Calibrating the Robertson’s Platoon Dispersion Model on a Coordinated Corridor with Advance Warning Flashers

Platoon dispersion (PD) is the foundation of traffic signal coordination in an urban traffic network. PD describes the phenomenon by which vehicles depart from an upstream intersection as a platoon and begin to disperse before they arrive at the downstream intersection. Recently, advance warning flashers (AWFs) have been applied in many high-speed corridors. There is a need to update the traditional PD model to include the effect of AWFs. This paper examines the traffic flow dispersion patterns when an AWF is present and tests the hypothesis that the AWF will affect PD on a coordinated signal corridor. Platoon vehicles, which are not affected by the operation of the AWF, are used for comparison. Results show that when the AWF effect is included in the PD model, the smoothing factor F of the Robertson’s PD model ranges from 0.11 to 0.13. This range is smaller than the smoothing factor without the AWF effect. The platoon arrival time coefficient a ranges from 0.777 to 0.819 with the AWF effect. This is approximately the same as the default value of 0.8 in the TRANSYT simulation model. The PD coefficient β increases from an average of 0.11 with the AWF effect to an average of 0.24 without the AWF effect, which indicates an increase in roadway friction. It was concluded that AWFs increase the dispersion of the platoons, which might affect signal coordination

Calibrating the Highway Capacity Manual Arterial Travel Time Reliability Model

The latest edition of the Highway Capacity Manual (HCM-6) includes, for the first time, a methodology for estimating and predicting the average travel time distribution (TTD) of urban streets. Travel time reliability (TTR) metrics can then be estimated from the TTD. The HCM-6 explicitly considers five key sources of travel time variability. A literature search showed no evidence that the HCM-6 TTR model has ever been calibrated with empirical travel time data. More importantly, previous research showed that the HCM-6 underestimated the empirical TTD variability by 70% on a testbed in Lincoln, Nebraska. In other words, the HCM-6 TTR metrics reflected a more reliable roadway than would be supported by field measurements. This paper proposes a methodology for calibrating the HCM-6 TTR model so that it better estimates the empirical TTD. This calibration approach was used on an arterial roadway in Lincoln, Nebraska, and no statistically significant differences were found between the calibrated HCM-6 TTD and the empirical TTD at the 5% significance level

New Travel Time Reliability Methodology for Urban Arterial Corridors

The need for reliable performance measures of urban arterial corridors is increasing because of the rise in traffic congestion and the high value of users’ travel time. Consequently, travel time reliability (TTR), which attempts to capture the day-to-day variability in travel times, has recently received considerable research interest. The basis of all TTR metrics is the underlying travel time distribution (TTD) along the given link or corridor. Estimating and forecasting arterial corridor TTDs for TTR analysis is the focus of this paper. This paper proposes a TTR methodology that addresses some of the limitations of the current U.S. state-of-the-art methodology which was published in the 6th edition of the Highway Capacity Manual (HCM6). Specifically, HCM6 can only estimate average TTD and not the population TTD. However, the population TTD is needed for accurate trip decision-making by individual drivers and logistics companies. In addition, HCM6 cannot be used to analyze the effect of new technologies, such as connected and automated vehicles, nor can it be used easily for long corridors or networks. The proposed TTR methodology, which is traffic-microsimulation based, was applied on a 1.16-mi arterial testbed in Lincoln, Nebraska, U.S. It was shown that the proposed TTR methodology, when calibrated, could replicate the empirical population TTD at a 5% significance level. The population TTD could also be transformed into an average TTD that also replicated the corresponding empirical average TTD at a 5% significance level

Analysis of Component Errors in the Highway Capacity Manual Travel Time Reliability Estimations for Urban Streets

