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Williams: A Closer Look At Lop-sided Roundabout Proposed For Central - N.M. 502

on March 7, 2016 - 11:23am
Image by Joel M. Williams
Los Alamos

The flier sent out to announce the latest about the N.M. 502 project does not give any feel for what the roundabout will look like or behave like. So, I thought I would provide the citizenry with a diagram of what one would expect in a standard roundabout versus what is proposed to be built. The proposed is a far cry from standard.

I have overlain color markings onto the latest drawings from the NMDOT in the figure. For those who wish to actually be enquiring minds, I am adding some notes after the figure to help you understand this "abnormal" roundabout.

The Roundabout is basically a single lane one as defined by the red ring and the four islands. The three "true" single lane areas are indicated in reddish brushing. Entry into, around, and out of this red circle (as indicated by the arrows) is what people who even know how to negotiate roundabouts would expect. The outer part of the truck "apron" of this standard "round" island is shown in the orange circle with the "apron" textured. Close inspection will indicate what the dashed line on the NMDOT draw (under the orange line; top right) means. The inner green is the "flower garden" area of a standard roundabout. This is what one would expect coming to a standard roundabout.
Hook markings (I assume on the roadway) are supposed to tell people where to go. Not sure what the blue lines are without more info; probably more markings, just more discrete "lane marking". Before addressing the skewings and operation of the roundabout, a question: with the effort to make 4th street a major part of the build, has anyone determined how much more traffic will result on Iris and parallel streets, asked residents their opinion of more traffic on their streets, and determined the potential that, because traffic on Canyon will find it almost impossible to get onto e-bound N.M. 502 in the pm, it will dump its e-bound traffic into the roundabout in order to be "first-in-line" going e-bound.

See below about what happens in Circle C. The traffic feeding this part of the roundabout will not be that which comes out of Central now, but the total that comes out of Central, 4th, and Canyon NOW - quite a bit of difference to be expected to residents in the area and on the pm operation of the roundabout.

Now for the skewings of a standard single lane roundabout to get this design.
The orange areas are full dual lanes into, through or out of the roundabout. Yellow areas are single lane ins and outs.
The upper right of the standard circle is flattened (NMDOT black lines) to handle dual (almost triple with the 4th offshoot included) lanes. This flattened portion makes the negotiation into the single lane through portion (circles A &B) more difficult than a standard roundabout. The angle to be negotiated around the roundabout to continue on NM502 becomes more acute than standard. My guess is that big rigs will negotiate this portion from the "right lane" that is supposed to be the feed to Central and ride all over the "apron" or just go down Central! The county is trying to reduce flow along Central. Why induce the natural flow to be to it? NM502 should be a through highway! What a contradiction in planning!

Circle area A looks particularly chaotic, all of the time, but esp in the am.
Traffic rounding the roundabout and wanting to do a U-turn will have a natural tendency to dump into Central when encountering the flattened portion rather than make the hard left; making easy U-turns is one of the things roundabout enthusiasts ALWAYS tout! Think what BIG rigs will do! Forcing more heavy vehicles down Central would be my guess! An the county wants to curtail flow down Central with all those "outers" along the street. Again, more contradiction to basic city traffic planning!
Now for Circle C. Vehicles in the circle [cars, trucks, semis, bicycles (as there are NO bike lanes!) have the "right-away". In the US traffic flows counter-clockwise. As the tangential arrow in circle indicates, traffic in the circle going onto N.M. 502 e-bound will naturally select either of the two e-bound lanes, but will tend to select the outer (drift). This means that both NM502 e-bound lanes MUST wait until all traffic in circle C has indicated where it is going to go and gone. Of course, as a number of letters have indicated, massive unidirectional flow as we have in the pm will probably end up forcing the issue by charging through and forcing the traffic in circle C to come to a halt. Not going to be a pretty sight!
I have tried to show how this distorted (to accommodate 4th street) roundabout will work. It is NOT what was originally proposed as a viable option to a signal at this intersection!
What I have NOT included are costs, land acquisitions, destruction of current landscaping, ped crossing safety, bike safety, motorcycle safety, etc, etc. Others have and are addressing these issues in other letters. There are LOTs of stuff being poo-pooed in order to justify cramming this "sucker" into this space. You'd be surprised, if you took the time to look!