Mini Master Highlights

6: Traffic Data for Operations

Highway Operations is to operate existing highway facilities to achieve their fully designed and constructed potential through a broad range of measures and activities but without significant physical earth moving efforts. Operations rely heavily on determining Travel Time Reliability.

Travel time reliability refers to the consistency and dependability of travel times from day to day, helping travelers manage unexpected delays. This is quantified using three key metrics: the Travel Time Index, which compares average peak travel time to free-flow conditions to show overall congestion; the Buffer Time Index, which represents the extra "time cushion" (as a percentage of the average) travelers add to ensure on-time arrival 95% of the time; and the Planning Time Index, which represents the total travel time needed (including both typical and unexpected delay) relative to free-flow speeds. Together, these measures allow drivers and planners to account for both average conditions and the worst-case delays experienced on a route.

The measures and activities for traffic operations include demand management, traveler information system, Automated Traffic Signal Performance Measures (ATSPMs), incident management and other activities.     

Topic # 6-1: Transportation Demand Management (TDM)

Transportation Demand Management, also known as TDM, is a set of policies, strategies, and methods that aim to maximize traveler choices.

All efforts are aimed at minimizing, reducing, and balancing traffic flows on the highways. Traffic data, such as the ones listed below, are often used to measure and gauge the effectiveness of such efforts.

Vehicle Occupancy

The number of people in a vehicle. Reducing single-occupancy vehicle trips is often the goal.

Transit and Other Micromobility Modes

The modal share information provides insights regarding travelers' choices among auto, bus, bike, and other travel modes. Percentages of travelers using auto vs. other modes are often used to gauge program effectiveness

Tolls and Fees

By implementing congestion pricing, parking fees, and other tolls, agencies generate revenue while simultaneously reducing and balancing traffic flow. To evaluate the effectiveness of these pricing strategies, planners typically monitor changes in VMT and AADT.

Topic # 6-2: Traveler Information Systems

Traveler Information Systems provide real-time or near-real-time updates to the public on current traffic conditions, incidents, speed, and travel time. Information may be delivered pre-trip (e.g., websites, apps), in-vehicle (e.g., GPS routing), or roadside (e.g., dynamic message signs). These systems enhance situational awareness and enable travelers to make informed routing decisions. Traffic data supporting this process includes:

• Travel time
• Traffic volume
• Vehicle speed
• Incident detection
• Incident condition
• Mode-specific data (e.g., auto, truck, bicycle)

Topic # 6-3: Optimizing Traffic Signal Timing and Synchronization

Traffic signal optimization and synchronization are essential for improving traffic flow, reducing congestion, minimizing stops, and enhancing road safety. FHWA's Traffic Signal Timing Manual provides a list of key traffic data items as illustrated below.

Traffic Volume

Number of vehicles approaching the intersection in a given time.

Vehicle Speed

Average speed of vehicles on a road segment.

Queue Length

Number of vehicles waiting at an intersection.

Vehicle Classification

Classes of vehicles (e.g., cars, trucks, buses).

Occupancy

The percentage of time a detector is occupied by a vehicle.

Pedestrian and Bicycle Counts

The volume of pedestrians or bicycles.

Signal Timing Data

Current signal phase and timing at intersections.

Topic # 6-4: Ramp Metering

Ramp metering controls surges in traffic demand by regulating entry onto a roadway segment, typically via ramp signals or arterial gates. Dynamic systems use real-time traffic flow performance metrics to adjust metering rates, while static systems rely on historical traffic demand and periodic monitoring. Traffic data supporting this process includes:

• Historical demand traffic volume data.
• Real-time traffic volume and system performance.
• Observed facility conditions in terms of queueing and delay.

Topic # 6-5: Incident Management

Traffic Incident Management (TIM) is the ability to detect traffic incidents and crashes and respond effectively to ensure smooth operation of highways, minimize delay, improve travel time reliability, and save lives. Traffic data plays a critical role in this process and is discussed below.

Incident Detection

Real-time traffic speeds, volumes, and occupancy data:  identify abnormal congestion or stopped traffic. Automated Incident Detection algorithms analyze traffic data to trigger alerts.

Verification

Traffic video and sensor feed data verify the incident type, location, severity, and lanes affected.

Response Coordination          

Data informs dispatch of emergency responders, tow trucks, traffic control personnel, and maintenance crews. Traffic volumes and speed guide selection of alternate routes for responders and travelers.

Traveler Information 

Updated travel times and congestion data feed dynamic message signs (DMS), 511 phone and web systems, mobile apps, and navigation platforms. Real-time info encourages drivers to use alternate routes or modes.

Clearance & Recovery

Continuous monitoring of post-incident traffic flow. Detects whether lanes reopen or if residual queues persist, guiding adjustments in traffic controls. The four national TIM performance measures are:

• Roadway clearance time (RCT) is the time between the first recordable awareness of the incident to time all lanes open for traffic flow.
• Incident clearance time (ICT) is the time between the first recordable awareness of the incident to the time at which the last responder has left the scene.
• Secondary Crash is a crash that occurs at the scene of an original crash or in the queue, including the opposite direction.
• Responder Struck By records any instance that a responder is struck by a vehicle while working the scene of an incident.

Performance Evaluation        

Archived incidents and traffic data help analyze incident response times, clearance durations, and recurring hotspot locations.