Modern Roundabout Truck Aprons 4

[TrafficDesigner]

I am researching different types of truck aprons for a roundabout design group that I am a member of.

I am interested in aprons used in the construction of Modern Roundabouts and I am curious as to what experiences anyone has had and if they prefer one type over another.

Specifically, what slope have you used, did you drain it inward or outward, apron width and material type.

If possible, any lessons learned after construction was completed. (good or bad)

I have read Ourston's guide, and FHWA guide along with some others, but I am more curious to learn from what people have actually done and the results of their work.

Thanks in advance for any advice or comments, in return I'll share what I know about the design of Modern Roundabouts.

 

[TrafficDesigner]

I haven't used an oval one. I did find an egg shaped kind of make shift traffic circle once though. I think it was the Architects version of on-site traffic control though, as it was built in a shopping center near an entrance. It had stop signs and one way signs etc... and on one leg of it, in order to enter the thing you had to make a right hand turn at the stop sign. I'll post an aerial photo if I can find it.

Attached is a .PDF file of one of the truck aprons I have used on a couple of projects. I like this one because the curb is high enough that a smaller car is less likely to drive on the apron and yet a large truck can drive right up on it.

 

[Debaser]

I'm sorry to resurrect and slightly de-rail this thread, but could a US engineer tell me exactly why roundabouts are treated with so much suspicion and it seems, on occasion, hatred.

Having had them for forty-odd years in the UK, I think they're one of the easier highway features to understand, even if we do have to first turn left in order to turn right.

 

[TrafficDesigner]

Well said Debaser! I believe the negative reaction to them comes from all of the poorly designed traffic circles that were constructed in the U.S. before we caught on to the modern roundabout that other countries have modifed and groomed over the years.

With the previous traffic circles you don't know who has the right of way and some of them are not signed or striped and are very confusing. The right of way is given to the most aggresive driver or the one with the least expensive vehicle.

Most of the negative feedback I hear, is from people describing an old traffic circle and not a roundabout.

I have to agree with some of their comments on the old traffic circles. They should be converted where they can be, or yield signs added at a minimum.

 

[ACtrafficengr]

In a word, neophobia.

Also, I think it is because signals take away a lot of the need to think, and roundabouts work in part because drivers are forced to think.

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust

 

[Debaser]

Thanks, TrafficDesigner and ACtrafficengr.

I've got to admit to a sly smile whenever I've read discussions about roundabouts on US websites. They seem to be the work of the Devil, or worse, 'furriners'.

I've attached a photo of a fairly run-of-the-mill urban roundabout from near my workplace. It's 70yds north-south and 75yds east-west. Three lanes on the circulatory (wide lanes by our standards), one approach with four lanes, and during peak hours relatively heavy flows. And yet a very good safety record. The worst case being periods of light traffic when approach speeds are higher and gaps (apparently) larger.

I imagine (based on those discussions I read) that such a layout in the US would lead to carnage, if it ever got built in the first place, of course.

 

[Cara413]

I work for the Wisconsin DOT, and just this summer was part of the construction oversight of a multi-lane concrete roundabout. Much of what we did was already mentioned: 10' truck apron, 2% pitch to the mountable curb & gutter on the outside of the apron, verticle curb on the inside. This was an urban roundabout, replacing a very busy and ineffective signalized intersection. There were inlets in the gutter surrounding the truck apron. I believe the truck apron width is partially determined with the Rodel software? I've only worked on the design of one, and my memory fails me.

A couple other things I learned:

1. Our state has determined that coloring the concrete of the truck apron is fine, but stamping it is too much--trucks don't realize it is for them. So don't make it too aesthetically pleasing, if that makes sense. If you are going to require stamping, consider the pattern and how it will be constructed. (Ours was stamped bc it was before the new standard. The contractor used a roller with a rubber stamp to accomplish a herringbone pattern.)
2. Concrete is much more complicated than asphalt for the roadway. The joint pattern needs to be well thought out and very clear in the plans. Consider cross slopes with the joint pattern. The longitudinal joints should predominantly match the pavement marking. Getting the joints done correctly was the most challenging component. Give dimensions and tons of survey points!
3. Ours was not constructed under traffic, but completed in its entirity in about a week's time (and then cure time). Traffic control planning is so important.
4. I don't want to jinx it, but 5 months and counting with no accidents. This thing also really moves traffic.
5. I could probably download plan sheets and construction pictures if anyone is ever interested. (Including pics of the apron construction.)

 

[TrafficDesigner]

Cara413, great post! Actually, I use some of your states standards for checking the designs that I have worked on.

I have never used Rodel to determine the apron size though, I am curious to see what it would say. I use AutoTURN to determine the apron sizes by creating the path of the vehicle from 6' off of the face of the inscribed (outer) circle diameter.

Example:
If my roundabout is 140' across and my design vehicle is a WB-67 truck, I know I will need 36' for the trailer to sweep with 2' clear from tire to curb. I subtract 20' clear for emergency vehicles and that tells me my apron needs to be 16' wide. This of course is for a single lane roundabout.

That's interesting about the stamped apron. I wasn't aware of that but it kind of makes sense. Can you give the location of the roundabout so we can look it up on Google Map? I would be interested in the striping and design.

Thanks for providing information on this roundabout.