Retroreflective Raised Pavement Markers (RRPMs) supplement other pavement markings to provide guidance to road users. Previous research concerning durability of the RRPMs suggests that their performance has been degrading over the years. One of the main causes for underperformance of the RRPMs is the lack of appropriate laboratory testing standards that can test the adequacy of the RRPMs to perform in field conditions. There is a need to modify the existing standards or develop new testing procedures that can better simulate field conditions. This requires identifying critical locations and magnitudes of stresses inside the markers during the tire-marker impacts that happen on roads. The goal of this research was to identify critical magnitudes and locations of the stresses in RRPMs during the tire-marker impacts by doing the finite element modeling and simulation of the impacts, and use the information to recommend laboratory testing procedures that could simulate real-world conditions. The researcher modeled and simulated the tire-marker impacts using the finite element tools Hypermesh and LS DYNA. He calibrated the material properties of the marker models to improve the tiremarker model. Based on the tire-marker impact simulations, the researcher concluded that the critical compressive stresses during impacts are located at the edge contacts of retroreflective sides with the top surface. The critical stresses may also occur at lower and upper corners of the marker. The other areas, especially the lower half of the marker, had tensile stresses. Angle of impact was found to be a critical external variable that affected the stresses inside the markers and the marker-pavement interface forces. The researcher then modeled and simulated a few laboratory-testing procedures that could simulate the field performance of the RRPMs. Based on these simulations, the researcher recommended that the ASTM compression test for evaluation of RRPMs be continued or a similar test be developed. He suggested development of one new test (named as offset compression test) that could better replicate the field conditions. He also recommended having a review of the ASTM flexural test.

Head mounted projection display (HMPD) technology, as an alternative to conventional head mounted displays (HMD), offers a potential of designing wide field-of-view (FOV), low distortion optical see-through HMDs (OST-HMDs). Existing HMPD designs, however, suffer from problems of low luminance and low image resolution, which limits the applications of such information displays for the scenarios which require high luminance and high image fidelity. The design of a polarized head mounted projection display (p-HMPD) was recently proposed to overcome the challenge of low luminous efficiency in existing HMPD designs. Polarization management was employed to reduce the light loss caused by beamsplitting in an HMPD.The work in this dissertation focuses on the development and evaluation of an SXGA resolution, high efficiency p-HMPD system. The main contributions are as follows. First, the key elements in the polarization management scheme of a p-HMPD were selected and their polarization performances were characterized by measuring their Mueller matrices, based on which the overall display performance of a p-HMPD was analyzed.Second, based on a pair of ferroelectric liquid-crystal-on-silicon (FLCoS) microdisplays, a compact illumination unit and a light-weight projection system were designed, from which a p-HMPD prototype was built. Following the prototype implementation, a series of calibrations were performed to obtain correct color presentation, desired focusing setting, and optical system characteristics necessary for achieving accurate registration between virtual objects and their counterparts in the real world.Third, the imaging properties of a retroreflective screen which is an essential part of a p-HMPD or HMPD were studied and its effects on the image resolution of an HMPD system were further characterized.Finally, the performance of the system was evaluated through two objective user experiments, including a visual acuity assessment and a depth perception accuracy assessment.

This thesis documents Phase III of a research program undertaken by the Virginia Transportation Research Council and the Virginia Tech Transportation Institute in cooperation with the 3M Company and the Virginia Department of Transportation for the evaluation of visual performance of retroreflective signs of various color combinations. Phase I was an off-road field experiment conducted to determine the best sign color combination, letter stroke width, and letter size for the emergency sign. Based upon the results of Phase I, three color combinations were chosen for testing (black on coral, black on light blue, and yellow on purple) against a baseline color combination of black on orange.Phase II was conducted using an instrumented vehicle through a construction zone-related detour. Questionnaire data were also obtained. The independent variables of interest were sign color combination, age, and visibility condition. The findings of Phase II indicated that use of a color combination other than the traditional black on orange sign would improve driver performance and safety when used for trailblazing during critical incidents, especially when the incident route overlaps a work zone detour. A serious limitation of Phases I and II is that the use of fluorescent colors was not evaluated. Anecdotal evidence suggests that the use of fluorescent colors on signs improves their conspicuity. The purpose of Phase III was to evaluate fluorescent sign color combinations for incident management trailblazing purposes. This study consisted of an on-road investigation using an instrumented vehicle over a 12.2-mile route in urban and rural areas of Montgomery County, Virginia. The following conclusions were made:*A non-fluorescent yellow on non-fluorescent purple sign is least preferred by both older and younger drivers when compared to the other sign color combinations employed in this study.*Both younger and older drivers have a preference for a black on fluorescent yellow-green sign.* Fewer late braking maneuvers and fewer turn errors were recorded during daytime conditions than during nighttime conditions. *Older drivers tended to register more late braking maneuvers than did younger drivers. / Master of Science

