Memorandum by the Institute for Transport
Studies, University of Leeds (RTS 39)
INTELLIGENT SPEED ADAPTATION
1. INTRODUCTION
This memorandum, written in response to the
invitation by the Committee to submit material for the inquiry
on Road Traffic Speed, is focussed on how new technology in the
form of Intelligent Speed Adaptation (ISA) can assist in tackling
the problem of excess and inappropriate speeds. Over the last
few years, the technologies and systems that can deliver ISA have
matured to the point where ISA is now a completely practical proposition.
2. WHAT IS
ISA?
Intelligent Speed Adaptation (ISA) is a system
by which the vehicle "knows" the permitted or recommended
maximum speed for a road. The standard system uses an in-vehicle
digital road map onto which speed limits have been coded, combined
with a positioning system which could be GPS, ie the satellite
Global Positioning System, but could also be GPS enhanced with
map matching and dead reckoning. ISA can take various forms:
— In terms of intervention level, it
can be advisory (the driver is informed of the limit and of violations),
voluntary (the system is linked to the vehicle controls but the
driver can choose when to have the system enabled), or mandatory
(no override is possible).
— The speed limit information can potentially
be extended to incorporate lower speeds at certain locations in
the network and even in the future variation with current network
conditions, based on weather, traffic density, the presence of
incidents etc.
In addition to research in the UK, ISA trials
have taken place in Tilburg in the Netherlands and Aalborg in
Denmark. Large-scale trials are currently almost complete in four
locations in Sweden.
3. AN ISA TYPOLOGY
An ISA system can be characterised by how intervening
(or permissive) it is. Here the standard variants are:
1. Advisory—display the speed limit
and remind the driver of changes in the speed limit;
2. Voluntary ("Driver-Select")—allow
the driver to enable and disable control by the vehicle of maximum
speed;
3. Mandatory—the vehicle is limited
at all times.
An additional possible variant between (2) and
(3) is a mandatory system which allows excursions allowed, eg
for overtaking. Such excursions could be limited in number per
unit of time or frequency per length of road.
Another dimension for differentiating ISA systems
is that of the currency of the speed limits themselves. Here the
major typology is:
1. Fixed—the vehicle is informed of
the posted speed limits (those displayed on static signs by the
side of the road);
2. Variable—the vehicle is additionally
informed of certain locations in the network where a lower speed
limit is implemented. Examples could include around pedestrian
crossings or the approach to sharp horizontal curves. With a Variable
system, the speed limits are current spatially.
3. Dynamic—additional lower speed
limits are implemented because of network or weather conditions,
to slow traffic in fog, on slippery roads, around major incidents,
outside a school at drop-off and pick-up times, etc. With a Dynamic
system, speed limits are current temporally.
4. THE FINDINGS
OF THE
EXTERNAL VEHICLE
SPEED CONTROL
PROJECT
This project, funded by DETR as it then was,
ran from 1997 to early 2000. The partners in the project were
the University of Leeds and the Motor Industry Research Association
(MIRA), and the project had a wide-ranging brief to look at almost
every aspect of ISA, ranging from suitable technologies, through
public attitudes and willingness to pay, to side effects in terms
of travel time and fuel consumption, and finally to accident savings
and implementation aspects. A major aspect of the project work
was a set of user trials both on real roads (where driver behaviour
could be studied in a naturalistic setting) and on a driving simulator
(where complete control over the conditions experienced by the
drivers could be assured).
4.1 ON-ROAD
TRIALS
This study required volunteer drivers to drive
a predetermined route in a car equipped with an ISA system. A
Ford Escort was equipped with two versions of ISA, Driver Select
and Mandatory. The software compared the appropriate speed limit
with the car's actual speed. If the car was travelling below the
speed limit, it behaved as a normal car. However, if the driver
attempted to exceed the speed limit, engine management and, if
required, mild braking were used to curtail vehicle speed.
The test route was selected to include roads
of varying speed limits and classes, and was approximately 42
miles in length. Speed limits varied from 30 to 70 mph and included
urban roads with mixed traffic and a high number of pedestrians,
rural roads and a motorway section. In total there were 18 speed
changes on the test route. The cars were instrumented for automatic
data collection. Behavioural observations were made by two in-car
observers with regards to driving errors, interaction with other
drivers and conflicts. Workload and acceptability were assessed
using questionnaires. There were 24 participants in the experiment.
