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Well then let me take a stab at an explanation.  <o:p></o:p> The RHGC Handbook also says grade crossings should be eliminated in instances where the train speed limit is 110 mph or higher.  So, for grade crossings, there is an upper speed threshold for the trains and for the highway vehicles, which is 70 mph for vehicles, and 110 mph for trains.   <o:p></o:p> I can see some rationale that could explain these limits, and it falls into two distinct categories as follows:  <o:p></o:p> 1)      The ability for a vehicle or train to avoid a collision. 2)      The consequences of a collision.  <o:p></o:p>  <o:p></o:p> Regarding item #2:  For the train speed, the higher the train speed, the greater the potential to cause damage to the train, either by the impact with a vehicle, or by a derailment caused by striking a vehicle.  <o:p></o:p> Generally, for average vehicles, a higher vehicle speed will not have a greater potential to cause damage to a train or cause a derailment.  However, in the case of the Nevada crash, we have seen that with the heaviest class of vehicles, a higher speed can indeed inflict serious damage to the train, including a derailment.  <o:p></o:p> The consequences to the vehicle in a train/vehicle crash would seem relatively unaffected by vehicle speed unless the vehicle runs into the side of the train.  In cases of a train broadside colliding with a vehicle, a higher vehicle speed might actually reduce the effect of the impact on the vehicle.      <o:p></o:p> Regarding item #1:  I cannot see any reason why increasing train speed should have any effect in reducing the crossing protection system’s ability to provide adequate warning to drivers.  Increasing the train speed does increase the stopping distance, but train stopping distance does not often play a role in a collision with a vehicle (even though train stopping distance is routinely cited as the most important factor in grade crossing danger).  In any case, it is an accepted premise that trains require a long stopping distance, even at low speeds.      <o:p></o:p> The highway vehicles, however, are required to yield to trains, so if you increase the highway vehicle speed, it will affect the ability to stop if yielding requires a stop.  To comply with the yield requirement, drivers must be informed of its existence by a warning system consisting of signs or a combination of signs and automatic warning devices.  Therefore, an increase in vehicle speed will require extending the reach of the warning system.   <o:p></o:p> Theoretically, the highway vehicle speed could be increased indefinitely if the warning system were extended correspondingly.  However, one problem with that is that if you create too large of a gap between the advance warning and the crossing, a driver might forget about the warning by the time he or she arrives at the crossing.  Therefore, not only would the advance warning need to be extended for increases in vehicle speed, but also advance warning continuity would need to be provided between the advance warning and the crossing.      <o:p></o:p>
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