Overhead Signs Research Articles

Development of the Guidance on the Tightening of Large Anchor Rods of Support Structures for Sign and Luminaires

Across the United States, various state Departments of Transportation (DOTs) are finding that the base anchor-rod nuts on critical support structures for overhead signs are coming loose. Retightening loose nuts imposes a significant drain on state DOT resources. In addition, the loosening of these nuts increases the failure risk of tall and overhanging structures. In many of the inspection engineer’s observed cases, anchor-rod nuts were loose immediately after installation. Even after tightening, it was found that anchor-rod nuts had consistently come loose just 2 years after retightening. The objective of this study was to evaluate the resistance to the loosening of anchor-rod tightening procedures proposed by Chen et al. and to develop improvements to the procedures based on stakeholder feedback. To achieve this objective, field deployment of the previously developed procedures was conducted on multiple sites. After field deployment, improvements to the Chen et al. procedure were investigated on a full-size laboratory specimen to ensure revisions did not affect connection performance. Overall, it was found that the pretension levels proposed by Chen et al. were effective, and the revised procedures only use torque, or force-controlled tightening, as opposed to displacement-controlled turn-of-nut.

Wind Loads on Overhead Sign Structures: A Comparative Study

Road signs are prone to extreme winds that cause significant damage. Overhead sign structures can disrupt traffic and cause harm to the traveling public if a failure occurs under extreme wind conditions. In this paper, we employ Computational Fluid Dynamics (CFD) in a comparative study to understand the aerodynamics of standard, porous, and curved signs. The study shows the viability of porous and curved overhead boards for lessening aerodynamic loads, which can mini-mize damage and enhance safety on roadways. Porous overhead signs can decrease the drag forces; however, the size of the openings is a vital parameter in reducing wind loads. Small and uniform perforations lead to higher drag forces, compared to larger ones, under the same porosity ratio. Introducing porosity to a solid panel moves the vorticity region further downstream, reducing the magnitude of pressures on the leeward side and decreasing the drag force. However, curved panels further enhanced the force reduction.

The Ohio: The Historic River in Vintage Postcard Art, 1900–1960 by John A. Jakle and Dannel McCollum

Reviewed by: The Ohio: The Historic River in Vintage Postcard Art, 1900–1960 by John A. Jakle and Dannel McCollum Virginia C. Young The Ohio: The Historic River in Vintage Postcard Art, 1900–1960. By John A. Jakle and Dannel McCollum. (Kent, OH: Kent State University Press, 2017. Pp. 172.) Postcards may seem passé now, but I love them because they provide a unique view of history. My grandparents collected postcards from all over the world, and my father recently passed the collection on to me, so I was delighted when I was asked to read The Ohio: The Historic River in Vintage Postcard Art, 1900–1960. Written by John Jakle, professor emeritus of geography at the University of Illinois, and former Champaign, Illinois, mayor Dannel McCollum who has a graduate degree in history, the book includes reproductions of 169 vintage postcards to give the feel of an early-twentieth-century journey on the Ohio River. There is a wealth of scholarship on the Ohio River region; however, historians have focused primarily on specific portions of the region or on particular topics. Jakle and McCollum consider the river as a whole to emphasize its importance to the development of the Midwest and the nation. In doing so, they hope to promote its designation as a national heritage corridor. Previous efforts to that end failed in the early 1990s, at least in part because government officials did not appreciate that Ohio River communities were bound by a “common heritage” (viii). The authors wrote this book to demonstrate the region’s shared heritage. That heritage comes alive through descriptions of Ohio River communities between 1900 and 1960 and through the postcards. The authors use vintage postcards rather than photographs to emphasize that shared heritage because, they argue, postcards “suggested what was important to an area and how those things ought to be viewed” (ix). Thus, postcards uniquely help us understand what Americans were encouraged to value and how those shared values fostered a shared heritage. The book’s organization follows the path of the Ohio River from its beginning at Pittsburgh, Pennsylvania, to its end where it joins the Mississippi River at Cairo, Illinois. This gives the reader a feeling of actually traveling its [End Page 116] length. The introduction includes a brief history of the river and some of the historiography on the topic as well. There is also a fascinating discussion of the history of postcards in the early twentieth century, including how postcard images were often changed in order to emphasize certain positive aspects of a subject while downplaying others that were considered less desirable. For example, it was commonplace to make a city street look more modern by removing things such as overhead telephone lines or signs that were on a building. There are seven chapters, with the first exploring the city of Pittsburgh. The remaining chapters each focus on a particular geographic section of the journey, beginning with “Pittsburgh to Wheeling” in chapter two and ending with a trip from “Evansville to Cairo” in chapter seven. The book’s strength is the postcards, which provide a window into the cities and towns that popped up along the river. While each postcard is unique, many of them depict common themes, such as downtown areas, railroads, bridges, factories, and the 1907 and 1937 floods. And while many readers may be familiar with certain locations along the Ohio River, they can still expect to have their interest piqued by the postcard images. For example, a few include handwritten notes on the front such as a postcard of downtown Steubenville, Ohio, circa 1900, upon which the sender wrote to their grandmother asking, “Don’t you think this street looks rather citified. [sic] We have others just as good, too” (51). I can’t help but wonder why the sender wanted to convince their grandmother that Steubenville was indeed a city. It is a daunting task to describe the Ohio River and its communities in one book, but Jakle and McCollum do a good job if you are looking for a brief introduction to these towns and cities in the early twentieth century. Historians will benefit from the extensive bibliography. Casual fans...

