Are Rail Bridges Built Better Than Highway Bridges?

Highway and Road Bridges are designed for a loading designated as AASHTO HS-20-44. Additional loadings include dead weight, railings, lighting, wind, impact, etc.

Railroad bridge engineers normally start the design with AREMA's  E-80 loading. This loading is based upon a heavy 2-8-0 Consolidated locomotive double headed.

Now type in "Structural Engineering Influence Lines" to become completely confused.

An interesting story (well I think it is). Many years back I was working on Conrail’s clearance improvement project by preparing the design, plans, and specifications for raising bridges over the railroad. At a meeting with Jeff May who was Conrail’s Chief Bridge I asked him why the minimum thickness of steel plates was 4 times what was needed to carry the necessary loads. His answer was because we know we will not do any maintenance and they will be rusting away.

Again as I said years ago, bridges are designed differently than buildings. Stricter design codes and better steel.

I once designed a building  column that shared a bridge support. Architects couldn't understand why my column was so much smaller than the bridge support. The large sized bridge support interfered with the architects' plaza design.

Since the bridge engineer worked at my engineering firm, the architects wanted me to convince the bridge engineer to reduce the support size.

Never happened.

@AlanRail posted:

Again as I said years ago, bridges are designed differently than buildings. Stricter design codes and better steel.

Not stricter design codes just different design codes.  The requirements placed on a building may be less restrictive in some areas, but they are no less stringent than that placed on a bridge.  Life safety is the foundation of all building codes, and a lot of testing and science has gone into how those codes are written.  The pure amount of regulation for life safety is very comprehensive when one looks at the number of different codes and regulations that apply considering the IBC, IECC, NEC, NFPA, IPC, IMC, and other building codes combined with federal laws such as the ADAAG.

As to better steel, my AISC steel manual has the same design values as everyone else's.

AlanNH - Quit it you are killin me.  Your Bridge Engineer is like most Engineers (Look at my occupation).  If you ignore suggestions from people that don't have a clue what you get paid to do, eventually they will leave you alone.

Let’s add railroad tunnels to the mix.

How long will a railroad tunnel last before it has to be replaced?

Open to railroad traffic on July 26, 1910. The owner is the Canadian Pacific Railway and in the 90’s the tunnel on the left was raised to handle auto racks & double stack intermodal transports.

I took these photos at the Detroit Windsor Railroad Tunnel last year,

To see how this tunnel was raised in the 90's, check out this seven minute YouTube video.

https://www.youtube.com/watch?v=fnSfOuCJdR4

Gary 🚂

@trainroomgary Thanks for the informative video.   This is an interesting topic.  Thanks to all those who have replied.

Some good responses on here, Jack L's comes to mind. When you design a bridge there are myriad factors, whether it is road traffic or rail traffic but the fundamentals are the same. Engineering practice used to be to design at close to 2x expected load values, these days I hear it is much less, like 1.25. It could be they used to overdesign or they reduced the safety margin because of cost (my knowledge of this is not based on me being a CE, but I had members of my family who were).

As to why a bridge needs to be replaced and whether a rail bridge is 'built better' than a road bridge, a lot of the same factors come into play. Most bridges are built where they have an expected lifespan, the old Tappan Zee Bridge, built in the 1950's, was supposed to have a roughly 50 year lifespan; its replacement was finished several years ago. In theory with proper maintenance any bridge can last a long time, but that is the catch, proper maintenance. Given the cost of that kind of maintenance, and the vagaries if financing it (private or public, it doesn't matter), so what often happens is bridges aren't maintained well, they get patched, then they find later it is in bad shape and can't be patched and they finally have to replace it.

There are also things like vibration that damage bridges as well. One thing road bridges face is constant traffic, think of a major feeder highway to a city area. Obviously some train bridges face the same thing (there is a clunky old drawbridge over the Hackensack river in the Great Jersey Swamp aka "Meadowlands", the portal bridge, that once again today got stuck and train travel for Amtrak and NJ  Transit into NY Penn is suspended for the day, has a lot of traffic), but I suspect some roads have the factor of constant traffic. 

Road bridges and rail bridges have a common foe, salt. Highway bridges where they use salt are under assault every winter. Bridges, road or rail, that cross bodies of salt water, are exposed to salt water laden winds (the poor bridges across the East River face that in NYC, as well as road salt).

As far as buildings, they are designed to different parameters, their loads and stresses are much different than a bridge faces, though most of the physics is the same.

Some bridges are well designed, others are not. The Brooklyn Bridge happened to be way overdesigned, partially because that was the nature of the Roeblings (if you cut the 4 main cables of the Brooklyn Bridge, the roadway would not go down, the cables radiating from the towers (similar in principal to a cable stayed suspension bridge) would hold it up, albeit with a lot of sag). The Brooklyn bridge actually is interesting, you can say it is both types, it was designed (or rather, redesigned in the middle of building it) to handle standard passenger trains of the time, steam engines and all. The Brooklyn bridge is such that if they do routine maintenance, including replacing the cables every so often, would likely last forever as would many structures.

