Manhattan Bridge Speed Limit

[SubwayGuy]

The speed limits being there has less to do with the vibration caused and more to do with the ability of trains to CLIMB the grade...and the "safest speed" (post Willy-B accident) permissible on the downgrade that allows the train to stop reasonably quickly.

 

That said, the Manhattan Bridge does "twist" more because the tracks are at the outside rather than the center, but that's not "why" the speed limits are there.

[Kingsbridge Bus]

That R160 was probably slowing down, because they usually leave R68s in the dust.

 

Probably

 

Is the speed also different cause of how long the cars are cause 75fters may have to make sharper turns than the 60fters

[YankeesPwnMets]

They are the same speed limit, but you gotta remember R68s are MUCH heavier than R160s

[Eric B]

Yeah, the Manhattan bridge is a perfect example of poor bridge design. Since the Manhattan is a suspension bridge, it has much more flexibility. With the tracks at the extreme egdes of the deck, the deck twists a lot when a train runs over the bridge, which is not good for the steel deck when it happens hundreds of times a day. The proper design would have had the tracks in the middle (like the Williamsburg or the Brooklyn - look for older pictures) so that the bridge doesn't twist as much under the load.

 

However, I believe that the speed restriction is due to the very steep grades of the bridge itself and the complex trackwork that follows after each portal - the turn to Canal St. and the Chrystie St connection on the west and the crazy Flatbush Ave Extension interlocking/tunnels.

But we were comparing to this the Ben Franklin Bridge tracks, which are also on the outside. But I guess it's just one track per side instead of two.

Also, the grade seems similar to the Manhattan and Williamsburg, from what I remember.

[fordhamkid7721]

My R68 actually beat an R160 across the bridge & was going about 5 mph faster

Lol IMO it was probably because leaving Canal you have a steeper up grade and sharper curves than leaving Grand so the had an advantage.

[Forest Glen]

Yeah, the Manhattan bridge is a perfect example of poor bridge design. Since the Manhattan is a suspension bridge, it has much more flexibility. With the tracks at the extreme egdes of the deck, the deck twists a lot when a train runs over the bridge, which is not good for the steel deck when it happens hundreds of times a day. The proper design would have had the tracks in the middle (like the Williamsburg or the Brooklyn - look for older pictures) so that the bridge doesn't twist as much under the load.

 

However, I believe that the speed restriction is due to the very steep grades of the bridge itself and the complex trackwork that follows after each portal - the turn to Canal St. and the Chrystie St connection on the west and the crazy Flatbush Ave Extension interlocking/tunnels.

 

They added diagonal stays to the Manhattan Bridge that limits its swaying. Even a perfectly designed bridge will have wear and tear after a heavy subway car goes across it. Trains crossed the Brooklyn Bridge for over 60 years. The damage was so profound that it had to be rebuilt and is limited to passenger cars.

[Grand Concourse]

Point is the trains should be in the center of the bridge than on the sides. Willy B was probably pretty fast, but because of the crash the trains have been restricted by timers ever since.

[DJ Flxible]

Every time I take a train ride over the Manhattan Bridge I feel as if my life could be at stake. You can feel the bridge oscillating under the weight of the train and to people riding a bike over the bridge a passing train can feel like an earthquake. The towers are practically 2D so even passing trucks can really shake things up as the whole structure just acts like a bow. Every passing train can lead to microfractures as every train deflects the structure by 4 feet, so two trains crossing from opposite sides simultaneously can cause a whopping 8 foot twist. It's not quite as ludicrous as running trains across the Brooklyn Bridge was, but if they don't build a new tunnel for the trains they're eventually going to have to replace the bridge. :eek:

[Y2Julio]

huh? You can't be serious.

[nel070]

The Manhattan Bridge wasn't really designed properly for train usage.

 

Very true

[Grand Concourse]

They are the same speed limit, but you gotta remember R68s are MUCH heavier than R160s

 

I'm not sure, but I think a 600' R160 train might be heavier than a 600' R68 train.

