Data Quality

Data must be timely and accurate and cover most of the corridor for the model to generate meaningful results. Data quality affects network modeling and calibration, estimation of origin-destination trip patterns, evaluation of response plans, and more. The quality of the work thus depends directly on the quality of the data:

  • Missing data reduces situational awareness and the ability to locate routes with available capacity.
  • Bad data can lead to bad management decisions and worse traffic.

Ensuring data quality is therefore an ongoing requirement for an ICM system. Key aspects to consider include:

Basic detector health Data accuracy
  • Do we know and agree where the sensors are?
  • Are the sensors labeled and configured correctly (no sensors on the wrong side of the freeway, no HOV sensors mistaken for mainline sensors, etc.)?
  • Do the sensors capture a full cross section of traffic flow?
  • Are the sensors turned on and communicating data regularly?
  • Is the data provided by a detector trustworthy?
  • When we compare traffic flowing into and out of each section of freeway, do the numbers make sense (flow balance)?
  • Are data consistent with traffic engineering expectations?

The process the Connected Corridors team used to address these questions is described briefly in Processing Received Loop Data for the ICM System.

Freeway Data

Since August 2016, members of Caltrans System Monitoring Team and PATH meet weekly to review freeway data quality and implement improvements. Data quality tools have been created to track average weekly loop sensor availability from Caltrans Performance Measurement System (PeMS). Every week, the tool automatically updates the aggregated status of each sensor category along I-210, I-605, and SR-134 within the corridor pilot area, as well as a section of I-10.

The team has been able to correct problems and help to install additional detectors so that data can be obtained from all lanes. One example of a problem that was fixed through close monitoring was sensors being labeled on the wrong side of the road, or as an HOV or mainline, when they were the opposite. The team also corrected configuration issues between PeMS and the Active Traffic Management System (ATMS) that prevented data from being reported to PeMS.

While the numbers are improving overall, construction projects in the corridor have caused large sections of sensors to go offline during the construction period. The CC team’s goal is to bring these sensors back online as quickly as possible following the construction period.

Arterial Data

Arterial data is collected from all of the stakeholder cities and LA County. The team regularly processes and reviews detector health reports with traffic flow data collected from loop detectors. Much of this data is currently available through the sensor monitoring tool making it easier for the CC team to quickly see the sensor health of the entire corridor. The team also collects signal phasing information which includes green light times and cycle lengths. Since the team does not have the ground-truth data from video recordings, the team has developed a set of criteria to determine whether the retrieved data is accurate.

The connection for the data to be transmitted through each stakeholders’ network was first established with the City of Arcadia in 2016. Their current detector health is now around 80% and improvements are continuing to be made. The County’s connection is through the Information Exchange Network (IEN) which sends data for itself, and the cities of Duarte and Monrovia. Both the County and City of Pasadena connections are now functioning with the goal of having a stable connection (meaning weekly data transmissions) in the near future.

Detector health reports are reviewed with stakeholders so that the data can be improved. Problematic detectors are identified and repairs are underway for numerous locations.

Both the quality and quantity of the data is important to the team. Incomplete sensor coverage and low detector health make it difficult to model the data and develop effective response plans. Thus the team is making every effort to improve the quality and quantity of the data wherever possible. The stakeholders’ commitment to data quality, and ultimately success for Connected Corridors, remains crucial to this effort.


Additional information on data quality can be found in the AMS Phase 2 presentation.