Search

BackgroundFirst pass effect (FPE), defined as single-pass complete or near complete reperfusion during endovascular thrombectomy (EVT) for large vessel occlusion (LVO) strokes, is a critical performance metric. Atrial fibrillation (AF)-related strokes have different clot composition compared with non-AF strokes, which may impact thrombectomy reperfusion results. We compared FPE rates in AF and non-AF stroke patients to evaluate if AF-related strokes had higher FPE rates.MethodsWe conducted a post-hoc analysis of the DIRECT-SAFE trial data, including patients with retrievable clots on the initial angiographic run. Patients were categorized into AF and non-AF groups. The primary outcome was the presence or absence of FPE (single-pass, single-device resulting in complete/near complete reperfusion) in AF and non-AF groups. We used multivariable logistic regression to examine the association between FPE and AF, adjusting for thrombolysis pre-thrombectomy and clot location.ResultsWe included 253 patients (67 with AF, 186 without AF). AF patients were older (mean age: 74 years vs 67.5 years, p=0.001), had a higher proportion of females (55% vs 40%, p=0.044), and experienced more severe strokes (median National Institutes of Health Stroke Scale (NIHSS) score: 17 vs 14, p=0.009) than non-AF patients. No differences were observed in thrombolytic agent usage, time metrics, or clot location. AF patients achieved a higher proportion of FPE compared with non-AF patients (55.22% vs 37.3%, adjusted odds ratio 2.00 (95% CI 1.13 to 3.55), p=0.017).ConclusionsAF-related strokes in LVO patients treated with EVT were associated with FPE. This highlights the need for preparedness for multiple passes and potential adjuvant/rescue therapy in non-AF-related strokes.

The benefit of combined treatment with intravenous thrombolysis before endovascular thrombectomy in patients with acute ischaemic stroke caused by large vessel occlusion remains unclear. We hypothesised that the clinical outcomes of patients with stroke with large vessel occlusion treated with direct endovascular thrombectomy within 4·5 h would be non-inferior compared with the outcomes of those treated with standard bridging therapy (intravenous thrombolysis before endovascular thrombectomy).

Supplemental Digital Content is available in the text.

Supplemental Digital Content is available in the text.

BackgroundIntrinsic hospital factors leading to time delay to inter-hospital transfer for endovascular thrombectomy (EVT) have not been adequately investigated, leading to uncertainty in generalizability of hub and spoke EVT services. We investigated the contribution of intrinsic hospital factors to variations in time delay in a multicenter, retrospective study.MethodsThe setting was a hub and spoke EVT state-wide system for a population of 6.3 million and 34 spoke hospitals. We collected data on acute large vessel occlusion strokes transferred from spoke to hub for consideration of EVT between January 2016 and December 2018. The primary endpoint was the proportion of variability in delay-time in transfer cases contributed to by intrinsic hospital factors estimated through variance component analysis implemented as a mixed-effect linear regression model with hospitals as random effects.ResultsWe included 434 patients. The median age was 72 years (IQR 62–79), 44% were female, and the median baseline National Institutes of Health Stroke Scale (NIHSS) was 16 (IQR 11–20). The median onset to CT time was 100 mins (IQR 69–157) at the spoke hospitals and CT acquisition at the spoke hospital to time of transfer was 93 min (IQR 70–132). 53% of the observed variability in time from CT acquisition at the spoke hospital to transfer to the EVT center was explained by intrinsic hospital factors, as opposed to patient-related factors.ConclusionsIntrinsic hospital factors explained more than half of the observed variability in time from CT acquisition at the spoke hospital to departure for transfer. We recommend that the design of hub and spoke EVT services should account for intrinsic hospital factors to minimize hospital transfer delay.

Nerinetide, an eicosapeptide that interferes with post-synaptic density protein 95, is a neuroprotectant that is effective in preclinical stroke models of ischaemia-reperfusion. In this trial, we assessed the efficacy and safety of nerinetide in human ischaemia-reperfusion that occurs with rapid endovascular thrombectomy in patients who had an acute ischaemic stroke.

Supplemental Digital Content is available in the text.