A single R68 will be heavier than an R160 car because it is longer, but in sets I think the r160s edges out the R68s.

[Rutgers Tube]

The Manhattan Bridge wasn't really designed properly for train usage.

 

Remember that streetcars ran on the bridge for several years from the time that opened until the BRT took over pushed the streetcars upstairs. NYC DOT recently added a truss stiffening system to reduce the amount of twisting on the bridge. The Williamsburg, though traditionally referred to as a suspension bridge, actually has cantilevered side spans, while the center span is that of a suspension bridge. The 59th Street (Queensboro) Bridge had two train and four streetcar tracks for close to fifty years, and is also a cantilever design. 59 and Willy can use the cantilever design because of their approach grades; Manny can't. The twisting action caused by the trains, coupled with the winds coming off the Wallabout Bay and from the Narrows add to the issue, and the steep entry and exit and complex interlockings at both side are most likely the cause of the speed restrictions.

 

In reality, the most-perfect (and my personal favorite) bridge in NYC is the Hell Gate, with its through-arch design. Read up on how perfectly designed and constructed it was. If humans ceased to exist in NYC, most of the bridges would seriously deteriorate and collapse at around 300 years. The Hell Gate would go a 1,000 or more. That's sick.

[SmallParkShuttle]

The speed limits being there has less to do with the vibration caused and more to do with the ability of trains to CLIMB the grade...and the "safest speed" (post Willy-B accident) permissible on the downgrade that allows the train to stop reasonably quickly.

 

 

...the steep entry and exit and complex interlockings at both side are most likely the cause of the speed restrictions.

 

In reality, the most-perfect (and my personal favorite) bridge in NYC is the Hell Gate, with its through-arch design. Read up on how perfectly designed and constructed it was. If humans ceased to exist in NYC, most of the bridges would seriously deteriorate and collapse at around 300 years. The Hell Gate would go a 1,000 or more. That's sick.

 

That's what I've been trying to say on the issue!

 

However, if everyone else is right, then I believe they need to restrict the R160's speed on the uphill climbs, because their power basically nullifies any speed restriction that any other fleet would get on the uphill climbs.

 

Rutgerstube: Yes streetcars did use the tracks before the trains, but the comparative weight to a train is quite negligible. I would more compare them to trucks than trains.

 

The hell gate is a beautiful and well designed bridge (though upon research, it is said that the HUGE stone abutments are more aesthetic than structural) and it was built for one purpose: trains.

[Forest Glen]

Despite it's design flaw, the Manhattan Bridge is probably the strongest bridge in the city. The Manhattan Bridge and the Williamsburg Bridge are the only two major bridges (not counting the Broadway Bridge) that carry subway lines. Still, had it been designed correctly, money spent on its extensive rehabilitation could've been saved.

[NX Express]

I'm not sure, but I think a 600' R160 train might be heavier than a 600' R68 train.

A single R68 will be heavier than an R160 car because it is longer, but in sets I think the r160s edges out the R68s.

 

You're right. While ONE R68 is heavier than ONE R160, a set of R68s is lighter than a set of R160s.

[Rutgers Tube]

Despite it's design flaw, the Manhattan Bridge is probably the strongest bridge in the city. The Manhattan Bridge and the Williamsburg Bridge are the only two major bridges (not counting the Broadway Bridge) that carry subway lines. Still, had it been designed correctly, money spent on its extensive rehabilitation could've been saved.

 

Anyone here know what the average number of trains per day/week is that cross the Hell Gate? I'd think that refuse/freight headed to Oak Point, NJT and possibly Amtrak (depending on the service) would all weigh more than an NYCT train at 5 pm crossing weight the Manny or Willy, but the number of trains running across the two would be substantially larger than what crosses the H.G. I still think the H.G. is the strongest and least-structurally compromised of any of the bridges in NYC, through the VNB is definitely a strong contender.

