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UK Evaluating Intelligent Speed Adaptation Systems for Road Safety and GHG Emissions Reduction

Summary results of impact of ISA systems on CO2 emissions. Click to enlarge.

The UK government’s Commission for Integrated Transport (CfIT) and the Motorists’ Forum (MF) recently issued a joint report evaluating the impact of implementing an Intelligent Speed Adaptation (ISA) system across the entire road network on reducing deaths and injuries on the UK roads and on reducing fuel consumption and emissions of CO2 and criteria pollutants. They partners commissioned the Institute for Transport Studies, University of Leeds to produce the report.

ISA systems use enhanced navigation systems which incorporate speed limit as a road attribute to compare the local speed limit to the vehicle speed. The ISA system automatically detects the road on which a vehicle is travelling—and hence the speed limit—without any user intervention. ISA systems take three basic forms:

  • Advisory ISA, which advises the driver when the vehicle is exceeding the speed limit with an audible and/or visual warning;

  • Overridable (or Voluntary) ISA, which controls maximum speed based on location but allows the driver to override the speed limiting function and regain full manual control until a new speed limit is encountered and/or the road speed drops beneath the current speed limit at which time ISA regains control; and

  • Mandatory ISA, which uses a speed limiting function that the driver cannot override to control maximum speed.

Research on ISA in the UK has been going on for more than 10 years, including a major ISA-UK project funded by the UK’s Department for Transport (DfT) between 2001 and 2006. The new report builds on and extends this previous work, including the final report on the ISA-UK project published by DfT in September 2008.

Of the two proposed benefits of ISA—GHG emissions reduction and increased road safety—the Leeds researchers concluded that the calculated social benefits of the accident savings far outweigh the values of fuel or CO2 saved. Among the findings presented in the report:

  • Overall, changes in CO2 emissions are not very significant on roads with a speed limit of 60 mph or lower. But on 70 mph roads, there is potential for a substantial reduction in CO2 emissions of 5.8% (+/- 0.7%) with a mandatory ISA system.

  • On the modeled rural network, neither overridable nor mandatory ISA make a major impact on overall CO2 emissions or fuel consumption rates at any level of penetration.

  • In the two modeled urban networks, increasing ISA penetration had a small detrimental effect on both CO2 emissions and fuel consumption, increasing both by up to 3%. The detrimental effect is stronger at levels of ISA penetration above 20%. This is because cars tend to operate most efficiently at speeds above 30 mph. On the other hand, the more elaborate emissions modelling of the speed profiles from the UK trials indicated small savings in CO2 emissions and fuel consumption on both 30 and 40 mph roads, most likely because of reduced acceleration.

  • No substantial effects were found regarding other pollutants.

  • The implementation of ISA systems is likely to make a negligible contribution to reducing overall broadband noise levels.

  • Universal usage of mandatory ISA could eliminate nearly 29% of injury accidents.

  • The potential for reducing accidents is greatest on 30 mph roads where there is considerable propensity to exceed the speed limit and crashes involve collisions with pedestrians and cyclists

  • Advisory ISA is predicted to be substantially less effective than the intervention based (overridable and mandatory) forms of ISA.

  • In less than 15 years, under virtually every scenario, ISA recovers its implementation costs. Over the period 2010 - 2070, the benefit to cost ratios are very large, apart from the Advisory only ISA scenario, which is not considered a realistic option because it can be assumed that some parts of the market will choose to adopt overridable ISA.

  • Attitudinal work found that the public is segmented into three major groups: those who are extremely hostile to ISA and who declare that no amount of incentive would sway them to purchase or use ISA; those who are non-committed and could be persuaded by incentives; and those who conclude their is a safety potential in ISA and do not require incentives to adopt it. “Thus there is the potential for incentive to be wasted on those who do not need them, and a danger that, if adopted, there would be a considerable minority of refusers.

The study has predicted substantial benefits from the introduction of ISA. These benefits consist principally of the savings in accidents and in particular in more severe accidents. The savings are substantial under all the scenarios examined, and strategies that promote higher penetration of ISA and earlier adoption of intervening forms of ISA lead to greater impact. Thus ISA can be considered as a system with major safety potential.

The environmental benefits of ISA are real but less considerable. They consist in the main of reductions in fuel consumption and in consequent CO2 emissions.

...Interestingly, there was significant support in the focus groups for the government moving ahead not only with requiring fitment but also in the longer run with requiring usage. The analogy was drawn with the history of seatbelt wearing. Even among the strong opponents of ISA, there were statements that it they were required to use it, they would comply.

