Slower speeds limits needed in Tulsa?

[sgrizzle]

quote:Originally posted by Gaspar

Just as I suspected, the average high-end fuel economy speed for modern gasoline powered vehicles is around 60 mph (according to the Consumer Energy Commission and the California Energy Commission and Stanford University and Edmonds and The Department of Energy).

Mine was 60 but I've recalibrated it down to 50 because I do more city driving. A recent news story said the bad light timing in tulsa could actually be effecting our MPG by something close to 20%. That has more of an effect on me than anything.

[cannon_fodder]

quote:Originally posted by si_uk_lon_ok

With lower speed limits at one end with a residential speed limit of 20mph

Do you mean roads in neighborhoods or surface streets in general?  Ie.  do you mean 38th St. or Harvard?

ON the former, people readily ignore 25 MPH, so I imagine 20 would be equally ignored.  If you mean Harvard, you would more than double many peoples daily commute (me!) so I doubt that would happen.
- - -

On a sightly different note, so long as you are not working your engine harder - wouldn't there be LESS emissions as it would require less running time?  My engine is at 2K rpm at 40MPh and at 20Mph, I imagine the net emission are higher running for 2 hours at 20 mph than 1 at 40.

[bbriscoe]

quote:Originally posted by mrhaskellok

quote:Originally posted by cannon_fodder

Most/many charts I have seen show gas mileage peaking around 40-50 mph running,of course, at a constant speed and relatively constant RPM (slow down slight up hills, allow yourself to go faster down).  Above that and wind really starts to pick up it's resistance.  Below that and the aerodynamics and power of most cars are under utilized.

Per congestion, slower speed limits would only HELP if they timed the lights accordingly.  Else I would think it is a hindrance as traffic seems to flow well at 40 mph on major streets.

Yeah, but helping is all it may take to stay off the filthy city list.  I have been driving 55 on the hwy and I have to say, it isn't bad.  I also noticed that vehicles passing me were right in front of me most of the time.  I travel from Bixby to Owasso quite frequently and I am continually surprised at how little of a difference it makes in the time it takes simply driving 55.

According to this site, you can save 20-50% in fuel economy by simply staying below 55mph.  

Drive 55

A panel in Washington state said that if they would lower the maximum speed to 55 in Washington they would cut emissions by 10%.

RM, do you know what the numbers are for Tulsa in the summer?  How much of an impact would 10% reduction in vehicle emissions have?  I don't mind driving slower for cleaner air and cheaper fuel.  Anyone else?

Driving 55 on the highway when everyone else is going 65 will cause worse gas milage for everyone unless there is hardly any traffic on the roads.  Normally that slow car will block off the right lane causing people to have to slow down until they can switch lanes and then speed up again.  Then often the passing cars will cut off the slow car in the right lane causing the slow driver to have to hit the brakes and kill the cruise control (or else keep cruising inside of the unsafe 2 second following distance until the passing car gets far enough ahead).  All this speeding up and braking can't possibly be good for gas milage.  

Everyone needs to drive the same speed on the highway.

[mrhaskellok]

quote: Driving 55 on the highway when everyone else is going 65 will cause worse gas milage for everyone unless there is hardly any traffic on the roads. Normally that slow car will block off the right lane causing people to have to slow down until they can switch lanes and then speed up again. Then often the passing cars will cut off the slow car in the right lane causing the slow driver to have to hit the brakes and kill the cruise control (or else keep cruising inside of the unsafe 2 second following distance until the passing car gets far enough ahead). All this speeding up and braking can't possibly be good for gas milage.

Yeah but I am saving $$$  []

I spend over 4 hundred a month on fuel.  I take the savings where I can.  [)]

[mrhaskellok]

CF, I wish I could find some good numbers here.  It appears that there are two conflicting sets of data...one says it lowers emissions (Washington study) and others say its false.  

