SARF/IRF 2014 | 2-4 September, South Africa

Implementing PBS in the Design of Heavy

Vehicles in South Africa

F Kienhöfer University of the Witwatersrand (Wits)

R Berman Wits / CSIR

R Benade Wits / CSIR

P Nordengen Council for Scientific and Industrial Research (CSIR)

Billing J (2008) Evaluation of the Dynamic

Performance of Truck-recreational Trailer

Combinations

Transport is a conflict between

PRODUCTIVITY vs SAFETY?

Driving at a low speed is safe but travel time is longer and

productivity is lost.

Driving at a fast speed is unsafe but travel time is shorter and

productivity is gained.

Heavy Vehicle Weights and

Dimensions

Heavy vehicle weights and dimensions also a

compromise between PRODUCTIVITY vs SAFETY

What makes a vehicle safe?

Canadian Vehicle Weights and

Dimensions Study (1984-1986)

• Testing and simulation

• Vehicle characteristics affecting safety

• RTAC, CCMTA, UMTRI, Carleton University

• Developed 7 safety performance measures

• Guide to specifying weights and dimensions

† Billing J (2008) Evaluation of the Dynamic Performance of Truck-recreational Trailer Combinations

†

PBS (Performance-based Standards)

• Regulate the safety performance rather than

weights and dimensions.

• What the vehicle

looks like

• What the vehicle can do

Prescriptive Legislation Performance-based

Standards (PBS)

Regulate height, mass & length Regulate safety and road wear

directly

Profitable

Roads Safe

Vehicle design

Profitable

Roads Safe

Vehicle design

PBS (Performance-based Standards)

– Improved safety

– Higher productivity

– Reduced road wear

– Reduced fuel usage

– Reduced CO2 usage

Australian NTC develop a PBS

regulatory framework

• Sixteen performance measures

• Six manoeuvres: 90° turn, uneven road

surface, a pulse-steer, a constant radius turn

at slowly increasing speed or tilt table test,

lane change, gradient tests

• Four levels

PBS History in South Africa

• PBS steering committee

• Letter of support from Minister of Transport

• PBS steering committee adopts Aus. PBS

framework

• Sappi and Mondi demonstration projects

(used Aus. consultants)

• RTMS-scheme prerequisite

• South African consultants developed

Longitudinal Performance

• Startability

– engine size

• Gradeability A

– traction

• Gradeability B

– engine size

• Acceleration Capability

– gearing, coefficient of drag, engine inertia

† http://fleetwatch.co.za/

†

Low-speed Directional Performance

• Low-speed Swept Path

– road width used

• Frontal Swing

– swing out of front - DoM and MoD

• Tail Swing

– swing out of back

• Steer-tyre Friction Demand

– tyres won’t saturate

† http://www.nzta.govt.nz/

†

Dynamic Performance Measures

• Trackability on a Straight Path

– amount of swaying on a rough road

• Static Rollover Threshold

– rollover

• Rearward Amplification

– whipping from an evasive lane change

• High-speed Transient Offtracking

– swing out from an evasive lane change

† http://www.nzta.govt.nz/

†

Evasive Lane Change

Pulse Steer Manoeuvre

Safety Performance Evaluation

Wits

Wits

ARRB

Safety Performance Evaluation

Completing PBS Assessments

• Lesson 1

– tyre data are impossible to get hold of

• Lesson 2

– auxiliary roll stiffness data are almost impossible

to get hold of

• Lesson 3

– the Aus. longitudinal performance limits are too

strict

Completing PBS Assessments

• Lesson 4

– tail swing swing-out is measured relative to the

entry path tangent

• Lesson 5

– use a tilt table to measure SRT

Designing Safer Vehicles

• Lesson 1

– lowering CoG – underslung/overslung, air-susp.

• Lesson 2

– increasing auxiliary roll stiffness by adding anti-

roll bar or anti-sway bar can increase SRT

• Lesson 3

– reducing wheelbases and adding articulation

points has drawbacks in stability

Designing Safer Vehicles

• Lesson 4

– super singles versus dual tyres

• Lesson 5

– large rear-overhangs cause tail swing problems

Vehicle

type

Rear Overhang Tail Swing

Australia

ADR 43/04

South

Africa NRTR

Australia

PBS Level 1

South

Africa NRTR

Rigid truck 3.7 m 5.01 m 0.30 m 0.60 m

Semitrailer 3.7 m 6.32 m 0.30 m 0.87 m

Tag-trailer 3.7 m 7.00 m 0.30 m 1.25 m

Designing Safer Vehicles

• Lesson6

– Truck rigid drawbar trailer – good traction, low

offtracking

– B-double – good stability, versatility

Three South African Strengths

• Through RTMS we collect productivity as well

as safety data

• We are on the cutting edge of assessing road

wear

• We have a young talent pool involved in PBS

Automated Design

Performance

Based

Standards

Current SA

Standards

Collaboration / Learning

ACKNOWLEDGEMENTS