MnDOT and Local Road Research Board

This Research Summary was part of the final deliverable for Report 2024-19, "Implementation of Inductive Loop Signature Technology for Vehicle Classification Counts," published in December 2024.

This study evaluates recent technology that uses inductive loop detectors, traditionally used for collecting traffic volume and speed data, to provide vehicle classification data by examining the high-resolution signature produced when a vehicle passes over the sensor. The project aims to verify the accuracy of the new classification system, collect additional heavy vehicle data to help improve system accuracy, and familiarize MnDOT staff with the technology through training and the development of a field deployment manual. Through collaboration with MnDOT and the technology vendor CLR Analytics, Inc., the VSign vehicle classification system has been installed at five sites in Minnesota with preexisting loop detection systems. The final sites are representative of MnDOT facilities, feature a mix of heavy vehicle traffic, and provide accessibility for deployment staff. Data from the VSign system was compared with manually verified ground-truth data collected from video under both the Federal Highway Administration (FHWA) and Highway Performance Monitoring System (HPMS) classification schemes. The system demonstrated high accuracy for passenger vehicles but varying accuracy for different classes of heavy vehicles, though performance improved under the HPMS classification scheme. The VSign system was also evaluated against the video-based iTHEIA™ system at one site, which VSign outperformed in both classification accuracy and detection rate. The results suggested that the VSign system was more effective at locations where vehicles maintained consistent speeds and were centered in the lane due to the negative effects of variations in speed and lateral position on the consistency of vehicle signatures read by the detector.

This research sought to identify best practices for channelized right-turn lanes (CRT) that better accommodate the safety and accessibility needs of all road users. This was accomplished through a comprehensive literature review, a state-of-the-practice survey of state and local roadway agencies (nationwide and within Minnesota), a review of agency policy and guidance materials (nationwide and MnDOT), and a series of focus group meetings focused on vulnerable road users. Feedback received both from the survey of transportation agencies and the focus group sessions performed as a part of this research suggest that roadway agencies throughout the United States are moving toward proactive policies for the use of CRTs that emphasize safety and mobility for vulnerable road users. This movement is generally based on the concerns for the safety of vulnerable road users outlined in the prior section and commonly includes 1.) minimizing the use of CRTs at urban and suburban intersections and/or 2.) designing new CRT facilities or retrofitting existing facilities with mitigation strategies to improve the safety and accessibility for vulnerable road users. This information was synthesized along with the best practices found in the research literature and agency policy/guidance materials to develop implementation guidance, which is organized within the report as follows: 1.) guidance for use of CRTs based on the project scenario; 2.) traffic control recommendations for CRTs; 3.) recommended design features for CRTs; and 4.) recommended mitigation strategies intended to improve CRT safety and/or accessibility for vulnerable road users.

The Minnesota Department of Transportation (MnDOT) recognizes the importance of subsurface drainage in pavements. Various studies have indicated that adequate drainage of pavement layers enhances performance of pavements in general. MnDOT thus uses various types of subsurface drainage in varying degrees of styles, frequency of use, and minor variation in construction practices in the various transportation districts of the state. The subsurface drainage technologies include Open Graded Aggregate Base (OGAB), Drainable Stable Base (DSB), Permeable Asphalt Stabilized Base (PASB), Geocomposite Joint Drain (GJD) and Class 5Q aggregate. This study examines the various drainable bases in the network and identifies their locations and limits. Using performance data from the pavement management system, the performance, measured via Ride Quality Index (RQI), of test sections with drainable base systems was compared to contiguous sections without the systems so that traffic and environmental factors as well as other variables were held constant. Reliability and logistic analysis were conducted to ascertain if there were performance advantages in the drainable systems. The difference between the systems was found to be advantageous in certain districts, and an operations research survey reflected advantages in the drainable systems where and when they were associated with proficiency in construction practice.

This research summary is part of Report 2024-18, "Pedestrian Risk on Anishinaabe Reservations in Minnesota: Overview and Phase 2 Results," published in June 2024.

This research summary is part of the final deliverable for Report 2024-23, "Re-Use Of Minnesota Waste Material In Sustainably Designed Soils: Part 2, published in September 2024

Minerals, forestry, agriculture, and industrial activities in Minnesota generate substantial by-products and waste. Strategies to reuse or recycle these can reduce landfill waste, enhance public health, conserve resources, and cut costs and emissions. Building on the frameworks by Johnson et al. (2017), Saftner et al. (2019), and Saftner et al. (2022), this project extended its scope across Minnesota to include materials like dredge sediment from Mississippi River, RCA (recycled concrete aggregate) and VersaLime. Researchers identified, selected, and characterized various waste, by-products, and commercial materials statewide, as well as tested engineered soil mixes for roadway applications, assessing their stormwater retention and support for native plants. Laboratory methods characterized these mixes, which were implemented and evaluated in situ. A preliminary environmental life cycle assessment (LCA) was also conducted quantifying the environmental impacts of the engineered soil mixtures. Results were compiled into a design guide for the Minnesota Department of Transportation (MnDOT) engineers.

Many Minnesota bridges have older barriers or parapets that met the design code at the time of construction in the 1950s. Many of these bridge barriers no longer meet current strength and performance requirements of NCHRP Report 350 or the Manual for Assessing Safety Hardware (MASH). As the Minnesota Department of Transportation (MnDOT) begins to rehabilitate older existing bridges; a determination needs to be made as to whether the existing older type of barrier can remain in place or if it should be rehabilitated or replaced with a newer style barrier. This research documented the number of bridges in Minnesota that have One-Line Rails and type G; J; and F barriers and when they were built. Evaluations were then performed for both the structural strength and crashworthiness of each type of barrier and recommended guidance and evaluation criteria were developed to determine when an existing barrier should be upgraded or replaced.

This Research Summary accompanies Report 2024-26, "Toward implementation of max-pressure control on Minnesota roads: Phase 2."

Max-pressure (MP) traffic signal control is a new and innovative control algorithm that uses upstream and downstream vehicle counts to determine signal timing that maximizes throughput. While this method has been extensively tested in simulation, it has not yet been tested on actual traffic signals in the US. To close this gap, this report presents the results of the development of a hardware-in-the-loop traffic signal testbed where microsimulation is used to simulate realistic traffic conditions, and the MP algorithm is used to control the signal display using a traffic controller (Q-Free MaxTime controller). The hardware-in-the-loop results demonstrate that MP can be safely deployed on North American traffic signal control hardware.