They drove on three separate occasions; 16 drove the car once
without an ISA system and the following two times with one version
of the system (eight with the Driver Select version and eight
with the Mandatory one). The other eight participants drove all
three times with the system off, to provide a baseline reference
group. Thus there were 72 drives in all.
With regard to the Driver Select system, drivers
were generally happy to leave the system engaged, but as soon
as the opportunity to exceed the speed limit arose, they chose
to disengage the system. Thus, it was exactly in the locations
that the system would have had the most impact, ie the rural villages
and urban roads where traffic generally exceeds the speed limit,
that drivers were more inclined to switch the system off in order
to break the speed limit. It was also noted that drivers used
the system less on their second drive, indicating there may be
shifts in behaviour depending on the amount of exposure to the
system.
The Mandatory system, as would be expected,
had a far greater impact on driver behaviour. Large reductions
in maximum speeds were noted on most road sections, especially
in urban areas and rural villages, as can be seen from Figure
1.
The data shows quite clearly that, in the absence
of the ISA system, drivers are poor at adapting to low speeds
after travelling through a higher speed limit area. ISA was effective
in preventing speeding. There was no change in speed distribution
at the lower end, indicating that drivers were not "driving
on the system", something that opponents of ISA have predicted
as an effect. Instead, they were properly responding to traffic
conditions around them.
The in-car observers counted conflicts, ie critical
interactions with other road users. With ISA, performance improved
as compared with the initial run without ISA. In addition those
subjects who drove every time without ISA tended to have more
conflicts with increasing familiarity with the route. From the
questionnaires, drivers with the Mandatory system felt they paid
more attention to the driving task, and as a result were more
aware of upcoming hazards. They also reported they felt they had
more time to make decisions due to their lowered speed.
In terms of driver acceptance, the Driver Select
system was thought to be more useful than the Mandatory system.
Generally, driver opinion about the systems changed little over
the course of the trials. The interviews revealed that drivers
regarded the Driver Select system as more of a safety system than
the Mandatory, and less of a source of frustration. So the objective
data indicate better performance with the Mandatory system, but
there was a clear preference for the Driver Select version.
4.2 DRIVING SIMULATOR
EXPERIMENT
The aim here was to evaluate behaviour with
a variety of ISA systems. The simulated road included urban, rural
and motorway sections, providing a range of speed limits between
30 and 70 mph. Other cars in the scene provided the opportunity
to study overtaking scenarios, gap acceptance tasks and car-following
situations. The road environment also featured traffic lights
and pelican crossings in order to instigate possible violations;
and sub-standard curves were included in both the urban and rural
sections. Workload and acceptability were also monitored.
The results suggest that ISA had little impact
on mean speeds, but reduced maximum speeds. The effects of ISA
on speed were most prominent at specific locations, such as village
entry. Several additional changes in behaviour were identified.
It was found that, when using ISA, gap acceptance behaviour at
junctions altered. The mean gaps accepted and the minimum times
to collision reduced in size, suggesting that drivers were exhibiting
somewhat riskier behaviour. There were also observed changes in
car following behaviour. When driving behind a slow moving vehicle
(with no opportunity to overtake), drivers using ISA were more
likely to want to engage in close following on both urban and
rural roads.
Subjective mental workload scores were obtained
and, both time pressure and frustration increased as drivers used
the system more and more. This time pressure does not translate
into actual loss of time, as there was little change in total
journey time for each of the progressive runs. Thus this increased
time pressure is only imaginary, not actual, but it does serve
to explain the gap acceptance and close flowing results.
The results confirm the potential benefits of
ISA, with reduced maximum speeds and improved speed adaptation
in speed limit transition zones. But there were also some secondary
effects of using ISA. These effects are unlikely to outweigh the
substantial safety benefits of reduced maximum speed and reduced
variability in speed, and they may just be short-term effects
resulting from not being accustomed to using ISA. Only data from
long-term trials can show whether such effects persist.
4.3 PREDICTED
ACCIDENT SAVINGS
Table 1 shows the best estimates of the accident
savings, at various levels of accident severity, for the permutations
of ISA. ISA systems are divided into the broad classes of Advisory,
Driver Select, and Mandatory systems. Each broad class can have
speed limits in fixed, variable or dynamic forms (where dynamic
also includes variable capability). The predictions are based
on the premise that all vehicles could be fitted with ISA instantaneously.