[cannon_fodder]

I was just postulating, but it made sense to me.  Further research seems to support my contention. A study by The AA (the UK's AAA) found reducing the speed limit from 30mph to 20mph reduced fuel efficiency by up to 5.8mpg and raised emissions by more than 10%.  
http://www.theaa.com/public_affairs/news/20mph-roads-emissions.html

Makes sense to me.  RPMs burn gas, gas creates emissions.  If I can get more miles with the same amount of gas, it should be less emissions.  

Also interesting int he study, speed bumps increase fuel consumption on a given stretch of road by over 40%.  Which makes sense when though about, BRAKE, ease over the bump, accelerate - repeat.

[Wilbur]

What you are proposing is setting speed limits 'artificially low.'

In the vast majority of instances, motorists determine the speed limits of the road.  Like I've posted before, traffic engineers conduct speed studies then put the speed limit at the 85th percentile.  The natural feel of the road, the amount of traffic and so forth cause most people to drive a certain speed where they are most comfortable.

Setting speed limits 'artificially low' will mean nothing because most folks won't do that.  It would be like putting a 30 mph zone on an expressway.  No one will do 30.

The safest streets are where everyone goes the same direction at the same speed without having to stop.  The more in conflict with that rule you are, the more unsafe the road becomes.

[mrhaskellok]

Wilbur,

I agree.  Consistency is needed.  It is interesting to note though after all this reading how much of an impact cars have and driving habits have on emissions.  Is there a more passive way to correct our emission problem?


CF,

I agree, it appears most government data suggest that.  There are many independent studies that contradict it, but I don't give them as much weight. (hope FOTD doesn't read this)  []

[tulsacyclist]

For the first time ever, I tried driving the speed limit on my way home yesterday and it felt like I was going so very slow. I had people blowing by me left and right and giving me dirty looks. I was in the right lane. I usually go about 75-80.

Tonight, I'll be trying to do 60mph.

I did it all for the MPG'Z!

[Ed W]

Some cities have taken steps toward actively discouraging motor vehicle use through lower speed limits and difficulty in finding parking.  Copenhagen reduced speed limits in some areas to 30 kph or about 18 mph.  London instituted congestion pricing.  Most of these measures resulted in an increased mode share for walking, cycling, and mass transit.  And congestion pricing really did reduce traffic in central London.

It's true that reduced speeds result in markedly better crash survival for all road users.  If I recall right, 35 mph is the dividing line.  So if we reduced the speed limit city wide to 25, we could expect reduced pedestrian, cyclist, and motorist fatalities.  What are those lives worth when compared to gas mileage?

Another point: Oklahoma permits low speed golf carts to operate on streets with speed limits of 25 mph or less.  If the city speed limit were 25, more of these vehicles would be a normal part of traffic, and it could be expected that their design would be ideal for those speeds.  In other words, they would have the optimal speed vs fuel consumption.  But I honestly do not know if they emit more unburnt fuel and greenhouse gases than a car equipped with a catalytic converter.

Still, it would be nice to have lower speeds with lower overall noise levels.  A sedate pace in traffic would contribute to livability issues, and again, there's no way to equate that in dollars.

[inteller]

someone already stated it on the TDI deal, but with more and more cars coming out with 6, 7 speed and even CVT transmissions, I think all of these graphs and statistics are a little outdated.  It is all about RPMs and if you can find a transmission that keeps the rpms down at higher speeds, your fuel economy will not suffer.  I wonder if fuel economy goes down on that one lexus with the 8 speed tranny......I bet not.

[waterboy]

quote:Originally posted by inteller

someone already stated it on the TDI deal, but with more and more cars coming out with 6, 7 speed and even CVT transmissions, I think all of these graphs and statistics are a little outdated.  It is all about RPMs and if you can find a transmission that keeps the rpms down at higher speeds, your fuel economy will not suffer.  I wonder if fuel economy goes down on that one lexus with the 8 speed tranny......I bet not.

Agreed. Its hard to argue with the graphs and the numbers but they are misleading people. It depends on the torque of the engine at a particular rpm and the gearing on the drive axle and the transmission to best use that torque. Diesels are great for low rpm torque which is why the TDI was getting good mpg at a low speed and why it is a good city car. It would need either a higher geared rear end or an 8 speed transmission to also get that mileage on the highway. Most tractor trailers have plenty of gears in their trans to accomplish highway speeds but still be able to pull such heavy loads from a stand still. Some even have multi-speed rear ends. One for city, one for highway.

