Naturalistic Study of Truck Following Behavior
Emily.Nodine@dot.gov, Andy.Lam@dot.gov, Mikio.Yanagisawa@dot.gov, Wassim.Najm@dot.gov Volpe National Transportation Systems Center US DOT
Timing and duration of tests
SPMD: One-year test (2012-2013) with 8 single-unit trucks and 10 drivers during the Safety Pilot Model Deployment (SPMD) IVBSS: 10 month test with 10 tractor-trailer trucks and 18 drivers as part of the Integrated Vehicle Based Safety System (IVBSS) project
Location(s) of tests
SPMD: Ann Arbor, Michigan IVBSS: Greater Detroit, Michigan area. Line haul routes went as far as northern Michigan and Ohio.
No automation. The trucks had forward collision warning (FCW) systems, but some of the FCW systems were based on V2V communications, and thus were active only some of the time.
Level of automation tested
Level 0. This was a study of naturalistic truck following behavior, intended to provide a baseline for the evaluation of automated truck platooning applications.
Tested use cases
”Following scenarios” were defined as constant speed, highway driving scenarios above 45 mph (72 kph) where trucks were following a lead vehicle that was less than 77 m (253 ft) away, for at least 20 seconds
Tested transport system
Single unit trucks and tractor trailers, operating on a highway
Purposes of testing
- Assessment of driver behaviour (human, vehicle) / road user behaviour
- Assessment of impacts on safety (short-term, long-term)
- Interaction with other traffic participants (automated vehicles, conventional vehicles, vulnerable road users)
- Objectives, as stated in the report, were to address the following questions: 1. How closely (time and distance) do trucks follow other trucks and light vehicles on highways? 2. How does this following behavior vary by highway type, road condition, weather, and visibility (day/night)? 3. Are there particular following safety events or conditions that should be considered when developing automation technologies? 4. At what following distances do vehicles cut in between the truck and the lead vehicle? 5. What is the safety impact of truck following at different headways?
Definition of baseline
Not applicable. This research is aimed at developing a baseline.
1. Define and extract “following events.” On highway, constant speed > 45 mph (72 kph), similar speed to lead vehicle at distance less than 253 ft (77 m), at least 20 seconds 2. Analyze video to validate the following event 3. Perform statistical analysis, including use of the Safety Impact Methodology (SIM) tool to assess rear-end crash risk given observed following distances and assumed driver response times.
Method of testing
Naturalistic field tests
Test fleet, participants and environment
Number and make of vehicles
SPMD: 8 straight trucks IVBSS: 10 instrumented 2008 International TransStar 8600 tractor-trailer trucks
Description and number of participants/drivers
SPMD: 8 professional truck drivers IVBSS: 18 professional heavy truck drivers
Tested environment and facilities
SPMD: Primarily on pickup and delivery routes in the Ann Arbor area IVBSS: Both Pick-up/delivery and line-haul routes based out of the Detroit area
Legal and ethical aspects
Duration of testing
SPMD: Trucks were driven 259K miles (417K km), of which 102K miles (164K km) were on highways. 17K following events were identified. IVBSS truck driving: 484K miles (779K km), of which 235K (385K km) were on highways. 18K following events were identified.
Input parameters and assumptions of simulation tests
- Communication data (V2V, V2I, V2U, etc.)
- In-vehicle cameras
- Map data
- Other cameras
- Sensor data
- Situational data (e.g. weather, traffic situation)
- System internal data
Specifications for the data sources
- In-vehicle cameras: Driver face, cabin (IP)
- Other cameras, specify: Forward view, left side, right side
- Communication data (V2V, V2I, V2U, etc.), specify: in SPMD, V2V
- System internal data, specify: vehicle dynamics (speed and acceleration of the truck)
- Sensor data, specify: information about forward vehicles and the vehicle’s location within their lane (using a vision-based ranging sensor)
Key Performance Indicators (KPIs)
Following distance Time headway Lead vehicle mean deceleration and acceleration Minimum distance Probability of a rear-end crash
Situational data available
Highway type, road condition, weather, visibility/lighting
Subjective data collected
Issues that affected the impact assessment
Trucks had forward collision warning (FCW) systems. In SPMD, the FCW depended on the other vehicle also being connected (V2V); another vehicle was in range only about 15% of the time. IVBSS trucks had FCW and headway advisory warning. Analysis of following behavior with and without the FCW systems being activated revealed no significant differences. Therefore, all data were used.
Tractor trailer trucks follow passenger cars at shorter distances and headways than they follow heavy trucks at distances under 60 mph, but follow other heavy vehicles at shorter distances and headways at speeds greater than 60 mph; truck drivers generally follow other vehicles at much shorter headways (around 2 seconds) than are recommended in state Commercial Driver’s License driver handbooks; vehicles rarely cut-in between two trucks who are following at a distance of 40 m or less; and crash risk increases considerably when trucks follow other vehicles at headways of less than 1 s. Other results: Lead vehicle decel: average ~1 m/s, 95th %-ile ~3 m/s Lead vehicle accel: average ~1 m/s Analysis with fast (0.3s) reaction time (assumed for AV), brings rear-end crash risk near zero.