The experimental observation that certain crystal faces do not grow, despite being in contact with supersaturated solution, is a widely reported phenomenon. This concept of a growth “dead zone” has been known for many years, but its origin remains an unresolved problem in crystal growth. Sometimes it seems to be an inherent feature of the solution growth process, while at others it appears that an impurity is an essential element for its appearance. Here we review existing data and provide new experimental evidence to confirm the widespread existence of the dead zone across a range of molecular materials. Available crystal growth kinetics are confronted with mechanistic models. Examination of the packing arrangements of appropriate crystal faces suggests that this behavior is linked to molecular-scale surface roughness.

Supplemental Digital Content is available in the text.

IMPORTANCE: The positive treatment effect of endovascular therapy (EVT) is assumed to be caused by the preservation of brain tissue. It remains unclear to what extent the treatment-related reduction in follow-up infarct volume (FIV) explains the improved functional outcome after EVT in patients with acute ischemic stroke. OBJECTIVE: To study whether FIV mediates the relationship between EVT and functional outcome in patients with acute ischemic stroke. DESIGN, SETTING, AND PARTICIPANTS: Patient data from 7 randomized multicenter trials were pooled. These trials were conducted between December 2010 and April 2015 and included 1764 patients randomly assigned to receive either EVT or standard care (control). Follow-up infarct volume was assessed on computed tomography or magnetic resonance imaging after stroke onset. Mediation analysis was performed to examine the potential causal chain in which FIV may mediate the relationship between EVT and functional outcome. A total of 1690 patients met the inclusion criteria. Twenty-five additional patients were excluded, resulting in a total of 1665 patients, including 821 (49.3%) in the EVT group and 844 (50.7%) in the control group. Data were analyzed from January to June 2017. MAIN OUTCOME AND MEASURE: The 90-day functional outcome via the modified Rankin Scale (mRS). RESULTS: Among 1665 patients, the median (interquartile range [IQR]) age was 68 (57-76) years, and 781 (46.9%) were female. The median (IQR) time to FIV measurement was 30 (24-237) hours. The median (IQR) FIV was 41 (14-120) mL. Patients in the EVT group had significantly smaller FIVs compared with patients in the control group (median [IQR] FIV, 33 [11-99] vs 51 [18-134] mL; P = .007) and lower mRS scores at 90 days (median [IQR] score, 3 [1-4] vs 4 [2-5]). Follow-up infarct volume was a predictor of functional outcome (adjusted common odds ratio, 0.46; 95% CI, 0.39-0.54; P < .001). Follow-up infarct volume partially mediated the relationship between treatment type with mRS score, as EVT was still significantly associated with functional outcome after adjustment for FIV (adjusted common odds ratio, 2.22; 95% CI, 1.52-3.21; P < .001). Treatment-reduced FIV explained 12% (95% CI, 1-19) of the relationship between EVT and functional outcome. CONCLUSIONS AND RELEVANCE: In this analysis, follow-up infarct volume predicted functional outcome; however, a reduced infarct volume after treatment with EVT only explained 12% of the treatment benefit. Follow-up infarct volume as measured on computed tomography and magnetic resonance imaging is not a valid proxy for estimating treatment effect in phase II and III trials of acute ischemic stroke.

Two- lane highways constitute a large proportion of the highway system in the United States, particularly in rural areas. Performance evaluation on those highways is the basis for planning, upgrade, and improvement programs. Such evaluations are conducted using performance measures that should ideally be correlated to performance determinants on those highways. Unlike other highway facilities, two-lane highway performance is notably affected by the platooning phenomenon, which is believed to be a function of traffic level and passing opportunities. Over the last couple of decades, several studies have addressed performance measures on two-lane highways, and are mainly driven by the reported limitations of the current measures used by the Highway Capacity Manual(HCM). This review aims to summarize the performance measures that have been published in the literature or used in practice both in the United States and abroad. The review starts with an historical overview of the HCM performance measures since its inception in 1950. It then discusses the most important criteria for measures to be more effective in describing performance, before presenting the review results for measures that have been proposed in literature or reported as being used in practice. Finally, a subjective assessment of all performance measures against the set of criteria outlined in the article is presented. The review presented in this paper provides information that is valuable for practitioners and researchers in understating the alternative measures for assessing performance on two-lane highways, and the limitations and merits associated with those measures.

