A recent ballot to remove an onerous requirement for ATN systems with offline stations and less than 25 passengers received 24 yes-votes, two abstentions and zero no-votes from ASCE APM Standards Committee members. This requirement mandated that a following vehicle must assume a preceding vehicle can stop instantaneously (as in hitting a brick wall that suddenly appears in its path). It effectively limits ATN systems to minimum headways of three to four seconds.
The requirement is replaced with a requirement to rigorously maintain a separation zone between any two vehicles based on the maximum stopping speed of the front vehicle and the minimum stopping speed of the rear vehicle including any effects of latencies and failures in either vehicle and/or wayside equipment. In a perfect world, this could allow sub-second headways. Even if headways only improve by a factor of two, this will be significant to the viability of ATN.
At their May 2, 2018 meeting in Tampa the Committee dealt with comments raised in the balloting process. They then agreed to move ahead and incorporate this change in the 2018 edition of the Standards due out later this year.
ATRA President Muller discusses balloting comments at the ASCE APM Standards Committee Meeting in Tampa