Analysis of driving behavior at expressway toll plazas

Drivers are required to make many rapid decisions at expressway toll plazas, which could result in drivers’ confusion, speed variation, and sudden lane change maneuvers. Thus, toll plazas are considered one of the most dangerous segments on expressways. Nevertheless, only a limited number of studies have explored the factors that affect driving behavior and safety at toll plazas. This study assessed driving behavior at a section, including a hybrid toll plaza, on one of the main expressways in Central Florida using a driving simulator. The details of the section and the plaza were accurately replicated in the simulator. Overall, 72 participants were recruited and each driver performed three different scenarios out of a total of 24 scenarios. Subsequently, four behavioral variables were extracted from the experimental data (i.e., average speed, speed variation, standard deviation of lane deviation, and standard deviation of acceleration) to explore risky driving behaviors with various paths, signs, pavement markings, segment lengths, and traffic conditions. In addition, the effects of drivers’ individual characteristics on driving behavior were investigated. A series of linear mixed models with random effects to account for multiple observations from the same participant were developed to reveal the contributing factors for driving behavior at toll plazas. The results uncovered that drivers experiencing the open road tolling (ORT) have safer driving behavior than those who use the tollbooth. Also, providing dynamic message sign (DMS) on the ramp before the toll plaza has a significant effect on reducing sudden lane change maneuvers. Adjustment of the locations of overhead signs was also recommended in this study. Moreover, the existence of arrow pavement marking before and after the toll plaza is important for reducing unsafe driving behavior before and after the toll plaza.

Recommended Guidelines for Nighttime Overhead Sign Visibility

Guidelines for the provision of effective nighttime performance of overhead signs were developed. Relevant policies and guidelines with regard to sign lighting currently provide little useful information to determine when sign lighting is needed, and the reference material available to practitioners is out of date. Two complementary nighttime visibility studies were conducted, which were designed to produce results useful in developing updated guidelines for overhead sign visibility. The first was conducted on a closed course and investigated the legibility distances of three sign legend and background configurations under various sign lighting treatments. The second was conducted on the open road. It investigated the effects of sign luminance and visual complexity on the distance at which a driver can read overhead signs during a recognition task. The combined findings were used to develop revised guidelines designed to provide adequate nighttime visibility of overhead signs. The proposed guidelines are based on the needs of nighttime motorists and have been formatted specifically for AASHTO’s Roadway Lighting Design Guide, which is being updated. The revised chapter on roadway sign lighting was provided to the AASHTO task force responsible for revisions. The guidelines include a list of recommended retroreflective sheeting materials that can be used to meet nighttime driver needs for specific complexity levels.