BackgroundEndovascular thrombectomy (ET) is safe, effective, and cost-effective for large artery occlusion ischemic stroke, even if under different selection criteria.PurposeTo study the preferences for ET selection criteria by surveying clinicians and consumers, where number needed to treat to achieve functional independence is the only factor being considered.MethodsA survey providing visual representation of the proportion of patients treated and expected functional outcomes, based on the selection criteria in each of the recent randomized trials of ET, was distributed nationwide in Australia and New Zealand to clinicians and consumers. The preferred selection criteria were identified by the frequency of first choice and using decision-analysis techniques to assess consensus by treating respondents as a panel of experts and aggregating their preferences on selection criteria.Results104 clinicians and 107 consumer respondents (43/107 (40%) stroke survivors) took part in the study. Selection criteria of EXTEND-IA were ranked as the most preferred by the consensus process analysis and were the first choice of 64 individual clinicians (61.5%; 95% CI 52% to 71%). ESCAPE trial selection criteria were ranked as the most preferred option and chosen by 42 individual consumers (39%; 95% CI 29% to 48%). Most clinicians based their choice on the ratio of patients benefiting from ET, while consumers considered the absolute number of patients benefiting.ConclusionsConsumers favor maximization of the absolute number achieving good outcome in comparison with clinicians. This finding suggests that less restrictive criteria may be favored in clinical practice.

BackgroundFollow-up infarct volume (FIV) has been recommended as an early indicator of treatment efficacy in patients with acute ischemic stroke. Questions remain about the optimal imaging approach for FIV measurement.ObjectiveTo examine the association of FIV with 90-day modified Rankin Scale (mRS) score and investigate its dependency on acquisition time and modality.MethodsData of seven trials were pooled. FIV was assessed on follow-up (12 hours to 2 weeks) CT or MRI. Infarct location was defined as laterality and involvement of the Alberta Stroke Program Early CT Score regions. Relative quality and strength of multivariable regression models of the association between FIV and functional outcome were assessed. Dependency of imaging modality and acquisition time (≤48 hours vs >48 hours) was evaluated.ResultsOf 1665 included patients, 83% were imaged with CT. Median FIV was 41 mL (IQR 14–120). A large FIV was associated with worse functional outcome (OR=0.88(95% CI 0.87 to 0.89) per 10 mL) in adjusted analysis. A model including FIV, location, and hemorrhage type best predicted mRS score. FIV of ≥133 mL was highly specific for unfavorable outcome. FIV was equally strongly associated with mRS score for assessment on CT and MRI, even though large differences in volume were present (48 mL (IQR 15–131) vs 22 mL (IQR 8–71), respectively). Associations of both early and late FIV assessments with outcome were similar in strength (ρ=0.60(95% CI 0.56 to 0.64) and ρ=0.55(95% CI 0.50 to 0.60), respectively).ConclusionsIn patients with an acute ischemic stroke due to a proximal intracranial occlusion of the anterior circulation, FIV is a strong independent predictor of functional outcome and can be assessed before 48 hours, oneither CT or MRI.

This is in response to 'Cardinal error or doing the right thing?.' by Joe Feuerherd (NCR, March 26). The article's focus was on now-rejected Maryland legislation designed significantly to change [...]

Supplemental Digital Content is available in the text.

