Overview of TIM Program
The Nevada Department of Transportation (NDOT) launched a unified TIM program in 2008. Nevada’s TIM program is a partnership of agencies and organizations that works together with the goal of reducing clearance times and secondary crashes. There are two primary TIM coalitions in Nevada: the Northern Nevada TIM Coalition and the Southern Nevada TIM Coalition, both of which focus primarily on urban issues. A statewide coalition was formed in 2012 to address TIM issues in rural areas of the state. Unique challenges faced by rural areas include the response time to incidents that occur in remote locations, wildfires, and the availability of resources.
The Regional Transportation Commission of Southern Nevada (RTC), through the Freeway and Arterial System of Transportation (FAST) system, is leading the efforts to collect, analyze, and report TIM performance in Las Vegas. FAST operators monitor and maintain traffic incident cameras and provide traveler information via dynamic message signs (DMS) along freeways throughout the Las Vegas area. NDOT also provides both a Freeway Service Patrol (FSP) and Incident Response Vehicles (IRV) in both the Las Vegas and Reno areas. The hours of operation for the FSP vary depending on the route. Figure 1 shows the routes and hours of operation for the Las Vegas area.
Figure 1. Las Vegas Metropolitan Area Freeway Service Patrol and Incident Response Vehicle Routes and Hours of Operation
Data Collection and Management
FAST collects its TIM performance measures data primarily through its dashboard system interface, which was built in-house to improve access to and ease of use of incident-related data. The database provides FAST with data that are ready to use. Prior to having this system, the data were in a raw format (CSV file), which made it difficult to get access to the data for analysis. The dashboard provides FAST with a graphical user interface that traffic management center (TMC) staff use to enter incident-related data, along with a powerful back-end database. Incidents are tracked using an incident entry screen that appears after an incident has been identified, either by TMC operators, 911 dispatchers, or FSP/IRV patrols. Figure 2 shows a screenshot of the incident entry screen in FAST’s database system. The data elements circled in red are those required to calculate two of the three national TIM performance measures, roadway clearance time and secondary crashes. The data elements circled in blue show those desired for conducting TIM performance analyses (e.g., incident type, number of lanes blocked, severity). The data in the database are stored automatically and can be queried in real-time.
Figure 2. Traffic Incident Management Performance Data Elements on Freeway Arterial System of Traffic Incident Entry Screen
FAST’s success lies in having good camera coverage and its internal database and dashboard, which provide data that are automatically processed and ready to use. The database has allowed FAST to take a big step forward in understanding the impact of incidents and TIM performance. The database and dashboard program came about as a combination of a strong champion that provided the vision, the desire at the agency level to get the data, and having available staff with the necessary skill set to develop the program. The process has evolved over time.
Performance Analysis and Reporting
FAST records and reports several TIM performance measures, including: time of vehicle removal to the shoulder (essentially roadway clearance time), number of incidents, number of incidents managed, number of incidents on the shoulder in 10 minutes or less, number of incidents that block two or more lanes, number of remaining incidents, travel time, and secondary crashes. Data for TIM are shared in a monthly report to the operational and management committee for TIM as well as to NDOT. FAST also allows the public to access real-time information through an interactive online dashboard and real-time traffic camera website. A screenshot of the online public-facing dashboard is shown in Figure 3.
Figure 3. FAST Dashboard
FAST analyzes incidents against a “30-60-90” RCT calculation for NDOT using the following categorization of incidents:
- An incident meets the 30 minute roadway clearance criterion if it involves no injuries and it is removed from the travel lanes in 30 minutes or less.
- An incident meets the 60 minute roadway clearance criterion if injuries are involved and it is removed from the travel lanes in 60 minutes or less.
- An incident meets the 90 minute roadway clearance criterion if it involves a fatality and it is cleared in less than 90 minutes.
To aid with these calculations, FAST added a check box on the incident entry screen for TMC operators to indicate when an injury or ambulance is involved (see Figure 2). In addition, FAST archives CCTV snapshot images taken during the incident timeframe in 15-second intervals at the incident location, as well as of adjacent roadway segments, such as ramps or arterial streets (Figure 3). By reviewing these snapshots, analysts can examine the impacts of the incidents on the roadways to obtain additional details. FAST makes use of these snapshot archives to help generate reports to NDOT.
Figure 4. FAST Snapshot Archiving
FAST also uses heat maps to show the impact of an incident on congestion. A heat map is a graphical representation of data where the individual values contained in a matrix are represented as colors. An example of a heat map from FAST is shown in Figure 4. In this heat map, the colors represent the average speed along one corridor over a 24-hour period. It can be seen in the plot how using heat maps could aid in determining if a crash is a secondary crash, an approach that is favored by FAST over the TMC operators making the determination at the time of the crash.
Figure 5. FAST Heat Map of Average Speed
Benefits of TIM Performance Measurement
As a result of the collection and analysis of TIM performance measurement data, NDOT is able to calculate RCT and analyze performance against the “30-60-90” minute goals. This allows NDOT to track how often incidents meet the roadway clearance criterion, thus showing accountability for how the program is performing.
Another benefit of TIM performance measurement in Nevada is the ability to measure secondary crashes. By being able to track secondary crashes, NDOT can make efforts toward mitigating them in an effort to improve safety on roads for both responders and the traveling public.
 Nevada DOT, Freeway Service Patrol Program website, https://www.nevadadot.com/Traveler_Info/Freeway_Service_Patrol/Freeway_Service_Patrol_Program.aspx. Accessed March 24, 2016.