Grade now, Pave later 2

[CygnusX1]

My municipality has a new 4-lane divided arterial project where we will grade now for the entire template, but only pave half of it & leave the final 2 lanes to complete in 15-20 years when the traffic demand warrrants it. This way, the right of way acquisition and rough grading is completed initially, making a fairly easy future completion. I wonder if other agencies have tried this approach, and specifically:

* Whether they constructed stormwater inlets & pipes initially for the future lanes

* How the future lane area was graded, drained, and maintained

* Any unforseen problems or benefits.

Thanks

 

[cvg]

yes, it has been done. catch basins might have to be removed and replaced with curb opening type, but the pipe should already be in the ground and set at approx future required elevation. Drainage can then be accomplished with interim ditches and area drains. May require some removal and replacement of drainage structures if the future widening plan changes. Sediment and trash must be controlled in the ditch in order to avoid clogging the storm drain. Storm drain laterals and catch basins may have very shallow cover and the basins may have to be set low so that they are traversible to cars leaving the roadway.

 

[francesca]

Do they plan on adding topsoil and stabilizing the site? Erosion can be a problem, particularly on steep grades. We had one subdivision where they graded the roads for Phase 2 and didn't pave them or stabilize and they developed large ruts in a short period of time... not to mention were violating their NPDES permit.

 

[CygnusX1]

Thanks cvg and Francesca,

Yes, we plan to tosoil and seed the future lane area. The grades are somewhat gentle, 4% max.

I was also trying to think of innovative uses for the future lane area, perhaps some LID stormwater treatements (grassed swale, etc) without messing up the subgrade under future pavement. Any other ideas?

 

[TerryScan]

I guess my thoughts are:

Grade from the center toward the outside. Pave the "outer" 2 lanes and let the unpaved lanes be a larger median. Then one should be able to place all storm (sized for completed project) and not need to install any when the additional inner lanes are added.

 

[cvg]

that can be done, however there are some issues with that approach. If you don't stabilize the median area, than you will have erosion and sediment issues which will also affect the paved lanes. You can grade the median as a ditch which would be useful for water quality and for drainage. But you will need to provide temporary storm drain to drain it. Not sure what you would do with the temp system once you build out. The other problem is at intersections where you will have a divided road. Or, you may need to construct the ultimate intersection at the outset which will cost more.

 

[CygnusX1]

Thanks all for the thoughts.

I was also considering a reverse crown approach, where the 2 pavements drain towards the center median. This would be beneficial for a number of reasons (saves inlets and pipe, etc) but I know this is not commonly done. My research shows a lot of municipalities not allowing reverse crown streets.

Has anyone had any experience with this?

It seems a natural fit for LID techniques, getting all that water onto a center median area which can be dealt with in a number of ways (planter beds, grassed swales, etc.)

Salt would be a problem here in MO, but I understand that as long as the drainage doesn't clog and water is flowing thru the system, salt will take care of itself.