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Automotive News & Views Should the US government bring back the 55 mph max speed limit again?
1418 messages, Last post on Dec 16, 2008 at 11:21 AM
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Replying to: douglasr (Feb 06, 2008 12:48 pm) That doesn't make any sense. Your car does not use the same amount of gas per unit of time at varying speeds. While you will be in your car longer if you slow down your car will burn less gas per hour too. Cars use gas in a miles per gallon rate, Presuming that rate is constant you will burn the same amount of gas no matter what speed you drive. So if your car gets 35 MPG and you drive 35 miles you will burn a gallon of gas, you will burn a gallon if you drive at 35 MPH at 45 MPH or at 85 MPH. Now the thing is that cars will start a reduction in their MPG figures above a certain speed, There are few, if any, cars out there that will get the same or better mileage ar 100 MPH than they will get at 50 MPH, So if you can get better MPG at 50 MPH than at 100 MPH driving 50 you will spend more time on the road but you will use less gas. |
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Replying to: kernick (Feb 06, 2008 1:45 pm) And when you reach a certain point of congestion, cars can no longer maintain distance, and traffic jams occur. thats just the thing, if you maintain a higher speed cars need more space between them. Slow down traffic and less room between cars is needed hence more cars can be on the road. So if you take traffic from 65mph to 55 mph, you will at least increase congestion by - 10/65 = 15.4%. In reality you reduce congestion. At 65 MPH one lane of road can safely hold 47 cars safely in any one mile stretch, any more and there will be at least one car following to close. Now at 55 MPH that same mile of one lane can hold 55 cars safely (of course if weather conditions are right and the road conditions are good). I think if you do that on many urban highways at many times of the day, you will create traffic jams where speeds drop to 15mph, and then you really screw things up and waste fuel. You are putting th cart before the horse here. In rush hour its not a lower speed that creates the congestion its the congestion that causes the lower speed. |
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Replying to: louiswei (Feb 06, 2008 8:31 am) |
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Replying to: douglasr (Feb 06, 2008 12:48 pm) 
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Replying to: nippononly (Feb 06, 2008 1:58 pm) Yes and if you slow people down you will have more cars on the road during any particular time. Example: If me and 20 other people in my city, drive 30 miles to your city 30 miles away and we leave at 5:00pm. And you and 100 other people in your city are getting on this same road at 5:30, then if we drive 65mph we're getting off the road before you folks get on. less congestion. If we drive  55mph the 100 of us are just getting to your city as your trying to get on, so now there's 200 cars instead of 100. It's pretty simple that if you want to get the water in your pool, you either turn up the flow (speed of the water) or use a larger diameter hose. If everyone drove 5mph, the roads would be impassable. Everyone can not get in their car and be on the road at the same time. To have traffic-flow requires you get a person on and off the road reasonably quickly.
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Replying to: nippononly (Feb 06, 2008 1:58 pm) If disparity in speed causes congestion, then attempting to slow people down through reducing the speed limit will increase congestion, because lower speed limits do not slow everyone down...most people continue to drive at the speed at which they feel comfortable, regardless of the speed limit. The disparity in speeds causes vehicles to "cluster" in groups. This past weekend I drove to the Philadelphia Auto Show from Harrisburg to Valley Forge on the Pennsylvania Turnpike. The speed limit is posted at 65 mph...but virtually everyone was driving 75 mph...even soccer moms in minivans and a grandpa-grandma couple in a Buick Regal. The "natural" speed on that road, given the condition of the road, present vehicle technology and traffic levels, is 75 mph, and everyone knows it...even the police don't bother with people driving 75 mph, as long as they weren't tailgating or weaving in and out of traffic. The people who were driving at 65 mph were quite conspicuous, although they did at least stay in the slow lane. We tried to "slow" everyone down before, and it failed...the only things we got out of that experiment were increased disrespect for traffic laws and the people who enforce them, a boom in CB radio sales, the invention of the radar detector and a cheesy-but-fun Burt Reynolds-Sally Field movie...we need to learn from history. |
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kernick: I know you feel you have a strong intuitive grasp of the way it SHOULD work, but the data is counter-intuitive here. grbeck: well there's the rub, you have put your finger right on it. The least congestion will occur when the maximum number of people are conforming to a given speed ("driving with the flow"), and there is plenty of data to suggest that there will be more non-conformists the lower you reduce the speed limit. The plain and simple fact is if we lowered the speed limit to 55, and we could count on everyone going 65, we would save a lot of gas because of all the people NOT driving 75 any longer, and we would avoid increasing congestion because we would still have most people driving with the flow. But we CAN'T count on everyone doing that. Instead, we will have a significant number of people still driving 75 (the new revenue generators for local municipalities  ), a bunch driving 65, and just enough going 55 to really muck things up by increasing speed disparities greatly. So we won't save a lot of gas, and we will increase congestion, because of peoples' disinclination to follow the law. 
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Replying to: euphonium (Feb 06, 2008 9:40 pm)
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Replying to: nippononly (Feb 07, 2008 8:15 am) Which is why attempting to save gasoline through reduced speed limits is both ineffective and ultimately counterproductive. It gives the appearance of "doing something" instead of actually...doing something (worthwhile). The price of gas has been falling lately...this makes it a good time to increase the gasoline tax and use the additional revenue for infrastructure improvements. If people survived with $3-a-gallon in December 2007, guess what, they will still survive if it's $3-a-gallon in 2008, only now a larger percentage of that purchase price will be going for infrastructure improvements. Plus, the $3-a-gallon level has spurred interest in real fuel sippers. Increased sales of those cars will lead to real long-term fuel savings...even Ford is gearing up to bring us a production version of the snazzy Verve, which, if it is anything like the show car, will be a stunner. Sounds like a worthwhile trade-off to me...of course, if the goal is to pass annoying laws that do no real good, increase public cynicism, help the radar-detector industry and allow people to put off hard choices, then by all means we should support the return of the 55 mph speed limit.
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