Tag Archives: High Occupancy Toll lanes

Traffic and Safety

Refined ROI Methodology Shows Added Benefits of MnPASS Lanes

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Researchers have developed a more comprehensive, standardized method for evaluating and selecting MnPASS managed lane projects. The new methodology uses a return on investment (ROI) and benefit–cost analysis framework that includes a more extensive set of factors, variables and perspectives than earlier methods. After applying the broader range of impact categories from the new methodology to an earlier study of a MnPASS corridor, researchers found that the MnPASS projects provide more benefits than previously reported.

In the past, MNDOT used a series of evaluation methods—cost estimation, performance measures and travel demand forecasting—to select new MnPASS corridors. While the recommendations and results from these assessments were adequate, each evaluation used a different set of objectives and assumptions. The range of benefit–cost factors in earlier evaluations was also limited to travel time savings, operating costs and crashes.

2017-37-p2-image
An overhead sign above a MnPASS express lane explains that drivers must have MnPASS or two or more occupants in a vehicle to use the lane during peak travel time of 6 a.m. to 10 a.m., Monday through Friday.

“Our previous corridor studies each had different benefit–cost elements, making direct comparisons difficult. This project makes it possible to quantify the transit, environment and travel time reliability benefits that we knew were there all along,” John Wilson, Economic Policy Analyst, MnDOT Office of Transportation System Management

MnDOT needed a more thorough and consistent benefit–cost analysis methodology to help decision-makers better assess MnPASS project alternatives; compare potential MnPASS corridors; and communicate why MnPASS is a financially effective, long-term strategy for addressing mobility and congestion issues.

What Was Our Goal?

The goal of this project was to develop a refined, standardized methodology to more accurately assess the ROI of MnPASS programs and projects. A refined assessment framework would include a broader range of financial and performance measures, allowing MnDOT to more thoroughly evaluate MnPASS investments.

What Did We Do?

Using ROI as the central framework, the research team set out to generate a more comprehensive method for estimating benefits and costs. To begin, team members identified limitations in the existing benefit–cost analysis methodology and developed a list of factors to include in the refinement process. Then they interviewed stakeholders from various agencies to better understand MnPASS planning and operations needs, as well as the data required to support the research and system benefits and costs.

Next, they began to develop the enhanced framework by defining economic, environmental and social ROI categories for MnPASS investments, and mapping the relationship between these categories and their associated benefits and costs. Benefit– cost analysis methods then were used to build the refined framework and to estimate benefit–cost ratios for projects. Finally, researchers applied the new framework to an earlier benefit–cost analysis of the Interstate 35 West (I-35W) North Managed Lanes project to compare the results of the new framework with the results from the earlier analysis.

What Did We Learn?

Researchers used additional benefit factors such as transit use, travel time reliability, emissions and noise to refine the ROI calculation methods. When they applied the new ROI framework to the I-35W project, they found that the MnPASS benefit–cost ratio significantly improves with the inclusion of transit and travel time reliability benefits.

“Benefit–cost analysis had not changed for a long time; we had looked at travel time, vehicle operating costs and safety. Now we have added travel time reliability, which is important because we are moving people, not just vehicles.”—Paul Morris, Senior Associate, SRF Consulting Group, Inc.

What’s Next?

The results from the comparative analysis yielded a notably higher benefit–cost ratio of 3.40 for the test corridor compared to a benefit–cost ratio of 2.11 in the original study, indicating that MnPASS projects have more positive effects than previously identified. Based on these findings, MnDOT will revise its benefit–cost guidance for evaluating MnPASS investments.

The research team was also able to measure the impacts of specific categories on the overall outcome of the calculations. Team members found that while the measures for reliability and transit impacts produced a meaningful change in the overall benefits, those for emergency response, emissions and noise impacts were very small relative to overall project costs. MnDOT will consider these findings in establishing updated procedures.

