During weekdays the population of Manhattan grows to 3,940,000 people[1]. This population consists of 1,460,000 local residents, 1,610,000 commuting workers, 374,000 local day-trip visitors, 70,000 commuting students, 404,000 out of town visitors, and 17,000 hospital patients[1]. If we add the workers and students with the local day-trip visitors we find that 2,060,000 people need to enter and exit Manhattan around the same times each day. Currently the majority of these trips are provided by transit, with only 16% of people commuting by personal vehicle[2]. So how would things be different if Manhattan was not served by transit and everybody drove instead? BRIDGES AND TUNNELS The first thing to consider is the road space available for vehicles entering and existing Manhattan. The existing automobile lanes provided by the 20 bridges and tunnels connecting Manhattan are counted in Table 1.
INBOUND | OUTBOUND | REVERSIBLE | |
1. Brooklyn Battery Tunnel[3] | 2 | 1 | 1 |
2. Brooklyn Bridge[4] | 3 | 3 | |
3. Manhattan Bridge[5] | 2 | 2 | 3 |
4. Williamsburg Bridge[3] | 2 | 2 | 4 |
5. Queens Midtown Tunnel[3] | 2 | 1 | 1 |
6. Queensboro Bridge[3] | 4 | 3 | 2 |
7. RFK Bridge[6] | 3 | 3 | |
8. Willis Av Bridge[7] | 0 | 4 | |
9. 3rd Av Bridge[8] | 5 | 0 | |
10. Madison Av Bridge[9] | 2 | 2 | |
11. 145th St Bridge[10] | 4 | 4 | |
12. Macombs Dam Bridge[10] | 2 | 2 | |
13. Alexander Hamilton Bridge[11] | 4 | 4 | |
14. Washington Bridge[12] | 3 | 3 | |
15. University Heights Bridge[10] | 2 | 2 | |
16. Broadway Bridge[10] | 2 | 2 | |
17. Henry Hudson Bridge[13] | 4 | 3 | |
18. George Washington Bridge[14] | 7 | 7 | |
19. Lincoln Tunnel[15] | 2 | 2 | 2 |
20. Holland Tunnel[16] | 2 | 2 | |
TOTAL | 70[17] | 65 |
A freeway lane operating under ideal conditions can transport 2,000 vehicles per hour[18]. From this we can determine how many vehicles per hour could enter and exit Manhattan under ideal conditions, and the amount of time for 2,060,000 vehicles to do that. The results are presented in Table 2 below.
INBOUND | OUTBOUND | |
Hourly Vehicle Capacity | 140,000 | 130,000 |
Total Time For All Vehicles To Enter/Exit | 15 hours | 16 hours |
This situation would be problematic because it leaves less than no time for other activities. In order to make this scenario function we will assume enough capacity is needed for all vehicles to enter Manhattan within a 4 hour AM peak period and exit within a 4 hour PM peak period. This would require 380 additional traffic lanes, a 280% increase, which could be provided by 48 new 8-lane crossings.[19]
PARKING The other thing to consider for this auto-oriented Manhattan is the additional parking required. The 2,060,000 people driving into Manhattan need at minimum one parking space each. With 30m2 [20] required for an off-street parking space this adds up to a total of 62km2 of parking. Manhattan is 60km2 [21] so this is equivalent to a layer of underground parking under the entire island. If we assume the local residents drive to get around and own vehicles at the US average of 82 vehicles per 100 persons[22] that will result in 1,200,000 more vehicles in Manhattan. This means 2,270,000 parking spaces if each vehicle has a space available at home and one available at work (130,000 Manhattan residents work elsewhere [1]). In total a very conservative estimate for the amount of parking required is 2 layers underneath all of Manhattan.
