Protected Sidewalks on Vehicular Bridges

[STrctPono]

Our State has (in my opinion) a rather strange stance on providing protection to pedestrians when traversing a bridge and I wanted to get everyone else's input on what the standard of practice is in their State.

For example, new highway design, speed limit less than 45 mph. Highway has sidewalks on both approaches to the bridge. No protection between roadway and sidewalk for pedestrians. Just a 6" "mountable" curb. Once you get on the approach slab/bridge, MASH barriers are required between roadway and sidewalk to protect the pedestrians!? This creates strange details for how you transition from this MASH barrier to guardrail and how the guardrail transitions to either end treatment or back to the guardrail on the outside of the sidewalk. In my opinion, not a very aesthetic design, isn't rational, and is a pain to detail for the Engineer.

 

[bridgebuster]

In NY it's case by case. Generally no barrier unless it's a high speed roadway or there isn't a raised sidewalk. I was involved with 2 bridge project and a highway project with barrier between the sidewalk and roadway.

This is a bridge along a high speed parkway (in NY a parkway is limited access highway without trucks), we have single slope barrier along the travel way which extends beyond the approach slabs and transitions to corrugated beam guiderail. Unlike your situation we didn't have to tie the inner guide rail to the outer.

Link

On another project, we have a corrugated beam guiderail along the travel way. The outer barrier is concrete parapet on retaining wall. Again, they're not tied together. At the leading end of the guide rail we have an attenuator type section. You might be able to see it at the top of the photo. The trailing end is anchored in line with guide rail.

We have another project under construction - rehabilitation of a viaduct that also carriers a rapid transit structure. There is concrete barrier along the travel way, which is intended to protect the columns of the RT structure. The columns are right at the edge of the roadway. The leading ends have tapered sections. There isn't any guide rail beyond the bridge.

 

[BridgeSmith]

The rationale I heard for having traffic rail to protect pedestrians on the bridge but not off of it, is that off the bridge there is an escape route for pedestrians (over the rail). On the bridge, there's nowhere for a pedestrian to go. Don't know if that's realistic, or not, but that's the explanation I was given.

Our metal post and beam railing system has a turn-down end treatment for locations where it doesn't transition to a guardrail.

Even where it does transition to a guardrail, there hasn't been a direct connection developed and approved yet (that we know of), so we've been using an 8' concrete parapet/barrier section to connect the bridge rail to metal guardrails. It's a PITA.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[MIKE_311]

Is it more of an issue in having MASH compliant barriers? I know the states I work in, if you place a TL-4 barrier on a raised sidewalk, the barrier drops to a TL-2, because the sidewalk can launch a truck over the barrier. Often time pedestrian fences and railings aren't MASH compliant so you have to put a MASH compliant barrier somewhere.

 

[BridgeSmith]

On low-speed roadways, the curb is assumed to be adequate to redirect an errant vehicle back into the roadway. On higher speed roadways, it takes something more substantial.

We usually avoid the problem by routing the sidewalk behind the guardrail, away from the roadway. If we can't do that, we continue a guardrail or bridge rail along curb, mounted to a reinforced curb, or reinforced curb and sidewalk combination.



Rod Smith, P.E., The artist formerly known as HotRod10

 

[OSUCivlEng]

Where I live the DOT typically uses an 8" raised sidewalk with no barrier between the sidewalk and the traffic. Typically sidewalks are only on roads with a speed limit of 45 mph or less. I believe the AASHTO LRFD Bridge Specs require a barrier between the sidewalk and traffic if the speed limit is greater than 45.

I did work on a large project for the Turnpike where sidewalks were placed on the overpasses going over the mainline. The sidewalk was at the same level as the deck and separated from the traffic by a TL-4 barrier. The outside parapet for the sidewalk was solid and 42" tall. The TL-4 barrier was 32" tall and also solid. I didn't understand why the barrier between the sidewalk and the traffic wasn't required to be 42" tall because that appears to be what AASHTO requires for pedestrians.

When I drive around the largest municipality where I live I see a lot of sidewalks separated from the traffic by a TL-3 barrier with openings that don't meet AASHTO requirements for openings.

I don't understand why the opening requirements only apply to the outside rail/parapet, but not the inside? Maybe some people conveniently ignore that.

 

[BridgeSmith]

I don't understand why the opening requirements only apply to the outside rail/parapet, but not the inside? Maybe some people conveniently ignore that.

Pedestrian railing that keeps people from falling over the edge is required to be 42" tall. Depending on the design speed, the traffic barrier may only need to be 32" tall in order to redirect an errant vehicle back into the roadway.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Settingsun]

I'm in Australia so pretty far removed, but US requirements do filter into our requirements to a degree.

Bridges usually trigger a requirement for some type of barrier even if the approach road didn't require it. Then, it is preferred to protect the pedestrians with that barrier if practical.

