3. Test setup for far-side excursion
Far-side excursion scoring is only as credible as the test that produces the data. A far-side event is fundamentally different from a near-side impact: the occupant is loaded indirectly, through the belt and the seat, and is displaced across the cabin rather than into a structure. That means the test setup must reproduce three things faithfully — the lateral acceleration pulse applied to the buck, the restraint geometry that converts that pulse into occupant motion, and the occupant's starting position relative to the belt anchorages. Get any of these wrong and the excursion metric becomes a measurement of the fixture, not of the restraint system.
This chapter covers the practical decisions that define a far-side test: which crash configuration to run, how to build the sled pulse, which ATD to install, and where to place it. The emphasis is on the choices that materially change the excursion outcome, and on the evidence you need to record so the result can be defended later.
Vehicle crash configurations: what "far-side" actually means in a test matrix
In a vehicle-level test, far-side loading arises when the struck side is opposite the occupant. The two configurations that dominate regulatory and consumer programs are the oblique moving deformable barrier (OMDB) impact and the pole or rigid-barrier side impact with the occupant seated on the non-struck side. For excursion work, the OMDB configuration is usually the more demanding case because it combines a significant lateral ΔV with a yaw rotation of the occupant compartment, and that yaw is what drives the occupant across the seat rather than simply pinning them against the door.
When specifying a vehicle crash configuration, record at minimum: impact angle (commonly 15° or 20° from the vehicle's longitudinal axis for OMDB), barrier speed, barrier face geometry and stiffness class, overlap, and the vehicle's yaw rate history. The yaw rate is not a secondary parameter — it is the mechanism that produces relative lateral motion between the occupant and the seat. A test that matches ΔV but under-represents yaw will under-predict excursion.
Full-vehicle far-side tests are expensive and have poor repeatability for occupant kinematics because of build variation. Most excursion development therefore runs on a sled, with the vehicle test reserved for confirmation. The sled must be configured so that the occupant sees the same belt geometry, seat contour, and lateral pulse as in the vehicle.
Building the sled pulse and buck
A far-side sled is a lateral-pulse machine: the buck is accelerated laterally (or decelerated, depending on the rig's orientation) while the occupant is restrained only by the seat and belt. The pulse is derived from the vehicle test by integrating the compartment's lateral acceleration at the occupant's seating reference point, then reproducing it on the sled within the rig's capability.
A workable procedure for pulse development:
- Extract the lateral acceleration time history at the seat track or sill for the target vehicle configuration.
- Integrate to obtain lateral ΔV and compare against the vehicle-level target (for example, a 25–35 km/h lateral ΔV band typical of OMDB-class events — treat this as an illustrative range, not a specification).
- Fit a sled pulse whose ΔV matches within a few percent and whose peak acceleration and duration fall inside the rig's validated envelope.
- Verify with a rigid dummy or calibration buck that the achieved pulse matches the commanded pulse before installing the ATD.
The buck itself must carry the real seat, the real belt with production anchor locations, and the real buckle stalk. Substituting a generic sled seat changes the friction and contour that the occupant slides against, and that friction is a first-order term in excursion. If a production seat cannot be used, document the substitution and its expected effect on belt-to-occupant coupling.
ATD selection
ATD choice determines which excursion channels you can even measure. The table below summarizes the practical trade-offs for far-side work.
| ATD | Strengths for far-side | Limitations | Typical use |
|---|---|---|---|
| Hybrid III 50th male | Mature instrumentation, broad correlation base, well-understood head/neck response | Stiff lumbar spine; limited lateral compliance; poor biofidelity in lateral bending | Baseline comparison, regulatory-style runs |
| THOR 50th male | Improved lateral neck and thorax response; more realistic spine kinematics | More complex setup, fewer historical correlations, higher cost | Development and research programs |
| Hybrid III 5th female | Small-occupant excursion sensitivity; relevant to out-of-position and cross-cabin reach | Scaled response, limited lateral data | Occupant-size sensitivity studies |
| Q-series / child ATDs | Booster and child-restraint far-side cases | Narrow applicability | Child occupant protection programs |
For excursion scoring specifically, the ATD must be able to report head lateral displacement, head rotation about the vertical axis, and torso lateral displacement relative to the seat. Confirm before the test that the head CG accelerometer array and the angular-rate sensors are installed and that the ATD's neck is in the correct pre-test condition — a neck that has been left in a cold room or previously loaded will bias the excursion result.
Seating positions and pre-test positioning
Far-side excursion is evaluated for the occupant opposite the impact. In a left-hand-drive vehicle struck on the left, that is the right-front passenger; in a right-hand-drive vehicle struck on the right, it is the left-front passenger. Rear-seat far-side positions are increasingly included because the absence of a door-mounted airbag on the far side makes the belt the only lateral restraint.
Positioning procedure that should be followed and documented:
- Set the seat to the program-specified position (often the mid-track, design or nominal H-point position) and record fore-aft, cushion height, and backset.
- Set seat back angle to the specified value (commonly 25° from vertical for front occupants) and verify with an inclinometer on the head restraint posts.
- Place the ATD with the H-point within the program tolerance of the seat reference point, then apply the specified belt routing and pretension.
- Record belt payout, buckle engagement, and any gap between the ATD and the seat back before release.
The pre-test gap between the occupant's torso and the seat back matters: a larger gap allows the torso to build lateral velocity before contacting the seat, increasing excursion. Programs typically specify a small controlled gap or full contact; whichever is chosen, it must be consistent across the comparison set.
Instrumentation and evidence to capture
The excursion metric is only defensible if the supporting channels are recorded. At a minimum, log: sled/buck lateral acceleration (triaxial at the seat track), ATD head CG accelerations and angular rates, upper-neck and lower-neck loads, chest deflection (where the ATD supports it), belt force at the shoulder and lap, and high-speed video from both a lateral and an overhead view. The overhead camera is essential — it is the only channel that directly shows the cross-cabin trajectory that the excursion score is meant to quantify.
Typical failure symptoms and their likely causes:
- Excursion far below expectation: check that the belt is actually loading the torso (belt force channel flat), and that the ATD is not contacting the seat bolster prematurely.
- Excursion far above expectation: verify pre-test torso-to-seatback gap and D-ring offset; a mis-set D-ring is the most common cause.
- High run-to-run scatter: check ATD neck conditioning, belt payout consistency, and seat foam settling between runs.
The setup decisions in this chapter — configuration, pulse, ATD, and position — define the boundary conditions of every excursion number that follows. Recording them with the same rigor as the occupant response channels is what makes the eventual score reproducible and reviewable.