Enhancing parade balloon safety through science.
The giant balloons that step off from New York’s Central
Park West each November are a much loved tradition in Macy’s Thanksgiving Day
Parade. On a good day, they float effortlessly down the parade route, but New
York’s strong, gusty winds and overhead obstacles, such as streetlights and
traffic signals, have caused concern over the balloons’ safe passage throughout
the parade’s history.
In addition, parade balloons have grown considerably since the first, an air-filled Felix the Cat, was carried along the parade route in 1927. Today’s helium-filled balloons typically are up to 60 feet long, 30 feet wide, and 50 to 70 feet tall, requiring careful maneuvering down crowd-lined city streets.
After a 1997 accident due to high winds knocked a lamppost
into the crowd, the city engaged the wind engineering experts at RWDI and
Parsons Brinkerhoff Quade & Douglas to report on how wind affects parade
balloons. Based on that report, a city task force issued operational guidelines
for flying the balloons based on specific conditions under which they could be
used.
Even with those guidelines in place, a strong gust during
the 2005 parade resulted in guy lines from a balloon snagging a streetlight
luminaire, raining debris onto the bystanders below. The city then asked RWDI
and PBQD to revisit existing operational guidelines and develop ones that were more
stringent.
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The Challenge
Accurately predicting local wind behavior in Manhattan’s dense urban landscape is a complex task. This is especially true with regard to wind gusts at street intersections, where the combination of “urban canyon” terrain with winds that can come from any direction results in highly turbulent conditions.
Our engineers set out to discover the correlations between recorded wind speed and directional data at the local airports and the actual wind effects on balloons within the street canyons of Manhattan. Our intent: to establish the best possible data sources upon which to base balloon operational decisions.
Our Approach
Because buildings can dramatically affect local wind conditions, we set up a six-block field test to measure actual wind data and its effect on a representative balloon. The test was conducted on a windy day, May 22, 2006, along Broadway from 42nd Street to 37th Street, which included a block on each end for staging.
To monitor local wind conditions we installed exposed wind monitors on lampposts at the four intersections from 41st to 38th to measure crosswind gust speeds. We also installed tension meters – simple mechanical spring scales – on the handler lines for the Pikachu balloon we used for the field test to understand the maximum forces imposed on the handlers.
As expected, general background wind conditions held fairly steady for the five test runs. Although we also collected information about the average wind direction, we found that wind was highly turbulent and likely to come from any direction in a way that was not predictable based on weather forecasts or concurrent measurements taken at anemometers located elsewhere in the city in a more open setting.
All in all, this field test confirmed the complexity of Manhattan’s wind flow patterns and the value of relying on local anemometer data on the day of the parade to gain an understanding of local gust speeds along the parade route.
Because we saw how suddenly gusts could arise or change direction, we recommended discontinuing the practice of relying on peak wind gust readings taken just prior to a balloon’s entering an intersection to determine how to navigate the intersection. Rather, we recommended that balloon captains refer to statistically determined “expected peak gust” wind speeds when deciding the flying height to cross an intersection.
By comparing the body of data collected from the intersection wind monitors to wind speeds recorded at LaGuardia Airport, JFK Airport, and Central Park, we confirmed the appropriateness of the multiplier suggested in the earlier report for predicting maximum probable gust speeds based on the mean airport wind speed.
The Outcome
The city’s adoption of our various recommendations has improved public safety for the millions who line New York City streets for the Thanksgiving Day parade. At the same time, our science-based guidelines for balloon operation have taken much of the guesswork out of the balloon captains and handlers’ responsibilities, reducing the potential for accidents and preserving a great holiday tradition.