Wearing a Helmet in a Car

[turnkey4099]

The "speed kills" is much, much too simple. The reality is "speed differental kills". Whether running into a stationary object or a moving vehicle there has to be a differential for the accident to happen. That is why the safest speed is the speed of the majority of the traffic, otherwise called "the flow" no matter what that speed is. It will almost always be above the limit by about 10% IME and will not result in being stopped for speeding (except for blatant speed traps).

It is vehicles cutting in and out, moving either faster or slower than the 'flow' that causes traffic turbulance and thus a decrease in safety.

Harry K

 

[Bird]

You're right about "speed differential" in that it's more of a cause of accidents. And then when an accident does happen, higher speeds increase the severity. As for the "flow" being 10% over the limit, in my opinion, that appears to be a pretty good guesstimate, although I don't know of any factual surveys or studies to substantiate it. In setting speed limits, a number of factors are taken into consideration such as road conditions (type of surface, width of lanes, curves and hills or lack thereof, sight distance, etc.) and potential hazards (pedestrian traffic, cross streets, driveways, traffic volume, etc.). Another common method, used either independently or in conjunction with the above is to clock current traffic and set the limit at the speed below which 85% of the traffic is currently driving.

 

[turnkey4099]

You're right about "speed differential" in that it's more of a cause of accidents. And then when an accident does happen, higher speeds increase the severity. As for the "flow" being 10% over the limit, in my opinion, that appears to be a pretty good guesstimate, although I don't know of any factual surveys or studies to substantiate it. In setting speed limits, a number of factors are taken into consideration such as road conditions (type of surface, width of lanes, curves and hills or lack thereof, sight distance, etc.) and potential hazards (pedestrian traffic, cross streets, driveways, traffic volume, etc.). Another common method, used either independently or in conjunction with the above is to clock current traffic and set the limit at the speed below which 85% of the traffic is currently driving.

Yes, the mythical 85% rule. The problem is that it is always set with Law Enforcement already in effect, thus if posted say 60, the flow will be around 65/66, so they raise it to 65 and the flow instantly jumps to 71/72. Keep repeating and supposedly it will eventually reach a posted speed that is a true 85%. The reality is that if it ever did, that speed would be dangerous considering the poor driving ability of the vast majority of the drivers on the road.

Harry K