|Rail wear illustration|
Rahn had just elaborated on what caused him to decide that Metro couldn't run from one day to another. At one point he said "unfortunately the engineers were off" referring to a 2015 estimate how long the existing rails would last. He than talked about the "rail slope" (technical speak: Gauge Face Angle (GFA) which is supposed to not be over 26 degrees.
Secretary Rahn flanked by administrator Quinn reported first to the County and then the City delegations. He stated that the wear had been regularly measured and visually observed, but apparently Metro doesn't have the right wear measurement tools such as "the Mini-Prof instrument and software" to get results. Rahn noted that over the observation period the angle values went up but that "some went down" explaining this with "This isn't an exact science".
In the end MTA relied on a consultant doing additional rail observations between January 23 and 29. The results are summarized in a report from the engineering firm HNTB which was made public this week and which indicates Gauge Face Angles in curves as high as 28.7, i.e 2.7 degrees above what is considered a conservative safety limit. Deviations are also measured in inches of top and side wear, anything over a 3/4" is considered beyond the safety standard. The one or the other condtion was observed in most curves above and below ground. The 26 degree metric is not universal, some systems use higher numbers.
|Secretary Pete Rahn in Annapolis on Friday|
In response to the Delegate's question Rahn emphasized: “Once we are informed that something isn’t safe we act”. He didn't say that this was more a matter of liability than one of an actual threat to life and limb, especially since trains already ran at reduced speeds of 20-25mph across the worn sections of rail. It is probably true that no train would actually have derailed in the next two days or even two weeks, but the truth is that no lawyer would absolve the MTA from the full liability should it have continued to run trains even after it had received explicit knowledge of the safety standard deviation. "We couldn't wait until summer", Rahn explained, presumably the time when a full rail replacement had been planned anyway. The bummer: Rahn explained that the current repairs won't replace the summer shutdown. That remains on the schedule.
The matter was deemed urgent enough that even colleagues from WMATA were dispatched on Monday, WMATA being a system that has experienced a 29 hour emergency shutdown of a much larger system in 2016. WMATA's General Manager Paul Wiedefeld served as MTA's administrator from 2007-09.
|Steel wheels need to be calibrated and "trued"|
The Washington Post observed that
"the shutdown announcement elevated Baltimore’s three-decade-old subway to poster-child status in the conversation about the nation’s decaying infrastructure on the day the Trump administration announced its long-awaited infrastructure plan". (WP)Robert Puentes, a national transportation expert noted that an abrupt one month shutdown of an urban rail system was unprcedented in the US. There are, of course, troubling circumstances around this shut-down, including:
- why the extensive single tracking of the last few months done precisely for track repair wasn't used to eliminate the most egregious wear points within the inconvenience that the single tracking already caused riders.
- why there was no contingency plan ready to be implemented in the case of a shutdown that would organize a functional bus bridge and the signage and personnel needed to guide riders to the buses. (Instead Governor Hogan needed the weekend to find $2 million of emergency funds that allowed leasing of 21 intercity coaches from the private bus company Dillon).
- why excessive wear continued after unusual track wear had already been observed. Track wear can be reduced through vehicle "wheel truing" and rail lubrication
- the publish wear measurements do not look alarmingly worse than those of 2016
|Diagram explaining stresses on rail in curves|
In the mundane world of conventional rail technology steel wheel trains race with 200-300 miles per hour over conventional tracks every single day. In the mundane world of subways, legacy system in Phildelphia, New York, Boston, Chicago, London and Paris have been in service for over a hundred years and never experienced an extended full system shutdown.
Rail wear happens on any of those systems, the faster, the more wear. Baltomore's Metro top speed is 60mph, not earth shattering, but in tight curves it can still create the friction that one can often hear as wheel squealing.
For railed vehicles rounding a bend, dynamic behavior modifies a combination of centrifugal and tread steering forces determined by speed, track radius, track cant and vehicle wheelbase. Forces opposing movement include air resistance, bearing friction and rolling resistance.Baltimore's anemic subway of a single line at its peak transported 50,000 riders every day. Current ridership levels (before the shutdown and single tracking) were provided as 40,000 daily riders. That is about the entire population of a city such as York Pennsylvania. Too many people to leave stranded at locked gates without access to any type of transit that would travel on the same route. Of course, the MTA realized that as well, and only the about 17,000 weekend riders were really left high and dry until the so called "bus-bridge" had been installed. The first day of the bus bridge was an unmitigated mess, but by now it works pretty well according to MTA Administrator Kevin Quinn.
Engineers state that vehicle primary performance and steering force occurs in a tiny interface area between the coned wheel tread and the transversely-radiused railhead, known as the contact patch. (Understanding the wheel/rail interface)
|Min-Prof tool for measuring rail|
A full shut-down is also planned for Light Rail in order to fix the rails on Howard Street which are in such poor condition that a layperson can see the degradation and misalignment with the naked eye. What the agency doesn't seem to understand is that jaded riders may never come back to ride the rails once they have been shut out. MTA already shut down light rail once before when it installed a second track under Governor Glendening. The system never recovered from the disruption, ridership levels that had been around the 30,000 a day projection is hovering ever since in the mid and lower 20k range.
Klaus Philipsen, FAIA
|Measurements of rail in different loactions (ML) 2016 and 2018 comparison|