Inverted Crown in Public Street 1

[chengineers]

The developer I'm working with would like to use an inverted crown design for public roads within a large commercial development. He would like to create a more pedestrian friendly atmosphere by draining runoff away from the roadside parking. We'd then use inlets along the road centerline to convey the runoff elsewhere. We're in MT, so the developer would like people parking to not have to worry about ice or water when entering/exiting their vehicle.

Has anyone had experience with inverted crown streets or know of a city that accepts them as a standard?

Thanks!

 

[GeoPaveTraffic]

I've seen the detail in alleys, but not in a street.

The City of Clayton, Missouri using them in alleys. Try talking to them about their thoughts.

Mike Lambert

 

[Ron]

Inverted crowns are common in private parking lots, but not so much for municipal roadways.
There are problems with inverted crowns. First, there's a joint in the inverted crown. Not only is that bad because all the water flows across or along this joint to the inlet, but the joint itself is difficult to construct properly. "Pinch" rolling is more difficult and cross rolling can't be done if the slope is reasonable...it causes gouging. As a result, the joint in the asphalt starts to separate earlier than for other joints and the result is deterioration along the joint.

While the developers reasons for using the inverted crown might seem laudable, they are not pragmatic for the performance of the pavement.

 

[oldestguy]

So in winter there will be the usual snow banks along the edge of the road? No difference there. Or will there be curb and sidewalks also? What kind of longitudinal slopes? Make them a little steeper than near flat, and you maybe will take care of center puddles, maybe. Will you have to go through a zoning or development committee. I foresee quite a promotion show needed there. Explain to the alderperson what a clogged center drain inlet does for traffic with the ice possibly resulting in winter. Will teen agers be contesting to see how far they can splash to the sides as they drive along the center line during a rain storm? I take it there will be no cross walks so no one will cross these center puddles, or stand them as traffic goes by. If the old time dosing was there, at least no traffic hits the puddles. It's difficult to justify changing the usual past practices so problem situations like these will have to be overcome in getting acceptance by old timers in those committees.

 

[ameyerrenke]

All great points above. Also, when roads are icy, cars have a tendency to slip down the roadway's crown when starting/stopping, typically this would direct them toward the curb, but in this scenario it would direct them toward oncoming traffic. May not be a big concern, but another unintended consequence.

 

[DDBPE]

If you will be adding a drainage system anyway, why not construct the main travelway with normal crown and for the parking areas, use a pourous asphalt. The road would drain to it and then into the drainage system.

 

[civilman72]

An inverted crown is definitely a viable design if vehicle speeds are low. Considering this is a commercial development, I would anticipate that you could design enough traffic calming devices to control vehicle speeds.

The Town of Grand Lake, CO has an inverted crown on Main Street. One key to the design is a continuous concrete pan in the flowline (which address the concerns mentioned by Ron). See attached photo of Main Street, and ignore the hot blonde.

 

[oldestguy]

Besides the distraction, note the joint between concrete and the blacktop. Where there is water standing, low or high speed traffic will erode the pavement, causing potholes. It's that forceful velocity of the squished out water that does it. Any joint is then a starter place.

So, if it has to be used, better recommend all concrete.

Question, why is there foot traffic down the center of the road anyhow?

 

[Ron]

civilman72...was there a pavement in that photo?

 

[cvg]

historically inverted crowns were allowed around here, but they have since been banned by every local agency in the area. a better option might be a central median to capture and infiltrate storm water. not sure how pedestrian friendly an inverted crown would actually be. don't forget that during heavy rain, vehicles will need to drive through the water.

 

[civilman72]

While there is one small area of asphalt that is failing at the joint, the rest of the joint looks acceptable to me. This is probably because the asphalt was clearly constructed a bit higher than the edge of concrete which allows proper drainage onto the pan.

From my experience, the construction of the seam between the asphalt and concrete is more important than whether you move the water to the middle or the edge of road. I've seen plenty of asphalt and concrete fail at the joint on the outside of crowned roads, due to improper drainage. This occurs due to runoff/snow/ice accumulation at the seam and not necessarily due to vehicular traffic.

As far as foot traffic down the center of the road... the concrete pan in the middle or the road is not intended for foot traffic (not sure if that is why you were asking). Most people use the wood boardwalks next to the shops and on the outside of the road.

 

[Pinwards]

There was a street in that photo?

#

 

[oldestguy]

Civil Man: as to pedestrians in the street, guess the detraction sort of sways one's interpretation of the photo.

Ron: Guess you got swayed also. Same goes for Pinwards. But for me, at 85, I managed to see the rest of the shot, but it was tough. Wife came in the room.

 

[Ron]

OG...never too old to look...except when the wife's around then age doesn't count!

 

[ACtrafficengr]

CVG, I was wondering if an inverted crown with vegetated swales or other infiltration practices in the median would work. Do you know if it has been tried anywhere?

 

[civilman72]

I Googled "Grand Lake Main Street" and that photo was the only one that showed the whole cross-section of the street. I'm glad that some of you enjoyed it (Merry Christmas??). But you should have had the guts to keep it open when your wife showed up. This is an engineering site after all, I'm sure she would understand...

CVG: Was the use of inverted crowns banned because of the reasons listed above (i.e. vehicles driving through water, tendency for cars to slide towards oncoming traffic, asphalt seam construction issues, etc.) or were there other reasons?

As also stated above, inverted crowns are very typical in parking lots, so I'm trying to understand why they would not be allowed in a low-speed road.

 

[cvg]

yes, we use vegetated swales in the median

I'm not sure I know all the reasons for eliminating inverted crowns, but the reasons stated previously are all valid.

 

[civilman72]

cvg: How do you keep vehicles out of the vegetated swale and still allow runoff to get to the swale? I'm assuming curb/gutter with openings.

 

[cvg]

yes, curb and gutter with scuppers to capture the water

 

[beej67]

So THAT'S what she means by "inverted crown."



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