Quote:
Originally Posted by wwmiv
What about the weight of the CARS!?
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Cars are of course heavy (duh), but you can pack more people onto a bridge than you can cars. Cars simply take up more space than people do.
Let's look at this.
The bridges that cross the river are around 700 feet long each. The South First and Congress bridges have 6 lanes, (3 in each direction). The Lamar Bridge actually only has 4 lanes total. So let's use the South First Street Bridge for our measurements.
Most cars are between 15 and 18 feet long. Let's go with 18 feet as the length of each car.
700 feet divided by 18 feet = 38.8888889. Let's round that up to 39 cars. So you could fit 39 cars onto one lane on the bridge. But of course there are 6 lanes, so 39 x 6 = 233.333333 cars on all 6 lanes. So let's round it up to 234 cars.
Now, most cars weigh 2,500 to 5,000 pounds. Let's go with 5,000 pounds. It's more likely that cars traveling the bridges would be smaller, compact cars and probably weigh less, but for the sake of this argument, let's go with 5,000 pounds.
So, 5,000 pounds x 234 cars = 1,170,000 pounds. So you could fit 234 cars that weight 5,000 pounds each on the bridge. That comes out to 1,170,000 pounds of cars on the bridge.
Again, cars take up more space than people do. Think about a Chevrolet Suburban. They're the biggest SUV on the road now. I know for a fact that they're 18 feet long since my parents had one back in the early 90s. Suburbans have seating for 8 people. Let's say each one of those persons weighs 200 pounds. 8x200=1,600 pounds. Now think about that. Suburbans are 6 feet wide, 18 feet long and weigh around 5,000 pounds. Yet, 8 people can fit inside, and they weigh 1,600 pounds just by themselves. Think about how many people you could place shoulder to shoulder on the footprint (area) a Suburban covers. Let's say those 200 pound people take up 2 square feet where they stand. A Suburban, which is 6 feet wide and 18 feet long. So 6 x 18 = 108 square feet. So 108 square feet divided by 2 square feet = 54. So you could stand 54 people shoulder to shoulder on the footprint of a Suburban. So, 54 people x 200 pounds = 10,800 pounds. And that is the weight of people covering just 108 square feet of the bridge (a Chevrolet Suburban's footprint). Earlier I said that you could fit 39 cars onto a single lane of the bridge. I was using the the 18 foot long number for a car (a Suburban). As I mentioned above, I came up with 1,170,000 pounds for the total weight of those Suburbans on the bridge.
So now let's measure the width of the bridge. The South First Street Bridge sidewalk to sidewalk is 100 feet wide. So 700 feet long x 100 feet wide = 70,000 square feet. So the South First Street Bridge has an area of 70,000 square feet. Remember that we estimated that those 200 pound people took up 2 square feet where they stood? So 70,000 square feet divided by 2 square feet = 35,000 square feet. So then 35,000 square feet x 200 pounds = 7,000,000 pounds (7 million).
So, you can fit 234 Chevrolet Suburbans on the South First Street Bridge (bumper to bumper), weighing a total of 1,170,000 pounds.
BUT, you can fit 35,000 people shoulder to shoulder on the South First Street Bridge. This number would include the sidewalk space. The total weight of the people would be 7 million pounds. Now of course there would never be that many people on the bridge, because let's face it, who wants to be shoulder to shoulder and front to back with that many people? So even if you divided that number by three, it would still be more weight than the total number of cars you could fit on the bridge. Divided by three it would be 2 333 333.33 pounds. So a little over 2.3 million pounds. About 600,000 more pounds than the weight of the total number of cars you could fit on the bridge.
Check out Google Earth, look at the bridges. At most, there's 8 to 10 cars on each bridge.
By the way, the Pfluger Bridge is narrower than all three auto bridges. It's only around 50 feet wide at its widest spot.
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