Automated Highway Sign Extraction Using Lidar Data

Traffic signs are integral elements of any transportation network; however, keeping records of those signs and their condition is a tedious, time-consuming, and labor-intensive process. As a result, many agencies worldwide have been working toward automating the process. One form of automation uses remote sensing techniques to extract traffic sign information. An algorithm is proposed that can automatically extract traffic signs from mobile light detection and ranging data. After the number of signs on a road segment has been determined, the coordinates of those signs are mapped onto the road segment. The sign extraction procedure involves applying multiple filters to the point cloud data and clustering the data into traffic signs. The proposed algorithm was tested on three highways located in different regions of the province of Alberta, Canada. The segments on which the algorithm was tested include a two-lane undivided rural road and four-lane divided highways. The highway geometry varied, as did vegetation and tree density. Success rates ranged from 93% to 100%, and the algorithm performed better on highways without overhead signs. Results indicate that the proposed method is simple but effective for creating an accurate inventory of traffic signs.

LIDAR-INCORPORATED TRAFFIC SIGN DETECTION FROM VIDEO LOG IMAGES OF MOBILE MAPPING SYSTEM

Mobile Mapping System (MMS) simultaneously collects the Lidar points and video log images in a scenario with the laser profiler and digital camera. Besides the textural details of video log images, it also captures the 3D geometric shape of point cloud. It is widely used to survey the street view and roadside transportation infrastructure, such as traffic sign, guardrail, etc., in many transportation agencies. Although many literature on traffic sign detection are available, they only focus on either Lidar or imagery data of traffic sign. Based on the well-calibrated extrinsic parameters of MMS, 3D Lidar points are, the first time, incorporated into 2D video log images to enhance the detection of traffic sign both physically and visually. Based on the local elevation, the 3D pavement area is first located. Within a certain distance and height of the pavement, points of the overhead and roadside traffic signs can be obtained according to the setup specification of traffic signs in different transportation agencies. The 3D candidate planes of traffic signs are then fitted using the RANSAC plane-fitting of those points. By projecting the candidate planes onto the image, Regions of Interest (ROIs) of traffic signs are found physically with the geometric constraints between laser profiling and camera imaging. The Random forest learning of the visual color and shape features of traffic signs is adopted to validate the sign ROIs from the video log images. The sequential occurrence of a traffic sign among consecutive video log images are defined by the geometric constraint of the imaging geometry and GPS movement. Candidate ROIs are predicted in this temporal context to double-check the salient traffic sign among video log images. The proposed algorithm is tested on a diverse set of scenarios on the interstate highway G-4 near Beijing, China under varying lighting conditions and occlusions. Experimental results show the proposed algorithm enhances the rate of detecting traffic signs with the incorporation of the 3D planar constraint of their Lidar points. It is promising for the robust and large-scale survey of most transportation infrastructure with the application of MMS.

LIDAR-INCORPORATED TRAFFIC SIGN DETECTION FROM VIDEO LOG IMAGES OF MOBILE MAPPING SYSTEM

Abstract. Mobile Mapping System (MMS) simultaneously collects the Lidar points and video log images in a scenario with the laser profiler and digital camera. Besides the textural details of video log images, it also captures the 3D geometric shape of point cloud. It is widely used to survey the street view and roadside transportation infrastructure, such as traffic sign, guardrail, etc., in many transportation agencies. Although many literature on traffic sign detection are available, they only focus on either Lidar or imagery data of traffic sign. Based on the well-calibrated extrinsic parameters of MMS, 3D Lidar points are, the first time, incorporated into 2D video log images to enhance the detection of traffic sign both physically and visually. Based on the local elevation, the 3D pavement area is first located. Within a certain distance and height of the pavement, points of the overhead and roadside traffic signs can be obtained according to the setup specification of traffic signs in different transportation agencies. The 3D candidate planes of traffic signs are then fitted using the RANSAC plane-fitting of those points. By projecting the candidate planes onto the image, Regions of Interest (ROIs) of traffic signs are found physically with the geometric constraints between laser profiling and camera imaging. The Random forest learning of the visual color and shape features of traffic signs is adopted to validate the sign ROIs from the video log images. The sequential occurrence of a traffic sign among consecutive video log images are defined by the geometric constraint of the imaging geometry and GPS movement. Candidate ROIs are predicted in this temporal context to double-check the salient traffic sign among video log images. The proposed algorithm is tested on a diverse set of scenarios on the interstate highway G-4 near Beijing, China under varying lighting conditions and occlusions. Experimental results show the proposed algorithm enhances the rate of detecting traffic signs with the incorporation of the 3D planar constraint of their Lidar points. It is promising for the robust and large-scale survey of most transportation infrastructure with the application of MMS.

