Letter to the Editor: N.M. 502 18 MPH?

Los Alamos

The New Mexico Department of Transportation held an open house Feb. 20 to solicit comments on the latest conceptual design for N.M. 502.

This might be the last opportunity for public comment on the major features of the road. I didn’t count, but I’d guess there were roughly 50-75 people in attendance.

That seems like a pretty small sample on which to base a decision that affects everyone in Los Alamos (though less so for White Rock residents.)

I think the single design feature that most determines the nature and quality of the road is the proposed roundabout at Central Avenue and Trinity Drive.

For me, the biggest single question associated with an artery like Trinity Drive is, “How easy is it to get from where you are to where you would like to be.”

From this perspective, a roundabout is a poor choice. Here are the reasons.

The roundabout proposed is somewhat like that installed at Diamond Drive and San Ildephonso Road. It is a hybrid, with some aspects of a single lane roundabout and some portions that will behave like a two-lane roundabout.

However, there are some important differences between the two intersections. First, the traffic is somewhat heavier at Central Avenue and Trinity  Drive.

Second, the traffic pattern is very different. This makes a significant difference in the efficiency of travel in different paths, as well as for access by pedestrians and bicycles.

For automobile drivers and passengers, I think the roundabout at Central Avenue is a poor choice. First, every car passing through it at any time will be required to slow down to about 15-20 mph.

Some people like this idea as a “traffic calming” measure. I dislike traffic calming, because I value my time, and I prefer to drive in uncongested conditions.

Second, the traffic path for “straight-through” traffic on Trinity Drive is terrible. Eastbound, the car must deflect right, then left, then right – always.

Westbound, the low-traffic path is similar, except that, for the geometry that is forced by the available land, the deflections are larger, involving travel around 200 degrees of the circle.

Third, whatever traffic exists on Central Avenue must merge with the straight-through traffic on Trinity. This further constricts traffic during peak times. Depending on the size of the roundabout (which has not been specified), the indirect path constrains transit by long vehicles.

As planned, pedestrians would need to negotiate yields with cars that are using the roundabout. Nominally, pedestrians have the right of way.

This is hopeless at peak traffic times: either the pedestrians will wait our of fear or politeness, or they will attempt to take their right-of-way and the cars will form lines with stop-and-go traffic.

Roundabout pedestrian crossings are known to be especially challenging (i.e., less safe) for children, the elderly, and handicapped persons [USDOT.]

There is a “fix” for this, placing signals that stop traffic when pedestrians wish to cross. This feature is not included in the present design, and improves service for pedestrians at the expense of further interruptions of vehicle traffic.

The only option for bicycles is to either merge with traffic or to dismount and cross as a pedestrian. The safety record indicates that roundabouts are more hazardous than signalized intersections for bicycles and motorcycles [various sources.]

A traffic signal, on the other hand, offers relative advantages over a roundabout. The main path through the intersection is straight and simple.

Using a smart light, traffic is unimpeded when there is no traffic from Central. Avenue. The green phase can be synchronized with other lights on Trinity Drive, so the total number of stops in passing along Trinity Drive would not increase as much as one might think.

To illustrate, the number of stops along the length of Trinity Drive with existing lights is typically 0 to two. Adding a light would not increase this by one for most cars at most times.

If you do not act, there will very likely be a new roundabout at Central Avenue and Trinity Drive. If you wish to express your views on the current design, you may transmit comments by email to eric@marroninc.com by March 6.

Those who prefer U.S. mail can send comments to Eric Johnson, Marron and Associates, 7511 4th Street NW, Albuquerque, NM 87107.


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