Research Reports

This report examines how full-depth colored concrete performs in Minnesota roadways, and includes recommendations for improved specifications for construction and for repair of existing installations.

This report presents the evaluation of chemical treatment practices known as flocculation for purifying construction site runoff of sediment, suspended solids and colloidal particles. Flocculation is generally used in combination with traditional sedimentation and filtration methods related to stormwater pollution prevention and dewatering fluid treatment. In particular, this report presents the best management practices (BMPs) for evaluation and design of flocculant treatment methods and technologies and the associated sizing for flows representative of field operations. Soil samples from across Minnesota, representing the wide range of geologic and geomorphological conditions, were used to identify differences in flocculant applicability and effectiveness.

Various agencies have discussed the possibility of using turbidity as an effluent standard for construction site. Turbidity monitoring can be difficult for dynamic construction sites. This project investigated turbidity relationships for conditions of Minnesota and developed protocols for the design and installation of cost-effective monitoring systems. Turbidity characteristics of fourteen different soils in Minnesota were investigated using the laboratory protocols. Trends in turbidity with sediment concentrations were well represented by power functions. The exponent of these power functions was relatively constant between soils and the log-intercept, or scaling parameter varied substantially among the different soils. A regression analysis for the scaling parameter was a function of percent silt, interrill erodibility, and maximum abstraction. A power value of 7/5 was chosen to represent all soils. The field studies were also used to develop turbidity monitoring systems that would be adaptable to construction sites and to collect turbidity data on construction site runoff. Construction site turbidities often exceeded 1000 NTUs and sometimes surpassed 3000 NTUs.

Dynamically priced High Occupancy Toll (HOT) lanes have been recently added to the traffic operations arsenal in an attempt to preserve infrastructure investment in the future by maintaining a control on demand. This study focuses on the operational and design features of HOT lanes. HOT lanes' mobility and safety are contingent on the design of zones ("gates") that drivers use to merge in or out of the facility. Existing methodologies for the design of access zones are limited to engineering judgment or studies that take into consideration undersized amount of observations. Case in point is the fact that the design philosophes between the two HOT facilities in Minnesota are diametrically opposed. Specifically, the I-394 freeway, the first dynamically priced HOT lane, was designed with a closed access philosophy, meaning that for the greater length of the roadway access to the HOT lane is restricted with only specific short-length sections where access is allowed. In contrast I-35W, the second HOT corridor, was designed with an open access philosophy where lane changes between the HOT and the GPLs are allowed everywhere except for a few specific locations. This contradiction generated questions as to effect each case has on safety and mobility. This study presents an assessment of safety and mobility on the two facilities as they operate today and highlights the issues present on either design.

By using a relatively new technology, mobile Light Detection and Ranging (LiDAR) and imagery, MnDOT obtained accurate roadway data in a safe and efficient manner. Using a manual extraction technique, MnDOT created a Geographic Information System (GIS) inventory of geospatial coordinate locations, asset attributes, and condition data for plate beam guardrails and concrete barriers. The LiDAR data was utilized for internal communication and visual rendering and will be used in the future to assist with roadway design. The project challenges were mostly technical in nature and highlight the importance of having a clear quality assurance/quality control process. The benefits of the project include, but are not limited to: calculating barrier replacement costs, scoping and budgeting future projects based on condition and future fed/state standard changes, allowing for better planning of maintenance activities, utilizing the imagery to extract other assets, and construction cost savings due to increased design accuracy.

This report provides a procedure for the evaluation of uncontrolled pedestrian crossing locations that takes into account accepted practice, safety and delay. The analysis procedure builds on previous research and adds in delay considerations to develop a methodology appropriate for use by jurisdictional agencies in the evaluation of treatments at uncontrolled pedestrian crossings.

Highway agencies with an inventory of traffic signs must adopt a method of maintaining those signs so that the retroreflectivity exceeds established thresholds. Understanding expected sign life can help agencies phase sign replacements over a number of years in order to manage maintenance costs. The primary goal of this research is to provide objective data about sign life based on the degradation of retroreflectivity and color over time. A literature review found sign retroreflectivity research around the country, however, none of the studies are conclusive. Eight Minnesota agencies took retroreflectometer readings on in-place signs across the state. Disaggregated measurements by sheeting material and color did not leave a large enough sample for conclusive results, and very few signs fell below minimum retroreflectivity thresholds. Data suggests sign life exceeds the manufacturer's warranty and that a controlled environment with known conditions will produce more reliable data. MnDOT established a test deck at MnROAD to take multiple retroreflectivity and color readings over time to the point of failure in a controlled environment. The best information inferred from the results is an estimate for an expected sign life of 12 to 20 years for beaded sheeting and 15 to 30 years for prismatic sheeting. Agencies are encouraged to move forward and adopt a sign maintenance method and expected sign life by bringing sign management decisions under an umbrella of immunity. This document has suggested best policy practices and statements for sign maintenance and management assembled by a panel including engineers and risk management specialists.

Active Traffic Management (ATM) strategies are being deployed in major cities worldwide to deal with pervasive system congestion and safety concerns. While such strategies include a diverse array of components, in the Twin Cities metropolitan area the deployment of the Intelligent Lane Control Signs (ILCS) allowed for the implementation of Variable Speed Limits (VSL). The VSL system in the Twin Cities aims to detect congestion and preemptively warn upstream drivers to reduce speed. By reducing the severe change in speed between upstream and downstream traffic, safety and operational benefits are sought. This report presents an investigation of the effect the I-94 VSL system has on the safety of the high frequency crash area located on the westbound lanes of the freeway through downtown Minneapolis (I-94/I-35W commons). This report describes several methodologies that were used to examine the impact of the VSL system within the I-94/I-35W commons high crash area. Numerous data sources were utilized, including video records of crash and near crash events, loop detector traffic measurements, machine vision sensor data, and actuations from the VSL system. A before-after approach was taken to examine the incident rates for crashes and near crashes using visually identified events within video data. Utilizing the unique capabilities of the Minnesota Traffic Observatory's I-94 Freeway Lab, high resolution traffic measurements, collected by machine vision sensors at the bottleneck location, were used within a new cross-correlation based analysis methodology to measure and visualize shockwave activity before and after the implementation of the VSL system.

This study provides design information for temporary stormwater ponds with floating head skimmers. The purpose of the ponds is to remove suspended sediment and nutrient loads from stormwater runoff on active construction sites. The design information is directed at meeting the standards in the National Pollution Discharge Elimination System (NPDES) general permit which includes storing runoff from the 2-year, 24-hour rainfall event or providing the equivalent sediment control. The study results include: Research of currently available floating head skimmers, Estimation of runoff hydrology and hydraulics from active constructions sites using HydroCAD, Estimation of water quality improvements using P8, and Design plans. The study shows several available technologies for pond skimming. The pond and skimmer design manages a 2- year, 24-hour rainfall event while removing an average of 80 percent of total suspended solids (TSS) from runoff. Smaller systems do not operate equivalently without additional treatment such as adding flocculants. Plans, maintenance requirements, and special provisions are included.

This report documents the efforts of engaging the public in decision making regarding local road policy issues in Minnesota, specifically in Beltrami, Dakota, and Jackson counties, and make recommendations based on the findings.