—Speed limit adherence and its effect on road safety and climate change




Hopefully this joint report leads to a serious effort at implimenting automated speed control. Anyone concerned with road safety could see this coming years ago when GPS systems became available for vehicles. If a GPS/ISA system can interact with the vehicles engine control unit, it can limit the speed of the vehicle to the posted limit. This will save tens of billions of dollars in crash expenses and more than ten thousand lives a year in this country. Speed above the posted limit has always been illegal under any circumstances (including when passing), so nobody will have a legitimate complaint about big-brotherism.

Drivers of gas tankers, school buses, metro buses, etc have no business ever exceeding the limit, but large numbers of them do it habitually and intentionally. Some (like my Washington DC metro bus driver) do it while texting on their cell phones. Mandatory ISA would be an excellent technological solution to this madness.

Brian P

You seriously think this isn't "big-brotherism"??

At least in this area, a good many speed limits are set too low based on engineering principles. (Note: UK motorways 70 mph = 112 km/h, we have 100 km/h. Most other rural roads in UK are 60 mph = 97 km/h, we have many rural roads at 80 km/h but some are - absurdly - as low as 60 km/h, which no one follows.)

I will not tolerate any attempt to make me rigidly follow a speed limit which is too low to begin with.

It's obvious which of the three camps that I am in.

By the way, attempts to predict reductions in injuries or fatalities as a result of speed limit changes have a history of inaccuracy. The revocation of the US national 55mph speed limit was NOT followed by carnage on the roadways.

Travelling excessively slowly leads to boredom and fatigue. I would rather be awake and alert at 130 km/h (which is about what the motorways are designed for and is the speed limit through most of Europe), than falling asleep at our 100 km/h limit.


I agree completely, Brian. The report seems to indicate little benefit on the pollution/mitigation front, and will be even less relevant as EV's are phased in. But the control of speed limits argument only works if the speed limits are set at a reasonable level.

I speed almost every time I drive, and so do most of the other drivers I see in Sydney or on the highways. Our highway limit is 110kmh and I think it is too low. I just came back from Canberra on the highway and I call the 110 the 'drone zone', it sends me to sleep just droning down the highway.

When so many people speed so often, you have to wonder whether the speed limit is an ass. Politicians in this country have demonised 'speeding' but I am much more concerned about unlicensed drivers, drivers under the influence of alcohol or drugs, drivers of uninsured vehicles, and drivers behind the wheel of some clapped out wreck with no brakes than a driver of a late model vehicle doing 130kmh in a 110kmh zone on a decent, dual carriage highway.

The licensing system in this country is a joke - I have not had to sit any sort of mandatory re-license exam or other since I first obtained my Provisional licence in 1987. Yet many road rules have changed dramatically since then. I am sick of politicians casting a regulatory net over everybody with blanket messages of 'speed kills'. Make a licence difficult to obtain and then police the roads properly rather than dumbing everyone down to the lowest level.


I didn't say it's not big-brotherism! However this is only a euphemism for government passing unpopular laws like seatbelt and motorcycle helmet laws.

Why, when speed limits and discussed, people only talk about high speed? Most accidents occur in urban and suburban areas were speed limits are low. Personally I wouldn't mind if all speed limits were increased 15 kph as a compromise to mandatory ISA. But parents will need to keep their kids out of the road.

What about gasoline tanker drivers - should their vehicles be fitted with mandatory ISA?

John Taylor

I think that a speed limit advisory on the GPS is a great idea. Often finding those speed signs is a pain.

The auto speed control is ok in some cases ... like where you are overdoing it enough to gain a serious fine ...

But while everyone is fudging the limits by 10km or so, having a 'big brother' regulate you as a slowpoke is going to be a bad idea.

Roads are safer if everyone goes at the same speed. This technology has the potential to be great and improve safety if it is introduced properly.

My recommendation ... have it override at +10km, with a special switch to let the driver disable the system in emergency situations (like taking a sick kid to the hospital).

Brian P

"Most accidents occur in urban and suburban areas where speed limits are low" - this is true, and in many urban areas (I know this is the case in Toronto) around half of traffic fatalities are pedestrians. But, there is no "reasonable" speed limit low enough to "assure" the safety of a pedestrian. A lot of these happen when a pedestrian goes across the road without looking. Forcing a driver to go unnaturally slowly just encourages the driver to pay more attention to the cell phone, blackberry, radio, passengers etc ... or just fall asleep.