The Highway Capacity Manual 6th edition (HCM6) includes a new methodology to estimate and predict the distribution of average travel times (TTD) for urban streets. The TTD can then be used to estimate travel time reliability (TTR) metrics. Previous research on a 0.5-mi testbed showed statistically significant differences between the HCM6 estimated TTD and the corresponding empirical TTD. The difference in average travel time was 4 s that, while statistically significant, is not important from a practical perspective. More importantly, the TTD variance was underestimated by 70%. In other words, the HCM6 results reflected a more reliable testbed than field measurement. This paper expands the analysis on a longer testbed. It identifies the sources and magnitude of travel time variability that contribute to the HCM6 error. Understanding the potential sources of error, and their quantitative values, are the first steps in improving the HCM6 model to better reflect actual conditions. Empirical Bluetooth travel times were collected on a 1.16-mi testbed in Lincoln, Nebraska. The HCM6 methodology was used to model the testbed, and the estimated TTD by source of travel time variability was compared statistically to the corresponding empirical TTD. It was found that the HCM6 underestimated the TTD variability on the longer testbed by 67%. The demand component, missing variable(s), or both, which were not explicitly considered in the HCM6, were found to be the main source of the error in the HCM6 TTD. A focus on the demand estimators as the first step in improving the HCM6 TTR model was recommended

In-vehicle Evaluation of Rumble Strips in Pre-and Post-chip Sealed Maintenance Periods

Chip sealing will reduce the depth of rumble strips (RS) by approximately 1/8 . Will this depth reduction affect RS functional characteristics (audible and tactile warnings)? There is no detailed study on the effectiveness of RS that have been chip sealed. USEFULNESS The results will be useful to the Nebraska Department of Roads to determine: Operations: Whether RS will need to be re-milled after chip sealing. Cost & safety implications. Design: New RS guidelines for highways expected to be chip sealed in the future. It can be shown that a 1/8 reduction in the current milled RS design depth, as a result of chip sealing, does not result in a practical reduction in the RS effectiveness at producing audible and tactile warnings to alert drivers. There are statistically significant differences between the in-vehicle noise levels and vibration levels when vehicles are in a travel lane (off RS) and when on a chip-sealed RS. The difference will be clearly noticed by an average driver using a car or pickup truck at speeds of 45 mph, 55 mph, and 65 mph

Arterial Roadway Travel Time Reliability and the COVID-19 Pandemic

This paper evaluated the effect of the COVID-19 preventive orders on arterial roadway travel time reliability (TTR). A comparative analysis was conducted to examine average travel time distributions (TTD), and their associated TTR metrics, before and during the COVID-19 pandemic. Travel time data for four urban arterial corridors in Nebraska, disaggregated by peak period and direction, were analyzed. It was found that in 2020, the average TTD mean and standard deviation values for all 16 scenarios were reduced by an average of 14.0% and 43.4%, respectively. The travel time index, the planning time index, the level of travel time reliability (LOTTR), and the buffer index metrics associated with these TTDs were reduced, on average, by 14.0%, 19.7%, 3.5%, and 35.0%, respectively. In other words, whether the test corridors were more reliable during the pandemic was a function of which TTR metric was used. The paper concludes by arguing for a fundamental change in how arterial TTR is measured and reported to different user groups

In-Vehicle Evaluation of Milled Rumble Strips at Pre- and Post-Chip Sealed Maintenance Periods

Driver fatigue and drowsiness can have a profound impact on safety. Centerline and shoulder rumble strips (RS) are popular countermeasures designed to produce audible and tactile warning when vehicles deviate from the travel lane onto the RS. This reduces the risk of lane departure crashes. Studies show that the noise produced by RS is a function of many variables. RS depth is known to have the greatest impact on alerting drivers. However, chip-seal pavement maintenance operations have the tendency to reduce the original RS design depth, which may have an impact on the functional effectiveness of the RS. The purpose of this paper is to conduct a controlled experiment to understand the relationship between milled RS depth and noise and vibration in the vehicle cab. In-vehicle noise and vibration levels were collected on five different RS depths (i.e., 1/8 , 1/4 , 3/8 , 1/2 and 5/8 ), on three RS types (i.e., shoulder, single centerline, and double centerline), on three highways in the state of Nebraska, and using two vehicles travelling at speeds of 45 mph, 55 mph, and 65 mph. RS depths at 1/8 intervals were used to simulate the influence of a chip-seal on the RS effectiveness. On the basis of the in-vehicle sound and vibration levels of all the tested RS depths, it was shown in this research that a 1/8 reduction in the current milled RS design depth, as a result of chip-sealing, does not result in a practical reduction in the RS effectiveness at producing audible and tactile warnings to alert drivers. Re-milling of rumble strips after chip sealing is therefore not recommended if the chip seal reduced the rumble strip depth by 1/8

