I just hope it's more successful than a similar project which opened here in the UK in 2003 which involved building a new freeway to bypass a congested freeway which ran through the urban area. Unfortunately the high tolls put people off and traffic congestion on the old (free) route continues to plague the area. To use the 27 mile road one way during the week is roughly $7.60 so someone making a return journey will pay over $15.
Some of us do know about the M6 Toll and other important British roads, so please feel free to refer to them by name.
I've only driven through Phoenix during one week last February and the section of I-10 near Sky Harbor was slow running when I used it but away from the central area it flowed fine so perhaps an extension of Loop 101 and Loop 202 around the southwest of Phoenix could be the answer rather than a toll road which could potentially put some people off using it if the tolls are expensive.
A Loop 202 bypass southwest of Phoenix is already planned--this is the South Mountain Corridor. It is controversial however, with construction not scheduled to begin for several years, and the scope keeps changing (at one point it was supposed to be 10-lane but this has apparently been reduced to 6 lanes).
Toll roads are only feasible if there are no alternates, or if tolls are low enough. In case of the M6 Toll, the tolls are obviously too high. They need to do some serious cost-benefit surveys based on realism.
It is not always the case that reducing prices increases patronage, or vice versa. Demand for the M6 Toll is low, but fairly inelastic with regard to price, and the concessionaire's pricing policies nowadays seem oriented at managing downside risk. Those who won't use a toll road at all (especially if paying on their own) can avoid the M6 Toll just as well at £5 (or whatever it is now) per transit as at £3 per transit. The higher toll, charged across a steady traffic, gives the concessionaire a better chance of meeting its loan charges (the M6 Toll loses money when interest is figured in).
I assume they want to build a toll road south of Phoenix to bypass the downtown area? The main problem is traffic volumes are probably low, even if it was untolled and no new sprawl would appear.
AIUI, the South Mountain Corridor is to be untolled. The toll road under consideration sounds like the long-mooted I-10 Phoenix-Tucson bypass, the most feasible alignments for which cross current I-10 between Phoenix and Tucson, thus allowing the project to be decomposed as separate Phoenix and Tucson bypasses.
Traffic volumes on I-10 west of Phoenix are only around 20,000 AADT. If 50% of that traffic has a destination or origin in the Phoenix area, that leaves only 10,000 AADT potential traffic for a tolled bypass. Given the resistance of the American public and truckers to toll roads, I'm afraid traffic volumes would be way to low.
I don't think it is toll-viable either, but much depends on the degree of development in the Phoenix-Tucson corridor. Part of the appeal of an I-10 bypass toll road is to serve anticipated new development in Pinal County, between Phoenix and Tucson. A bypass freeway would improve accessibility in Pinal County and allow greater specialization of existing I-10 to serve medium-distance traffic. A bypass freeway in Pinal County would make a lot of sense (as much sense as the Kansas Turnpike between Emporia and Kansas City, for example) if one of the small communities grew to the size of Topeka within two or three decades, for which there is a lot of precedent in Arizona.