![]() Radar guns register only the fastest vehicle speed in the platoon, so there may be some upward bias. This average length varies according to the mix of autos and heavy vehicles present on the facility by time of day and direction. Single loop detector occupancies are converted to speeds based upon an estimated average vehicle length during the survey period. Recent technological advances such as vehicle signature and platoon signature matching, may allow measurements of elapsed time between stations. Technological variations include: single loop detectors, double loop detectors, portable machine double hose counters, radar, lidar, microwave, and infrared sensors, and video camera sensors. They are "location-based sampling" methods which suffer from the biases inherent in measuring speeds at a point and assuming the speed is applicable to other points on the roadway. Roadside sensors include in-the-road loop detectors, roadside radar, microwave sensors, video sensors, and infrared sensors. These techniques are very cost-effective at gathering large amounts of speed data for specific segments of the transportation system but cannot provide door-to-door travel times. Spot speed measurement techniques use roadside sensors to measure the instantaneous speeds of vehicles either at specific spots of the roadway or at specific times of the day. The Transportation Research Board Publication, Highway Capacity Manual, 2000 also provides some limited guidance on travel time, speed, and delay data collection in the appendices to Chapters 15 and 16 of the manual. ![]() The mechanics of employing many of these techniques are described in the Institute of Transportation Engineers publication, Manual of Transportation Engineering Studies, Edited by H. Trip maker tracking techniques are similar to vehicle tracing techniques but measure traveler trip times rather than vehicle trip times.Vehicle tracing techniques measure vehicle travel times only for a select portion of all trips.Spot speed measurement techniques measure vehicle speeds only for a given point of geography or a given point of time.There are numerous speed and travel-time measuring techniques, but they can all be grouped into three large categories according to their method of sampling the travel-time universe. The FHWA publication number FHWA-PL-98-035, Travel Time Data Collection Handbook, dated March 1998, prepared by the Texas Transportation Institute provides a complete overview of techniques for gathering travel-time data (see ). Then the v/c for any other period can be estimated by taking the ratio of the counted demand to the observed capacity. Volume/capacity (v/c) ratio cannot be measured in the field unless there is a time period when the facility is observably at capacity. The measurement of these performance measures in the field is described below in the following sections. ![]() For arterial streets it is mean speed of through traffic. ![]() For two-lane rural highways it is percent time delay. For freeways it is density in terms of equivalent passenger cars. The Highway Capacity Manual to date has used single field measurable performance measures for level of service. This chapter identifies how field measurements are processed to estimate the eight MOEs selected for further investigation in the previous chapter. Traffic Analysis Tools Measures of Effectiveness 3.0 Field Measurement of MOEs ![]() Definition, Interpretation, and Calculation of ![]()
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