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| Re: A a Vision Zero Town Hall Meeting (292353) | |||
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Re: A a Vision Zero Town Hall Meeting |
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Posted by Stephen Bauman on Wed Apr 16 11:06:37 2014, in response to Re: A a Vision Zero Town Hall Meeting, posted by BrooklynBus on Tue Apr 15 14:48:00 2014. It's the dangerous actions we need to stop like speeding at 50 or 60 mph in a 30 mphDefine what you mean by "dangerous?" Is going through a red light dangerous? If so, then the approach speed to a traffic signal must be consistent with the signal's yellow change interval. That interval was based on a 30 mph speed limit. That's a standard based on reaction time and a modest braking rate. If your approach speed is faster, you will not be able stop before the signal turns red. Your continued insistence that the yellow change interval should be increased contradicts your assertion that approach speeds "modestly" in excess of 30 mph are safe. Do you know why NYC adopted a 30 mph speed limit with respect to traffic signals? It's to maximize vehicular crossings through an intersection. The transition time GR-YR-RR-RG is dead time. No vehicles can travel during this interval. There are 2 such intervals for a complete cycle for a simple intersection. NYC's standard traffic signal cycle is 90 seconds. That means 11% of possible travel time is lost due to changing signals. Want to increase the yellow change interval to 4 seconds (40 mph approach speed)? The change interval increases to 13.3%. Want to increase the cycle time to increase the travel through the intersection? The limit is how much traffic will accumulate during a red cycle. It's not very long in NYC with 20 blocks per mile being the norm. Does your definition of "dangerous" extend to damage caused to non-vehicular road users? They outnumber motor vehicles in NYC by nearly 2:1. They were also there before automobiles were allowed to use the roads. They have not disappeared. The single most important determining the severity of damages caused to pedestrians is impact speed. Almost the entire injury severity range is compressed into 20 to 40 mph impact speeds. A 40 mph impact speed means 85% chance of death and 15% chance of injury. A 30 mph impact speed means 45% chance of death and 50% chance of injury. A 20 mph impact speed means a 5% chance of death and 65% chance of injury. If you have no compassion for your fellow humans nor any guilt for having caused them death or injury, consider the damage an impact will cause your car. |
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