The graphs that show best mileage around 60mph probably are the result of Detroit gearing the car (matching efficient motor rpm to final drive ration of transmission to rear end ratio) for the best performance at that speed. Any number of ways to adjust that from shutting off cylinders, changing timing or changing the gearing. I bet cars that run the Autobahn are geared for better mileage at higher speeds which may account for the poor mileage figures that Mercedes and BMW log up on our roads. I'm guessing a CVT trans uses variable gearing which would be cool too.

Not to be too confusing but a combustion engine is not effiecient at all rpm's. So the design the engine has a lot to do with what gearing it has and for what purpose. For instance my Corolla has a little four that seems to have very little low rpm torque but plenty from 40-55. At 60 it is reluctant to go into a lower gear because the engine will scream (out of its power band) so it has little torque for passing other cars but it gets 30mpg no matter what speed you do. The v-8 in the Impala SS would not have such problems but since its power band is around 5500 to 6000 rpm it will pass other cars easily but only get 12-18mpg no matter what driving you do.

I used to read a lot of Road & Track kinds of mags. []

[mrhaskellok]

quote:

Some cities have taken steps toward actively discouraging motor vehicle use through lower speed limits and difficulty in finding parking.  Copenhagen reduced speed limits in some areas to 30 kph or about 18 mph.  London instituted congestion pricing.  Most of these measures resulted in an increased mode share for walking, cycling, and mass transit.  And congestion pricing really did reduce traffic in central London.

It's true that reduced speeds result in markedly better crash survival for all road users.  If I recall right, 35 mph is the dividing line.  So if we reduced the speed limit city wide to 25, we could expect reduced pedestrian, cyclist, and motorist fatalities.  What are those lives worth when compared to gas mileage?

Another point: Oklahoma permits low speed golf carts to operate on streets with speed limits of 25 mph or less.  If the city speed limit were 25, more of these vehicles would be a normal part of traffic, and it could be expected that their design would be ideal for those speeds.  In other words, they would have the optimal speed vs fuel consumption.  But I honestly do not know if they emit more unburnt fuel and greenhouse gases than a car equipped with a catalytic converter.

Still, it would be nice to have lower speeds with lower overall noise levels.  A sedate pace in traffic would contribute to livability issues, and again, there's no way to equate that in dollars.

I agree on both points.  I was just having that discussion with someone.  My background is emergency services (Combat Medic army, Firefighter EMT civilian) and I have seen first hand how devastating the increased speeds can have on people and cars.  Sure, we would all get somewhere faster, but all of us agreeing that 40k people a year is an acceptable sacrifice for our inconvenience is sort of like committing national negligence.  

Of course we can't equate for MISTAKES other people make like driving left of center, but again, my point is we have already surrendered certain responsibilities to our local government (safe driving speed), why can't we openly address the large scale carnage that is occurring on our streets daily.    
Final point on this then I will shut up...[][][]  Auto accidents still account for more deaths of people under 75 than any cancer or heart failure or anything else.  We are very willing, at least it appears that way sometimes, to change our lifestyle to minimize the risk of say heart failure, but why are we not  willing to slow down...an act that may actually save far more lives that if we all went to the gym.  We need to value life more and focus on building safer roads and enforce the laws to the fullest extent if we do violate these laws.  I get peeved when people complain about getting a speeding ticket for doing 75 down a two lane hwy.  I don't think people realize that they are FAR more likely to die AND kill whoever they hit at that speed then even at 65mph.  Don't believe me just do a ride along with your local ambulance service for a week...you will get to see what I mean.

WHEW!  Sorry, just got out of a council meeting and I am obviously all worked up!  []

Lovin every minute of it!

[si_uk_lon_ok]

quote:Originally posted by Wilbur

What you are proposing is setting speed limits 'artificially low.'

