Relieving Congestion with Adaptive Cruise Control

Last month, the National Transportation Safety Board listed mandatory adaptive cruise control and other collision-avoidance technologies as one of its ten most wanted safety improvements in 2013. Such a mandate, the NTSB estimates, could reduce highway fatalities by 50 percent.

Honda’s illustration of how adaptive cruise control can reduce congestion. In normal traffic, when a lead vehicle slows down, everyone else must slow and usually slows a little more for safety reasons, thus leading to stop-and-go traffic. If one vehicle in the middle of a platoon has adaptive cruise control, it won’t slow as much, interrupting the pulse of congestion.

Research has shown that adaptive cruise control can also significantly reduce congestion by interrupting the “pulses” of slow traffic that takes place when someone hits the brakes, even if only briefly, on a crowded highway. The research suggests congestion will significantly decline if only 20 to 25 percent of vehicles on the road are using adaptive cruise control. tHowever, researchers fret that too few vehicles are being made with adaptive cruise control to have an impact on congestion in the near future.

During the Antiplanner’s recent visit to San Antonio, someone suggested that state transportation agencies might find it less expensive to promote adaptive cruise control than to make expensive expansions of highway capacity. Texas, for example, has about 9 million private automobiles. Would it be possible to retrofit 20 percent of those cars with adaptive cruise control?

A web search indicates that a few people have retrofitted their cars with adaptive cruise control, but it wasn’t easy and it would work on only a few cars. One person retrofitted a 2008 Audi A8 with used parts that, if purchased new, would have cost about $4,000. Someone else retrofitted and Audi Q7 with parts costing only about $500.

These retrofits were possible only because both models of cars were designed with an adaptive cruise control option, meaning they already had the on-board electronics, including drive-by-wire technologies, to allow adaptive cruise control to work. Regrettably, it would very very expensive to retrofit my 1986 Mazda with adaptive cruise control.

As an alternative to retrofitting, and assuming the federal government doesn’t mandate adaptive cruise control, states could hasten its adoption by giving people tax credits to include the option when they buy new cars. The price of adaptive cruise control has come down since it was first introduced in the 1990s: as an option it costs $925 on a Dodge Charger, $995 on a Ford Fusion, and $1,295 on a Subaru Outback. The adaptive cruise control on these cars only works at speeds down to 25 mph or so. Audi and Volvo both offer an adaptive cruise control that works down to 0 mph, but charge $2,100 for it.

Wikipedia has a list of cars that offer each type of adaptive cruise control today. The list indicates that some cars only offered it in selected years, but I suspect it is still available on those cars. For example, for Dodge Charger it says 2011; but it is also available on the 2012 and 2013 Charger.

Texas has about 9 million private autos, about half of which are used for commuting in major cities. For about a billion dollars–less than the cost of many proposed highway expansions–the state could offer a $1,000 tax credit to the first million people in one of the state’s major metropolitan areas who buy cars with adaptive cruise control (which usually also comes with collision avoidance and other safety enhancements). Since the auto fleet turns over at the rate of about 5 percent per year, this could result in 20 percent of people on the road using adaptive cruise control in as little as four years–through probably longer since not everyone will buy such cars.

I suspect that low-end cars (those listing for under $20,000 new) probably do not have the built-in electronics that would allow for installation of adaptive cruise control. Assuming half the cars sold include this technology, and considering that some cars on the road today already have it, the 20 percent threshold would be reached in less than 8 years. Though I hesitate to support government programs, I don’t see any problem with this in theory since everyone on the highway would benefit from reduced congestion and increased safety, not just those who actually have the technology.

If the feds fail to mandate adaptive cruise control for safety reasons, states like Texas could mandate it for both safety and congestion-reduction. I would have a harder time supporting such mandates, especially if they would significantly increase the cost of low-end cars and thus could potentially reduce some people’s mobility.

This means the next question for research is how much it really costs to include the necessary electronics in low-end cars. If the cost is high, states wanting to accelerate introduction may have to subsidize only purchasers of high-end cars, which could be controversial. But the cost may be low and the auto industry is merely using its standard practice of initially offering it only to buyers of high-end cars in order to maximize its profits before introducing it to low-end cars. While that’s an appropriate practice for luxuries such as on-board entertainment systems, more rapid introduction makes sense for features that reduce accidents and other externalities such as congestion.


6 thoughts on “Relieving Congestion with Adaptive Cruise Control

  1. irandom

    You hit on one of my pet peeves, that infamous pulse of congestion hours after an event. I can’t quite figure out how people will drive fast in every condition on a freeway, except at the end of that pulse with a clear freeway in front of them. I wonder if that helps maintain it by making sure the tail end doesn’t dissipate quicker. Good to know in a few decades there might be a solution. I’m surprised inflexible transportation advocates aren’t pushing it to the back burner.

    prk166 Reply:

    irandom, if I’m picking up what you’re laying down, I’m curious too. I’ve been close enough where I’m in no hurry to go 70 again since I’m afraid that I’m just going to find myself saying “OH CRAP!” and slamming on the brakes as traffic in front of me has stopped again.

    But I think you’re referring to things just a little later or further back where there seems to be all sorts of people still going along at 30 – 45 while a few others are trying to drive at least the speed limit on what is not an uncongested section.

  2. bennett

    The Car Guys took this on a couple of years ago. According to Click and Clack technology isn’t needed. People just need to stop driving like jerks.

    Leave lots of room and the space gets taken by aggressive drivers. Here in Austin it almost impossible not to tailgate because some jackhole will cut you off given the slightest amount of space, and then have to slam on their breaks.

    Dan Reply:

    Aaaaa-men. I’m in FL right now and the traffic during peak is unbelievably bad, mostly due to DWE and DWA-H. Can’t wait to GTFO.



  3. Sandy Teal

    I can’t find them on Youtube, but I remember seeing time-lapse videos of how a traffic slowdown moves backwards like a wave, even after the slowdown is resolved.

    But a lot of these effects occur only in traffic very close to capacity, so that any little trigger will cause congestion. Extreme measures to avoid one type of congestion is not that great because another source of congestion will pop up.

  4. Rickey Racoon


    In this article, you don’t sound like you’re dedicated to the sunset of gov’t planning. Instead, you sound just like a big wasteful government planner. Better living through more gov’t mandates, regulations and higher taxes for gov’t subsidies to private businesses. Shameful.

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