Introduction:CT performed 24h post-treatment is widely used to assess radiological outcomes in stroke studies. Even without visible hyperattenuation, occult angiographic contrast may persist in the brain and confound Hounsfield Unit-based imaging metrics such as Net Water Uptake (NWU), a measure of cerebral edema based on tissue hypoattenuation. We aimed to assess (1) the presence of retained contrast post-thrombectomy on 24h CT by comparing NWU measurements with and without adjustment for iodine using dual energy CT (DECT), (2) factors associated with amount of retention, and (3) its impact on the accuracy of NWU.Methods:In a prospective study of patients with anterior circulation large vessel occlusion who had post-thrombectomy follow-up DECT performed 24h post-treatment from two Comprehensive Stroke Centres (November 2021 to May 2022), NWU was calculated by interside comparison of Hounsfield Units of the infarct lesion and its mirror homolog. Retained contrast was quantified by the difference in NWU values with and without adjustment for iodine. We tested correlation between NWU and tissue swelling using relative hemispheric volume (rHV) and midline shift (MLS). Patients with visible hyperdensities from hemorrhagic transformation or visible contrast retention, and bilateral infarcts were excluded.Results:Of 125 patients analysed (median age 71 [IQR 61-80], baseline NIHSS 16 [IQR 9.75-21]), reperfusion (eTICI 2b-3) was achieved in 120 patients (96.8%). NWU measured with iodine adjustment was significantly higher than NWU measured without adjustment (17.1% vs 10.8%, p<0.001). In multivariable median regression analysis, age (p=0.031), number of passes (p<0.001) and having CT perfusion at baseline (p=0.008) were independently associated with amount of retained contrast. NWU measured with iodine adjustment correlated with rHV (p=0.043) and MLS (p=0.033), but NWU without adjustment did not (rHV p=0.350; MLS p=0.347).Conclusion:Occult angiographic iodine contrast significantly affects NWU on CT at 24h. Our data suggest adjustment for retained iodine using DECT is required for accurate NWU measures post-thrombectomy. Future studies analysing CT post-thrombectomy should consider the significance of occult contrast retention.

This paper reports on the combined microsimulation and small scale demonstration evaluation of the freeway performance effects of a specific connected vehicle implementation of speed harmonization (The Prototype). The microsimulation testing was performed on a 10 mile stretch of freeway in San Mateo County, California. The small scale field demonstration was performed with 10 equipped vehicles on 17 miles of the I-5 freeway in Seattle, Washington.

Whether moving across the country or across the street, relocating corporate offices can be a daunting task. Recognizing the myriad challenges associated with corporate moves, many landlords will now offer [...]

This paper presents a planning-level methodology for the analysis of freeway facilities. The proposed approach is based on and compatible with the operational method of the Highway Capacity Manual 2010(HCM 2010). The approach is specifically constructed with the intent to minimize input data requirements. The method covers both under- and oversaturated flow conditions and produces estimates of travel time, speed, density, and level of service. The underlying methodology relies on developing a relationship between a basic freeway segment’s delay rate per unit distance and its demand-to-capacity ratio. For weaving segments, the study develops capacity adjustment factors on the basis of volume ratio and segment length. With these factors, demand-to-capacity ratios on weave segments were adjusted and the segment was treated similarly to a basic freeway segment. For merge and diverge segments, a novel methodology is proposed to estimate their capacity on the basis of demand level, free-flow speed, and space mean speed. Subsequently, capacity adjustment factors are calculated on those segments and their demand-to-capacity ratios are adjusted accordingly. The proposed approach is applied to two examples in the HCM 2010 and produced very promising results. For undersaturated flow conditions, facility travel time is at most 3.4% and density was at most 1.1% at variance from the results found by applying the HCM 2010 operational methodology. The corresponding differences for oversaturated conditions are 6.7% and 13.0%, respectively.

The composition of occlusive thrombus in acute ischemic stroke may affect treatment success. Neuroimaging characteristics may correlate with thrombus composition. In this study we aimed to investigate the relationship between the hyperdense artery sign (HAS) on imaging and thrombus composition.

Perianeurysmal edema is rare and is associated with expansion of intracranial aneurysms despite adequate endovascular treatment. The natural history of this condition is poorly understood. We present a case series of perianeurysmal edema to investigate the incidence, natural history and management of these aneurysms.

The article focuses on the results of the survey on active traffic management (ATM) in the U.S. published in National Cooperative Highway Research Program (NCHRP). It states that the survey provides an overview of state of practice related with designing, implementing, and operating ATM. It mentions that it focuses on strategies to manage traffic and congestion actively on arterials.

The purpose of this study was to analyze whether treating ruptured intracranial aneurysms within 24 hours of subarachnoid hemorrhage improves clinical outcome.

This paper describes a methodology for predicting the impacts of active transportation and demand management (ATDM) measures on highway performance that can be applied using either microsimulation or Highway Capacity Manual (HCM) analysis techniques.

