I had the honor of presenting my motorcycle collision reconstruction course to an Australian group this week, and the topic of naturalistic braking behavior came up during discussions, which reminded me of an excellent paper by the rising superstar, Swaroop Dinakar.

Braking behavior in LTAP events

If you’re not down with the lingo, LTAP = left turn across path, a situation we're commonly analyzing. Swaroop and Jeff Muttart analyzed 122 naturalistic responses of through drivers in LTAP events and published the results in a paper titled: Driver Behavior in Left Turn across Path from Opposite Direction Crash and near Crash Events from SHRP2 Naturalistic Driving.

The paper also contains tons of great response time data, but today’s topic is braking, starting with latency, which is the duration between onset of braking and achievement of a certain threshold, say 0.70 g’s. The authors found that two parameters had statistically significant effects on latency: the through drivers' lane position and whether the left-turning vehicle was obscured. A summary of the results is below.

The data show, for instance, the average time to reach 0.7 g’s when the through driver is one lane away from the left turner is 0.51 s. If the driver was two lanes away, that duration goes up to 1.10 s.

It should be noted, not all drivers achieve all thresholds. With some help from Swaroop, I was able to calculate the following from the reported data:

100% of braking drivers hit 0.4 g's
99% hit 0.5 g's
90% hit 0.6 g's
58% hit 0.7 g's
30% hit 0.8 g's

It's worth considering the above during your next avoidability analysis. Thanks for reading along. May your weekend bring tidings of comfort and joy,

Lou Peck
​Lightpoint | Axiom​

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