The most powerful and versatile form of ISA, the Mandatory Dynamic
system, is predicted to reduce overall injury accidents by 36
per cent, fatal and serious accidents by 48 per cent and fatal
accidents by 59 per cent. Because there is a particularly strong
relationship between collision speed and the probability of injury,
of serious injury or death in accidents involving pedestrians
and cyclists, vulnerable road users would be among the major beneficiaries
from ISA.
Table 1 BEST ESTIMATES
OF ACCIDENT SAVINGS BY ISA TYPE AND BY SEVERITY
System
Type |
Speed Limit
Type |
Predicted Injury
Accident Reduction
| Predicted Fatal and
Serious Accident
Reduction
| Predicted Fatal
Accident Reduction
|
| | Fixed
| 10% | 14%
| 18% |
| Advisory | Variable
| 10% | 14%
| 19% |
| | Dynamic
| 13% | 18%
| 24% |
| | Fixed
| 10% | 15%
| 19% |
| Driver Select | Variable
| 11% | 16%
| 20% |
| | Dynamic
| 18% | 26%
| 32% |
| | Fixed
| 20% | 29%
| 37% |
| Mandatory | Variable
| 22% | 31%
| 39% |
| | Dynamic
| 36% | 48%
| 59% |
The predicted savings with Mandatory Dynamic ISA are considerably
greater than was achieved with perhaps the most effective single
measure to date in Britain, the introduction of compulsory seatbelt
wearing for front occupants, which achieved a 20 per cent reduction
in fatalities to front seat occupants, ie a 7 per cent reduction
in fatalities overall (Harvey and Durbin, 1986). It is perhaps
worth noting that this prediction of the safety potential of speed
limiters for Britain is almost exactly in line with the prediction
of a 30-40 per cent reduction in injury accidents for Sweden from
Va«rhelyi (1996).
4.4 IMPLEMENTATION TIMETABLE
The External Vehicle Speed Control project recommended that
the Mandatory Dynamic system be the ultimate target. But even
if the goal is to move towards only a voluntary system, the requirements
and timetable are virtually the same. Figure 2 shows the major
prerequisites and stages to implementing ISA. The stages and decision
points are:
| 2000-05 | Further research
|
| 2005 | Decision to move forward towards full implementation
|
| 2005-10 | Preparation and enactment of standards
|
| 2010 | Promulgation of standards
|
| 2010-13 | Preparations for production on new vehicles
|
| 2013 | Mandatory fitment on new vehicles [62]
|
| 2013-19 | Voluntary usage
|
| 2019 | Potential requirement for mandatory usage
|
In many ways this timetable is disappointing, because the
benefits are postponed so far into the future. Earlier work on
standards and other enabling technologies, such as the preparation
of an authorised national digital road map incorporating speed
limits would assist here, not least in promoting voluntary take-up
particularly by fleets.
4.5 Cost-benefit analysis
A cost-benefit analysis was carried out using the standard
UK procedure. The analysis took into account:
— The predicted accident savings.
— Estimates of fuel savings obtained by modelling
of various road networks. This work indicated that, depending
on road category, overall fuel consumption savings with ISA would
range from 1 per cent to 8 per cent, with an overall figure of
5.5 per cent.
— The estimated costs at various dates of the equipment
required on the vehicle to provide ISA. For the dynamic systems,
costs of sensors and broadcast were also computed, and for all
types of ISA the costs of maintaining a national database of speed
limits was included.
— The transition time to ISA implementation, including
the gradual rollout of ISA vehicles into the national fleet.
The results are shown in Table 2. Clearly the Dynamic Mandatory
variant provides the most attractive solution, with a benefit-to-cost
ratio of 12.2 for the low GDP growth scenario, and 16.7 for the
high GDP growth scenario.
Table 2
BENEFIT-COST RATIOS FOR ISA
| | Low GDP Growth
| High GDP Growth
|
| System | Fixed
| Variable | Dynamic
| Fixed | Variable
| Dynamic |
| Advisory | 3.6
| 3.8 | 5.0
| 4.9 | 5.1
| 6.8 |
| Driver Select | 3.7
| 4.0 | 6.1
| 5.0 | 5.4
| 8.3 |
| Mandatory | 7.4
| 8.0 | 12.2
| 10.0 | 10.9
| 16.7 |
All the benefit-to-cost ratios are in excess of 3.5, ie they
would indicate a positive decision to move ahead under standard
investment guidelines. Mandatory ISA has considerably higher benefit-cost
ratios than the Advisory or Driver Select systems. The largest
ratios are for the Mandatory Dynamic system: 12.2 for the low
GDP growth scenario, and 16.7 for the high GDP growth scenario.