Field Study of Ohio’s Structural Support Inspection Program for Overhead Signs, Traffic Signals, and High-Mast Lights

The Ohio Department of Transportation (DOT) undertook a field study to evaluate its overall structural inspection programs for overhead sign supports (including those mounted on bridges), high-mast light supports, and traffic signal supports. This paper describes the Ohio DOT’s current support inspection program, the field study performed, and the recommendations that resulted from the field study. This research evaluated the adequacy and frequency of the current structural support inspection program for the studied supports. To assess the current program, a detailed, hands-on inspection was conducted on 202 supports. The results were then compared with the Ohio DOT’s current ground-based, visual inspection process. The hands-on inspection process found almost 87% more deficiencies; some deficiencies detected during the hands-on inspections could not have been observed from the ground. In addition, the different inspection procedures used by each district often produced inspection reports that varied in the amount of information and level of details collected during inspection. Recommendations were made to address the inventory process and inspection procedures for each type of support. A long-term goal should be to establish the current structural adequacy of every support in the Ohio DOT’s inventory at the time of inspection.

Stochastic Analysis of the Duration of Occlusion of an Overhead Sign by a Leading Heavy Vehicle: Application to Sign Design

AbstractWith the increase in multilane expressways the use of overhead signs has also increased. A driver can miss an overhead sign because of occlusion of the sign by a leading heavy vehicle. Little or no research has been carried out to mathematically analyze conditions under which the driver of a light vehicle will not be able to read a sign because of a leading heavy vehicle. The lack of an analytical understanding of this phenomenon is reflected in the available design standards of the day. This paper analyzes the conditions that lead to occlusion of overhead signs because of a leading heavy vehicle. Next, the duration for which the occlusion occurs is determined. Subsequently, the results for duration of occlusion are used to evaluate whether enough time is left for the driver to read the sign. If enough time is not available then the driver is said to have “missed” the sign. Assuming that the speeds of the light and heavy vehicles and the distance headway between them vary randomly (around some exp...

Test Driven Design of a System for Removing Graffiti from Retroreflective Signs

The remediation of graffiti from highway signs is a labor intensive and potentially hazardous task. Accordingly, this paper presents the initial design stages of tools that could be used to clean graffiti from signs. Two design concepts are presented – one for pedestrian accessible signs and one for overhead signs – and the concepts share a common end-effector design. The paper is primarily aimed at developing an understanding of the interactions between the end-effector's scrubbers and the sign's resultant retroreflectivity. This is accomplished through a factorial experiment to test the effects of load, speed, brush type, and sign surface material on the retroreflectivity. This work shows the feasibility of such a tool for cleaning graffiti from signs along the roadways.

Field Evaluation of In-Lane Pavement Markings in Advance of Freeway Interchanges

Freeway interchanges with lane drops, double-lane exits with optional lanes, and other unusual geometries violate driver expectations and may result in late lane changes and erratic movements near the exit gore. In-lane pavement markings can reiterate the information provided on overhead signs that depict the geometry of the upcoming interchange. Researchers at the Texas Transportation Institute designed and conducted field studies at freeway interchanges to evaluate the operational impacts of route shield and directional arrow in-lane pavement markings. The addition of route shields resulted in better utilization of optional and inside exit-only lanes. In addition, motorists made lane changes farther upstream of the exit and made fewer unnecessary lane changes after the installation of the route shields. The addition of directional arrows also positively affected the lane distributions and lane change rate, but the effect on unnecessary lane changes was not as evident. Researchers concluded that the installation of in-lane pavement markings (either route shields or directional arrows) improved operations and, potentially, safety at the interchanges studied. There is evidence to suggest that a combination of route shields and directional arrows may be more beneficial to motorists than directional arrows alone.

