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Between 2018 and 2019, MnDOT installed a lane constrictor design at 66 side-street, stop-controlled intersections in Minnesota. The lane constrictor design narrows the lane width for mainline approaches via a striped median with centerline rumble strips. By narrowing the mainline lane, the goal of this design is to encourage mainline traffic to slow down as it approaches the intersection. The striped median also provides greater separation between mainline directions and draws more attention to the location of the intersection. Following the installation of lane constrictors at MnDOT intersections, overall crash rates have seen little change but there have been decreases in fatal and serious injury (KA) as well as fatal and all injury (KABC) crash rates. These results indicate the addition of lane constrictors have a positive impact on crashes by reducing the severity of crashes, swapping injury crashes for property damage only crashes.

Recent changes in laws regarding the use of volatile organic compounds impact the type of pavement marking material that many communities use to mark or delineate their roads. This report presents information on the various types of pavement marking materials available and summarizes information on pavement marking material terminology, the various types of pavement marking materials, their durability, and their retroreflectivity. The report explains changes in formulas relating to laws regulating the use of volatile organic compounds, as well as the impacts of those changes. Additionally, it includes a list of best management practices. This report indicates that for low-volume roads [annual average daily traffic (AADT) of 10,000 or less], a conventional product, such as paint, may be the most cost-effective material. For roadways with higher volumes (AADT of 10,000 or more), a more durable product, such as epoxy, tape or thermoplastics, may be more cost effective and may reduce worker exposure to traffic.

In pursuit of unimpeded high peak traffic flow, the "Design Guidelines for Super Two Highways" (Ekem, 1998) suggested several treatments for the right side of the roadway. But the left side is where drivers experience great speed differentials between their own vehicles and oncoming traffic. The authors examined centerline treatments and possible recommendations for Super Two guidelines. The current US standard (12-ft lane/4-in. dashes) was compared with combinations of wider lanes, wider dashes, and buffer areas. With each of the centerline treatments examined, participants kept the left side of the vehicle in the approximate center of the lane. All treatments resulted in shifting the center of the lane farther from the centerline than it was in the standard condition. Two conditions appear to be most effective in keeping drivers away from the centerline: 1) 14-ft lanes with both longitudinal rumble strips and 4-in.-wide dashes marking the centerline, and 2) 12-ft lanes with 4-ft buffer marked by 4-in.-wide dashes. However, implementing any of the centerline treatments should result in vehicles driving farther from the centerline, thus making it less likely that drivers will meet an oncoming vehicle. Data were gathered in a driving simulator. Further testing should be conducted in real driving situations.

This report presents a study of the impact lane markings and signing have on driving behavior at a two-lane roundabout located in Richfield, Minnesota. After its completion in 2008, this roundabout sustained a suspiciously high amount of crashes. In response, through this study, engineers experimented with changes in the roundabout's signs and lane markings, as roundabout design regulations are relatively lax and nonspecific in contrast to those for standard signalized intersections. An observational study was conducted that reduced 216 hours of before and after video records of the roundabout into a database of all the violations committed by drivers. Along with the observational data, crash records were analyzed and demonstrated that improper turns and failing to properly yield account for the majority of collisions. The changes implemented in the approaches to the roundabout and specifically the extension of the solid line seems to have reinforced the message to the drivers that they must select the correct lane before approaching the roundabout entrance. Although choosing the correct lane does not directly address yielding violations, it does reduce the occurrence of drivers conducting an improper turn and to some extent reduces the need for a driver to change lanes within the roundabout. The implemented changes produced a 48% reduction in normalized occurrences of improper turns, and a 53% reduction in normalized occurrences of drivers choosing the incorrect lane a month after the changes, while a year later, these reductions were 44% and 50%, respectively.

This Rumble Strip Noise Evaluation study presents results of sound level monitoring of three types of longitudinal rumble strips installed along the edge of two-lane rural roads in Polk County, Minnesota. The study is in response to objections raised by some landowners about the unwanted noise caused by vehicles traveling over rumble strips when they drift over the edge or centerline of the roadway. By changing and modifying the design, the ultimate goal is to provide the maximum safety by capturing the driver's attention through tactile and sound levels while minimizing the associated external noise generated by the rumble strips. Both exterior and vehicle interior sound levels were measured from three longitudinal edge of pavement rumble strip designs - California, Pennsylvania and Minnesota. Simultaneous digital audio files were also recorded. Three vehicles were used - a passenger car, pickup, and semi-trailer truck. Tests were performed at 30, 45 and 60 mph. Comparison of exterior and interior sound levels and audio shows that the Pennsylvania design is the quietest, both interior and exterior. The interior level of the Minnesota and California designs are similar but exterior levels are higher for the Minnesota design.

