New Concrete Highway Means BIG MPG Boost!

Rolling Resistance I guess. The wind here seems to kill any attempts at my breaking 55 mpg tho.

 

The different road surfaces here have different elevations, wind patterns, etc. Makes it hard to compare.

I work just outside of Sanford FL, and I've been getting 50MPG tanks.

Regards,
Peter

 

Went on a long trip recently (San Diego-Monterey) and took advantage of the opportunity to record my MPG over numerous stretches of highway at various speeds (using cruise control), flat terrain, 95-degree outside temperature, 100% sunny, AC on. In summary, on I-5 northbound (north of the mountains north of LA), I averaged 60MPG at 65MPH for 60 miles. When I got off the interstate, travelling SR 46 (Paso Robles Hwy), I dropped down to 55 mph and averaged 55 MPG for a good 30-40 miles. As far as I could tell, all conditions were the same except for the average speed and the road surface. Wind was negligible. I checked that there was minimal elevation gain on my GPS.

Not being a "road surface expert", as far as I could tell, the interstate was concrete, and the SR-46 was some sort of cemented gravel (not smooth asphalt, not concrete).

The results were a bit shocking. I was expecting my MPG to go up 5 to 10MPG after slowing down from 65 to 55mph, but just the opposite occurred. The only explanation I can think of was due to the difference in road surfaces, although a 10-15mpg difference from the expected mpg seems excessive to attribute to the road surface.

 

I have found, as have others on the forum, that there seem to be speed (MPH) sweet spots in the Prius that seem to depend on the temperature and maybe humidity. I have noticed that at certain temp & speed combinations, my MPG shoots way up to the 60's and 70's. 1 MPH more or less and the MPGs go down again. The trick is to find the right speed for the current temperature.

Give it another try on those roads and drop/raise your MPH and see what the MPG does.

 

never noticed any change in mpg's but i did notice the HUGE reduction in road noise on concrete...unfortunately, concrete is so expensive that its not used much around here.

it is nice to drive on though... the lack of noise is eerily pleasant.

 

I don't know about that. Every concrete highway I've every driven on feels and sounds like a horse galloping. Thump-thump... thump-thump...thump-thump...

 

that is true, but better than a constant hum i think... plus, i have also noticed that the expansion joints dont always make a lot of noise... sometimes, its just the slight bump is all that i notice even with modest stereo volume

 

A well made/well maintained concrete road can be silent. I drove over one a few weeks ago that had recently had work done to remove unevenness and it was one of the quietest roads I've ever been on. It was far from new looking but the patch work was incredibly level. IIRC correctly only the right lane had been finished, making the "truck lane" the preferable one to drive on, usually the passing lane is smoothest.

"Thump-thump" roads make me think of Louisiana and Arkansas where highway maintenance has often been atrocious.

 

I would beg to differ about the noise.

I have found, without exception, that the asphalt highways in SoCal are significantly quieter than the concrete highways. And it doesn't seem to matter much what car I'm driving. Asphalt and concrete seem to be equally interspersed all around the region, so there's ample oppurtunity to sample each flavor.

Each time I transition from asphalt to concrete, I cringe due to the extra noise and reluctantly turn up the volume on my radio just to achieve a similar level of SNR.

 

according to cummins truck mpg secrets or whatever its called... concrete has one of the SMALLEST rolling resistances out there.

 

all these posts makes me thinks, all concrete is not created equally

 

One more factor to consider which applies to both asphalt and concrete: the age of the road surface. From recent experience (nearly all the roads in the county have had sections resurfaced) a newly resurfaced asphalt road is much smoother and quieter than six year old concrete.

 

If there is a regular "thump-thump" it's probably an old Portland cement concrete (pcc) road (even with an asphalt concrete overlay that has been there a while), with regularly spaced formed transverse joints. These were typically reinforced with relatively short steel rods intended to prevent vertical offsets in the surface. Short wheel bases (think tandem semis) resonate and increase effective loading on the edges of each slab at the transverse joints, with progressive deflection and failure. Vehicle speeds cause impact loading when there are surface irregularities. Improvements to that scheme include skewed sawcut joints at random spacing and continuous reinforcing. One reason for joints is to allow for temperature shrinkage of pcc --pcc is much better in compression than in tension. The latest is to post-tension slabs, permitting much longer segments, eliminating most transverse joints.

As between pcc and asphaltic concrete (ac): Pcc is deliberately made rough in finishing (in the old days by "transverse brooming" and now by dragging a cylinder on the surface before it sets up. If the surface is thought too smooth for traction and/or resistance to hydroplaning you might see longitudinal saw cuts or grinding (also used to bring the profile into spec.). Pcc is hard, so think high pressure in your tires. There is the concept of "concrete wheels on rubber roads". Old tires are being recycled into a component of ac, with a quieter (for passengers and neighbors) and smoother ride. A new ac overlay on existing pavement will likely be much smoother than pcc because it can be laid in much longer stretches between construction joints and underlying irregularities will be (at least temporarily) patched over. Some jobs put down a structural plastic mesh which somewhat distributes longitudinal stresses.

Costs of both materials are influenced by the oil market--asphalt is petroleum, and portland cement is the result of high temperature generated by one fuel or another (often natural gas). Both pcc and ac are recycled in one way or another. Ac pavement can be ground down and reused for base material or even as part of a new mix. Both material require good aggregate and good base material, not always handy. All the materials are heavy (finished weight about 150 pounds per cubic foot). In some areas one material or another may have a significant cost advantage. More thought is now being given to "life-cycle" costs with longer life a key factor. (Many components of the Interstate system were based on 50-year life-spans, and Ike was President when?)

Structural deterioration is mostly related to loading cycles and then mostly as a function of vehicle weight. Light vehicle traffic is good for keeping weeds from growing in the cracks, while maximum weight or overloaded trucks will have serious effects over time.