In this country, gasoline tankers (and most other over-the-road trucks) are already fitted with speed limiters and there was no law (until now - just passed) to force this to be the case. Fuel cost increases exponentially with speed for these vehicles because of the huge aerodynamic drag, and the most economical travel speed is somewhere around 105 km/h anyway because of this, so that's (roughly) where they are set. I know someone who drives a fuel tanker. It's limited to 95 km/h. Reason - in the event of a collision, the trucking company wants absolutely no chance of the driver being accused of speeding and thus causing liability for the collision. Also, liquids are inherently tippy because the load sloshes around.

Driving a governed truck like that across the prairies is a dreadful exercise in boredom.

You can already program some handheld GPS units with the locations of fixed speed cameras ... and some premium european cars have a user-settable speed warning system (not GPS based) due to the number of speed cameras over there. And the new Nissan GT-R has a top-speed limiter (mandatory in Japan - at 180 km/h) which disables itself when the GPS detects that the car is at a known location of a racetrack.


I think this would exacerbate the “speed limit setting problem”.
When the maximum safe speed for good drivers is 100 in normal conditions, 80 during marginal evening conditions, 70 at night, 60 for a good but bored driver and 50 for a bored, minimal (but unimpaired) driver at night, then big brother sets the limit at 50 - or less.
Then few drivers go 50 (and they are a hazard) - but (prior to photo radar) you could drive 70 with impunity.
The state probably will not set the limit up to 60 or 70, even with auto-enforcement, because this is not ALWAYS safe.
Unless the automated system adjusts for time of day, weather and speed of adjacent traffic, I think it will face fierce objections and will SLOW traffic flow and just keep cars on the road longer, adding more congestion.


If the speed limits were set reasonably, and if you had (say) a 30 second override for overtaking once every 15 minutes (or whatever), it might not be too bad.

AS long as it worked properly, but what if it thinks you are in a 30 mph zone instead of a 70 (or vice versa)?

Most things fail occasionally, or at least fail till the bugs get worked out - so what would you do - make it disableable(?) or just crawl along.

Either failure mode is bad - you either hold up traffic, or you inadvertently break the speed limit - perhaps by a large margin.

On the other hand, if you believe we are on the path to automated driving, then this will be a waypoint on the route.

If you think about fly-by-wire airliners, there are thousands of those in use daily, without safety issues (but then think about the amount of time spent maintaining them).


Like most driving regulations, the majority of safe, reasonable drivers are being penalized for the weak-skilled or reckless minority. Speed only kills if it is in the hands of the overly-aggressive, poorly-trained, or in an unsuitable vehicle. But what can be done? Especially when the overly-aggressive care not for tickets, suspensions, or other users of the road. Just because they can handle it, what about the average person trying to pass? Especially when the poorly-trained think that they are the safest on the road when the drive 10kph lower than the speed limit in the middle lane causing other traffic to stream around them.

I think that the bottom-line is to measure risk and assess casualty rates as a society and determine (clinically and cold-heartedly - unfortunately) what is 'acceptable'. We will never live in a risk-free society and i don't think that it is even desirable. Is one car death (even a pedestrian or non-rule-breaking bystander vehicle) acceptable once a month in a small city of 100,000? What would it cost to make it 0.5 deaths per month? What limitations and restrictions would have to be put in place that may or may not make it viable to drive and affect traffic flow? Is it worth it?

I personally don't think it is reasonable to drive 20kph over the 'speed of traffic' for any reason - it just throws all other users of the road out of balance. There is no situation so dire or boring that people must drive so much out of line with the conditions around them. Notice that i wrote 'speed of traffic' not 'speed limit'. Here in Toronto, we have a toll highway where I would say that the average speed at almost all times of day is 25 to 40 kph above the posted speed limit of 100kph. Just listening to the news daily, it is obvious that the LEAST number of highway accidents happen on this road despite fairly high, but not congested volumes. That being said, the toll highway also has far fewer trucks, far fewer old crappy vehicles, and a fairly conscious group of users who let people pass them from behind and try to stay in a lane appropriate to their speed. Though there are a few weavers, the drivers are typically safe and confident (they're certainly dedicated drivers rich enough to afford the $20 - $100+ per month of the toll road). But this is a special group of drivers probably not reflective of all drivers in general. And therein is the problem - too many weak drivers that make the drive a lot more dangerous than it needs to be. It only takes a few 'weak' drivers to ruin traffic flow or cause an accident. Better 'weak' drivers = less rules.


So it seems the consensus here is keep government out of the driver cockpit. But insist on stricter regulation of licensing to week out "weak" drivers. It's a brave new world.

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