Calibrating the Highway Capacity Manual Arterial Travel Time Reliability Model

The latest edition of the Highway Capacity Manual (HCM-6) includes, for the first time, a methodology for estimating and predicting the average travel time distribution (TTD) of urban streets. Travel time reliability (TTR) metrics can then be estimated from the TTD. The HCM-6 explicitly considers five key sources of travel time variability. A literature search showed no evidence that the HCM-6 TTR model has ever been calibrated with empirical travel time data. More importantly, previous research showed that the HCM-6 underestimated the empirical TTD variability by 70% on a testbed in Lincoln, Nebraska. In other words, the HCM-6 TTR metrics reflected a more reliable roadway than would be supported by field measurements. This paper proposes a methodology for calibrating the HCM-6 TTR model so that it better estimates the empirical TTD. This calibration approach was used on an arterial roadway in Lincoln, Nebraska, and no statistically significant differences were found between the calibrated HCM-6 TTD and the empirical TTD at the 5% significance level

Development of an Improved Arterial Roadway Performance Reliability Methodology

The need for reliable performance measures of urban arterial roadways is increasing because of the rise in traffic congestion and the high value of travel time. Consequently, travel time reliability (TTR), which combines components of measures of central tendency and measures of dispersion of travel times, has recently received considerable research interest. The basis of all TTR metrics is the travel time distribution (TTD). Estimating and forecasting arterial TTDs for TTR analysis is the focus of this dissertation. This dissertation proposes a new TTR methodology that is a marked improvement on recent TTR estimation and forecasting methodologies including the current US state of the art methodology which was published in the 6th edition of the Highway Capacity Manual (HCM6). The HCM6 TTR methodology is a very important step because it is the first reliability methodology proposed in the HCM. However, there is no evidence that the HCM6 TTR methodology has been calibrated with empirical TTD data. The HCM6 TTR methodology was analyzed on four principal arterials in Nebraska. These corridors have historical empirical Bluetooth and INRIX TTD data. It was found that there were statistically significant differences between the HCM6 and empirical TTDs at a 5% significance level. More importantly, the HCM6 tends to severely overestimate the corridor’s reliability. The sources and magnitude of the HCM6 error were investigated and a calibration methodology was proposed. It was shown that the calibrated HCM6 TTR methodology can replicate the empirical TTDs. Based on the preliminary work a new TTR estimation and prediction methodology was developed. The contributions of this dissertation are threefold: (1) it provided the first comprehensive performance analysis of the HCM6 TTR methodology, (2) it developed a methodology for calibrating TTR methodologies, including that used in the HCM6, and (3) it developed a new TTR methodology that addresses the limitations of the HCM6 TTR methodology. Unlike the HCM6, the new TTR methodology can be used to estimate the population TTD and analyze changes in arterial roadway supply and demand components that impact travel time. Such changes may include the adoption of automated vehicles and the use of advanced signal controls

Banks of the Neris between Karmazinai and Kernavė (Iron Age settlements)

During 2009-2010, the Scientific Research Department of the State Cultural Reserve of Kernavė conducted a field survey in the Ncris valley, mostly on the first terrace above the floodplain, in the Karmazinai, Grabijolai, and Kernavė regions. Exploratory test pits were excavated roughly every 50 m and in the wider valleys, in several rows. In this way a segment of river bank about 16.5 km long was investigated and 23 unenclosed settlements from various Iron Age periods were found. The articles aim is an analysis of the Iron Age settlements discovered during 2009-2010 in the context of the other archaeological sites in the regions. It attempts, with the help of this research, to illustrate the main stages in the habitation of the Neris valley and to discover the special features of the development of the social landscape and the network of Iron Age settlements. It investigates the possible connection of the settlements with the existing burial sites, i.e. barrow cemeteries. It attempts to discover the change in the functional meaning of the hillforts during the various periods of the regions' habitation. And it analyses the chronology, size, special features of the environment, and other questions about the discovered settlements