10-11-2012, 05:15 PM
RESEARCH REPORT RR 5/96 Speed Control Devices for Cars
RESEARCH REPORT.pdf (Size: 364.95 KB / Downloads: 183)
Introduction
Background
The Ne w South Wale s (NSW) "Spe e d Manage me nt Program and Action Plan
(1995-96)" contains a range of tasks de signe d to re duce the incide nce and
consequences of speeding related vehicle crashes. Part of the vision of the Plan is to
achieve the situation where "vehicle design requirements and standards are conducive
to compliance with appropriate spe e ds". One propose d task is to inve stigate the
potential of speed limiters for cars and other light vehicles.
The Spe ed Management Program and Action Plan de fine s s p e e d i n g as "trave lling at
spe e ds which are e xce ssive , or which are inappropriate for conditions such that the
level of safe ty is unacce ptable ". Exce ssive spe e d is "trave lling in excess of the speed
limit". Inappropriate speed is "travelling at a speed that might be below the legal limit,
yet greater than suitable for the prevailing conditions".
Overview of speed control devices
The re is a range of ve hicle e quipme nt which can dire ctly and indire ctly affe ct
speed-related road crashes. A top speed limiter, which physically prevents the vehicle
from exceeding a pre-set maximum speed will mainly affect excessive speeding in rural
areas. An automatic speed limiter, which adjusts to the local speed limit could affect all
types of excessive speeding but requires some type of communication system with the
roadway in orde r to de te rmine the poste d spe e d limit. The se de vice s and othe r
e quipme nt, such as spe e dome te rs, cruise controls, crash re corde rs or ve hicle
monitoring devices, can also affect excessive and inappropriate speeding by influencing
driver behaviour or improving the information available to drivers.
Issues such as engine power, vehicle handling and braking performance are related to
spe e ding. The se issue s are , howe ve r, le ss like ly to have a positive affe ct on drive r
speeding behaviour and they were outside the scope of the project.
Current Technology
Speedometer
The speedometer is an essential item of equipment to enable the driver to control the
spe e d of the ve hicle . Spe e dome te rs have , of course , be e n fitte d to cars as standard
e quipme nt for many de cade s although the Australian De sign Rule 18 only re quire d
spe e dome te rs to be fitte d to ve hicle s manufacture d from the mid-1970s. The ADR
requires the speedometer to display speed in km/h to an accuracy of +/-10% (i.e when
the ve hicle is trave lling at 110km/h the spe e dome te r must display not le ss than 99
km/h). This relatively high tolerance could affect the ability of Police to enforce speed
limits and, with mode rn te chnology, it might be appropriate re vie w the tole rance on
underestimating speed. For example, in industry, a 2% tolerance is more usual for this
type of instrumentation. Speedometer accuracy is also affected by changing wheels and
tyres but these are not relevant considerations for a tolerance on newly manufactured
vehicles.
The ADR does not re strict the maximum scale value on the speedometer. Most cars
have a spe edomete r which re ads to 180km/h plus. Many popular high powe re d cars
have a maximum spe e d pote ntial in e xce ss of 200km/h. Whe n trave lling at the
maximum le gal spe e d limit in Australia (110km/h) the spe edomete r on most cars is
bare ly half-way around the scale . This practice adve rse ly affe cts discrimination of
readings in the range of interest (0 to 110km/h). It also gives a false impression about
t h e safe speed capabilities of the vehicle and it must have an adverse effect on drivers'
attitudes to speeding (indeed, it is conceivable that a motorist involved in a very high
spe e d crash could comme nce litigation against a ve hicle manufacture r for "false
labelling").
Speed Limiters
ADR65/00 "Maximum road spe e d limiting for he avy goods ve hicle s and he avy
omnibuses", applies to heavy trucks and buses manufactured from 1991. Speed limiting
is usually achie ve d through e ithe r e ngine manage me nt syste ms or add-on de vice s
which control throttle operation or fuel injector operation. Our investigations indicate
that either technology can be applied to cars and other light vehicles. Details of a brief
survey of manufacturers are contained in Appendix B and a summary is set out below.
Engine Management Systems
Many ne w cars are fitte d with e le ctronic e ngine manage me nt syste ms as standard
equipment. Most of these already have a pre-programmed top vehicle speed or could
be re adily adapte d with such a fe ature (a fe w are base d only on e ngine RPM). At
pre se nt the pre-programmed top spe e ds are we ll in e xce ss of statutory spe ed limits.
Although no estimates of costs of such a change were sought during the survey it is
expected that the cost of providing a realistic top speed limit (say 120km/h) into these
syste ms would be ve ry low - le ss than a dollar pe r ve hicle for popular mode ls in
Australia.
Automatic Speed Control
Most work on automatic cruise control systems is based on 'headway' - detecting the
speed and distance to the preceding vehicle and adjusting the vehicle speed to suit the
circumstances. Despite an extensive literature search no references were found to the
concept of a roadway system which informs the vehicle's cruise control system of the
statutory (or advisory) spe e d limit for a give n se ction on roadway. R e f e r e n c e t o
statutory speed limits is noticeably absent from the major ITS strategies.
An automatic spe ed limiting syste m which is base d on statutory spe ed limits can be
implemente d in the short te rm and the te chnology can be re adily applie d to curre nt
ve hicle s. Almqvist e t al (1991) and Hyde n (1993) de scribe the trial of a syste m in
Swede n. Pe nding the introduction of roadside transmitte rs at locations whe re spe e d
limits change , an e valuation was conducte d using obse rve rs in the ve hicle and the se
observers manually adjusted the speed limiter according the speed zone. The tests were
confine d to urban are as. The initial findings we re that ave rage spe e ds de cre ase d by
4.5% (which the authors suggest could lead to very high safety benefits), travel time
for an 18km trip increased by 33 seconds (2% increase), NOx emissions reduced by
5%, CO e missions re duce d by 1.4% and fue l consumption was unchange d.
Behavioural changes (mostly favourable) were also noted.