 

I also found this to be really interesting, read here:

 

http://www.nycroads.com/crossings/manhattan/

 

As applied on the Manhattan Bridge, deflection theory allowed for economies of material, cost and time. However, the theory did not take into account the problem of the subway trains on the outer parts of the lower deck. Over the years, heavy subway traffic caused considerable twisting of the deck. Maximum torsion occurs when subway trains start to cross opposite sides of the bridge at the same time. At that moment, one side of the roadway dips four feet to the north side, while the other side of the roadway dips four feet to the south side, creating a total roadway deflection of up to eight feet.

 

 

Special thanks goes to Eastern Roads at

 

http://www.nycroads.com/.

[SmallParkShuttle]

They added diagonal stays to the Manhattan Bridge that limits its swaying. Even a perfectly designed bridge will have wear and tear after a heavy subway car goes across it. Trains crossed the Brooklyn Bridge for over 60 years. The damage was so profound that it had to be rebuilt and is limited to passenger cars.

 

I am assuming the diagonal stays were added under the deck, right?

 

As applied on the Manhattan Bridge, deflection theory allowed for economies of material, cost and time. However, the theory did not take into account the problem of the subway trains on the outer parts of the lower deck. Over the years, heavy subway traffic caused considerable twisting of the deck. Maximum torsion occurs when subway trains start to cross opposite sides of the bridge at the same time. At that moment, one side of the roadway dips four feet to the north side, while the other side of the roadway dips four feet to the south side, creating a total roadway deflection of up to eight feet.

 

Ok I understand the first part, but the second part about the total roadway deflection doesn't make sense to me. If the north side dips 4 feet, and the south side dips four feet, doesn't that mean that the entire roadway deflects four feet, since both sides deflect in the same direction?

[DJ Flxible]

You may have seen this already. Maybe it's an illusion, but as the approaches to the towers sag, the center span seems to rise.

 

 

[Y2Julio]

You may have seen this already. Maybe it's an illusion, but as the approaches to the towers sag, the center span seems to rise.

 

 

 

Bridges are designed to be flexible. All Bridges move like that. If they didn't they would collapse. That video is also timed lapsed.

[SubwayGuy]

Bridges are designed to be flexible. All Bridges move like that. If they didn't they would collapse. That video is also timed lapsed.

 

Correct. If bridges had no flexibility they would rip themselves apart. Not to mention all the damage that would be caused in warmer weather when heat causes the steel to expand.

[Rutgers Tube]

Ok I understand the first part, but the second part about the total roadway deflection doesn't make sense to me. If the north side dips 4 feet, and the south side dips four feet, doesn't that mean that the entire roadway deflects four feet, since both sides deflect in the same direction?

 

No. Trains are entering the bridge from opposite directions on opposite sides, as in exact opposite corners of the bridge. The bridge can move like a Barry Zito curveball.

 

Bridges are designed to be flexible. All Bridges move like that. If they didn't they would collapse. That video is also timed lapsed.

 

I like Y2Truelio better.

That's precisely why joints, struts, arches, plates, shells, ties, beams, columns and a whole lot of education, time and money are put into a bridge. The average citizen doesn't realize that there aren't any Build-A-Bridge or Bridge-In-A-Box kits at Home Depot. Bending and buckling capacities and essentially and very carefully factored into every billionth of every inch and too little or too much can make for some real messes. Think of vehicle's (car, truck, bike, skateboard... whatever) suspension. And as far as the video goes... I wish traffic around these parts moved that rapidly!

[NX Express]

Although the video is in fast-forward, it shows why the Manny B was closed for 20 years (partially).

[38th Street Yard]

the broadway way side is slower with the timers than the 6th ave side is

[Harry]

the broadway way side is slower with the timers than the 6th ave side is

 

Do you know this for sure?

[38th Street Yard]

Do you know this for sure?

 

yes somethimes with my friend he is a T/O and his has 15 years and he told me there is a different broadway is slower when your on the down grades going north and south