Modern Roundabout Truck Aprons
Modern Roundabout Truck Aprons
(OP)
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.
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.





RE: Modern Roundabout Truck Aprons
RE: Modern Roundabout Truck Aprons
One of the most common myths of modern roundabouts is that they are the same thing as traffic circles and the general knee jerk reactions are as you have described. Modern roundabouts (when designed correctly) address the issues as you have mentioned.
What I was looking for specifically is standards or experiences with the truck aprons. I have seen a couple of general different ways to build them, but I was looking to make some comparisons and learn from what others have done.
RE: Modern Roundabout Truck Aprons
The round-a-about is located in a residential area and is performing very well.
RE: Modern Roundabout Truck Aprons
RE: Modern Roundabout Truck Aprons
Modern roundabouts when designed correctly control the speeds that a vehicle can enter and circulate through the intersection while at the same time keep traffic moving. When the standards aren't followed you end up with another traffic circle that has problems. Even the amount of traffic should be considered before the design even starts, otherwise it could fail from day one. I have seen intersections that should not have a roundabout or they are designed for a single lane when they should be a double lane roundabout or they are too close to a traffic signal. It all falls back on the designers and engineers to take the time to educate themselves on Modern Roundabouts and follow the standards or stop trying to design them.
When their design fails everyone gives the roundabout a bad name, when it technically is not even a roundabout but just another poorly designed traffic circle or circular intersection.
RE: Modern Roundabout Truck Aprons
Thanks...
RE: Modern Roundabout Truck Aprons
http://www.alaskaroundabouts.com/links.html
Here is one link from alaskaroundabouts link page. They have a lot of good information.
Wisconsin DOT has a pretty good guide that was written by Scott Ritchie if I understood correctly.
http://www
https://www.nysdot.gov/portal/page/portal/index
I learned a lot from Howard McKulloch of NYSDOT in one of his courses that he gave. He's the one that opened my eyes to the differences between modern roundabouts and traffic circles.
Arizona
h
Kansas
htt
Maryland
h
These are a few and most of these have link pages that will take you to others.
RE: Modern Roundabout Truck Aprons
It kind of looked like an upside down small plate or saucer.
RE: Modern Roundabout Truck Aprons
I'm designing a RA w/ 12' wide truck apron, determined from truck turns. The grading will be tricky because my site is not flat, so my circulatory roadway (and probably the apron and center island) will be a flat disc tilted at 4% grade.
It is red colored concrete, with a stamped brick pattern.
Curb on the apron is important...we use a 3 or 4" traversable curb (rounded to 1" radius) so the truckers are not shy in utilizing them. A bigger curb can cause them some trepidation getting their trailer up on the apron.
I am also an admirer of Howard McCulloch's methods. His NYSDOT website is very good.
RE: Modern Roundabout Truck Aprons
I was surprised at first by the negative reactions too, but then realized they weren't describing roundabouts, but rather the old traffic circles.
Your description of the truck apron is what I am hearing some of our local jurisdictions describing. I think they are leaning that way now.
I just attended another seminar this morning that Howard presented through ITE. I think engineers and designers should really consider attending one of his courses if they are going to design these. It certainly couldn't hurt.
Here is another link page that links to a lot of the D.O.T.s.
http://www.azroundabouts.com/Roundabout_Links.php
RE: Modern Roundabout Truck Aprons
We have been recently working on a roundabout that includes the "egg shaped" center island. Additionally the roundabout included a slip lane to account for a particularly high demand for right turns from one leg to another through the roundabout (separated by a raised median section for those not utilizing the immediate right turn (thereby eliminating a weaving pattern). The egg shape stems from the off tracking of trucks through the roundabout. Just some food for thought.
Tbone1
RE: Modern Roundabout Truck Aprons
So does the egg shape design replace the truck apron?
I would love to see a .PDF of it if possible.
What is the circulating lane width, and did you have trouble with the smaller vehicles using it at faster speeds?
RE: Modern Roundabout Truck Aprons
RE: Modern Roundabout Truck Aprons
RE: Modern Roundabout Truck Aprons
I'm sure us in the US still have a lot to learn about designing roundabouts, but it's hard to argue with success.
"...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
RE: Modern Roundabout Truck Aprons
RE: Modern Roundabout Truck Aprons
I would be interested any information you care to share on the location or design. One thing I have found helpful is to visit the intersection after 6 months or so and do an observation study. General things like tire marks on curbs, speeds on approach and circulating etc... I have learned that the center island treatment / apron curbing is pretty important in controlling smaller vehicle speeds while circulating.
RE: Modern Roundabout Truck Aprons
If you have an opportunity or if you haven't already done so, check out the new 2009 MUTCD. It has a roundabout section in it now. One of the differences between the multi-lane roundabouts and the traffic circles is that in the multi-lane roundabouts, you shouldn't be switching lanes in the roundabout. The driver has to make the decision to get into the correct lane on approach to the roundabout, and then stay in their correct lane as they pass through it.
I have been seeing more of this kind of striping on 2 laners.
RE: Modern Roundabout Truck Aprons
RE: Modern Roundabout Truck Aprons
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.
RE: Modern Roundabout Truck Aprons
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.
RE: Modern Roundabout Truck Aprons
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.
RE: Modern Roundabout Truck Aprons
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
RE: Modern Roundabout Truck Aprons
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.
RE: Modern Roundabout Truck Aprons
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.)
RE: Modern Roundabout Truck Aprons
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.