We need to keep in mind when the bridges or other structures where designed and built. Most railroad bridges where designed and built in the late 19th century and early 20th century. The designed codes then were much different than they are today. Design methods have changed from Allowable stress design to Load & Resistance Factor design to Load Factor Design to Ultimate Strength design. Another huge difference is the development of sophisticated methods to analyze a structure to determine the forces to be designed for.

Here are a couple of points to consider:

1. Factors of safety are dependent on the reliability of the information with respect to applied loads and strength properties of the materials to be used.
2. In the late 19th and early 20th centuries the individual companies producing steel developed the design stresses to be used in the design of bridges and buildings. It wasn't until 1921 that the American Institute of Steel Construction came into existence and that for the purpose of bringing consistency to the design and construction standards for structural steel used in building construction.
3. The American Association of State Highway Officials (AASHO) was founded in 1914.
4. The American International Association of Railway Superintendents of Bridges and Buildings was formed in 1891.
5. Each of these associations prepared design codes and standards for their respective area of interest. The basic allowable stress in steel for railroads and highways is 0.55 fy while for buildings it is 0.6fy. If you were using A36 steel (fy = 36 ksi) the allowable stress for railroads and highways is 19.8 ksi while for buildings it is 21.6 ksi.

The North Portal Bridge over the Hackensack River that carries all the traffic from NY Penn Station is going to be replaced. While it is deteriorating the main advantage will be by raising the bridge it will no longer need to open for water traffic. Bridges with movable spans seem to be more susceptible to issues causes by lack of adequate maintenance.

The attached shows the planned new span and a great animation on the project.

New North Portal Bridge

@GG1 4877 posted:

Not stricter design codes just different design codes.  The requirements placed on a building may be less restrictive in some areas, but they are no less stringent than that placed on a bridge.  Life safety is the foundation of all building codes, and a lot of testing and science has gone into how those codes are written.  The pure amount of regulation for life safety is very comprehensive when one looks at the number of different codes and regulations that apply considering the IBC, IECC, NEC, NFPA, IPC, IMC, and other building codes combined with federal laws such as the ADAAG.

As to better steel, my AISC steel manual has the same design values as everyone else's.

When I was still in the steel business people would always ask me what the best or strongest steel was. My answer was always a question in return which is for what?  It's all application specific. Poor quality steel is out there but that's a separate subject.

You make good points for sure.  Most steel issues I've had are related to poor process control or incorrect design criteria.  The worst issues I had to deal with were improper quench post austenization.

The worst failures I saw though were due to improper application of a specific grade or strength level.

Personally after 30 years in the architectural profession and having obtained licensure in 7 jurisdictions including California that requires a separate exam is that it takes a team to deliver a project in the built environment that includes architects, engineers, building contractors, and those that are willing to fund these endeavors.  The best projects come from a highly functioning cohesive team and the worst come from those projects where a discipline or a team member feels that their role is more important than any of the others. 

To the OP, I think we see that the railroad bridges that were built prior to introduction of the automobile in the early 20th century are designed to a very high factor or safety.  The Rockville Bridge across the Susquehanna was designed as a 999 year leaseback to the PRR.  With ultimate strength design being introduced in an era when budgets started to matter more, we see that the replacement cycle might be more frequent. 

However, having said that I fully believe in buildings and on bridges that the lifespan is only as good as the maintenance received over its life.  On a building, first cost represents about 10%-13% of life cost.  Maintenance plays a big role in the life span of any built structure and deferred maintenance is often the reason we see degradation and failures in structures.

Lots of interesting points here.

The answer to the original question is a "qualified" NO.

One thing I have to say, that has been touched on in many of the posts is that design standards / philosophy are a product of the times.  I am a Mechanical Engineer not a Civil Engineer but designed Heavy Industrial Machinery for the bulk of my career.

I live along the Hudson River, which is spanned by some world Recognized Bridges.  GW, Tappan Zee, Bear Mountain and some lesser know.  One bridge close to me, is presently called the Walkway over the Hudson a reproposed RR Bridge (NH Maybrook Line).

https://en.wikipedia.org/wiki/Walkway_over_the_Hudson

Railroads at that time were building "bridges for the ages".  Read the link for more info.  If still required, it would be in RR service today.

As previously mentioned the Tappan Zee when built was designed for a 50 year life.

https://en.wikipedia.org/wiki/Tappan_Zee_Bridge_(1955%E2%80%932017)

Deferred Infrastructure replacement in this Country puts more lives in Jeopardy than most people realize.  This is not a political statement, it is Fact, that Engineers know and live with.  Read the link for more info.  If not for the I35 bridge collapse in the Twin Cities.  There probably would still be debates if another coat of paint could extend the bridge's life.

In between these two bridges, geographically and chronologically is the Mid-Hudson bridge.

https://en.wikipedia.org/wiki/Mid-Hudson_Bridge

Today is it's 92nd birthday!  It has another good 100 years in it!

So the summary Engineers and Bridge Builders, then and now, know what they are doing.  The Longevity of a bridge or any structure is determined by the design criteria given to them at the time of Construction.

BTW people are NOT infallible (despite what some people say Engineers are people, LOL).

https://www.youtube.com/watch?v=j-zczJXSxnw

Bridge maintenance, (a very good coat of paint) is part of longevity.  Then there is the lead based paint issue.

