This is really great work and fun to read!!
We have a bit of a file on this topic, if you search 'bituminous asphalt' in the research journals you can find some pretty great info on the different strategies employed by different municipalities, private contractors and even countries that can have some really big effects on Crr. I've talked to a lot of civil engineers and some course contractors over the years in an effort to better understand and here are the basics:
In an attempt to maintain flexibility at cold temperatures, this stuff is generally modified with plasticizers, rubber, and other stuff that makes it very high hysteresis when warm or hot. Some formulations are still pliable at -20C/-5F and have the consistency of a gummy bear at 90F. Different strategies are also applied in terms of thickness of the coating, I've seen it nearly 2mm thick in some applications, and when thick, it behaves very visco-elastically with damping coefficient in the 0.8+ range.
The rate of hardening is dependent on chemical makeup and heat, but it will continue to harden asymptotically approaching some maximum over it's lifetime.. it's likely 95+% hard at 1 year according to most.
Ironically, you are seeing the benefit of the roughness of the coarse stone chips on that part of the road.. the seal cannot build on top of the stone chip and rather drains into the gaps, leaving a much thinner effective coating that you are riding one.. so effectively you are decreasing surface hysteresis at the expense of increased surface impedance. The rather thick coating on the side of the road will be due to the large fill size of the stone (which is cheapest) and then needing more bitumen to fully fill the negative space and best stick it all down.
The strategy for both of your surfaces is to present a larger contact patch with lower pressures at the interface.. so yeah, bigger tires, lower pressures!
There were some surfaces laid down/sprayed/repaired for Tokyo that presented challenges in this area and were not this bad, but presented some challenges/opportunities to exploit...and now with the delays will be quite a bit faster as the games will be run 14-15 months after the work was complete!
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