This project is an in-depth investigation on the impact of lighting, marking and paint schemes on the operational aspects of police vehicles. This investigation consisted of two phases that ultimately consisted of four experiments. An array of lighting and marking schemes were implemented on police vehicles in a variety of jurisdictions for evaluation. The study then investigated the change in the visibility of police officers, the public reaction to these schemes, and the operational impacts of these systems. The first phase of the project was a naturalistic observation study where the goal was to better understand how traffic behaved around traffic stops. Test vehicles were positioned in simulated traffic stops and patrol locations to determine how traffic behavior was affected by various configurations of police lighting and markings. Camera and radar systems were used to measure the changes in driver speed and when drivers responded to the move over law. Based on the results of the naturalistic studies, the impact of the lighting system on officer visibility was investigated in a controlled human factors test where the ability of a driver to see a police officer outside of their vehicle was measured in the presence of the lighting systems. The purpose of this interjected effort was to verify that the experimental schemes would not increase risk to law enforcement despite data from the first phase indicating the vehicles were more visible. A second part to that study evaluated conventional methods of bolstering an officer's visibility outside of their vehicle at night. The second phase took the findings of the first phase and implemented changes to several police vehicles from local and state agencies to be in operation for at least 18 months. This was to assess the rate of near-misses and crash rate to relate the vehicle changes to law enforcement safety. Additionally, rates of citations were assessed, and surveys offered an opportunity for law enforcement to provide their own feedback on the implementations. The lighting systems evaluated included a completely blue lighting system, an enhanced all blue lighting system with twice the light output, a red and blue system, and a single flashing blue beacon. In terms of markings, retroreflective markings along the side of the vehicle, a retroreflective contour line, chevrons on the rear of the vehicle and unmarked vehicles were evaluated. Finally, a variety of vehicle colors were used to investigate the impact of the base vehicle paint color. The results indicate that both the red and blue lighting system and the high output blue lighting system increase the distance at which drivers moved over significantly. In general, at least 95% of traffic attempted to merge away from an actively lighted police vehicle, when possible. In terms of the speed change, drivers began reducing their speed by approximately 600 m from the police vehicle. Similarly, the addition of retroreflectivity to the rear of the vehicle showed an additional benefit for causing drivers to move over sooner. However, these benefits came at a cost to the officer's visibility. When outside of their vehicle, the high output blue system significantly reduced officer detectability while the red and blue configuration only impacted detection distance by 3 meters. The investigation did find that these impacts could be overcome with retroreflective vests worn by the officers. In the second phase, a preference revealed by officers favored the red-blue configuration. They stated that this configuration provided greater comfort for them and less glare to approaching drivers. The study also revealed that the alternative configurations did not impact the operational activities of police authority. / Doctor of Philosophy / This project evaluated how lighting, marking and paint schemes on police vehicles affected their visibility and how traffic responded to them. An observational study positioned police vehicles with alternative lighting and markings in simulated traffic stops and patrol locations to evaluate traffic behavior. Camera and radar systems were used to measure the changes in driver speed and when drivers responded to the Move Over law. A second study evaluated how the lighting systems on a police car affect the visibility of an officer at night in a traffic stop scenario. A followup experiment looked into methods for bolstering the visibility of officers at night through conventional implementations such as body worn LED lighting, the use of a retroreflective vest, or by using lighting on the police vehicle's light bar to increase illumination of the police officer. A third study took the findings of the previous experiments and outfitted 64 Virginia State Police vehicles for 18 months. Another 64 Virginia State Police vehicles participated in a control condition where no changes were made to their vehicles. Data collected included the rate of near-misses or crashes and the rates of written citations. Surveys were administered to each participating officer regarding their perception of safety and comfort and allowed their open feedback and suggestions. The lighting systems evaluated included a completely blue lighting system, an enhanced all blue lighting system with twice the light output, a red and blue system, and a single flashing blue beacon. In terms of markings, retroreflective markings along the side of the vehicle, a retroreflective contour line, chevrons on the rear of the vehicle, and unmarked vehicles were evaluated. Finally, a variety of vehicle colors were used to investigate the impact of the base vehicle paint color. The results indicate that both the red and blue lighting system and the high output blue lighting system increase the distance at which drivers moved over significantly. In general, at least 95% of traffic attempted to merge away from an actively lighted police vehicle, when possible. In terms of the speed change, drivers began reducing their speed by approximately 600 m from the police vehicle. Similarly, the addition of retroreflectivity to the rear of the vehicle showed an additional benefit for causing drivers to move over sooner. However, these benefits came at a cost to the officer's visibility. When outside of their vehicle, the high output blue system significantly reduced officer detectability while the red and blue configuration only impacted detection distance by 3 meters. The investigation did find that these impacts could be overcome with retroreflective vests worn by the officers. In the second phase, a preference revealed by officers favored the red-blue configuration. They stated that this configuration provided greater comfort for them and less glare to approaching drivers. The study also revealed that the alternative configurations did not impact the rate of citations.