NCHRP Project 3-70, Multimodal Level of Service Analysis for Urban Streets, is developing and testing a framework and enhanced methods for determining levels of service for the automobile, transit, bicycle, and pedestrian modes on urban streets. The proposed pedestrian level-of-service (LOS) model for arterials developed as part of NCHRP Project 3-70 is presented. This effort represents a progressive shift in evaluating the quality of service from a provider-based measure (how many vehicles or pedestrians can be moved and how fast) to a user-based measure (how well do drivers and pedestrians believe the facility meets their needs). To obtain feedback from potential pedestrian facility users, data for the model were obtained from participants in video simulation laboratories. The proposed model consists of a pedestrian density LOS and a pedestrian nondensity LOS. The density LOS is computed according to the methods provided in the Highway Capacity Manual. The nondensity LOS is a function of the pedestrian LOS of roadway segments, the pedestrian LOS of intersections, and the roadway crossing difficulty factor.

This paper presents the results of research to develop a national method for the multimodal assessment of the quality of service provided by an urban street. The method considers the level of service from the point of view of four types of travelers typically using the urban street: auto driver, transit passenger, bicycle rider, and pedestrian. Video laboratories and transit onboard surveys were used to develop data sets of the quality of service perceived by the general public for each of the modes of travel on the urban street. The laboratories were conducted in several different metropolitan areas of the United States. Four level-of-service (LOS) models were developed, one for each mode. The four LOS models share a common measure, user satisfaction. The models assign a letter grade LOS (A-F) based on the street cross section, intersection controls, and traffic characteristics (auto, transit, bicycle, and pedestrian volumes on the street). The models can be used in combination to compare the trade-offs of different street cross sections from the unique perspectives of each mode. The models are particularly useful for testing the impacts of converting auto through lanes to bicycle lanes, wider sidewalks, and wider planter strips.

This study focuses on the problem of measuring the queue discharge flow rates for a nonbottleneck freeway section and on developing an approach for estimating the impacts of intelligent transportation system (ITS) measures on the mean and variance of the queue discharge flow rate. The whole-year mean and variance of the queue discharge flow rates for the subject section of freeway are computed on the basis of measured 5-min congested flow rates over the course of a year. The flow data are categorized into congested and uncongested flows on the basis of a speed threshold that separates congested flow conditions from uncongested conditions. The speed threshold is determined by plotting the change in speed between observations and identifying the speed at which speed is most unstable. The mean and variance of queue discharge flow rates for incident conditions are then computed by identifying when incidents were present on the freeway over the course of a year, identifying the corresponding flow rates in the study section for those periods, and segregating the observed flow rates for incidents into congested and uncongested flows by using the same speed threshold as before. Once the means and variances of the queue discharge flow rates have been obtained for the whole year and for incident conditions during the year, the variance decomposition formula is used to compute the mean and variance of queue discharge flow rates for nonincident conditions during the year. A methodology is then proposed and demonstrated for computing the impact of ITS measures (such as faster incident detection or improved congested flow rates during incidents) on the observed portion of the total variance that is attributable to incidents susceptible to amelioration with ITS measures. This same approach can also be used to compute the effectiveness of measures to reduce other causes of nonrecurrent congestion.

Background and Purpose: Noncontrast spiral CT (NCCT) has emerged as the investigation of choice in patients presenting with renal-tract calculi. As management guidelines are based on stone size measured on plain radiography of the kidneys, ureters, and bladder (KUB), it is important to assess the accuracy of stone size measured on NCCT compared with KUB films.Patients and Methods: The NCCT and KUB studies obtained from 24 patients (27 stones) presenting to the emergency department at a major metropolitan hospital were analyzed randomly and independently by two urologists and one uroradiologist. The NCCT scans were assessed separately from the KUB films. Only size in greatest dimension and stone location were recorded. Results: The stone size was 2 to 38 mm on NCCT scans and 2 to 46 mm on KUB films. The mean stone size was 6.773 ± 6.146 mm and 7.747 ± 7.866 mm, respectively (P= 0.0398; Student's t-test). Almost three fourths (70%) of the stones were larger on KUB films than they were on NCCT scans, with a mean difference −0.974 mm (95% confidence interval −5.652, 3.703) for NCCT. Conclusion: Spiral CT underestimates stone size by approximately 12% compared with KUB films. This error may impact stone management as outlined in guidelines published by the American Urological Association, particularly for stones about 5 mm in greatest dimension. These patients may initially be managed conservatively when intervention would be more appropriate.

