Objective

We would like to improve the quality of loop detector data collected by the TMC. There are many causes of bad data. Some are caused by deteriorated installations such as a broken loop which requires construction to fix; some are due to crosstalk, low Q, low Meg, etc. It's possible that a number of these problems can be solved by replacing existing 222-type detector cards with the IST cards. In the first phase of this project, we will evaluate whether and how much data quality can be improved, and under what conditions, by simply replacing existing detector cards with the IST cards, while leaving the rest of the data collection system intact.

While a simple replacement may offer a quick improvement in data quality, a more powerful configuration that includes a PC and communication link may offer even more benefits. In the second phase, we will install IST systems in this configuration at selected locations and investigate advanced applications that can be supported. For example, problems with the current data collection system can be diagnosed by having a direct connection to the detectors. Also, since the remote PC would be much more programmable than the existing 170 controllers, it can fully exploit the capabilities of the IST detection system and provide higher fidelity data than currently available. Such data could further enable such advanced applications as vehicle classification and the direct measurement of link travel times.

Motivation

Traffic data are becoming widely used for performance measurement and freeway control. Loop detectors provide the majority of traffic data in California. Many loop detector stations are old and may have deteriorated, reducing the data quality at the TMC. If existing detector cards are used, some of these conditions can be fixed only by expensive construction to fix the installation or correct electrical problems. However, it is possible that a more advanced detector card can measure traffic even with deteriorated installations. This is an attractive alternative to repairing physical installations because it involves only replacing the detector card. Also, existing detector cards require complex manual adjustments. Some data errors may be caused by cards that are not configured correctly. The IST card requires little calibration and does not suffer from this problem.

The IST card are able to measure distinct vehicle signatures, which, when processed with the appropriate software, produce vehicle classifications and direct measurements of link travel time. This information is important in performance measurement, traveler information, and planning. Because the required processing exceeds the capabilities of the existing data collection system, a PC and communication link are needed to enable these applications in phase 2 of this project.

Methodology — Phase 1

We will perform a before-and-after study of data quality to assess the benefit of the IST-222 cards. On December 10, 2003, members of the CCIT met with District 4 Maintenance and Operations teams, who are in charge of the loop data collection system. They expressed an interest in being able to improve data quality without physical repairs of the loop installation. They have some experience with the IST cards and said that the IST cards improves data quality over existing cards in some conditions. They have agreed to help identify candidate locations in D4 as well as performing the installation. The following are tasks for this phase.

1.   Define data quality metric
First we need to define how data quality is measured. PeMS already has some measures of data quality in order to analyze the data. We will work with the district in finalizing the criteria to measure.

2.   Identify candidate locations
We will identify the locations where the cards will likely be useful. For example, locations that have no power or communications should not be considered; locations that are reporting good data do not need any improvement.

3.   Collect before data
While PeMS stores historical data, we need to make sure the "before" data are available from the candidate locations before we install the new cards.

4.   Install detector cards
District 4 will install the IST-222 cards at the designated locations.

5.   Analysis
CCIT will collect the "after" data from PeMS and perform the before and after study of data quality at the locations where the detectors were replaced. This study will determine whether the replacement improved data quality. These data will also allow us to further categorize the malfunction conditions and identify those conditions for which the IST-222 cards are most beneficial.

Methodology — Phase 2

Phase 2 of this project investigates the additional benefits of a complete system that includes a PC and communications. These are the tasks.

6.   Identify applications
While the PC-based configuration offers many possible applications, we need to choose the ones to implement and test. An important function that they provide is the ability to diagnose the existing data path. We may explore other applications such as vehicle classification, travel time estimation, and origin-destination analysis.

7.   Identify installation locations
We need to identify locations to install the PC-based configuration depending on the application we have in mind. For example, to diagnose data path problems, we would place the PC-based system at a location where we are not getting good data; to measure travel time, we need one system at each end of the selected freeway links, where both locations need to meet conditions under which the IST system provides adequate data. These locations may be different from those chosen for Phase 1.

8.   Installation
The systems will be installed in District 4 by the Traffic Operations division.

9.   Data collection
Since the PC-based configuration bypasses the existing data collection system, the software that collects data from the field systems and supports the classification and travel time applications will need to be obtained.

10.   Analysis
We will evaluate the performance of the system in the selected applications. This also includes its ease of installation, maintenance requirements, and general applicability to TMC needs.