But, if you are basically saying I am comparing apples with oranges, France's ongoing investment in urban light rail is currently eclipsing the United States by an embarrassing margin.
These are figures from 2009, so are a bit old and dusty, and they are from a pro-light rail source, but they say that France has committed $29 billion for urban rail, compared to the USA's $8 billion. http://www.lightrailnow.org/news/n_newslog2009q4.htm#LRT_200...
And this is just France, which has a population five times smaller than the USA. I could try and find figures for all light rail investment across Europe if you like, but then it would just start to look utterly ridiculous.
To give another comparison, The UK spent $8 billion just on widening the M1 motorway.
[edit] Although with that last figure, nobody is really sure where most of the money went. I personally suspect that they found a new and exciting way to create road surface entirely out of pulped ten pound notes and dried caviare.
Maybe they only count federal money? But http://fta.dot.gov/grants/13442.html shows around $10 billion per year (the $29 billion is for multiple years) - not all of that is light rail specifically, but it's all infrastructure investment, and doesn't include local (state, city) money, nor any of the other federal departments.
Local is more expensive since you are building right in the middle of populated areas. You have to get the land which is hard to do and expensive and when you do construction you are obstructing other traffic. The construction itself is more expensive too since you can't use very large machines to do it in bulk.
http://www.latimes.com/news/local/la-me-bullet-risks-2012051...