@Mike CT posted:

Bridge maintenance, (a very good coat of paint) is part of longevity.  Then there is the lead based paint issue.

Only issue with lead based paint is when they strip a bridge they have to be careful to catch the paint coming off since it could be lead based. They haven't used lead in paint in a long time, but there are a ton of old buildings and other structures painted by it.

Very cool topic.  I am an educator and not an engineer, but I was able to follow along well and understand well.  Thanks all!

Some amazing knowledge on here, it is always great to have a diverse group of people when discussing things. One of the bridges I always wonder about is the castleton on hudson bridge (CSX), that is located right next to the Mass Turnpike extension to the NY State Thruway. It is in operation, but honestly it looks like a pile of rust. I can't figure out if they have it primed and it is waiting painting, or if that is the color, but it looks pretty bad (least it did the last time I went that way several years ago). I am sure it is structurally sound and looks can be deceiving.

Projects like bridges as Jonathan and others have mentioned are full of tensions. The people who pay for it want to minimize the cost and then change their mind mid project, engineers tend to want to design things with a lot of fail safe built into it that could be expensive or difficult to implement, the people who have to construct it have their own ideas, so you get all kinds of things involved.

Sometimes too trends in engineering go in a way that turns out not to be a great idea. In the 1920s and 30 bridge builders (really suspension bridge engineers) wanted to build bridges that were relatively light and aesthetically looked like they were flying over what they were bridging. The Tacoma Narrows Bridge went down in 1940 because it was built without trusses and had a solid deck, that forced the air flow over and under the bridge deck , which created the movement it was known for (basically same principle as an airplane wing, only the lower/higher pressure could be on the top or bottom). On older bridge designs the wind would flow through the deck trusses.

The area where the bridge was located is subject to fairly high winds and on a high wind day it went into oscillations and the deck tore from the suspended cables. In the end the board of inquiry absolved the engineer who designed it , because he was using principles that engineers had been using and we considered safe (O.H Ahman, who designed many bridges in the NYC area including the George Washington and Verrazano, had to go back and retrofit the Whitestone Bridge , an expensive proposition, because he realized it was built to similar principles and could experience the same kind of collapse).

The Citibank building in NYC underwent an emergency retrofit of a sliding weight system designed to dampen the buildings motion in the wind when a hurricane was thought to be heading towards NYC. Engineers realized in those kind of winds, the build could move enough that the top of it might break off the building (I don't recall the whole story, remember seeing it on a tv program about engineering issues).If I recall correctly they were literally racing the clock (fortunately the hurricane went out to sea).

The bigger problem IME is maintenance, it is the first thing that gets cut back on when companies or cities experience financial issues (basically it is kicking the ball down the road, common human failing) and structures are complicated things in real life. Bridges have bearings that need maintenance and lubrication, expansion joints need to be clear, suspension cables have to replaced, suspenders need to have a certain amount of movement, and of course repainting the bridge regularly, including the zinc base primer that helps ward off rust. It is the old story of course, pay me now or pay me a lot more later.

Do a google search on CORTEN Steel, you may find this very interesting

This is used in most new modern bridges structures. It is left bare metal intentionally as it creates a surface rust coating that becomes weather resistant and protective to the underlying metal.

I realized although my prior post was lengthy, my sarcastic comment about putting another coat of Paint on the original Tappan Zee Bridge could be misinterpreted.  When the bridge's longevity is calculated Proper Maintenance is assumed.  The discussions on the replacement vs life extensions went well beyond that due to the costs involved.  Anyhow the I35 collapse is what really got things moving along (sad but unfortunate).

So can't help myself but gotta cite another bridge over the Hudson.  This time the Newburgh-Beacon I84 Bridge.  When I first starting driving over 4 years ago, I noticed the 2 Spans though similar in appearance are NOT the same.  Please read this.

https://en.wikipedia.org/wiki/...2%80%93Beacon_Bridge

To help disguise the fact the Older Span is NOT Cor-Ten, they paint it a rust color to "match".  LOL  Sorry, maybe only Engineers find that funny.

The Castleton Bridge, "I would bet" is properly maintained.  I would agree with bigkid, never judge a bridge by it's (rust) color.  Also surface rust does NOT necessarily mean the steel is compromised.  If you ever see I-Beams sitting around waiting to be installed on a construction project, they usually have a nice ""patina" of rust.

Many railroad bridges were built in the 19th century and would have been constructed out of wrought iron and cast iron. Wrought iron has the property of being resistant to corrosion so the bridge may look rusted but remain in good condition.

As far as CORTEN steel that was mentioned in some other posts is resistant to rusty, but does not far well when subjected to de-icing chemicals or other environmental conditions such as acid rain.

You also mentioned sandblasting and repainting in your initial post.  Almost all railroad bridges were originally painted with lead-based paints, and repainting them requires remediation.

To sandblast lead-based paint off of steel structures in a railroad bridge requires use of a hazmat contractor to capture all paint flakes and dust.  This is expensive, and not worth it to the railroad, in most cases.