This document represents efforts to design and evaluate a new sign design for emergency route trailblazing in a two-part series. Study 1 was an off-road field experiment conducted to determine the best color combination and letter design for the emergency sign. Based upon Study 1 results, black on coral, black on light blue, and yellow on purple signs were chosen for further testing against a baseline black on orange sign, all with 125-mm, D series letters. Study 2 was an on-road field study of conspicuity, conducted using an instrumented vehicle through a construction zone-related detour, and a survey questionnaire. The findings indicated that use of a color combination other than traditional black on orange will improve driver performance and safety when used for trailblazing during critical incidents. Based on the conclusions and other anecdotal evidence, the following recommendations were made: 1) Do not use black on orange signs for trailblazing around a critical incident if an existing detour/construction zone is in place; 2) Do not use a black on coral sign for trailblazing around a critical incident; 3) A light blue on black sign is recommended due to generally favorable subjective ratings and for minimization of turn errors in an overlapping detour; however, the black on light blue sign may resemble regulatory signs when headlights reflect onto it; and 4) If reject black on light blue signs based on (3), consider using yellow on purple signs, which resulted in fewer turn errors than black on orange and received generally favorable ratings. / Master of Science

Doctor of Philosophy / Department of Industrial & Manufacturing Systems Engineering / Malgorzata J. Rys / This dissertation is the result of studying different methods of increasing guide sign visibility and legibility to drivers during nighttime, to increase safety on roadways. It also studies intersection lighting to indicate the lighting benefits on nighttime crash frequency reduction. From a survey conducted, practices related to overhead guide sign illumination and retroreflectivity in United States were summarized. A laboratory experiment was conducted to compare light distribution of five light sources: Metal Halide, Mercury Vapor, High Pressure Sodium, induction lighting, and Light Emitting Diode (LED). Cost analysis of the five light sources was performed. Combining results of the laboratory experiment and the cost analysis, induction lighting was recommended for states that want to continue external sign illumination. A retroreflectivity experiment was conducted to compare three types of retroreflective sheeting: Engineering Grade (type I), Diamond Grade (type XI), and High Intensity (type IV), to determine the sheeting that best increases visibility and legibility. Diamond Grade (type XI) was found to be the optimal sheeting that increases visibility and legibility to drivers during nighttime. A glare experiment was conducted to expand the retroreflectivity experiment results. Four sheeting-font combinations of High Intensity (type IV) and Diamond Grade (type XI) materials and Series E (Modified) and Clearview fonts were compared. Results revealed an optimal sheeting-font combination of Diamond Grade (type XI) sheeting and Clearview font which increases the visibility and legibility of guide signs to drivers under presence of oncoming glare source. The Highway Safety Information System (HSIS) database was used to study the effect of intersection lighting on the expected crash frequency. Illuminated intersections showed 3.61% and 6.54% decrease in the expected nighttime crash frequency as compared to dark intersections in Minnesota and California, respectively. In addition, partial lighting at intersections decreases the expected nighttime crash frequency by 4.72% compared to continuous lighting in Minnesota. The recommended sheeting-font combination for Departments of Transportation was Diamond Grade (type XI) and Clearview. This combination will increase signs’ visibility and legibility to drivers, and consequently increase safety on roadways. Adding partial lighting at intersections will reduce the expected nighttime crash frequency, and increase safety on roadways.