The objective of this project was to fully implement the Pavement Marking Management Tool by incorporating retroreflectivity and striping data (MnDOT and contractors) and simplifying the process of data collection, storage, and analysis. As part of achieving full implementation, the researchers provided training to MnDOT central office staff and staff in each of the districts. Improved pavement marking management has the potential to reduce MnDOT's costs, improve pavement marking performance, and in return provide a more efficient and safe driving experience for the traveling public. The result of this effort included a web-portal for submitting pavement marking data (paint and retroreflectivity), a geographic information system (GIS) web based tool to manage, view, and create reports on pavement marking data, and training on the data collection and tool. This technical memorandum presents project findings by task.

The goals of this project were to develop a large-scale vehicle-mounted robotic roadway message painter that could be run by a single operator, and to develop software to enable the device to automatically paint various messages and symbols on roadways. A completely new articulated robot arm was design and constructed, complete with a control system, operator interface, paint delivery system, truck mount, and mobile power supply. The system was thoroughly tested, and programs were written to allow the robot to paint several symbols and messages on a roadway. The programs were tested and fine-tuned indoors, and then tested outdoors once the robot was mounted on a truck. An important finding of this research is that the traditional markings used by MnDOT are not ideal for robot application. Robotic painting can be better accommodated by altering the outlines of the markings somewhat, and by using directional hash lines to fill in the symbols rather than solid paint. These machine-made markings are faster to apply and use less paint, and in the end may be more effective for motorists than the traditional markings. The robotic roadway painter developed during this project has the potential to completely change the way in which markings are painted on roadways. The device has demonstrated the ability to paint roadway markings using an articulated robot arm mounted on the front of a vehicle. Expected benefits of the deployment of such a device include improved operator safety, improved productivity, and improved flexibility in roadway marking operations.

This research effort provided the Minnesota Department of Transportation (MnDOT) with field data on the performance of pavement marking materials when used as rumble stripes on MnDOT roadways. These field efforts provide a perspective on the impact that both wear and winter maintenance practices have on retroreflectivity. Given that these markings were installed by a variety of MnDOT contractors and at different times and roadways, this report also serves to document the range of retroreflectivity provided to drivers at any given time on similar two-lane MnDOT roadways under the installation practice guidelines at the time of installation (2012 to 2013). More specifically, these measurements consider the difference in retroreflectivity provided by direction of travel (e.g., for the same marking, what is the retroreflectivity while driving northbound versus southbound?) and by roadway. The long-term evaluation collected field measurements both initially and after two winters (18 months) for centerline rumble stripes only and on seven segments over three different roadways. The in-service evaluation included new centerline and profile rumble stripEs, all of which were installed as part of the 2013 mill and overlay projects on bituminous surfaces within District 4 on two-lane MnDOT roadways. The retroreflectivity data were collected one winter (approximately 12 months) after installation with no initial measurement data being available. This effort included measuring the centerline rumble stripe performance over eight segments on four different roadways and the profile rumble stripe performance over 18 segments on 10 different roadways.

This Sinusoidal Rumble Strip Design Optimization Study presents results of sound level monitoring of four types of centerline rumble strips installed along Trunk Highway (TH) 18 in Mille Lacs and Aitken counties in Minnesota. This study is in response to objections raised by some landowners about the unwanted noise caused by vehicles traveling over rumble strips when they drift over the edge or centerline of the roadway. By changing and modifying the design, the ultimate goal is to provide the maximum safety by capturing the drivers attention through in-vehicle generated sound levels while minimizing the associated external noise generated by the rumble strips. Tests on TH 18 were performed with three different vehicles passenger car, pickup truck and a class 35 tandem dump truck. A single speed of 60 mph was used, as this was shown to provide the most meaningful data in the previous study. For each of the designs, an initial test was performed with vehicles traveling on normal pavement, followed by three passes on the rumble strip. Rumble strip designs 1 and 4 created lower exterior sound level increases but created interior levels similar to designs 2 and 3. The external results correspond to the depth of the rumble strip design, with designs 1 and 4 having a maximum depth of 1/8 inch less than designs 2 and 3. The interior sound level increases are similar for all four designs but vary by vehicle type. All of the designs created increases greater than 10 dBA for the passenger car, which is a desirable level for gaining attention of the driver. For the pickup truck, the interior sound level increases ranged from 4.5 to 6.8 dBA, while the increases for the dump truck ranged from 0.8 to 2.7 dBA.

Pavement marking is important for safety. Maximizing pavement marking performance in terms of increased retroreflectivity; within limited budget constraints; allows agencies to make better decisions toward providing more effective pavement marking performance on their roadway networks. This research project included conducting a survey of local agencies' pavement marking practices; mining existing National Transportation Product Evaluation Program (NTPEP) pavement marking data; and developing recommendations for future pavement marking research to support local agency needs. The NTPEP pavement marking performance data (related to pavement marking products used by local agencies in Minnesota) was analyzed to provide guidance to local agencies in terms of pavement marking material selection based on performance. The objective included determining pavement marking products of interest to local agencies and developing performance metrics for these products based on existing NTPEP data. The analysis performed on the NTPEP included modeling the deterioration behavior as a function of time. Also two-way ANOVAs were performed to compare various performance measures and the impact of different conditions on these measures.