Toru Hagiwara

Overall Level of Service of Urban Walking Environment and Its Influence on Pedestrian Route Choice Behavior: Analysis of Pedestrian Travel in Sapporo, Japan

The objective of this study was to understand and quantify better the influence of the overall level of service (LOS) of the urban walking environment on pedestrian route choice behavior. A methodology for estimating the overall LOS of pedestrian walkways and crosswalks was developed on the basis of the concept of total utility value, which comes from a stated preference survey. Each sidewalk and crosswalk link was assigned an overall LOS according to its operational and geometric characteristics determined from field measurements. For analysis of pedestrian behavior, this study used data from a revealed preference survey on individual route choice behavior. A geographic information system network database was used to store the characteristics of the routes that pedestrians used. Network analysis with the ArcGIS program was used to analyze the routes, which included determination of the shortest-path routes and the optimized-LOS-path routes between origin-destination pairs. A comparative analysis of the actual routes and the estimated alternative routes was performed. On the basis of the results, a multinomial logit model was developed to express the route choice behaviors of pedestrians quantitatively. The model results indicate that pedestrians choose routes not only for distance but also for the overall LOS of sidewalks and crosswalks. On longer travel paths, pedestrians divert from the shortest-path route and are found to use sidewalks and crosswalks with high LOS. On shorter routes, pedestrians tend not to avoid sidewalks or crosswalks with low LOS. This analysis suggests that efforts to accommodate pedestrians in urban areas should focus on improving the walking environment of the road network.

Cellular Telephone Conversation While Driving: Effects on Driver Reaction Time and Subjective Mental Workload

The effects of conversation through a cellular telephone while driving on driver reaction time and subjective mental workload (SMWL) were investigated. Two vehicles equipped with measurement devices were used to measure reaction time. The drivers’ SMWL was measured by the National Aeronautics and Space Administration Task Load Index procedure. The experiment was conducted on an expressway in Japan. Thirty-one subjects participated in the experiment; 19 were young and 12 were elderly drivers. Each subject was asked to follow a leading vehicle and to keep a constant distance while following. The subjects performed four tasks: (a) following a leading vehicle, (b) operating a cellular telephone while following the leading vehicle, (c) performing a simple conversation task, and (d) performing a complex conversation task on a cellular telephone with the experimenter while following the leading vehicle. The results of these experiments indicated that the performance of the telephone tasks increases the reaction time and SMWL of the drivers, as was shown in a previous study. The results also indicated that the complex conversation task produced an increase in reaction time as compared to the simple conversation task, independent of age group. Furthermore, the experiment indicated that the SMWL also increased significantly in the complex conversation task as compared to the other tasks.

Application of Road Visibility Information System to Winter Maintenance

A road visibility information system (RVIS) was developed that uses images transmitted by multiple closed-circuit television (CCTV) cameras as road visibility information. Feasibility studies in the daytime during the winters of 2005 to 2006 and 2006 to 2007 were performed on national routes 230 and 231. During those two winters, the RVIS calculated visibility scale and road visibility index (RVI) automatically, accurately, continuously, and in a timely manner from road images recorded by multiple CCTV cameras. The RVIS processed 90% of the images transmitted by 14 CCTV cameras. The RVIS provided areawide visibility information in many formats and through many kinds of media and devices. On the basis of stored road visibility data, the finding was a high correspondence between the RVI and the subjective visibility evaluation for the same road images. In addition, this study demonstrates that the RVI monitoring website and e-mail alerts can speedily and reliably inform road administrators of snowstorm-induced poor visibility. The RVIS has the potential to collect data on road visibility reliably during daytime using images transmitted by multiple CCTV cameras. However, it is necessary to improve data collection at night and to capture still images accurately and quickly.