Assessing the Role of Pavement Macrotexture in Preventing Crashes on Highways

Objective: The objective of this article is to assess the role of pavement macrotexture in preventing crashes on highways in the State of North Carolina. Methods: Laser profilometer data obtained from the North Carolina Department of Transportation (NCDOT) for highways comprising four corridors are processed to calculate pavement macrotexture at 100-m (approximately 330-ft) sections according to the American Society for Testing and Materials (ASTM) standards. Crash data collected over the same lengths of the corridors were integrated with the calculated pavement macrotexture for each section. Scatterplots were generated to assess the role of pavement macrotexture on crashes and logarithm of crashes. Regression analyses were conducted by considering predictor variables such as million vehicle miles of travel (as a function of traffic volume and length), the number of interchanges, the number of at-grade intersections, the number of grade-separated interchanges, and the number of bridges, culverts, and overhead signs along with pavement macrotexture to study the statistical significance of relationship between pavement macrotexture and crashes (both linear and log-linear) when compared to other predictor variables. Results: Scatterplots and regression analysis conducted indicate a more statistically significant relationship between pavement macrotexture and logarithm of crashes than between pavement macrotexture and crashes. The coefficient for pavement macrotexture, in general, is negative, indicating that the number of crashes or logarithm of crashes decreases as it increases. The relation between pavement macrotexture and logarithm of crashes is generally stronger than between most other predictor variables and crashes or logarithm of crashes. Conclusions: Based on results obtained, it can be concluded that maintaining pavement macrotexture greater than or equal to 1.524 mm (0.06 in.) as a threshold limit would possibly reduce crashes and provide safe transportation to road users on highways.

Recent Changes in Headlamp Illumination Directed toward Traffic Signs

This study examined the differences in sign light between 1997 tungsten-halogen and 2004 high-intensity discharge (HID) low-beam headlamps manufactured for use on U.S. vehicles. The results indicate that the HIDs tended to deliver less light above the horizontal straight ahead and to the left of the vertical, and less light to the right of the vertical above about 1.5° up. The consequences of the changed beam pattern were analyzed in detail for three typical sign locations: center overhead, right shoulder, and left shoulder. The most frequent geometric conditions were modeled: a straight road, and very large-radius left and right curves, all with no vertical curvature. Viewing distances between 50 m and 300 m were considered.The results imply that with current HID low beams, sign retro-reflectivity would need to be increased to maintain the effectiveness that a given sign had a decade ago with tungsten-halogen low beams. This applies to overhead signs on straight roads and on very large-radius left and right curves, and to right and left shoulder-mounted signs on straight roads and on very large-radius left curves.

Legibility of Overhead Guide Signs with Encapsulated Versus Microprismatic Retroreflective Sheeting

A study was conducted to determine the legibility impacts of freeway guide signs when encapsulated retroreflective sheeting is replaced with microprismatic retroreflective sheeting. The study included freeway guide signs mounted in an overhead position and exclusively illuminated with vehicle headlamps. A total of 60 subjects divided into three age groups participated in this nighttime study. All 60 subjects drove two vehicles, a modern sport utility vehicle (SUV) and a late-model passenger car. The findings show that microprismatic sheeting does provide statistically longer legibility distances than encapsulated sheeting. Overall, the improvement was 53 ft, or 9.5%. However, for the modern SUV, the improvement was much greater (78 ft) compared with the late-model passenger car (28 ft). The main differences are related to the evolution of vehicle design and specifications. Today’s United States citizens prefer large vehicles such as an SUV, pickup, and minivan. These vehicles also meet recently revised headlamp specifications. These two issues inherently reduce the amount of headlamp light retroreflected from the sign back to the driver. Unfortunately, these counterproductive trends show signs of continuing. Considering the increasing proportion of older drivers in the United States, it becomes even more critical that transportation agencies do all they can to increase overhead-sign luminance. The findings show that increasing overhead-sign luminance by switching from encapsulated retroreflective sheeting to microprismatic retro-reflective sheeting results in significantly longer legibility distances. The magnitude of the difference will continue to increase as long as the SUV-like proportion of the U.S. fleet continues to grow and headlamp specifications continue to direct less light toward overhead signs.