This post pertains to Report 2017-37, “Refining Return on Investment Methodology/Tool for MnPASS,” published October 2017. Other research initiatives to improve MnPASS operations can be found by searching “MnPASS” on MNDOT Research Services’ project pages.

 

Traffic and Safety

New Software Models MnPASS HOT Lane Changes

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Until recently, Minnesota drivers could only enter or exit high-occupancy toll (HOT) lanes via select ramps and access points. But MnDOT has changed most of its MnPASS express lanes to an open-access system to allow more movement between general purpose and high-occupancy toll (HOT) lanes.

Although MnDOT prefers this open access system, there could safety concerns for allowing lane changes in certain locations, especially if traffic patterns change. A new design tool developed by MnDOT-sponsored research enables traffic engineers to evaluate existing or prospective HOT corridors and determine the impact of open or closed access. When data shows changes in traffic patterns and congestion, the software also allows technicians to model and design changes in MnPASS access to improve drive mobility and safety.

“Nothing like this has been developed anywhere else. There is a lot of debate around the country about high-occupancy designs. This tool helps us develop designs and monitor existing corridors,” said Brian Kary, Director of Traffic Operations, MnDOT Regional Transportation Management Center.

Background

In Minnesota, high-occupancy toll (HOT) lanes are used by buses, carpools and motorists with transponders that trigger payments for rush hour use. During rush hour, fees increase as congestion increases; at other times, the lanes are free for all users.

MnDOT research in 2014 concluded that both closed and open HOT lane configurations effectively and safely improve traffic capacity. But researchers anticipated that roadway sections on an HOT lane corridor may eventually experience safety and mobility problems if toll prices are lowered or traffic volume increases. During heavy traffic, driving speeds often vary dramatically between HOT and general purpose lanes. Drivers moving into MnPASS lanes may force other drivers to brake suddenly to avoid collisions and trigger shockwaves of slowed or stopped traffic behind them. MnDOT prefers open-access designs for the increased options they offer road users, but it was not clear how best to manage access to reduce the incidence of shockwaves and the safety and mobility problems they create.

A section of a MnPASS express lane.
MnDOT has changed most of its MnPASS lane markings from double solid lines to skipped double lines to allow more open movement between general purpose and HOT lanes. A new software tool allows RTMC engineers to reassess MnPASS access to respond to changing traffic patterns.

The goal of this research implementation effort was to develop a software tool that the Regional Transportation Management Center (RTMC) could use to assess corridor operations and design. Based on design recommendations from earlier research, the tool would allow RTMC users to predict the safety and mobility impacts of a change from open to closed HOT lanes, and estimate where in the corridor such changes could be implemented safely and effectively.

What Did We Implement?

This effort leveraged findings from three previous MnDOT studies. Models and methods from “Evaluation of the Effect of MnPASS Lane Design on Mobility and Safety” (Report 2014-23) were used for the architecture of this new system. Investigators drew on “Expanding and Streamlining of RTMC Freeway Network Performance Reporting Methodologies and Tools” (Report 2014-05) to implement methods for retrieving historical data from RTMC’s system, cleaning the data and integrating it into the new software package. The project team then incorporated data from “Safety Impacts of the I- 5W Improvements Done Under Minnesota’s Urban Partnership Agreement (UPA) Project” (Report 2017-22) to develop and calibrate the new tool for estimating traffic impacts and shockwaves. A car-following and lane-changing model developed in a 2013 University of Minnesota study provided effective methods for ensuring realistic vehicle modeling and shockwave generation.

How Did We Do It?

Investigators developed this system with links to MnDOT’s database to draw on historical data to identify patterns of traffic demand over time and generate predictions of points in the MnPASS lanes at which shifts from open- to closed-access HOT lanes will offer the most benefit. The program’s code integrates the various models, data sets and tools mentioned above into software that integrates smoothly with the RTMC’s current software and capabilities for collecting speed and volume data, developing interfaces to model impacts of changing open designs at certain points in the freeway corridor to closed designs. The tool includes a module for access design, a module for generating data and a web application.

