Wednesday, September 8, 2010

Anti Speed Camera Arguments - #3 - Concentration and Inattention

The third in my series of posts attempting to debunk the anti-speed-camera arguments of

They claim "It is very well known amongst skilled and advanced drivers that lower speeds demand lower attention, and that lower speeds promote lower attention."

I don't believe this is true. The most boring roads are those with the fewest hazards and distractions, being motorways. Motorways are - guess what- the fastest roads! Conversely, a busy car park has a very low vehicle speed but demands a high level of attention due to very frequent hazards ( cars manoeuvring, people walking to and from cars, children on foot). So there is no necessary correlation between low speeds and a low required level of attention.

However you could assert that driving slower on the same stretch of road in the same conditions is more boring because the frequency of hazards is lower. I imagine this is what they are actually trying to argue. Increased frequency of hazards would demand a higher level of attention, which I can accept.

But what effects does an increased frequency of hazards have on safety?

According to SS's argument, driving faster demands a higher level of attention and therefore there is a lower chance of accidents due to inattention. In their words "If we slow down vehicles over a wide area, particularly if we slow them significantly below the speeds that drivers are currently choosing, we risk increasing accidents due to inattention, poor concentration and sleepiness."

Clearly however, if you drive faster, the decreased risk of inattention may be offset by increased risks due to more frequent hazards. If SS are right, the most boring roads (motorways) would be the least safe, and the safest roads would be country lanes. The opposite is the case. Which is pretty bloody obvious. To take SS's argument to its logical conclusion, in order to make a road safer, you must make it more dangerous.
Now I do not deny that there are psychological factors in play. There is evidence that people adjust their level of risk-taking upwards in compensation if their environment feels safer. But your average driver in particular is poor at assessing risk. Many are unaware of the risks they are taking. Others have a high risk threshold. The point of speed limits and speed enforcement is to protect society from both groups of drivers. 'Safe speed' confuse the actual level of attention of drivers with the required level of attention for a given level of safety. There is no evidence they present that shows that either drivers on average reach the required level of attention, or how the gap between the required level and the actual level varies with speed. They are merely speculating that the the average actual level of attention goes further below the required level if the posted speed limit is lower.

Speed isn't the only factor that affects attention levels. I've identified hazard frequency above. Familiarity is another. A familiar road is likely to cause inattention, you would think. If a driver knows a road, he will require a lower level of attention to drive on it. Should you introduce new hazards such as cars parked on blind corners or spillages just to keep drivers on their toes?


  1. Familiarity breeds complacency "I've always pulled out here without looking, no need to this time". That's probably somewhat independent of the risk, because people are now judging the risk from their own experience, rather than the perceived situation.

    Another reason drivers can underestimate risk is because their view of the world comes from the car, with many features (soundproofing, suspension) to isolate you from the outside, and millions of pounds selling car features (ABS, airbags) as safety features. It would be a good experiment to see if people drove differently in the same vehicle based on how much of the external environment (sound, wind, etc) was passed through.

  2. In reply to Steve L's last sentence.

    Yes that would be an interesting experiment, which I predict would have the following result. Initially, there would indeed be a change in driving behaviour in the direction of alertness and caution, but after a while this beneficial effect would disappear.

    The reason I predict this is that even with the muffled sensory environment within a modern car there is still far too much information to pay attention to everything - there always is, everywhere, and no-one can pay attention to everything. It is suggested that the way the mind works to actually navigate around in a traffic situation is to use a simplified mental model - so people don't pay attention to (or simply don't even *see* - hence SMIDSY) bits of the road where nothing usually happens (like the edge, which is why you shouldn't hug the kerb on a bike). Boosting a driver's environmental input would therefore only have a temporay effect as after they had recovered from feeling a bit nervous, the (necessary) cognitive shortcuts would reassert themselves.

    Still, I agree it'd be interested if more experiments were done with that sort of thing.

  3. My first car was a 1985 mini, it didn't hide you from the environment. But I also found I liked the window down, because the air and the sound was a cue I needed.

    Now, on the bike, I have a mirror off my glasses because I'm used to that up-left-rear-view feature to get more knowledge of what's going on behind.

    I also have an MTB which hides some terrain info (front suspension, see), and whose disk front brakes hide details on wetness on the road. While the brakes don't have that same delay when wet as rim brakes, the tyres still get wet, so I'm maybe losing some data. I can see how the corruption begins...