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INV 805: This study evaluated the effectiveness of street lighting on isolated rural intersections in reducing nighttime crashes, using both a comparative analysis and a before-and-after study, and found that street lighting can reduce the number of crashes.

A number of studies have linked the benefits of roadway lighting to a reduction in crash rates at night for a variety of roadway types including rural intersections. Assessing the effectiveness of intersection lighting has primarily relied upon crash database modeling comparing lighted intersections to unlighted intersections. The current research effort gathered similar metrics for comparison but also measured the amount of lighting within isolated rural intersections. Sixty-three intersection locations were chosen for lighting measurement from six different counties within Minnesota. A vehicle mounted illuminance meter data collection system was used to collect data at each intersection. The data collection system utilized five separate illuminance meters and captured horizontal illuminance while driving through all 63 intersection locations. Following data collection, a series of negative binomial regression models were used to assess the horizontal lighting level in conjunction with the nighttime crash ratio, intersection configuration type, and proximity of an intersection to a curve in the roadway. The first model used data from the lighted an unlighted intersections. The results showed that across all intersections, an increase in the average horizontal illuminance (3.91 lux) by 1-lux (~0.09 fc) reduced nighttime crash rates by 9%. A second model used only lighted intersection data and showed an increase in 1-lux from average (6.41 lux) reduced crashes by 20%. A third and final model used unlighted intersections only. A 1-lux increase from average (0.20 lux) or increasing illuminance to lighted levels (as defined by the modeling), reduced nighttime crash ratios by 94%. Intersection configuration and proximity to curves also affected the nighttime crash ratios. The results of this effort are discussed in terms the impact of horizontal illuminance on crash rates. Additional items discussed include thresholds for minimum and maximum lighting levels and future research investigating and validating these efforts.

Street lighting improvements provide an opportunity for governments to save money and to reduce their environmental footprint. New energy-efficient technologies are being perfected that are more efficient than standard high-pressure sodium streetlights. Light-emitting diode (LED) and induction are two types that hold promise of saving money while using less energy to reach light standards. Many manufacturers have developed energy-efficient lighting products with a variety of performance claims. There has been limited in-field, head-to-head testing of these products, particularly in cold weather climates, to help governments choose the most suitable product. This research project had two aims: (1) compare lighting performance among induction, LED, and standard high-pressure sodium streetlights, and (2) compare lighting performance among six LED brands/manufacturers and three induction brands/manufactures to evaluate consistency by vendor. This research evaluates the LED and induction streetlights on several measures: (1) energy consumption, (2) operating costs, (3) maintenance calls, (4) light levels and quality, and (5) public reaction/acceptance.

In September 2011, MnDOT installed 10 LED and 10 HPS luminaires along a trunk highway. MnDOT employed data-logging meters to gather hourly electrical operational characteristics relative to both types of light sources. A light meter was used to collect lamp color temperature data and identify changes in the specified color temperature as the LED luminaires aged. This document presents the collected data.

The primary objective of this report is to present statistically reliable conclusions relative to the changes in crash frequencies and other crash characteristics at isolated rural intersections associated with the installation of street lighting. It was found through a comparative analysis of over 3,400 rural intersections and a Before versus After analysis of a sample of 12 intersections that the installation of street lighting reduced both nighttime crash frequencies (25% to 40%) and crash severity (8% to 26%). A Benefit – Cost analysis using statistics from the Before versus After analysis found that crash reduction benefits associated with the installation of street lighting at rural intersections outweigh the costs by a wide margin. As a result of the analysis, it was concluded that the installation of street lighting at rural intersections is a low cost and very effective strategy for mitigating nighttime crashes. This strategy should be added to the traffic engineer’s toolbox and agencies should be encouraged to increase the use of streetlights at rural intersections in order to reduce crashes and improve motorist guidance. It was also concluded based on a comparison to the results for other recent research that the use of street lighting to reduce nighttime crashes at rural intersections would likely be far more effective than either rumble strips or flashing overhead beacons.

The goal of this project was to understand the effectiveness of light emitting diode (LED) based lights for replacement of the standard strobes on Mn/DOT snow plows and to develop a set of specifications for LED based snow plow strobe lights. Intensity measurements were performed along with field testing in order to understand the correlation between optical power output of the lights and the conspicuity of the lights under typical viewing conditions. A robust correlation between intensity and conspicuity was not established, but we were able to make a qualitative connection between intensity and conspicuity for the LED based lights under the conditions tested. The results suggest that LED based lights are comparable in conspicuity to the standard strobe lights currently used on Mn/DOT plows, under specific conditions. We found that when viewed from a direction corresponding to that typical of a vehicle approaching from the rear; the LED based lights were equally conspicuous as the standard strobe. However, when viewed from other angles the standard strobe outperforms the LED lights in field tests. A specification was not completed, but recommendations were made for possible improvements to LED based lights to improve field test results.

Many state Departments of Transportation (DOT) across the US; including MnDOT; are experiencing problems associated with loose anchor bolts used in support structures (e.g.; overhead signs; high-mast light tower (HMLT); and tall traffic signals). Specifically; MnDOT inspection crews have found loose nuts at most anchor bolt locations; even at some newly installed signs. Many of these nuts became loose in less than two years; even after being tightened by the maintenance crew following current recommended procedures. This situation has placed great strain on the resources from the districts' maintenance group and also causes concerns related to inspection frequency and public safety. This project investigated causes of the loose anchor bolts and proposes solutions based on site surveying; field monitoring; laboratory study; and numerical analysis. The research team found that the tightening process proposed in AASHTO's specification is a sufficient alternative for MnDOT; though it requires modification in three key areas: defining snug-tight; accounting for grip length; and recommending verification procedures. The research team quantified snug-tight values; and defined the relationship between torque; tension; and nut rotation through empirical constants. Recommendations are made for a new specification for MnDOT structures.

Mn/DOT maintenance and construction vehicles are required to have emergency lighting to ensure the safety of workers and motorists. The current standard for Mn/DOT snowplows is high-intensity discharge strobe lighting, or HID. In an effort to reduce maintenance costs, Mn/DOT is exploring the possibility of replacing HID on snowplows with light-emitting diodes because LED-based strobe lighting is more efficient and reliable than HID lighting. However, observation suggests that under certain conditions and from certain angles, LED lighting is less visible than standard HID lighting and so may not be as safe. Further, very little data is available about the effectiveness and safety of using LED lights on snowplows. For Mn/DOT officials to make an informed decision about whether to move to LED lighting on snowplows and other highway maintenance and construction vehicles, they needed to consider the results of comprehensive testing of this new solution.

This Technical Summary pertains to Report 2018-27, “Re-Tightening the Large Anchor Bolts of Support Structures for Signs and Luminaires,” published August 2018.

This Implementation Summary pertains to Report 2016-17, “Implementation of LED Roadway Lighting,” published May 2016.