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GRANITE80 (Civil/Environmental) (OP)
19 Jul 07 15:28
I am looking for what other designers consider maximum parking lot grades for comfort and safety.  This particular case is for an office building - no shopping carts or loading necessary.  

I have been looking to hold a maximum cross-slope and forward slope of 5%, which results in a net slope of over 7%.  I have however, been keeping my drive aisles to a maximum cross-slope of 4%.  Any thoughts?  I'm dealing with an extremely steep site, so I want to max out the grades but not be pushing the envelope of comfort.  Thanks!  
civilman72 (Civil/Environmental)
19 Jul 07 16:33
Sounds like you have it about right.

Typical standards in mountains in Colorado include 5% parallel and perpendicular grades, which results in 7% cross-slope you mentioned.  We deal with ice/snow so people slipping while getting out of their car is a problem, but may not be for you.  I think the biggest design concern across the nation is that if you get too steep you will have to hold your door open to keep it slamming back onto you.  I've visited friends in San Fran and they park on 15% streets and holding your door open can be done, but it's not the best design, or very convenient.

Besides, that I can't think of any other major reasons for limiting your parking grades.
TerryScan (Civil/Environmental)
20 Jul 07 9:22
I work in an extremely flat area, so I do not encounter this extreme.  I am curious about ADA accessible route issues though.  I thought the max accessible route slope is 5% which would render the 7% net slope non-compliant. (of course one could insure that the area from accessible parking to the facility does comply).
civilman72 (Civil/Environmental)
20 Jul 07 9:57
Point well taken.  ADA accessible routes cannot exceed 5% in profile (without use of handrail) and 2% cross-slope, so you should tweak your parking lot grading when near the ADA spots.
GRANITE80 (Civil/Environmental) (OP)
20 Jul 07 13:52
Thanks for the comments - much appreciated!  And good reminder about the ADA issues.  This project is a great challenge!  I have a regulatory floodway on the property, with no fills allowed, a BFE elevation 8 feet above the elevation of my driveway approaches, slopes ranging from ten to thirty percent, and to top it off, a large irrigation canal on the hill ABOVE my proposed building.  To top it off, this is my first project being fully modeled using Autodesk Civil 3D.   Thanks again!  clown
Helpful Member!  hawstom (Civil/Environmental)
29 Aug 07 16:57
We have an parking space in front of our office that slopes upward 8%.  I don't think there is any door-slamming problem since the 8% is in the forward direction.  It may be that in the cross direction it would be a problem.  I will have to take our smart level out and run a few tests around town.

Tom
hawstom (Civil/Environmental)
29 Aug 07 17:18
I tested the 8% parking space in forward and reverse.  I believe it might be noticeably steep to a layman, but the car doors didn't have any trouble at all with it.  I think it would be a little excessive as a cross slope.  I wouldn't exceed by much 8% going into a parking space.

I couldn't test the 8% as cross slope yet, but I will do a little more testing and report back later.
DarthSoilsGuy (Geotechnical)
30 Aug 07 6:03
on a side note,
i'm ok parking spots that you have to open the door 4 or 5 times while you're putting in the groceries. i dislike parking spots that open the doors wider for you and make you look around to see if anybody was watching.

on a real note:
We start off with a default of a 2% cross-slope for all pavement and walks on the plans we develop.  we've had bad experiences with contractors messing up with slopes less than 2% and giving us birdbaths.
msucog (Civil/Environmental)
30 Aug 07 17:22
8% seems excessive to me unless you're talking about a mountainous area. here in the south, we see lots of stuff blow out during a heavy rain fall at 7-8%. typically, 5% is the upper limits of what i like to see. i'm pretty sure i would not want to be the handicapped person trying to go up an 8% slope (since you'd probably end up going backwards down the slope). i often see 3% and it works well.
hawstom (Civil/Environmental)
30 Aug 07 17:32
Clarification:

8% is not ADA compliant; around ADA spaces, the max slope in any direction is 2%.  (2% forward plus 2% cross-wise is 2.8% total and not allowed.)

8% is too steep for a cross slope; car doors won't stay put at that slope.

8% works only as a forward or reverse slope for non-ADA parking space.  And I might not use it for a downward facing space (too much weight on door just as it gets to the dangerously open point)

I hope that sounds better.

Tom
hawstom (Civil/Environmental)
4 Sep 07 12:08
I did some field work with a smart level.  Here are my field notes followed by some comments:

September 4, 2007 7:26 a.m.
7601 E Main ne corner, cross 8% lay notice, door will hold @ notches not heavy
Drive Entrance break 9.2%(6')+9.2%(long), scary, but no scrape
7715 E Main, cross 7.5% back, 9.6% front, very noticeable feel and look, doors somewhat heavy but hold at notches, unassisted close, unassisted open halfway.
9% down forward, no door trouble, seems steep for clutch & tran

Comments:
The main disadvantages of the tested slopes seemed to be
-18.4% drive entrance grade change was scary and my Honda Accord probably would have scraped bottom if the short side of the break (the sidewalk) were much wider than 6'
-Parking slope of 9% seemed a little much in the forward direction due only to clutch/transmission awareness, though there was no real absolute "problem".
-Parking cross slopes I tested are in the gray area where doors could possibly barely skip over their stops and gently tap neighboring cars on their own, but possibly no more likely than a hurrying and insensitive person to cause damage on a flat space.


Just because I have 15 years experience avoiding such steep slopes, I will probably still not exceed 8%, especially since at that slope a lot of elevation can be covered quickly.

I hope this is helpful.

Tom

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