Passenger Trains > Caltrain's Quint Street Bridge Crisis

Caltrain's bridge over Quint Street at m.p. 3 in San Francisco dates from the construction of the Bayshore Cutoff in 1907 and its deteriorating condition has reached the point where operations into the City are being impacted. Emergency repairs are needed to stabilize the structure and a 10 m.p.h speed restriction is in place for trains on track one(normally used by northbounds) since the supports on that side of the bridge are in the poorer state of decay. Many off peak and weekend northbounds are taking track two into the City to avoid that restriction with the single tracking resulting in minor delays.

KGO-TV had this report ten days ago:
http://abclocal.go.com/kgo/story?section=resources/traffic&id=9495515
Despite the emergency, planning is apparently still continuing as no repair work has started yet.

All photos taken this morning(4/17) with the second view proving that, hey, at least it can still support two trains at once.

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San Francisco's Harriman-era Quint Street Bridge, another example of our nations' decaying infrastructure, as a confident school bus driver makes a run for it. Caltrain schedules 92 trains plus extras over the bridge each weekday.



Edited 2 time(s). Last edit at 04/17/14 14:29 by shed47.

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Another example indeed... they are all over the place.

In Chicago both the CTA and Metra main near me rest on 80-100 year old structures. Some of the old steel bridges on the UP/Metra main are slowly being replaced, but the project is not comprehensive; it only covers a particular stretch.

Some CTA pictures are below. The first two show a bridge that has been replaced, the third shows a portion that has since been patched up but on the whole has to be replaced.

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I never understood how slowing a train down over weakened structure makes any difference, except to allow for shorter stopping distance should something be visibly out of place from the locomotive cab as it approaches. I can understand if this was on a curve, where lateral forces come into play, the need for a slow order, but on a tangent stretch of track I would think weight is weight, regardless of how quickly or slowly the train passes over the problem area. Does Mr. McGinley, or any other experts on such subjects here on TO have a simple explanation to this? Thanks in advance!

Desmond Praetzel, "451 Puff"

Lower Speed reduces Vibrations, which creates stress on the superstructure.

OTG Wrote:
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> Lower Speed reduces Vibrations, which creates
> stress on the superstructure.

Think of it this way, there is quite a difference between being hit by a baseball dropped from a foot above your head versus a 90 mile per hour fastball.

Lower speeds reduce dynamic loads that stuctures have to contain at higher speeds. Put another way there is a horizontal shear load that is present that increases with speed. That horizontal load pushes the bridge over while the supports push the bridge up. Its messy.

Posted from Android

Visually, it doesn't look that bad.

Add to this the long drawn out negotiations with the city to close Quint St here and replace the bridge with fill. A new street would be built to connect Quint along the west side of the tracks up to Jerrold. This also ties in with the city's desire to have a new station stop here, which could be built over the street but at a huge premium for the type of bridge structure it would require. The up charge for that bridge is far more than the city is willing to shoulder and Caltrain won't pay for anything more than the bridge it needs, hence the proposal to close the street. When and if the city comes up with the money to build a station, it will be easy to do.

The specific structural issues with the bridge are not unusual for 107 year old steel. Jerrold, just to the north, was replaced for similar reasons. Jerrold was easier to do since it did not have the extra burden of the city's desires for a station on top of it.

As someone said, its messy.

Thanks all for the physics lesson!
-Des