Road traffic signs provide regulatory, warning, guidance, and other important information to road users to prevent hazards and road accidents. Therefore, the traffic signs must be detectable, legible, and visible both in day and nighttime to fulfill their purpose. The nighttime visibility is critical to safe driving on the roads at night. The state of the art gives clear evidence that the retroreflectivity improves the nighttime visibility (detectability and legibility) of the road traffic signs and that the nighttime visibility can be improved by using an adequate level of retroreflectivity. Furthermore, nighttime visibility can be affected by human, sign, vehicle, environmental, and design factors.  The retroreflectivity and colors of the road signs deteriorate over time and thus the visibility worsens, therefore, maintaining the road signs is one of the important issues to improve the safety on the roads.  Thus, it is important to judge whether the retroreflectivity and colors of the road sign are within the accepted levels for visibility and the status of the signs are accepted or not and need to be replaced.  This thesis aims to use machine learning algorithms to predict the status of road signs in Sweden. To achieve this aim, three classifiers were invoked: Artificial Neural Network (ANN), Support Vector Machines (SVM), and Random Forest (RF). The data which was collected in Sweden by The Road and Transport Research Institute (VTI) was used to build the prediction models. High accuracy was achieved using the three algorithms (ANN, SVM, and RF) of 0.84.3, 0.93, and 0.98, respectively. Scaling the data was found to improve the accuracy of the prediction for all three models and better accuracy is achieved when the data was scaled using standardization compared with normalization. Additionally using principal component analysis (PCA) has a different impact on the accuracy of the prediction for each algorithm. Another aim was to build prediction models to predict the retroreflectivity performance of the in-use road signs without the need to use instruments to measure the retroreflectivity or color. Experiments using linear and logarithmic regression models were conducted in this thesis to predict the retroreflectivity performance. Two datasets were used, VTI data and another data which was collected in Denmark by voluntary Nordic research cooperation (NMF group). The age of the road traffic sign, the chromaticity coordinate X for colors, and the class of retroreflectivity were found significant to the retroreflectivity in both datasets.  The logarithmic regression models were able to predict the retroreflectivity with higher accuracy than linear models. Two suggested logarithmic regression models provided high accuracy for predicting the retroreflectivity (R2 of 0.50 on VTI data and 0.95 on NMF data) by using color, age, class, GPS position, and direction as predictors. Nearly the same accuracy (R2 of 0.57 on VTI data and 0.95 on NMF data) was achieved by using all parameters in the data as predictors (including chromaticity coordinates X, Y for colors). As a conclusion, omitting chromaticity coordinates X, Y for colors from the logarithmic regression models does not affect the accuracy of the prediction.

The thesis „Legal Context of Night-time Road Accidents with Pedestrian „deals with the interpretation of legal decisions on traffic accidents caused by the vehicle during the night and where the other participant was a pedestrian. The main aim of this thesis is to find the established limits for the assessing of blame in comparable accident situations in cases of traffic accidents of the vehicle and the pedestrian at the reduced visibility with emphasis on the assessing in relation to the circumstances of the cases from the technical and legal point of view and in relation to the health consequences. Legal interpretations of the law are defined within the theoretical part of the thesis with emphasis on the ones which appear repeatedly in the judicial decisions. Approximately 1530 judicial decisions were studied and analysed in the analytical part, of which 56 were selected, that corresponds to the requirements of this thesis. There are also 5 expert evidences provided by the Institute of Forensic Engineering of Brno University of Technology. In the above mentioned cases there were defined the limits for the assessing of accidents based on which the judicial decision was predicted in context with the defined established limits for the judicial decisions at the top of the court hierarchy.