Comparative Evaluation of Reported Speeds from Corresponding Fixed-Point and Probe-Based Detection Systems

Abstract

Point-based traffic sensors, such as microwave radar and acoustic sensors, provide the valuable capability of sampling the entire traffic stream. However, full network coverage with point sensors requires a significant initial capital investment and ongoing maintenance expenditures. Probe-based sensors can cover an extensive roadway network at a much lower cost because roadway-based field equipment is not required. Decisions regarding the relative level of point sensor- versus probe-based deployment for traffic monitoring involve evaluating the trade-off between the value of comprehensive detection versus total system costs. An essential step in evaluating this trade-off involves directly comparing collocated point sensor and probe vehicle systems to understand how the derived traffic stream measures from the two approaches differ. This study compared 5-min speeds from microwave radar and acoustic sensors with link speeds from Global Positioning System (GPS) probes for both directions at five freeway locations. Systematic differences were found at one location. Floating car GPS runs were performed to confirm that the systematic error lay in the point speeds. The speed differences at all sites were normally distributed, with three locations indicating a mean speed difference greater than 5 mph. Nonsystematic speed differences were identified; the difference was more than 1.5 standard deviations lower than the mean difference. This difference may indicate inherent inaccuracies in reported GPS speeds under heavy congestion, including instances of time lag in recovering from congested speeds.

Estimation of Hourly Traffic Flows from Floating Car Data for Vehicle Emission Estimation

“…However, Hu et al [28] reported that the magnitude of correlation varied with GT speeds for the arterials, ranging from −0.236 to 0.360, and the highest correlation was observed when the speed was between 40 and 45 mph. Chase et al [29] reported that the speed differences were normally distributed with a mean speed difference greater than 5 mph, and the nonsystematic differences were found to be caused by the time lag in recovery from slow speeds, which had an impact on the speed-flow relationship. Kim et al [30] evaluated INRIX speeds over a two-month period, including recurrent and nonrecurrent events.…”

Methodology for Calculating Latency of GPS Probe Data

“…Liu et al (3) observed a clear latency for reporting GPS-based data as well. Chase et al (4) further stated that GPS-probe data has greater latency when travel speed recovers after peak period, than the beginning of a peak period. None of these papers proposed a detailed quantitative latency measurement methodology.…”

Stereo vision-based real-time localization of electric vehicle battery in the complex environment

“…Microwave radar detection is highly accurate even in the foggy or rainy weather, [5,6] but it does not support multidirectional distance CONTACT Jing Chen cj@hdu.edu.cn measurement and the sensors are expensive. [7] Laser radar is accurate and cheap, [8] but prone to be affected by light rays. [9] The sensor performance will be degraded in the rains.…”