NOTES AND REFERENCES 1. Moss, M., & Quing, C. (2012). The Dynamic Population of Manhattan. p. 1. 2. Moss, M., & Quing, C. (2012). The Dynamic Population of Manhattan. p. 13. 3. Greenberger, D. https://groups.google.com/forum/#!msg/misc.transport.road/5a0SbUiJeyg/bIAzwePLcgIJ 4. http://en.wikipedia.org/wiki/Brooklyn_Bridge 5. http://en.wikipedia.org/wiki/Manhattan_Bridge 6. http://www.nycroads.com/crossings/triborough/ 7. http://www.nycroads.com/crossings/willis-avenue/ 8. http://en.wikipedia.org/wiki/Third_Avenue_Bridge_(New_York_City) 9. http://www.nycroads.com/crossings/madison-avenue/ 10. http://www.nyc.gov/html/dot/html/infrastructure/bridges-harlem.shtml 11. http://www.nycroads.com/crossings/alexander-hamilton/ 12. http://www.nycroads.com/crossings/washington-heights/ 13. http://www.nycroads.com/crossings/henry-hudson/ 14. http://en.wikipedia.org/wiki/George_Washington_Bridge 15. http://en.wikipedia.org/wiki/Lincoln_Tunnel 16. http://en.wikipedia.org/wiki/Holland_Tunnel 17. TOTAL = INBOUND + REVERSIBLE 18. Indevelopment (2004).Road Capacities. p. 9. 19. REQUIRED LANES = TOTAL TRAFFIC / LANE TRAFFIC FLOW / NUMBER OF HOURS REQUIRED LANES (INBOUND) = 2,060,000 / 2,000 / 4 = 258 TOTAL REQUIRED LANES = 258 x 2 = 516 TOTAL ADDITIONAL LANES = 516 – (65 + 70) = 381 381 / 8 = ~48 20. Shoup, D. (2005). The High Cost of Free Parking (p. 221). 21. http://en.wikipedia.org/wiki/Manhattan 22. U.S. Census Bureau (2010). State and Metropolitan Area Data Book: 2010. p. 79.
Thomas Beyer said:
Well said. We need indeed more transit, especially SUBWAYS in Vancouver. The question is: who is paying for it ?
keaswaran said:
I wonder if there’s a way to make this even more stark. It looks like there are 15 inbound lanes from Long Island, and 11 inbound lanes from New Jersey, while all other lanes only connect to the Bronx. There appear to be another 6 lanes from Long Island on the Bronx-Whitestone and Throgs Neck bridges (I’m not familiar with the area, so I’m just using words and lane counts I see on Google Maps, which may not be the most accurate). And there’s another 4 lanes from New Jersey if you go all the way up to the Tappan Zee bridge. (Verrazano Narrows can at best squeeze some more New Jersey and Staten Island commuters onto the Long Island accesses to Manhattan.) So if you count all the people coming from New Jersey, Staten Island, and Long Island, they all have to get through a total of just 36 lanes.
As long as fewer than half of the people entering Manhattan are doing so from Bronx, Westchester, and Connecticut, this problem will be even harder to solve (especially once you start counting people who commute from Long Island or New Jersey to Bronx or Westchester, since they all need to squeeze into these same bridges).
keaswaran said:
Oh, I missed the reversible lanes. That brings it to a total of 49 lanes connection NJ and LI to Manhattan/Bronx/Westchester, which might not be quite as stark as I thought.
Lobster said:
I don’t know if its the case with the manhattan area but in some places the local authority keeps traffic counts and provides them for free online. If they have them for free they’d most likely be somewhere on their website. This could help revise your estimate (or even make it worse than you imagined, if that is even possible)
Matt Taylor said:
To keep the analysis simple and on the conservative side I made the assumption that all of the crossings would be able move 2,000 vehicles per lane per hour. This is the amount of traffic flow you expect on uninterrupted segments of freeway. For bridges and tunnels funneling traffic into a city street network it is a generous assumption.
What I can tell you from the 2011 bridge traffic volumes is that during their peak periods the existing structures only move on average 1,000 vehicles per lane per hour inbound. Even the top performing crossings (George Washington Bridge, Holland Tunnel, and Queens Midtown Tunnel) only move 1,500 vehicles per lane per hour. During the peak morning hour about 70,000 vehicles are able to enter Manhattan.
Click to access bridge-traffic-report-11.pdf
We are envisioning a strange scenario where Manhattan is somehow reworked with 2 layers of underground parking beneath it, so it is hard to say what exactly could be achieved. But if we assumed that the maximum capacity on all the crossings was 1,500 instead of the 2,000 I previously used then the number of 8-lane crossings required would be 69.
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Levon Sanossian said:
What’s the point of this brain-numbing exercise please? How evil people with cars are, yet again? ugh.
If you would like to live on an island, pull up the bridges.
Matt Taylor said:
Two main points of the exercise, neither of which have to do with people in cars being evil 1) Manhattan could not exist as it does today without transit because there would be no conceivable way to circulate the traffic 2) If it were a workable scheme it is obvious that the costs associated with implementing it would be prohibitive.
An-auto oriented Manhattan does not work from either a physical or economic perspective. That much should be clear.
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Thomas Beyer said:
Let’s do a comparison to Vancouver .. with buses, since MetroVan favours buses so much. What would NY look like if it had no subways, just buses ?
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Liz Brisson (@lizonthebus) said:
Great stuff! It would be cool to add an estimated cost of all those bridges and parking to provide a better comparison point for recent transit investments like 2nd Ave subway.
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