Preferences for Permitted and Protected Left-Turn Signal Displays

Twenty-two different signal displays for permitted and protected left turns were evaluated from a driver comprehension perspective. The objective was to identify which alternate signal displays used to convey the same left-turn message to the driver are better comprehended and therefore recommended for use in the field. Protected displays compliant with the Manual on Uniform Traffic Control Devices were found to be better comprehended than certain noncompliant displays; however, some noncompliant permitted displays were found to outperform their compliant counterparts. Regional comprehension biases are nonexistent for the most part, regardless of display compliance with the Manual on Uniform Traffic Control Devices. Permitted left-turn signals using indications other than a steady green ball were found to enhance driver comprehension. The “Left Turn Must Yield on Green Ball” sign used with a “doghouse” display is beneficial during the permitted phase, but confusing when displayed during the protected left-and-through phase. Other supplemental signs used with various left-turn displays were also evaluated

An Evaluation of Age Effects on Driver Comprehension of Flashing Traffic Signal Indications using Multivariate Multiple Response Analysis of Variance Models

Objective: The objective of this experiment was to identify whether drivers comprehended traffic signals differently when turning left at signalized intersections where traffic signals were in “flashing mode” operation. Method:Multivariate multiple response analysis of variance models were used to analyze the simultaneous effects of displayed color combination, age, and geographical location on signal message interpretation. Data were gathered in a laboratory environment. Results: Left-turn and through-signal color combination had a significant effect on subject comprehension. Comprehension was found to be lowest for displays flashing red only, followed by displays flashing red on the left-turn, and yellow on the through-signal, with best comprehended displays flashing yellow only. No overall significant age effects were identified, with one minor exception. No geographical region effects were identified. Signal section arrangement and the use of an arrow or circular illuminated lens had no significant effect on comprehension. Discussion: Traffic signal displays in “flashing mode” operation were previously identified as the least well-comprehended displays for drivers turning left. The present effort identified that this is mainly due to displays flashing red indications on the through-signal. Comprehension of displays flashing yellow indications on the through-signal is comparable to that of permitted left-turn indications. Impact on the Industry: There is a need to develop alternatives for signal displays flashing red indications on the through-signal because a large percentage of drivers facing such indications mistakenly think they have the right-of-way when, in fact, they do not. However, use of such displays on minor streets intersecting major streets cannot currently be avoided when signals are placed in flashing operation. Practitioners using flashing signal operations need not be concerned about signal message comprehension differences among age groups. They can use any among the analyzed alternative signals that convey a given message without impacting signal message comprehension

Heavy Vehicle Performance During Recovery From Forced-Flow Urban Freeway Conditions Due To Incidents, Work Zones and Recurring Congestion

Information contained in the Highway Capacity Manual on the influence heavy vehicles have on freeway traffic operations has been based on few field data collection efforts and relied mostly on traffic simulation efforts. In the 2010 Manual heavy vehicle impact is evaluated based on “passenger car equivalent” values for buses, recreational vehicles and trucks. These values were calibrated for relatively uncongested freeway conditions (levels of service A through C) since inadequate field data on heavy vehicle behavior under congested conditions were available. A number of field data collection efforts, that were not included in deriving the passenger car equivalent values used in the Highway Capacity Manual, indicated that heavy vehicle impacts on traffic operations may increase as freeway congestion levels increase and freeways operate under unstable flow conditions. The goal of the present effort was to collect and analyze field data with an emphasis on heavy vehicle behavior under lower speeds and derive passenger car equivalent values under such conditions

The Short Rise and Long Fall of heterodox Economics in germany After the 1970s: Explorations in a Scientific Field of Power and Struggle.