Influence of Winter Road Conditions and Signal Delay on Pedestrian Route Choice in Japan’s Snowiest Metropolis

Investigation of pedestrian route choice behavior on icy surfaces is important for the effective improvement of walkways in winter. The objective of this research was to investigate pedestrian route choice behavior in winter. Field surveys and questionnaire surveys were conducted to fulfill this objective. Video cameras were used in the field surveys to clarify the movements of pedestrians. How pedestrians chose their routes was investigated by observing their movements. According to the field survey, when the signal was green, the probability that the pedestrian would cross became extremely high, regardless of the road surface conditions. However, when the walkway surface was icy, the probability that the pedestrian would wait for a green signal decreased by a considerable value. This indicates that when the wait becomes long, the probability that the pedestrian will cross becomes low during the snowy season. A questionnaire survey was also conducted to clarify the factors affecting pedestrian route choice behavior. The questionnaire asked about different road surface conditions. The results from the survey indicate that even if part of a road section has a good surface condition, it has a strong influence on route choice behavior. It indicates that pedestrians feel uncomfortable in walking on slippery walkways and they prefer to choose bare walkways. On the basis of the data from the field survey and questionnaire survey, logit models were developed to express quantitatively the route choice behaviors of pedestrians. These models can be used to predict the probability that a pedestrian will select a route as a function of pedestrian delay at signalized intersections and the road surface conditions in winter.

Effects of Road Geometry and Cross-Section Variables on Traffic Accidents: Study Using Homogeneous Road Segments

This study aimed at finding the effects of road geometry and cross-section variables on numbers of accidents. In addition, a methodology to combine variables by using decision trees was developed. Combination variables for road geometry and cross section were created by using the chi-square automatic interaction detection algorithm. Two negative binomial models were developed: one with homogeneous road segments and the other with 1-km road segments. Homogeneous road segments were divided on the basis of the horizontal alignment of the road. They were either curved or straight. The accuracy of the negative binomial model with homogeneous road segments was compared with that of the negative binomial model with 1-km road segments. The negative binomial model using homogeneous road segments was found to be the more accurate of the two models. The model with homogeneous road segments was used to draw conclusions with regard to the effect of variables on the number of accidents. Combination variables showed a significant effect on the number of accidents. The road geometry and cross-section variables were found to affect the number of accidents differently under various combinations of other variables.

Estimation of Time Lag Between Right-Turning Vehicles and Pedestrians Approaching from the Right Side

In Japan, where vehicles travel on the left side of the road (i.e., right turns correspond to left turns in the United States), right turns can cause difficulties for a driver at an intersection, because the driver has to judge the headway in oncoming traffic while avoiding pedestrians in the crosswalk. However, few investigations have addressed the drivers avoidance of conflicts with pedestrians in the crosswalk. This study investigates conflicts between the right-turning vehicle and the pedestrian coming from the right in the crosswalk. A field experiment was conducted to measure a drivers avoidance behavior according to the time lag, defined as the interval between the time that the right-turning vehicle reaches the conflict point and the time that the pedestrian coming from the right side reaches the conflict point. This study found that the time lag is constantly reevaluated during the right turn by the driver, and the driver slows and enters the crosswalk behind the pedestrian, if the time lag at the conflict point is less than 2 s. Also, the braking location of drivers who braked to avoid conflict with the pedestrian after starting was 10.3 m before the conflict point.

Method of processing closed-circuit television digital images for poor visibility identification

This study proposes a method for identifying poor visibility under adverse weather conditions by processing closed-circuit television (CCTV) digital images. The weighted intensity of the power spectrum (WIPS) was examined to determine its applicability as a value for the identification of poor visibility. The magnitude of WIPS represents the difference in spatial frequencies within the image on the basis of the human contrast sensitivity function. WIPS was calculated by the following image-processing procedure: the spatial frequency of the cutout image was calculated with a two-dimensional Fourier transform, and the power spectrum of the cutout image was calculated; WIPS was totaled at spatial frequencies that ranged from 1.5 to 18 cycles per degree. Two kinds of experiments were performed to determine whether WIPS represented the subjective visibility assessment values (SVAVs) given by the test subjects. Clear linear relationships between WIPS and SVAVs were found in both experiments. In addition, the tw...