Nighttime Expert Panel and Photometric Evaluations of Unlighted Overhead Guide Signs

A nighttime field evaluation of four different retroreflective overhead-sign sheeting combinations (ASTM D4956 beaded Type III legend on beaded Type III background, Type IX legend on beaded Type III background, Type IX legend on Type IX background, and Type VII legend on beaded Type III background) was conducted on a section of US-30 near Mansfield, Ohio. The test-material combinations were compared when lighted and unlighted (illuminated by low-beam headlights only). Twelve Ohio Department of Transportation engineers and technicians served as evaluators, riding the test loops in 2002 Dodge Caravans. The white Type IX legend on green-beaded Type III background sheeting combination received the highest evaluation scores for appearance, conspicuity, and legibility. The scores for the Type VII legend on beaded Type III background signs were only slightly lower in all three categories. The Type IX legend on Type IX background combination received slightly lower evaluation scores, and the beaded Type III legend on beaded Type III background combination received the lowest evaluation scores. The same signing material combinations were also photometrically (luminance and luminance contrast ratio) evaluated under low-beam illumination at selected approach distances from 200 to 1,000 ft (61 to 305 m) using a 1984 Peterbilt truck, a 2002 Chrysler Town and Country minivan, and a 2002 Toyota Camry sedan, both when lighted and unlighted (low beams). Unlighted overhead signs made with either the white Type VII or the Type IX legends on green-beaded Type III backgrounds provide nighttime motorists with adequate appearance, conspicuity, and legibility.

Single Piles and Pile Groups Under Lateral Loading

1R20. Single Piles and Pile Groups Under Lateral Loading. - LC Reese (Dept of Civil Eng, Univ of Texas, Austin TX) and WF Van Impe (Lab for Soil Mech, Ghent Univ, Ghent, Belgium). Balkema Publ, Rotterdam, Netherlands. 2000. 463 pp. Softcover. ISBN 90-5809-348-9. $45.00. (Hardbound ISBN 90-5809-340-9 $85).Reviewed by RD Holtz (Dept of Civil Eng, Univ of Washington, PO Box 352700, Seattle WA 98195- 2700).Many structures commonly founded on piles or groups of piles are required to resist lateral loads, both static and cyclic, in addition to the usual axial loads. Examples include bridges, power transmission structures, overhead signs, offshore platforms, quays, dolphins, and high-rise buildings subjected to wind and seismic loads. Design methods based on limiting equilibrium are quite adequate for estimating maximum or ultimate axial pile loads, but these methods are unable to accurately predict foundation deformations due to anticipated lateral loads. Instead, a method of analysis is required that considers the interaction of the soil and the pile. The field of soil-structure interaction has progressed rapidly in recent years, largely due to developments in digital computers and numerical methods that are necessary to solve complex systems of nonlinear equations. Specifically, the analysis of laterally loaded pile foundations has developed because of the interest of the offshore oil industry, together with a number of well-documented, full-scale instrumented pile load tests. This is an important book on a complicated subject that until now has not been dealt with particularly well in, for example, most textbooks on foundation engineering. Thus, this book is a welcome addition to the technical literature on foundation engineering. Its comprehensive treatment nicely complements the 1980 text by Poulos and Davis. Both authors are well qualified. Professor Lymon Reese is one of the leading experts on deep foundations in the US. His co-author, Prof William Van Impe of Belguim, is a distinguished foundation engineer. Thus, their book represents the best combination of US and European research and design practice. The introductory chapter discusses various design techniques as a way of introducing the p-y concept, which is the basis of the rest of the book. Chapter 2 presents the derivation of the beam-column equations and describes solution methods for the p-y method. A detailed example is also included. Various expressions for p-y curves for soils and weak rock under both static and cyclic loading are presented in Chapter 3, while Chapter 4 discusses some of the pertinent material and geometric characteristics of piles. Chapters 5 and 6 are the heart of the book. Both present detailed analyses methods for virtually all practical problems of laterally loaded foundations. Chapter 5 describes the analysis of pile groups subjected to inclined and eccentric loads, while Chapter 6 presents the analysis of single piles and groups subjected to active and passive loading. The formats of these two chapters are different. Five has the format of a state-of-the-art review, while six is more in textbook style with numerous examples and solutions. A number of case studies in which the results of full-scale field tests of instrumented piles at well-documented sites are described in Chapter 7. In Chapter 8, detailed procedures for conducting successful tests on full-size piles are given. Factors of safety including load and resistance factor design and a bit about probabilistic methods are discussed in Chapter 9. Finally, Chapter 10 presents a brief treatment of two additional design topics such as validation of computations and other topics not discussed previously. There are ten useful appendices covering topics such as the Broms method, alternative solution methods, comments on the Eurocode, and factor of safety. The book also contains a CD-ROM with student versions of LPILE and GROUP, well known design programs developed by Reese and his students. The list of references is extensive and up-to-date, with many from the late 1990s; a few mentioned in the text are inadvertently missing from that list. The book is generally well illustrated. Notation, always a source of some confusion in geotechnical writing, is discussed when used in the text, but a separate list of symbols would have been helpful at times. There are a few minor typographical errors. This reviewer is impressed by the number of worked examples included along with detailed procedures for obtaining soil and pile properties and for carrying out design calculations. This feature will be very useful to practicing foundation engineers and students alike. Single Piles and Pile Groups under Lateral Loading is strongly recommended for foundation engineers dealing with laterally loaded pile foundations. Both engineers and graduate students will be pleased with its modest cost in paperback.

