|
|
| Re: TA is obsessed with CBTC, and ''New'' tech for no reason. (581296) | |||
 |
|||
| Home > SubChat | |||
|
[ Read Responses | Post a New Response | Return to the Index ] |
|
||
|
Re: TA is obsessed with CBTC, and ''New'' tech for no reason. |
|
|
Posted by Jeff H. on Wed Mar 5 19:41:33 2008, in response to Re: TA is obsessed with CBTC, and ''New'' tech for no reason., posted by Stephen Bauman on Wed Mar 5 07:08:38 2008. At 40 mph and an average emergency braking rate of 3.2 mph/sec it will take40/3.2 = 12.5 sec to stop. OK, there is part of the source of error. You are using an average EB rate of 3.2 mph/sec, but the signal system was designed around a 3.0 spec. And to be more precise, the design was never, ever based on a single number! In determining safe stopping distances, a graph based on actual test results of stopping distances at various speeds and grades is used as the basis, with interpolation. Those graphs call out a distance of 437 feet at 40 MPH on level grade. To arrive at a similar number using the average brake rate method: It takes 40/3.0=13.3 seconds to stop from 40 MPH. In order to factor in the response time of the brake system, it is assumed that the train experiences no braking for 1 second after the trip cock is struck, and then full braking begins. The train travels 40*1.47=59 feet during this second. Then then stopping distance is 389+59=448 feet, which is pretty closed to the observed value of 437 feet. Service levels in excess of 30 tph can be achieved without station timers and with the T/O seeing only green signal 30 tph, generally yes, 40 tph very challenging without station time. But the argument is somewhat academic, because in most areas of the system where close headways are needed, station time is provided. |
|
|
|