A methodology is presented for estimating and predicting the total annual traffic congestion attributable to recurrent and nonrecurrent congestion. The methodology is applicable to freeways, conventional highways, and urban streets. The methodology is sensitive to improvements in facility surveillance and freeway service patrol strategies. Recurrent congestion is estimated by using Highway Capacity Manual speed-flow curves and data on facility demands, free-flow speeds, and capacities. Nonrecurrent congestion is estimated in terms of annual vehicle hours of delay caused by weather, work zones, incidents, and so forth. The methodology employs incident probability trees, incident duration (sensitive to surveillance and response times), and estimates of remaining capacity during incidents to estimate incident delay. Weather-and work-zone-related delays are estimated on the basis of frequency of occurrence and estimates of capacity reductions during periods of bad weather and work-zone activity. The methodology has been implemented in a spreadsheet.

The successful acceptance of traffic microsimulation software depends crucially on the verification and validation (V&V) procedures for testing the core behavioral algorithms. These must be sufficient to convince researchers, software developers, and practitioners that the algorithms are accurate and robust. V&V procedures must also be well documented to ensure public acceptance. A suggested V&V procedure is presented. The central theme is that verification and validation are integral parts of the entire algorithm development process. A three-stage algorithm development and V&V procedure for traffic microsimulation algorithms is recommended. Algorithm development includes identifying key variables and setting model parameters. Next, the software implementation of the algorithm is tested during the algorithm-level testing stage with a combination of hypothetical and simple real-world data. Finally, systemlevel testing of the algorithm software is done within a complete microsimulation modeling system. In the last stage, the system with the new algorithm is tested against complex real-world data sets.

The past few years have seen a rapid evolution in the sophistication of traffic microsimulation models and a consequent major expansion of their use in transportation engineering and planning practice. Researchers and practitioners have employed an extensive array of approaches to calibrate these models and have selected a wide range of parameters to calibrate and a broad range of acceptance criteria. A methodical, top-down approach to model calibration is outlined; it focuses the initial effort on a few key parameters that have the greatest impact on model performance and then proceeds to less critical parameters to finalize the calibration. A three-step calibration/validation process is recommended. First, the model is calibrated for capacity at the key bottlenecks in the system (the capacity calibration step). Second, the model is calibrated for traffic flows at nonbottleneck locations in the system (the route choice calibration step). Finally, the overall model performance is calibrated against field-measured system performance measures such as travel time and delay (the system performance calibration step). This three-step process is illustrated in an example application for a freeway/arterial corridor.

The 2000 release of the Highway Capacity Manual(HCM) provides for the first time a corridor analysis method that guides users in the application of various chapters of the HCM to the analysis of automobiles and transit in a corridor. Together with the recent publication of the Transit Capacity and Quality of Service Manual(TCQSM), the HCM 2000 represents a significant advance in the direction of multimodal level-of-service (LOS) analysis. However, relatively little guidance is given in either the HCM or the TCQSM on the compilation of automobile and transit segment levels of service into a measure of corridor level of service. In addition, bicycles and pedestrians are ignored in the corridor methodology. A methodology was developed and tested in Florida for measuring and reporting the user-perceived quality of service for highway corridors from a multimodal perspective. Automobile and transit LOS analyses are based on the HCM 2000 and TCQSM, respectively. Bicycle and pedestrian levels of service are based on the bicycle and pedestrian LOS models, respectively. Four classes of corridors are recommended, and the methodology was tested on two classes of urban corridors, with and without a freeway. The methodology is applied in three steps: (a) corridor definition, (b) computation of modal level of service, and (c) reporting of results. The methodology was applied to six case studies throughout Florida at generalized and conceptual planning levels. Conclusions about the methodology were drawn from the case studies; the main conclusion is that the methodology provided a reliable overall indicator of corridor level of service by mode.