In the vast majority of instances, motorists determine the speed limits of the road.  Like I've posted before, traffic engineers conduct speed studies then put the speed limit at the 85th percentile.  The natural feel of the road, the amount of traffic and so forth cause most people to drive a certain speed where they are most comfortable.

Setting speed limits 'artificially low' will mean nothing because most folks won't do that.  It would be like putting a 30 mph zone on an expressway.  No one will do 30.

The safest streets are where everyone goes the same direction at the same speed without having to stop.  The more in conflict with that rule you are, the more unsafe the road becomes.

You are right about he safest roads being single direction roads. However what can be safe for the motorist can be very unsafe for the pedestrian or cyclist and as they aren't the ones encased in steel and polluting the environment I think they should get priority.

I disagree with building roads to the 85th percentile and letting users set the speed limit. I think if the road feels like it should be driven faster than it is safe to do, it should be changed. Residential areas need low speed limits even if the road could be safely driven at 60mph. If it can be driven at that speed it needs to be changed, either narrowed, change the surface, have parked cars lining it or have bump outs. I think a safe speed limit should be set, enforced and if people still speed the road should be changed so it can't be sped down.

[spoonbill]

quote:Originally posted by mrhaskellok

quote:

Some cities have taken steps toward actively discouraging motor vehicle use through lower speed limits and difficulty in finding parking.  Copenhagen reduced speed limits in some areas to 30 kph or about 18 mph.  London instituted congestion pricing.  Most of these measures resulted in an increased mode share for walking, cycling, and mass transit.  And congestion pricing really did reduce traffic in central London.

It's true that reduced speeds result in markedly better crash survival for all road users.  If I recall right, 35 mph is the dividing line.  So if we reduced the speed limit city wide to 25, we could expect reduced pedestrian, cyclist, and motorist fatalities.  What are those lives worth when compared to gas mileage?

Another point: Oklahoma permits low speed golf carts to operate on streets with speed limits of 25 mph or less.  If the city speed limit were 25, more of these vehicles would be a normal part of traffic, and it could be expected that their design would be ideal for those speeds.  In other words, they would have the optimal speed vs fuel consumption.  But I honestly do not know if they emit more unburnt fuel and greenhouse gases than a car equipped with a catalytic converter.

Still, it would be nice to have lower speeds with lower overall noise levels.  A sedate pace in traffic would contribute to livability issues, and again, there's no way to equate that in dollars.

I agree on both points.  I was just having that discussion with someone.  My background is emergency services (Combat Medic army, Firefighter EMT civilian) and I have seen first hand how devastating the increased speeds can have on people and cars.  Sure, we would all get somewhere faster, but all of us agreeing that 40k people a year is an acceptable sacrifice for our inconvenience is sort of like committing national negligence.  

Of course we can't equate for MISTAKES other people make like driving left of center, but again, my point is we have already surrendered certain responsibilities to our local government (safe driving speed), why can't we openly address the large scale carnage that is occurring on our streets daily.    
Final point on this then I will shut up...[][][]  Auto accidents still account for more deaths of people under 75 than any cancer or heart failure or anything else.  We are very willing, at least it appears that way sometimes, to change our lifestyle to minimize the risk of say heart failure, but why are we not  willing to slow down...an act that may actually save far more lives that if we all went to the gym.  We need to value life more and focus on building safer roads and enforce the laws to the fullest extent if we do violate these laws.  I get peeved when people complain about getting a speeding ticket for doing 75 down a two lane hwy.  I don't think people realize that they are FAR more likely to die AND kill whoever they hit at that speed then even at 65mph.  Don't believe me just do a ride along with your local ambulance service for a week...you will get to see what I mean.

WHEW!  Sorry, just got out of a council meeting and I am obviously all worked up!  []

Lovin every minute of it!

Speed limits don't work unless harshly enforced. . .driving away traffic and making for a poor city atmosphere.

The solution is psychological methods of road development.  Decrease setbacks so that buildings but up to sidewalks and are closer to the road.  This causes drivers to slow down naturally and makes for a better pedestrian environment.  

Add curves to long residential and city roads when developing them or offset the grid at some intersections.