Combined speed factors & associated statistics, with ESL restriction
Combined Speed Factors & associated statistics - with ESL (electronic speed limiter) restrictions on top speeds
With a degree of shallow analysis & appraisal, some readers may conclude that the majority of very serious crashes are the result of head-on type incidents - and therefore the combined speed factor involved, invalidates the significance of limiting top speeds.
The 'Single Vehicle' Crash:
The above appraisal may be correct in terms of supporting an argument for deprecating the ESL benefits associated with fatal crashes that involve a single vehicle at high speed, impacting with a stationary object. It should nonetheless be ‘emphasized’ that this [lesser percentage of] nine to 14 percent of high-speed “single vehicle” incidents, continues to account for about 18% of all road fatalities (in New Zealand for example) - annually.
This percentage, though only around 18% of "total annual" deaths, clearly indicates that there would need to have been a very high velocity present, for these (single vehicle) crashes to be so serious.
There is a possible secondary aspect, that could well provide an addition to this [18 percent] statistical value. Could there be a previously unrecognized cause of ‘head-on’ crashes, that arises from an “inducement factor”? This “inducement” would relate to the ‘knowledge' by the driver that he/she is able to use a very high speed, albeit only briefly, to conduct a given manoeuvre.
As explained in the [more substantive] article 'Overtaking Scenario Competencies' and in many other articles in this website, the described “inducement to use a high&dangerous speed” (scenario) may be what has provided the ‘trigger’ for many an unwary driver to have become the at fault party... in some of the (needless) head-on tragedies - that are witnessed at times, on the ‘notorious’ highway black-spots.
If such an “Inducement Factor” [the availability of excessive speed] was able to be proven to be the overriding psychological trigger involved when a less experienced driver made an imprudent decision to overtake - refer to: “Overtaking Analysed” - then the 25 percent reduction in (fatal & injury) crash trauma applicable to a restriction of top speeds, may subsequently need to be calculated at a much higher statistical benefit - than 25 percent.
For example, this [greater percentage] would need to be proportionate with the fact that more than 50% of fatalities will have occurred in ‘head-on’ crashes.
Combined Speeds & the mathematical statistics:
To summarise: As much as 50 percent of fatalities and / or serious injury crashes involve head-on impacts. These impacts will occur at ‘varying degrees’ [angles] of opposing directions.
Nonetheless, where they generally arise from an impact with a vehicle from the opposing direction, they are termed “head-on”.
These incidents therefore, will usually produce the “combined speed” effect – that we are all acutely aware of in terms of potential for severity, in respect that the energy - of both the vehicles - is combined.
This ‘effect’ (then) obviously renders the potential of a speed limiter, mostly redundant in such scenario. This is because the two respective speeds of the vehicles therefore means that if at the point of actual impact, one vehicle is travelling at 114km/h, and the other at 75km/h, the combined speed total will be 189km/h.
It is therefore obvious, that in this scenario neither vehicle would have been rendered any safer, by a speed restriction of 120km/h.
However, what must be remembered is that many ‘cross-centre-line’ incidents will have - as their initiating aspect - a speed that is too excessive in the first instance, such as 130km/h or greater. These types of speeds [if used by only one of the vehicles involved] - may then result in that vehicle crossing the centre line.
A typical example of this type of incident - and that evidently did not involve an attempt to overtake using high speeds - was demonstrated on the Waitohi-Temuka highway, South Island New Zealand, January 2006. Read also: "Overtaking Analysed"
In that tragedy three people died, evidently because one vehicle was travelling at about 130km/h when the driver simply ‘lost control’ - and crossed into the path of the oncoming vehicle - (killing a much loved Grandmother).
The actual IMPACT speed of the offending vehicle in this incident may have reduced to 105km/h - at the point of impact - but this nonetheless produced enough energy dissipation to cause fatalities - through the combined speed effect.
Notwithstanding that the combined speed factor will mean that a high percentage of serious impact crashes could still occur when vehicles were restricted to a top speed of 120km/h, LTNZ (New Zealand) statistics strongly indicate that about 18 percent of serious impact crashes would in fact be prevented - resulting in at least a 25% reduction in associated trauma; i.e. fatal & injury [= 68 fewer fatalities in 2005].
With regard to the human cost (to this trauma percentage) reduction, it is important to appreciate that it would involve (and lessen) the more serious injury and deaths, that are having SUDDEN, traumatic impacts, on unsuspecting families; such as as those of the grandmother killed on the Temuka Highway- mentioned above.
Conclusions:
Because many “cross-centre-line” incidents [re: head-on crashes] have speeds above 130km/h as their initiating factor, it is patently obvious that a restriction to about 120km/h would prevent many incidents from occurring in the first instance - and reduce the ‘impact severity’ of any that did take place.
The argument, that having vehicles restricted to a ‘specified speed’ might somehow exacerbate a “scenario” where an overtaking vehicle becomes ‘trapped’ - in the face of oncoming traffic - is completely flawed when analysed concerning the statistics associated with these types of scenarios.
This is because - to cite just one obvious aspect - drivers are already making judgment errors that result in them becoming 'trapped' as it were - and in some of these instances, because their speed is exceptionally high, they are having serious crashes (in any case) - notwithstanding the ‘current’ 180km/h restriction of their vehicles.
See also: "Two Dead After Driver Passes on Yellow Lines".
- - -: < single-car-crash-kills-five/teenagers... >.