Sonographic examination of the renal vasculature provides considerable information that can be used in the assessment of conditions as varied as renal artery stenosis and tumor thrombus involvement of renal veins. Although extrarenal and intrarenal Doppler criteria in renal artery stenosis diagnosis are controversial, the role of sonography in renal tumor and renal vein assessment is straightforward. Imaging renal morphology and vasculature is also useful in infection and, to a certain extent, in obstruction. Techniques of examination are briefly reviewed, as is renal vascular anatomy. The role of recent advances, such as echo enhancers, is also outlined.

Skabardonis and Dowling recommended updated Bureau of Public Road speed-flow curves for freeways and signalized arterials to improve the accuracy of speed estimates used in transportation demand models. These updated curves generally involved the use of higher power functions that show relatively little sensitivity to volume changes until demand exceeds capacity, when the predicted speed drops abruptly to a very low value. Skabardonis and Dowling demonstrated that the curves provide improved estimates of vehicle speeds under both uncongested and queueing conditions; however, they did not investigate the impact of these curves on the performance of travel demand models. Practitioners have been concerned about the impacts of such abrupt speed-flow curves on the performance of their travel demand models. Spiess has stated that higher power functions are more difficult computationally for computers to evaluate and that more abrupt speed-flow curves adversely affect the rate of convergence to equilibrium solutions in the traffic assignment process. In this paper the impact of the Skabardonis and Dowling updated speed-flow curves on the performance of selected travel demand models is investigated. The updated speed-flow curves were found to significantly increase travel demand model run times. However, it is demonstrated that an alternative speed-flow equation developed by Akçelik has similar or better accuracy and provides much superior convergence properties during the traffic assignment process. The Akçelik curve significantly reduced travel demand model run times.

The ability to accurately measure and predict the average speed of traffic for different facilities and conditions has become increasingly important with the implementation of the Environmental Protection Agency's Transportation Conformity Rule. Average speed is a vital input into motor vehicle emission rate models. Three speed measurement techniques (floating cars, loop detectors, and aerial photographs) and two average travel speed prediction techniques (the Highway Capacity Manual method for arterials and TRANSYT-7F for signalized arterials) are evaluated. These techniques are compared and evaluated against 4 hr of field data gathered for an 8-mi (13-km) section of Ventura Boulevard in Los Angeles, California. The mean speeds measured by floating cars and aerial photographs were in close agreement (within 6 percent of each other). Loop detectors generally produced mean speeds 22 percent higher than the floating car measurements, even after correcting for the differences between the space mean speeds measured by floating cars and the time mean speeds measured by the loops. TRANSYT-7F was able to predict the average travel speeds on the arterial within 3 percent of the floating car measurements and 5 percent of the aerial photograph measurements. The Highway Capacity Manual estimates were uniformly 18 percent lower than the measured floating car speeds. A correction to the method improved the estimates but tended to slightly over-compensate. The adjusted estimated speeds were 9 percent higher than the floating car speeds.

Improved speed-estimation techniques for planning applications were developed and tested. Comparisons with field data and simulation results indicate that the recommended techniques provide better accuracy and consistency with the procedures contained in the 1994 update of the Highway Capacity Manual.These speed-estimation techniques will improve the accuracy of long-range transportation planning models for predicting travel time, delay, and air-pollutant emissions.

The results of the methodology development effort for FHWA project Predicting the Demand for High-Occupancy-Vehicle (HOV) Lanes are presented. This research project is a 2-year effort to develop a methodology and microcomputer software model for quickly analyzing HOV lane demand and operations. The methodology provides a set of quickresponse procedures for predicting and evaluating the impact of HOV lanes on person demand, vehicle demand, automobile occupancy, congestion, delay, air quality, and fuel consumption.

An interview with pianist and ragtime festival artist Richard Dowling is presented. He talks about ragtime music. When asked about his favorite ragtime music, he referred to Scott Joplin's "Maple Leaf Rag," James Scott's "Hilarity Rag" and Joseph Lamb's "Ragtime Nightingale." According to Dowling, William Bolcom's "Graceful Ghost Rag" is the best known and most influential contemporary ragtime music by far.