With apologies to Sammy - the 55 mile an hour speed limit is a non-starter. If this becomes a Democratic centerpiece (which I doubt) the Dems will lose a significant portion of the Mountain West.
Colorado Springs to Denver is 65 miles - 75 to 55 is adding a half hour to the drive. Also, the libertarian strain out here is "why the hell should the government tell me what to do?".
I have no problem allowing states to set their own speed limits. But when you are talking the expanses of these states with minimal or no mass transit, this is a non-starter.
You want a better idea - reduce the federal housing density standards for mass transit funding.
El Paso County just finished its 35 year transport plan out to 2035. Mass transit initiatives were limited to some new bus routes. Bike paths and other non-auto orientations were stressed but not mass transit. Why?
Because federal mass transit funding is based on housing density. Western cities frequently (and ill advisedly) have low density and can not qualify for mass transit funding. Without mass transit, housing stock is lacking one major incentive for increasing density - especially since many of these newer cities lack a true urban core.
In the same manner, bike traffic to work - especially in high temp environments - can be a health hazard. How many people are going to bike to work in Tucson in 115 degree heat? Better have the paramedics ready.
A good point would be to propose that the federal government will revisit and refund mass transit designed in a rational manner for western cities in a way that incentivizes increased population density, thereby reinforcing the mass transit financial performance.
The West keeps getting criticized for its lack of mass transit - the West has also never qualified for mass transit funding because the funding rules were set up to keep feeding money to NorthEast urban core mass transit systems to support them. (Not saying that was bad, just saying the rules sure screwed the west). You want us out of our cars - get us options. But adding several hours of drive time to trips is not a way to make many friends. If the economics cause us to slow down, you win. But the West will take very badly to the federal 55 - it was one of the causes of the "Sagebrush Revolution" that started this mess.
Carrots work better than sticks and the West really has a problem with "we know better". Explain, educate and implement - don't dictate. get the states to do it themselves, federal action by a full D majority in 09 will be ugly for the '10 mid terms.