Are drawings 0720-07 to -10 the sort of transitions you're referring to?

https://www.rms.nsw.gov.au/business...s/standard-drawings/road/safety-barriers.html

 

[STrctPono]

All,

Thanks for your input.

Bridgebuster, just by the looks of it, I too wouldn't feel comfortable riding a bicycle in the bike lane of that bridge without protection.

My issue with our State is that it is a blanketed requirement for all bridges. The one I am currently working on is a road with a speed limit 35mph or less and it is straight so I just don't really see the purpose.

The rationale I heard for having traffic rail to protect pedestrians on the bridge but not off of it, is that off the bridge there is an escape route for pedestrians (over the rail). On the bridge, there's nowhere for a pedestrian to go. Don't know if that's realistic, or not, but that's the explanation I was given.

I was also given this same explanation. Sounds like a huge stretch to me.

I didn't understand why the barrier between the sidewalk and the traffic wasn't required to be 42" tall because that appears to be what AASHTO requires for pedestrians.

Yes! This is also strange. So we protect pedestrians from falling over the edge of the bridge but don't protect them from falling over into traffic!?

There are just too many holes in the story for why someone should use protection barriers between a sidewalk and the travelway if the speed limit is 35mph or less. 45 mph or less is questionable and should probably be case by case. Over 45 mph is completely understandable to place a protection barrier.

 

[bridgebuster]

STrctPono - the Belt Parkway is posted for 55 mph. The barrier along the shoulder is the standard NYSDOT 42” concrete with a traffic rail, to prevent (hopefully) a bicyclist from falling over.

 

[r13]

Yes! This is also strange. So we protect pedestrians from falling over the edge of the bridge but don't protect them from falling over into traffic!?

I think it has to do with statistics and human nature. In where I live, many/most bridges does not have traffic guardrail, yet we rarely hear pedestrian fatality on the news. On the other hand, every once a while, there are reports on people been killed on the city street sidewalks, especially on the late night and down hours. People, in their right mind, are risk conscientious while walking on the bridges, and tend to walk on the side farther away from the traffics, also are more alert on the environment due to higher traffic volume and speed. But the alertness is reduced while walking on city streets with low speed limit. We tend to forget that careless drivers, and drivers influenced by alcohol and drugs are everywhere (now this group includes texting while driving).

The only thing I don't understand is the stubbornness on at grade railroad crossings, how many people are dead, and vehicles crashed each year. But this belongs to another topic.

 

[BridgeSmith]

So we protect pedestrians from falling over the edge of the bridge but don't protect them from falling over into traffic!?

A fall over the traffic rail is unlikely to cause serious injury, unless there happens to be a vehicle driving on the shoulder right at that instant. However, a fall over the edge of the bridge has a good chance of being fatal.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[OSUCivlEng]

BridgeSmith,

Could you show me where the AASHTO LRFD Bridge Design Specs differentiate between a pedestrian rail on the outside of a bridge and a barrier between a sidewalk and traffic lanes? Below is the best I could find.

The following guidelines indicate the application of various types of rails:

• Traffic railing is used when a bridge is for the exclusive use of highway traffic;
• A combination barrier in conjunction with a raised curb and sidewalk is used only on lowspeed highways;
• On high-speed highways, the pedestrian or bicycle path should have both an outboard pedestrian or bicycle railing and an inboard combination railing;

The walkway faces of combination railings separating walkways from adjacent roadways serve as pedestrian or bicycle railings.

 

[BridgeSmith]

I'm not sure what you're looking for OSUCivlEng. The AASHTO spec. Defines Combination Railing, Pedestrian Railing, Concrete Parapet, and Traffic Railing in Section 13.2. Section 13.7 has design requirements for Traffic Railing, and Section 13.8 has the design requirements for Pedestrian Railing.

Traffic Railing—Synonymous with vehicular railing; used as a bridge- or structure-mounted railing, rather than a guardrail or median barrier as in other publications.

Pedestrian Railing—A railing or fencing system, as illustrated in Figure 13.8.2-1, providing a physical guidance for pedestrians across a bridge so as to minimize the likelihood of a pedestrian falling over the system.

Combination Railing—A bicycle or pedestrian railing system, as illustrated in Figures 13.8.2-1 and 13.9.3-1, added to a crashworthy bridge vehicular railing or barrier system.

Pedestrian Railings must be 42" high, and has basically the same requirements for strength as a pedestrian railing per the building codes.

The height and strength of Traffic Railings is dependent on the Test Level (TL-3, etc.) required by the conditions (design speed, level and type of traffic, etc.).

A Combination Railing has meet the requirements for a Pedestrian Railing on the pedestrian side and meet the strength requirements as a Traffic Railing.

Rod Smith, P.E., The artist formerly known as HotRod10