Research Reports

Current Minnesota Department of Transportation (Mn/DOT) design practice for many traffic signals utilizes an arrangement of steel guard posts to protect the signal, and in particular the signal head, from short turning vehicles. None of the components (guard post or traffic signal support) had been evaluated for automobile impacts and Mn/DOT was concerned about the performance of these installations. Accordingly, a project was initiated to determine the performance of the guard post/signal support installation when impacted by a 1800-lb (800-kg) class vehicles. Pendulum testing was used to evaluate the guard post and signal supports separately. It was determined that the signal support performed satisfactorily whereas the guard post would require modification to perform satisfactorily according to current recommended acceptance criteria. Performance criteria were determined for the modified guard post and two different concepts were evaluated in pendulum and vehicle crash tests. The guard post design using a breakaway steel coupling is recommended for installation with the standard signal support based on satisfactory crash test results using 1800-lb (800-kg) Hondas impacting the installation at 20 (32) and 60 (95) mph (km/h).

This report looks at the effectiveness of microloops as replacements for the inductive loops that are used as advance detection sensors at actuated signalized intersections. It also evaluated whether different loop detector models from several manufacturers can operate satisfactorily and consistently when attached to the microloop, and also determined the performance accuracy of loop detectors attached to a one-probe microloop or to a two-probe microloop. Research results support the hypothesis that microloops can function as a reliable replacement for inductive loops in advance detection applications. To achieve optimum results, the microloops must be used with Canoga C800 series vehicle detectors with version 1.2 firmware as part of a matched component system. Different brands of detector amplifiers do not perform as satisfactorily with the M701 microloop. Only the detectors that incorporate algorithms specifically developed for use with microloops demonstrated a performance that approaches the performance of inductive loops. These detectors also can be used in Presence Mode, thus allowing the traffic engineer to use the microloop in a broad range of applications. The strong attributes of microloop-based traffic sensors include shorter installation time, less pavement invasion, and improved life-cycle costs compared to traditional saw cut inductive loops, while providing consistent and accurate performance under all environmental and road conditions.

While seal coating has been widely used as a cost-effective strategy in asphalt pavement preservation by the Minnesota Department of Transportation (MnDOT) and local agencies to extend the life of pavements, some cities and counties in Minnesota have reported their concerns about the premature stripping of street pavements that have been seal coated. The Local Road Research Board (LRRB) completed a study on seal coats titled, Is Seal Coating Counterproductive or Not? to address these issues. The purpose of this document is to provide users with quick access to some of the research and resources available in Minnesota

This Technical Summary pertains to project TPF-5(215), “Best Practices for Soil Stabilization Design and Construction,” completed September 2015.

The Minnesota Department of Transportation (MnDOT) investigated the use of dowels with various anchoring methods and their effects on pavement performance. In a previous study, the characteristics of various epoxy and grout anchorage systems at the interface between new construction and existing concrete were studied using cut-out slabs brought into the Minnesota Road Research Facility (MnROAD). This investigation seeks to validate the findings of that study. Twelve different anchoring materials and methods were studied and compared to a control using no grout. This study did not examine the effects of a reduced number of dowels across a lane but rather looked at only the anchorage materials and methods. This experiment was performed on westbound lanes of Interstate 94, adjacent to the MnROAD test track. The field experimentation and monitoring involved core samples and measured ride quality, International Roughness Index (IRI), and Falling Weight Deflectometer (FWD) load transfer and fault measurement. These results supplemented the findings from the previous in-house performance categorization experiment. The control experiment, conducted without any grout or epoxy, initially displayed a notably low Load Transfer Efficiency (LTE). However, over time, there was a gradual improvement, leading to a more consistent LTE, attributed to the deployment of non-mechanical load transfer. Based on the slab thickness, the 1.25-inch dowel did not indicate any statistically significant LTE or other performance improvements over the 1-inch dowel within the anchorage types examined. Overall, the Epoxy Experimental 1 performed best while the un-grouted and unrepaired cells had the lowest performance. Moreover, no material clearly indicated characteristically low performance.

KEY OBJECTIVES • Evaluate messages and styles of ads used by Construction Office in summer of '99 to promote awareness and safety in work zones. • Determine if use of construction site information is a productive use of airtime. • Assess better ways to convey the importance of driving safely in construction or maintenance work zones. METHODOLOGY: Four focus group interviews were conducted in early March of 2000. Participants were regular users of metro area freeways, with one group being specifically drivers who also traveled north of the Twin Cities at least three times during spring through fall of '99. The latter was to get a comparative base for the site info, which depicted highways 169 and 35E going north, in the previous ad campaign.

This report identifies the installation experiences, challenges encountered, and lessons learned for two types of radio interconnect systems implemented within the Twin Cities metropolitan area. Radio interconnect was found to be a viable and worthwhile communication technology that can be successfully and effectively implemented and operated.

The Physical Research Section of the Minnesota Department of Highways has developed and constructed a device to measure the retro-reflective characteristics of pavement marking materials. The device can be operated at highway speeds and during normal daytime working hours with a minimal disruption to traffic. The device is a useful research tool and has been used mainly in this capacity. However, with the recent increase in materials cost of pavement marking and the reduced availability of these materials, ERMA can and should be used as a maintenance management tool. This will enable us to paint when it is necessary rather than according to a time schedule. This is only a portion of the final report and is not intended to give a complete description of the development of the device and proof that it works and results are repeatable. The complete final report will show the data which was obtained and prove the value of the device. This report is intended to show how the device is constructed and operated and a description of the method used to correlate the device to what drivers observe as reflectivity level under nighttime driving conditions.

The purpose of this study was to evaluate thermoplastic as a pavement marking material on portland cement concrete and asphaltic concrete pavements. This report summarizes the data collected under Investigation 186 and Special Study 276 and presents guidelines for using thermoplastic on both concrete and bituminous pavements.

The purpose of this study was to determine whether breaking a concrete pavement prior to being overlaid would result, in any reduction in the amount of crack reflectance. This report describes the design, construction and performance of a typical widening and resurfacing project, on a portion of which a 59-ton roller was used to crack the old concrete slab prior to construction. This process was found to significantly reduce some types of cracking and is recommended for future projects of this nature