Nighttime ‘ghost jackets’ and the Science of Being Seen

[slowsider]

'From the front' is moot. Emerging traffic will not illuminate the jacket.

Really? You have just overlooked probably the most serious SMIDSY situation.

You've just told me that a front light will outdazzle the jacket...

[Horse]

'From the front' is moot. Emerging traffic will not illuminate the jacket.

Really? You have just overlooked probably the most serious SMIDSY situation.

You've just told me that a front light will outdazzle the jacket...

Not all SMIDSYs involve an emerging vehicle. The most serious are likely to be where both vehicles are approaching head-on.

Also, as Spin can tell you, many SMIDSYs are where the driver has obstructed view.

But you know all this.

[slowsider]

Really? You have just overlooked probably the most serious SMIDSY situation.

You've just told me that a front light will outdazzle the jacket...

Not all SMIDSYs involve an emerging vehicle. The most serious are likely to be where both vehicles are approaching head-on.

My initial point was that if I driver misidentified a motorcyclist as a cyclist because of the ghost jacket, there could be a problem. Your example illustrates that, if the 'cyclist' is wrongly perceived as slow moving. (Iirc there is a threshold speed at which drivers under- and over-estimate the approach speed of a ptw with lights on. ?)

[The Spin Doctor]

Which is an effect of them not being great retroflectors (compared to something like 3M DG3 microprismatic material).

Which is arguably what you want for this kind of urban application. It's all very well being visible half-a-mile away on main beam if you're a pedestrian or cyclist on an unlit rural road (I always used to carry a torch walking to the pub in Kent, to negotiate the bit with section pavement after a couple of near-misses) but the 'glow' is effective under streetlights.

I've seen one rider with LED 'enhanced' hi-viz. The effect was distinctly (or undistinctly) underwhelming.

I (kind of) spotted one recently too

[Horse]

My initial point was that if I driver misidentified a motorcyclist as a cyclist because of the ghost jacket, there could be a problem.

From the front or side, both are IMO highly unlikely. But you may be right.

If from the rear, what Spin said applies. If moped seen further away, then do you think that the rider could actually be worse off?

Your example illustrates that, if the 'cyclist' is wrongly perceived as slow moving.

Don't think that I said that, or intended that. Because of the likely smaller speed difference, the approaching driver will have more time to make decisions.

Here's what I said:

From the rear, it might be a concern if the bicyclist was mistaken for a motorcyclist, but not the other way - it will take longer for the approaching vehicle to catch up a motorcycle.

Iirc there is a threshold speed at which drivers under- and over-estimate the approach speed of a ptw with lights on.

Sadly, despite searching, I've not been able to track down the research to support that. If you do find its title / author etc, let us know.

[Horse]

No harm in another look.

Pre-internet stuff.

20210608_214128.jpg (337.35 KiB) Viewed 226 times

[slowsider]

Iirc there is a threshold speed at which drivers under- and over-estimate the approach speed of a ptw with lights on.

Sadly, despite searching, I've not been able to track down the research to support that. If you do find its title / author etc, let us know.

i have a note of Shaw 1979 but havent relocated the paper yet

My notes when I found it:

Compared the accuracy with which subjects estimated the speed of a motorcycle with headlamp on, and off.

Subjects over-estimated the speed for lower speed of approach
Subjects under-estimated the speed for higher speed of approach

The reversal from over- to under- took place between 50-55mph with the headlamp off, and between 35-40mph with the headlamp on

[Horse]

I think you mey heve en unrelieble source.

Try:

http://www.fema-online.eu/uploads/docum ... DL3331.PDF

(Not a brilliant pdf, it misses the end of some words)

Misestimation of speed and distance: Apart from Attwood 1976, the authors are not familiar with any satisfactory study that has attempted to evaluate the effect of daytime lights upon the estimation of speed and distance of vehicle by other road users.

For instance the motorcycle studies Shew et al 1979? and Stroud 1982 required test subjects to estimate the speed of an oncoming motorcycle in miles per hour.

However it is unlikely that drivers on the road estimate the speed of vehicles as a quantified speed; instead they do qualitatively as ‘slow’, normal’ or ‘fast’ by reference to what they view as a safe speed for the road in question.

If so, the findings of the two studies bear, not upon the accuracy with which the test subjects estimated the speed of the motorcycle, but merely the accuracy with which they translated their qualitative impression of the speed into miles per hour.


Shew RL, DaPolito FJ & Winn GL, ‘Motorists' judgements of motorcycle closure speed with the headlight on vs off’, University of Dayton, USA, June 1977

[slowsider]

Thet mey well be the cese.