Tuesday, May 27, 2008

Defining Deviancy Down at the Intersection of Death, Part Two

In Part One, we described how Montgomery County’s Planning Department relies on Critical Lane Volume (CLV) to estimate congestion at intersections across the county. Any statistical system that relies on just one measure, taken very infrequently, with little collaborating information is prone to fluky data. And that has happened at the Georgia Avenue-Forest Glen Road intersection, lovingly referred to by its neighbors as the Intersection of Death.

According to the Planning Department, this intersection went from being the most congested in the county to falling below the county’s allowable congestion standard for its policy area. Why? Because its morning CLV declined by 26% between surveys taken on 8/28/03 and 6/6/07. They would like us to believe that one-quarter of our traffic congestion has magically disappeared even though there have been no major engineering changes at the intersection. Similarly, only four of the ten most-congested intersections reported in 2006 have returned to the current 2008 list. Have the six intersections that fell off the list been “fixed,” surpassed by others that have become worse or simply fallen victim to bad CLV measurements?

While the Gazette covered our objections to traffic measurement at Georgia and Forest Glen, they spent a bit more time discussing the intersection’s infamous nickname than exploring the underlying data issues. I presented the following case study of the intersection to the Planning Board two weeks ago. Just looking at this one intersection calls into question the statistical validity of how traffic is measured in this county.


Testimony of Adam Pagnucco
Montgomery County Planning Board, 5/15/08
Item 8: Highway Mobility Report 2008

Good morning. My name is Adam Pagnucco. I am Chairman of the Forest Estates Community Association's Crossing Georgia Committee as well as my civic association's incoming county government liaison. Today I offer my observations on the planning staff's new Critical Lane Volume (CLV) estimates for the Georgia Avenue-Forest Glen Road intersection.

In the 2006 Highway Mobility Report, the Georgia-Forest Glen intersection was ranked as the most congested in the county with an AM CLV of 2106 and a PM CLV of 1643. Those counts were taken on 8/28/03. No one in the surrounding area was surprised. What was surprising were the new CLV counts taken on 6/6/07: an AM CLV of 1553 and a PM CLV of 1377. If those counts are to be believed, then congestion has decreased at this intersection by 26% in the morning and 16% in the evening in just four years.

Now let's remember the location of Georgia at Forest Glen. It is adjacent to the Forest Glen Metro station, one block away from the Beltway interchange and three blocks away from Holy Cross Hospital, the second-biggest hospital in the state. Any car coming from the north to the Beltway must pass through it. Most vehicles heading to Holy Cross, and all of them coming from the Beltway, must pass through it. And hundreds of pedestrians cross the street every day to use Metro. No other intersection in the county, and possibly the state, has this combination of characteristics.

The principal change in recent traffic conditions around the intersection was the 2005 expansion of Holy Cross Hospital. That expansion, the biggest in the hospital's history, added 210,000 square feet of new space to the facility. The hospital reports that it had 128,591 visitors in 2003 and 157,573 visitors in 2007, a 23% increase after the expansion was finished. But now the hospital claims that it is bursting at the seams and it intends to expand again. Its plan calls for a new parking garage that would hold 500-700 more cars, which the hospital says it needs because cars are stacking up in its existing garage. Given the phenomenal increases in patient visits and the hospital's need for another expansion so soon after its last one, how can anyone believe that traffic congestion at Georgia and Forest Glen has really declined by double digits in just four years?

But there is more. In 1995, the planning staff estimated CLV at Georgia and Forest Glen at 1511 in the morning and 1530 in the afternoon. If the 2007 CLV is to be believed, then current traffic congestion is only 3% worse in the morning and is actually 10% less in the evening than it was in 1995. That's right, we are told that evening rush has actually improved by 10% over the last 12 years. Considering the dramatic redevelopment of Downtown Silver Spring and the residential construction upcounty in that period of time, that is extremely difficult to believe.

Last December, I showed you our video of conditions at the intersection. Remember the sight of cars stacked up towards Wheaton as far as the eye can see? Remember the constant illegal left turns? Remember how the pedestrians had to maneuver past cars stopped in the crosswalk? Of course you remember and there is no need to show you that chaos again. As I recall, that video provoked quite a reaction in this room. Many things were said at the time, but I do not remember anyone saying, "Hmmm… now that intersection has great traffic flow!"

Perhaps the issue here is how CLVs are used for purposes of analysis. Critical Lane Volume is after all a volume measure. As the number of cars proceeding through an intersection goes up, the CLV goes up. Now imagine a perfectly gridlocked intersection. No cars can move. What would its CLV be? Exactly zero. After all, no cars would be able to get through. Is it possible that the Georgia-Forest Glen intersection's declining CLV indicates more congestion and not less?

Members of the Planning Board, it is highly unlikely that you will find anyone in my neighborhood who believes that the biggest expansion in the history of the state's second-biggest hospital has led to less traffic congestion over the last four years. It is equally unlikely that you will find anyone who believes that afternoon traffic flow on Georgia Avenue has actually improved since the mid-1990's. I hope that you will ask your staff to explain how their data contradicts the facts I have cited today along with plain common sense. I for one would like to hear their answer.


Tomorrow, we will show you a better way to measure traffic.