“This tool is calibrated for the Twin Cities. It takes real-time data and diagrams each location separately for lane changes and reaction time. It took theoretical ideas and made them usable,” said John Hourdos, Director, Minnesota Traffic Observatory, University of Minnesota.

What Was the Impact?

After receiving training in using the new software, RTMC engineers have embraced the MnPASS design tool to regularly report MnPASS performance to the Federal Highway Administration and to generate quarterly and annual analyses and recommendations for changing specific locations from open access to closed access. Closing requires restriping and changing signage—operations that allow MnDOT to respond quickly and easily to shifts in traffic patterns and potential mobility and safety impacts.

The project also offers data for the broader transportation community in which experts debate the relative merits of open- and closed-access HOT designs. With MnPASS, MnDOT has emerged as a leader in open design; this software allows sophisticated modeling of design impacts for the national traffic operations community.

What’s Next?

The MnPASS design tool effectively monitors corridor behavior and design changes. Improvements may yet be made to allow data calibration and validation for slower traffic speeds that represent mobility breakdowns, and to refine aspects of car-following and shockwave models. Increased density scenarios can also be further improved to better accommodate traffic density increases in regular lanes alongside HOT lanes.

In its current form, the tool will be used to analyze open- and closed-access designs on the Interstate 394 corridor to determine the best locations for changes to MnPASS lanes, and positions MnDOT and the RTMC to respond to traffic demand changes in the future.

This post pertains to Report 2018-11, “A Tool for Designing MnPASS
Access Spacing,” published March 2018. The full report can be accessed at
mndot.gov/research/reports/2018/201811.pdf.

 

Traffic and Safety

Infrared Sensing Not Yet Suitable for HOV/HOT Lane Enforcement

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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.

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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. 

Research, Traffic and Safety

MnPASS: Two systems, both work

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I-35W’s MnPASS lane, where vehicles can frequently enter and exit the high-occupancy toll lane, is just as safe as the MnPASS lane on I-394, where motorists only have a few shots to enter the system, a new study finds.

Researchers at the Minnesota Traffic Observatory undertook the MnDOT-funded study because of objections to open systems like the one on 35W.

“The federal government has very strong arguments against the open system. They’re saying it’s going to be dangerous – cause more disruption and more congestion,” said John Hourdos, director of the Minnesota Traffic Observatory. “We found that both roadways are working very well today because they were designed appropriately for their location.”

The definition of an open system is one that has more opportunity for access than restriction. On 35W, a dotted white lane means vehicles can enter the toll lane at will, and a solid line bars access.

Vehicles must have two occupants on-board or an electronic pay card to use the express lanes during rush hour.

MnPASS on Highway 35W.

The reason I-35W allows vehicles to enter MnPASS more frequently than I-394 is because there are more ramps where new vehicles are entering the freeway and might want to get on MnPASS.

Researchers studied whether accidents are more likely to occur by studying the number of accident-inducing vehicle movements along the 35W corridor. They found that areas where accidents are mostly likely to occur are also where the lane would have to allow access anyway under a closed system like 394.

The study also looked at mobility, determining that MnPASS users have just as good free-flowing traffic under the open system.

Helpful tools

Researchers also created design tools that engineers can use to determine where access points should be on MnPASS lanes.

Until now, engineers have relied on rule of thumb. For example, the general guidance for allowing access on a closed system was 500 feet for every lane between the entrance ramp and the HOT.

The tools can be used to automatically determine how fluctuations in the MnPASS fee will affect congestion within the lane.

The fee to use MnPASS depends on the time of day.

As the express lane become more congested, the fee to use it increases. This slows the number of cars entering the lane, increasing the speed of the vehicles already in the lane.

“We ran the tool on three locations on 35W and found that, for example, on Cliff Road, you can increase the traffic by 75 percent and still be okay,” Hourdos said. “You have more leeway there than north of the crossroads of Highway 62 and 35W, for instance.”

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