In the context of ongoing criticisms of the lack of pluralism in economics, the present article aims to discuss the development of ‘heterodox’ economics since the 1970s. Following Lakatos’s concept of scientific research programs (srp), and concentrating on the situation in Germany, the article will discuss classifications of economics, and will specify the understanding of diversity in the light of ‘axiomatic variations’ of the economic mainstream. This will form the basis for the subsequent description of the development of heterodoxy in Germany, with special reference to the founding of new universities and the reform movements in the 1970s. It can be shown that the heterodox scene flourished in this period, but that this pluralization remained fragmented and short-lived; by the 1980s at the latest heterodoxy was again on its way to marginalization. The history of heterodoxy in Germany thus presents itself as an unequal ‘battle of the paradigms,’ and can only be told as the story of a failure

Investigation of Peak-Hour Factor at Freeway Segments: Urban and Suburban Vicinities

The peak-hour factor (PHF) adjusts for traffic volume variability during the peak hour so that traffic demand can be converted to represent the busiest 15 min of the peak hour. Operational and planning analyses of freeways start by adjusting traffic demand by the PHF. Although the importance of the PHF is widely recognized, few efforts have been dedicated to a comprehensive understanding of this factor. The Highway Capacity Manual 2010 (HCM 2010) recommends the use of a single default freeway PHF value equal to 0.94 when local data are not available. The main aim of this study was to provide a quantitative analysis of the PHF values at freeways and the potential sources of its variability including the peak period (a.m., p.m., and weekend periods), day-to-day variation, traffic volume and level of service, early or late peak-hour onset, day of the week, month, season, and weather. Traffic data were collected at 54 sites along 10 freeway corridors in Milwaukee County, Wisconsin, during 2014. A massive data sample including 28,394 PHF records covering different daily, seasonal, and operational conditions was compiled. A wide range of PHF values was observed; they fluctuated considerably from day to day, even at the same site. Traffic volume, level of service, and peak period were found to be major sources of PHF variability; they deserve more attention in practice. Specific conclusions and recommendations for future editions of the HCM are summarized

Revisiting Merge-Influence Area Empirically: Operations Inside Recurrent Freeway Bottlenecks

The current effort aims to analyze traffic operations empirically at merge-influence areas positioned inside recurrent freeway bottlenecks. Four years of data at four bottlenecks in the Milwaukee County, Wisconsin, freeway system were used in the analysis. Bottlenecks were ranked on the basis of merge-area capacity use and were treated individually. The study evaluated how merge-area traffic mix influenced freeway breakdown characteristics such as prebreakdown flow (PBF), queue discharge flow (QDF), queue discharge speed, and congestion duration (CD). Merge-area traffic mix was evaluated with the ramp volume ratio (RVR), which was defined as the percentage of the ramp flow in the total merge-area traffic flow. For bottlenecks with heavily used merge areas, both capacities (PBF and QDF) and queue discharge speed were reduced when RVR increased in value. The value of CD appeared to be sensitive to RVR. The value of CD was found to double, triple, or almost quadruple when ramp flow composed a higher percentage of merge-area flow. Bottlenecks with lightly used merge areas sometimes showed different or even contradictory results. The study also modeled two capacity flows (PBF and QDF) stochastically at merge areas with the three-parametric Weibull distribution. From the current analysis, it appears that the maximum merge-area flow (4,600 passenger cars per hour) recommended by the Highway Capacity Manual is not a conservative design value

Use of Vehicle-Collected Data to Calculate Existing Roadway Geometry

The Federal Highway Administration has designated Highway Design Practices and Criteria as a high-priority research and development area. New design standards need to be developed to provide quantitative guidance on alignment consistency, based on the safety performance of a series of (not isolated) roadway features. Geometric information collected through a datalog vehicle for the entire State Trunk Highway System in Wisconsin provides the opportunity to identify and analyze such series of roadway features. An algorithm was developed to produce horizontal curve length, degree of curve, deflection angle, and maximum superelevation. The algorithm was validated for a two-lane highway. Software was developed to produce plan views, color-code curves to the left (right), and tangents, and to display numeric information (e.g., length of curve, degree of curve) for any chosen highway segment. Integration of the developed algorithm with a GIS base map was demonstrated. Availability of systemwide geometric information allows exhaustive searches of geometrically deficient highway segments and the identification of curve-tangent-curve combinations with prespecified geometries

