes.

The primary challenge was how to handle MnPASS traffic through the recently reconstructed I-694/I-35E interchange. After going over several design options, the team recommended what it termed a “hybrid” option, which creates a continuous southbound MnPASS lane and a discontinuous northbound MnPASS lane through the interchange.

Researchers also engaged community stakeholders and corridor users to gather feedback about the proposed alternatives and worked to illustrate options that could facilitate greater transit, carpool, and vanpool use in communities along this section of I-35E.

Additional recommendations developed by the team—in partnership with representatives from MnDOT, the FHWA, and the Metropolitan Council—included continuing to educate community motorists about the MnPASS program as well as expanding transit options by creating more park-and-ride sites, encouraging mixed land uses, and building better walking and biking connections.

Based on these recommendations, MnDOT is moving forward with the hybrid option for the project, says Brad Larsen, director of the MnPASS Policy and Planning Program. MnPASS lanes will be added to southbound I-35E between County Road 96 and Little Canada Road; through the I-35E/I-694 commons area, the existing inside lane will be designated as a MnPASS lane during peak periods. There will be no MnPASS lane northbound through the commons area, but a lane will be added north of the interchange from County Road E to County Road J.

Construction on the extension project is expected to begin in March 2016, with the lanes slated to open in late 2016.

More information:

(Featured photo courtesy of David Gonzalez, MnDOT.)

Major Ramp Metering Upgrade Reduces Freeway Delays

Motorists are experiencing less delay on metro-area highways, thanks to major changes to the Twin Cities’ ramp metering system.

The Minnesota Department of Transportation has reconfigured ramp meters to be more in sync with real conditions. With changes to the turn-on and turn-off criteria, the meters are actually running for a shorter period of time and are only activated when needed.

Ramp meters are traffic lights placed on freeway entrance ramps that control the frequency that vehicles can enter the highway. Sensors embedded in the pavement collect the vehicle traffic data used to time approximately 440 ramp meters.

Staff at the Regional Transportation Management Center, which manages the ramp meters, say the whole system is operating better because of changes that were implemented approximately one year ago (based off a 2012 study).

University of Minnesota-Duluth professor Eil Kwon developed the system’s new software algorithms. In a case study of Highway 100, he found that the delay on the mainline dropped by nearly half.

On northbound Highway 100, the amount of “delayed vehicle hours” — defined as the vehicle hours of traffic flow with speeds less than 45 mph — that motorists experienced dropped 48 percent during the months of October and November in 2012 when compared to the same period in 2011. During the same time period, total volume on that section of northbound Highway 100 increased by 2.7 percent, Kwon said. In spring 2013, the amount of delayed vehicle hours had been reduced by 17 percent.

These results are preliminary, as additional analysis is needed to determine if these results are typical throughout the system on other freeway corridors. However, based on a personal savings of $16.50 per hour, the scenario described above represents a cost savings to motorists of $1,353 to $3,447 per day (depending on the season). That’s as much as $339,150 to $861,640 per year for just a six-mile stretch of highway.

More efficient

Under the old system, each ramp meter would turn on based on current traffic conditions, but the criteria to turn on were easily met, causing the meters to turn on too soon. The old system did not have turn-off criteria, allowing meters to run until a pre-set time of day.

With the new system, improvements were made to make the meters respond more appropriately to current traffic conditions. The turn-on criteria were improved so that meters come on only when needed, and turn-off criteria were added, allowing meters to turn off when traffic conditions improved.

The new metering system is particularly effective at reducing the number of meters operating on light traffic days.

“On days like the ones leading up to Thanksgiving, where traffic may be 10-to-15 percent less than normal, instead of, say, 150 ramp meters being on at a particular time, now maybe only 50 ramp meters will be operating,” explained MnDOT Freeway System Operations Engineer Jesse Larson.

Upgrades to the ramp metering system also allow for a better picture of what traffic is like at a given moment, because it’s now based on corridor density rather than traffic flow.

Traffic flow is the measurement of the number of vehicles passing a given point. Using traffic flow was flawed, in that similar traffic flows can occur at different speeds. The old system couldn’t differentiate between 1,000 cars passing by at 20 miles per hour versus 1,000 cars passing at 60 miles per hour, for example.

Corridor density, on the other hand, is the number of vehicles per lane per mile. By measuring density instead of traffic flow, the system has a more accurate picture of what current conditions are like on the freeway.

Another bonus: ramp meters will no longer release a bunch of cars simultaneously once an entrance ramp fills up. That’s because the system can now detect the ramp filling up and release the extra cars gradually instead.

The amount of hours vehicles wait at entrance ramps fell by nearly 50 percent during the fall months along a section of Highway 100.
Twin Cities ramp meters now turn on and off based on live traffic conditions.

Related Resources

Development of Freeway Operational Strategies with IRIS-in-Loop Simulation study