This is therefore the system of choice.
5. THE CURRENT
ISA PROJECT
The new UK ISA project began in January 2001 and has a duration
of 52 months, which may be extended by six months. The project
partners are the University of Leeds and the Motor Industry Research
Association (MIRA). The main tasks of the project are:
— To investigate user behaviour with ISA by means
of a set of field trials;
— To study overtaking behaviour with ISA in a driving
simulator;
— To prepare an ISA design for motorcycles and large
trucks and to build a demonstrator of each;
— To prepare a system architecture for a mass production
configuration of ISA;
— To have an input into relevant standards activities
at an international level;
— To carry out a process of technology watch throughout
the project duration;
— To further investigate the costs and benefits
of ISA.
The field trials are the major focus of the project and their
overall aim is to study long-term behaviour with and acceptance
of ISA. It is planned to equip 20 vehicles with ISA and data collection
capability for the field trials. The field trials will start in
2002 and will each last for six months. Four successive trials
are planned:
1. West Yorkshire, private motorists
2. West Yorkshire, fleet
3. Midlands, private motorists
4. Midlands, fleet
The West Yorkshire area will be centred on Leeds and thus
will be mainly urban; the Midlands area will be mainly rural and
small town. The total period for the four trials will be 30 months
(there is an allowance of two months between each individual trial
for the refurbishment of the vehicles). At the moment, the project's
timetable envisages starting the first trial in October 2002.
The last trial would therefore end around March 2006.
The trials are designed to be non-intrusive—the vehicles
will look and behave like "normal" cars apart from the
ISA feature, data will be logged automatically, and data collection
will be remote through a digital mobile phone link. The ISA system
to be fitted will be of the voluntary type: drivers will be able
to opt out of ISA speed limiting at will via a button on the steering
wheel, although the default situation will be that ISA is on.
There will also be a kickdown feature so that sharp pressure on
the accelerator will result in the ISA going into standby, with
the ISA resuming only when the driver voluntarily comes below
the speed limit. The speed limit and ISA state will be indicated
to the driver by a screen which will be integrated into the dashboard.
It is intended to provide drivers with ISA support for a large
percentage of their regular driving, to include both the local
area and the national trunk road network.
The first year of the project has been spent on designing
and fitting a prototype vehicle, which is to be used as the basis
for the fleet of 20. This vehicle has been completed and is available
for demonstration through requests to DTLR.
6. RECOMMENDATIONS FOR
PROMOTING ISA
ISA is more than justified in cost-benefit terms, but its
main benefits are a long time in the future and there is a real
danger that the benefits will be even further postponed through
inaction and anxiety over the political fallout. It is my firm
belief that, once the debate is out there in the open, there will
be firm public support for moving ahead. There is no need for
a decision now on whether the UK should go with mandatory ISA,
but there is a need now to move ahead so as to enable ISA to be
realisable in some form. Concrete actions that should be taken
are:
1. Creating a national database of UK speed limits and
procedures for updating that database.
2. Assistance in developing standards, particularly on
how speed limits should be encoded into digital road maps.[63]
3. Encouraging voluntary take-up of ISA, particularly
by fleets.
4. Research on how to take forward dynamic ISA (in terms
of sensors, decision rules, procedures and communications).
5. Moving towards a European requirement for ISA capability
on all new vehicles sold from around 2013.
7. REFERENCES
Harvey, A C and Durbin, J (1986). The effects of seat belt
legislation on British road casualties: a case study in structural
time series modelling. Journal of the Royal Statistical Society,
A149, 187-227.
Va«rhelyi, A (1996). Dynamic speed adaptation based
on information technology: a theoretical background. Bulletin
142. Department of Traffic Planning and Engineering, University
of Lund.
Dr Oliver Carslen
Director of Research
January 2002
62
It is envisaged that the requirement for fitment of ISA capability
would be enacted at a European level. It would be left to the
Member States to decide how to use that capability-the national
requirement could be for ISA to be used in advisory mode, it could
be for voluntary (Driver Select) ISA, or eventually it could be
for mandatory ISA. Back
63
There is already an internationally agreed exchange format for
digital road maps, known as GDF3. Speed limits could easily be
accommodated within that specification. Back
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