DEVELOPMENT OF VISIBILITY ASSESSMENT METHODS WITH DIGITAL IMAGES UNDER FOGGY CONDITIONS

Basic methods are proposed for assessing poor visibility by using digital images from a road monitoring camera. An experiment was performed over 5 days in 2002 under artificial fog at a laboratory of the National Institute for Land and Infrastructure Management in Tsukuba, Japan. Twenty-one Landolt circles were prepared as targets, each with a different variation of Landolt circle (7 circle sizes X 3 circle-contrast levels). Digital image (8 bits, red-green-blue), illuminance, and transmissivity under artificial fog were recorded together while five subjects assessed the visibility of the circle. First, the digital contrast of the Landolt circle was examined in a digital image in terms of its applicability as a visibility assessment value. Second, the average intensity of grayscale (AIG) of the entire cutout image was examined in terms of its applicability as a visibility assessment value. The magnitude of AIG represented the difference in digital intensities within the image. Digital contrast and AIG were compared with the subjective visibility assessment values (SVAV) given by the subjects. During fog, both digital contrast and AIG increased as transmissivity increased. Relationships were found between both these values and SVAV. However, when digital contrast was used, the relationships depended on circle size. When AIG was used, the relationships depended on SVAV and not on circle size or circle-contrast level. These results suggest that AIG might be more appropriate than digital contrast for assessing subjective visibility level during fog.

Field Study of Driver's Curve-Detection Performance in Daytime and Nighttime

Effects of road scenes and traffic-control devices on driver’s curve-detection performance were investigated. Field experiments were conducted on a 19-km section of highway running through a hilly area in Hokkaido, Japan. The driver obtained directional information from the road scene ahead and traffic-control devices at the beginning of the target curve. Road scene characteristics were determined subjectively. Configurations of traffic-control devices at 32 curves were obtained from the road maintenance database and were measured on site for each curve. Each of the 17 participating subjects drove an instrument-equipped vehicle and pressed a button as soon as he or she recognized the direction of the target curve. Detection distance of each curve was measured. The experimenter determined the maximum detection distance (MDD) of each target curve. A curve-detection index, defined as the detection distance divided by the MDD, was used to compare detection performance for each curve. Characteristics of detection performance for the curves were determined by a cluster analysis and regression analysis. Curves were classified into five groups according to the results of the cluster analysis. Results of the within-subject regression analysis revealed that subjects driving in the daytime obtained directional information about the curve from the road scene, whereas in the nighttime the lighting midway through the curve had a greater effect on detection performance. Results indicate that visual cues should be considered when traffic-control devices are installed at a curve, and appropriate traffic-control devices should be selected to increase the detection performance of a curve.

Visibility of Laser Beams and Illuminated Delineator as Function of Fog Density

In dense fog, adequate visibility of the delineator is important for providing the driver with road geometry cues. A new illuminated delineator that uses laser beams is proposed. Very few data have been published with regard to the visibility of laser beams in fog. However, laser beams can be expected to be highly visible in dense fog because of their high intensity, high energy, and directivity that is both monoclinic and strong. A study was conducted to evaluate the visibility of laser beams in fog. The effectiveness of two types of laser heads and an illuminated delineator containing two 10-W glow lamps was investigated in artificial fog. The dependent variables were luminance at a specific point on the laser beam and estimated brightness. The major independent variables were fog density and illuminance in the observation room. The laser beams were observed as sharp lines of light in dense fog. The visibility of the laser beams in fog had an inverse relationship to that of normal light. In addition, subjects reported that the directivity of the laser beams could effectively indicate the direction of the highway. However, the visibility of the laser beams was strongly affected by the illuminance in the observation room, and care must be taken to prevent drivers from looking directly at redundant laser beams. On the basis of these results, it is concluded that laser beams may be useful lighting sources in dense fog if this safety problem can be overcome.