INVESTIGATING HEAVY VEHICLE ROLLOVER CRASHES AND THE INFLUENCE OF ROAD DESIGN

BY USE OF VEHICLE SIMULATIONS – A CASE STUDY IN NORWAY

Presented by Johan Granlund, WSP Sweden

Co-authors:

Rolf Mellum & Marius Hansen Raddum, both at Accident Investigation Board Norway

Rob Di Cristoforo, Advantia Transport Consulting, Australia

Rollover Crash at the Access Ramp to the E6 Freeway

Photo

: S

tein

Johnsen

E6 speed limit: 100 km/h.

Outline

Aim: Show benefits of vehicle simulation to crash investigation.

Case study of E6 rollover crash:

• Laser scanning road properties.

• Reviewing road design codes for access ramps to freeways.

• Assessing rollover stability of the crashed vehicle.

• Computer aided rollover reconstruction.

Feasible future applications for vehicle simulations:

1. Validation of safety for planned road designs.

2. A tool in curve speed & attention management.

Road Geometry & Pavement Condition

Crash site measured with high speed laser/inertial Profilograph.

Pavement in fairly good condition; low roughness & normal texture.

Several road geometry parameters where remarkable:

• Steep ramp with max negative gradient -10.4 %.

• Egg-shaped curve, radius tightens from about 56 m to 36 m.

• Crossfall only 5 % in the steep & sharp corner w. rollover initiated.

• Following HVTT13-paper by Granlund et al, rollover-critical CoG-

height was less than 1.7 m at the recorded rollover speed 49 km/h.

Review of Road Design Codes

WSP reviewed both Norwegian and Swedish codes for design,

maintenance and operation of access ramps to highways.

The overall conclusion was that the road standards in both countries

lack considerations to heavy vehicle dynamics.

Regarding crossfall & superelevation in curves, the study calls for

harmonization of requirements between construction of new roads and

maintenance of existing roads.

Requirements on superelevation should be designed as a function of

speed limit in Norway, as per international practice.

Vehicle Combination “Truck and Dog”

Crane at rear of truck.

Total vehicle length was 22.5 m.

GVW 60 tonnes, of which 38 tonnes timber log payload.

Photo: Stein Johnsen

Proper Values of Static Rollover Threshold (SRT)

SRT was assessed with a “tilt table” in the TruckSim® software.

The result showed SRT = 0.40 g for the trailer and SRT = 0.46 g for the

truck. Both values are much higher than the reference 0.35 g SRT, so

the vehicle combination had proper rollover stability.

Computer Aided Rollover Reconstruction

TruckSim® model was setup for the crashed vehicle combination´s

parameters regarding geometries, masses, stiffness, damping etc.

Input:

• Road geometry from

laser/inertial Profilometer.

• Speed profile from the

truck telematics log.

Result: Reconstructed rollover.

Load Transfer Ratio (LTR)

A reference value for vehicle operation with fair margin to rollover:

Load Transfer Ratio < 0.60.

Assessing Max Safe Speed

The TruckSim® model was run

with iteratively lowered speed,

until passing LTR < 0.60 limit.

Result:

Max safe HGV speed = 33 km/h.

Operational safety issue:

33 km/h is a very low ramp speed,

when merging the HGV with 100 km/h

E6 freeway traffic.

AIBN Safety Recommendation

The investigation of the timber accident on the access ramp to the E 6 revealed that the requirements in relation to road design does not take adequate account of the road's function for heavy and large vehicles.

AIBN Safety Recommendation ROAD No 2015/09T:

The Accident Investigation Board Norway advises that the Norwegian Public Roads Administration review its requirements in relation to the design and execution of access ramps in light of the function of the stretch of road for large and heavy vehicles. Internet: Report on incident near Svinesund in Østfold county on 5 May 2014 | aibn

Feasible Applications for Vehicle Simulations (1):

Validation of Safety for Planned Road Designs

By tradition, road design codes provide requirements of one road property a time.

Consequently, evaluation of road designs are made “one factor a time”.

However, real world safety is a function of all parameters together, in 3D.

Example:

Limit values for superelevation are set without respect to longitudinal grade. However, cornering stability at grades require larger superelevation than in flat terrain.

Vehicle simulations can be used to verify safety before the road is built, and can identify improper road designs with need for improved safety.

Feasible Applications for Vehicle Simulations (2):

A Tool in Curve Speed & Attention Management

Vehicle simulations can aid identification of hazardous existing curves and decisions on enhanced speed & attention mgmt.

Actions may include installation of curve warning or advisory speed signs for heavy vehicle drivers approaching access ramps, exit ramps, roundabouts and sharp curves.

Such approaches are in line with both Vision Zero and Safe System methodologies, advising predictability and consistency in the road system.

Efficient C.S. & A. Mgmt. is of increased importance if increasing vehicle weights without increasing vehicle length, thereby raising the CoG-height and the risk for severe rollover crashes.

Summary

Aim: Show benefits of vehicle simulation to crash investigation.

Case study of E6 rollover crash:

• Laser scanning road properties.

• Reviewing road design codes.

• Assessing rollover stability.

• Computer aided rollover reconstruction.

Feasible future applications for vehicle simulations:

1. Validation of safety for planned road designs.

2. A tool in curve speed & attention management.

Acknowledgement

Thanks to Daniel Nolan and Adam Ritzinger, Advantia Transport Consulting, for valuable contribution in the crash reconstruction work.