Impact of Ramp and Mainline Flow Mix on Freeway Breakdown and Capacity Characteristics

This study examined how the mix between ramp and mainline flows influences breakdown and capacity characteristics such as: pre-breakdown flow (PBDF), queue discharge flow (QDF), queue discharge speed (QDS), breakdown duration (BDD), and capacity change after breakdown. The mix between ramp and mainline flow was represented using the Ramp Volume Ratio (RVR) which is defined as the percentage that the ramp flow is of the total merge area traffic flow. The research also examined how results may alter if the analysis adopts the plain Ramp Volume (RV) itself, as a flow mix index, instead of the RVR. Four freeway bottlenecks in Milwaukee freeway system were used in the analysis. Because merge areas can have different utilization levels or congestion intensities, bottlenecks were ranked based on the utilization of the merge influence area and treated distinctly. For bottlenecks with heavily-utilized merge-areas, both capacities (PBDF and QDF) were reduced when RVR increased. Interestingly, BDD appeared to be very sensitive to RVR. BDD was found to double, triple or almost quadruple when ramp flow comprised a higher percentage of mainline flow. For bottlenecks with moderately-utilized merge-areas, results were usually different and counter-intuitive. For some cases, increasing the RVR resulted in a capacity flow increase and BDD decrease. The adoption of the RV index instead of the RVR index altered or reversed many results and trends for all bottlenecks. The study explains the difference between RVR and RV, demonstrates the impact of merge-area utilization, and provides further recommendations

Field-Derived Freeway Passenger Car Equivalents for Congested Conditions

Heavy-vehicle (HV) impact on freeway operations in the Highway Capacity Manual 2010 is evaluated on the basis of values for passenger car equivalents (PCE) for buses–trucks and recreational vehicles. These values were calibrated for relatively uncongested freeway conditions [Levels of Service (LOS) A through C] because inadequate field data on HV behavior under congested conditions were available; furthermore, field-collected headway information was based on the average headway for vehicles in a particular class, regardless of the type of vehicle that they were following. The goal of this paper was to collect and analyze freeway field data on HV headways with an emphasis on lower speeds typically associated with an LOS E (capacity) or F (forced-flow conditions). The effect that a leading vehicle has on headways was captured and analyzed for 10 leading–following vehicle pair types containing at least one passenger car (for example, buses followed by passenger cars). Headway statistics were analyzed for nine speed ranges (up to 20 mph, 20 to 25 mph, 25 to 30 mph, 30 to 35 mph, 35 to 40 mph, 40 to 45 mph, 45 to 50 mph, 50 to 55 mph, and over 55 mph) and 10 vehicle pair types. Values for PCEs were derived for each speed range on the basis of average headway for a specific vehicle pair type divided by the average headway between passenger cars. Leading and following vehicle classes and speeds were found to have a significant influence on headways and values for PCEs

How Weather Events Affect Freeway Demand Patterns

The ability to estimate freeway traffic demand during inclement weather events is critically needed for demand and supply management, level-of-service assessment, capacity verification, and other freeway operational and planning applications. Reliable travel demand prediction is also a useful input for freeway travel time reliability analyses and advanced traveler information systems. This paper investigates the effect of inclement weather on freeway demand with the use of hourly traffic and weather data collected for 5 years (2011–2015) at 15 urban freeway locations in the city of Milwaukee, Wisconsin, which represents a North American region experiencing distinct seasons with significant snowfall and cold temperatures in the winter. About 489,300 hourly traffic demand observations were used in the analysis, and more than 52,800 of those were under inclement weather. Freeway demand reduction factors were introduced for diverse weather variables, precipitation intensities, visibility levels, temperatures, weekdays and weekends, and different times of day. Variability across seasons and sites was also examined. The paper further explores traffic demand in the hours immediately preceding or following inclement weather events. Finally, freeway weather-related demand and capacity adjustment factors are compared. Lessons learned from the study along with recommendations for future Highway Capacity Manual editions are summarized