Evaluation of Clearview on Freeway Guide Signs with Microprismatic Sheeting

The legibility of the Clearview alphabet on freeway guide signs constructed with microprismatic retroreflective sheeting was studied. The Clearview legibility results were compared to the legibility of freeway guide signs constructed with the Series E (Modified) alphabet. A total of 60 subjects divided into three age groups participated in this nighttime study. The findings indicate that the Clearview alphabet provides statistically longer legibility distances than the Series E (Modified) alphabet. The largest 50th-percentile differences were 58 ft for shoulder-mounted signs and 54 ft for overhead signs. Depending on speed, these improvements can provide a driver with up to 0.7 s more time to read freeway guide signs. In terms of subject age, the largest benefits of Clearview were associated with older drivers.

Factors Affecting Driver Recognition of Regulatory Signs

The purpose of this paper is to explore the factors that determine conspicuity of regulatory signs, and to investigate how to install regulatory signs to increase the chances of attracting attention. Factors under consideration were types of signs, lateral clearance, location, roadside or overhead signs, the number of plates attached to one post and the road environment. The main results are as follows. The recognition rate for elderly drivers was similar to that of younger drivers. Overhead signs have higher recognition rates than conventional roadside signs. Signs were less conspicuous in arterial roads than in residential roads. The outcome of the quantification method shows that the most effective action to enhance recognition rates is to use overhead signs.

MATHEMATICAL ANALYSIS OF TRUCKS BLOCKING ROADWAY SIGNS

The problem of obstructed road signs is significant because a missed sign can lead to driver confusion and, consequently, safety hazards. One of the main instances when drivers experience blocked road signs is when a passenger car in the left lane has their field of vision obstructed due to the presence of a large truck in the right lane. Despite the significance of the problem, little research has been done to quantify obstruction of road signs. This paper develops a mathematical model that estimates the probability that a vehicle in the left lane misses a road sign due to a large truck in the right lane. A sensitivity analysis is then performed, and it is found that the volume of trucks is the most important parameter in whether or not a sign will be obstructed long enough so that the driver of a vehicle in the right lane misses the sign. After the sensitivity analysis, six alternative solutions to the problem of blocked road signs are detailed, and the advantages and disadvantages of each alternative are discussed. The alternatives are con structing higher signs, using overhead signs, repeating road signs, putting signs on both sides of a roadway, changing traffic patterns, and using Intelligent Transportation Sys tems instrumentation to decrease the number of signs that are missed by drivers. The paper also includes a section on the real-life field verification and validation of the developed mathematical model.