Travel Time on Arterials and Rural Highways: State-of-the-Practice Synthesis on Arterial Data Collection Technology
This report discussed current and emerging technologies used to detect travel times and improve traffic management on arterial roadways. A broad range of technologies were reviewed including Bluetooth detectors, toll tag readers, in-pavement magnetic detectors, automatic license plate readers (ALPR), machine vision, connected vehicle systems, radar/microwave/LIDAR, inductive loops, crowdsourcing, and cell phone signal monitoring.
To assess state–of–practice and identify lessons learned from experience a literature search was conducted. The following lessons highlighted experience from deployment of arterial travel time (ATT) systems in three cities.
Chandler, AZ (Bluetooth deployment)
This technology uses a wireless Bluetooth reader to communicate with in-vehicle devices programmed to pair with other Bluetooth devices. Matching Bluetooth handshake data (randomized for privacy) can be used to estimate travel times across the network. Researchers noted the following.
- Take advantage of open-source software. The Intelligent Roadway Information System (IRIS) software developed as part of the automated system used to post travel times on DMS was developed by a reputable agency and well documented. Open-source products can reduce development time and allow for customization without the need for advanced coding skills.
- Conduct preliminary tests (mockups) to improve requirements definition. Preliminary testing helped the agency better understand the capabilities and limitations of the technology, and better define functional requirements for proposed work.
- Weigh options across multiple vendors. In the case of Bluetooth detection, there are multiple vendors whose detector packages have a range of prices and services to support data visualization and processing functions, pricing, and services.
- Maintain backup servers and limit exposure to system failures. Keep servers local to improve oversight and explain issues associated with downtime (i.e., local storm power outages).
- Use the travel time data collected for multiple purposes. Data archives can improve analysis of travel patterns and trends. Makes travel time data available to public and private entities.
- Work with media outlets early in the project to minimize the likelihood of misleading stories regarding privacy. When the Bluetooth detection system was unveiled in Chandler, some media outlets referred to it as a tracking system, which caused some public concern.
St. Louis, MO (magnetometer deployment).
This system used an array of five in-pavement sensors at each detection station across the network at 1 to 1.25 mile increments to detect and match vehicle magnetic signatures and determine travel times. Researchers noted the following.
- Deploy the system incrementally. Enable time to identify issues and "fine-tune" the system.
- Use observation and experience to verify travel times provided. Tweak the processing algorithms on an ongoing basis.
- Keep accurate implementation and asset management records. Keep records so not to lose sensors to repaving or other construction efforts.
Essex County, UK (ALPR camera deployment)
This technology uses video image processing to read and match license plate numbers to determine roadway travel times. In Essex, more than 80 ALPR cameras were installed on arterial roads. Travel times were more difficult to calculate on urban arterials than on highways due to complex traffic patterns. Researchers noted the following.
The capabilities and limitations of APLR camera technology must be well understood to ensure that they are used effectively.
- Place cameras with consideration given to the origin-destination of traffic flow to increase matches and calculation of travel times.
- Aim cameras precisely to enable license plates to be read at a high rate of accuracy.
- Maintain operator vigilance of the camera feed. While data collection technologies can be configured to report faults to authorities, not all problems are identified as faults. For example, if an ALPR camera is bumped so that its field of view changes, it will still function, but will not be capturing data appropriately.